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15 Aug 2011

Volume 110, Issue 4, Articles (04xxxx)

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back to top Magnetism and Superconductivity

Investigation of the switching wave propagation in linear chains of magnetic elements

L. Kaganovskiy, D. Litvinov, S. Khizroev, and S. Wilcox

J. Appl. Phys. 110, 043901 (2011); http://dx.doi.org/10.1063/1.3624619 (6 pages) | Cited 1 time

Online Publication Date: 16 August 2011

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A micromagnetic study employing OOMMF1 simulator of magnetic switching wave propagation along magnetic data channels is presented. The optimization of the wave propagation as a function of geometry and physical parameters is investigated, which resulted in an order of magnitude increase in the depth of magnetic signal propagation. Unlike unoptimized rapidly decaying waves, the resulting wave stays practically the same throughout the channel, improving wave detection characteristics. When the in-plan dimensions of the channel are scaled proportionally, the optimized propagation length remains relatively constant. This indicates a possibility of the scalability in the data channel, which has significant technological applications.
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75.78.Jp Ultrafast magnetization dynamics and switching
75.30.Gw Magnetic anisotropy

Numerical study of the effective magnetocrystalline anisotropy and magnetostriction in polycrystalline FeGa films

Julian Dean, M. T. Bryan, N. A. Morley, G. Hrkac, A. Javed, M. R. J. Gibbs, and D. A. Allwood

J. Appl. Phys. 110, 043902 (2011); http://dx.doi.org/10.1063/1.3618684 (5 pages) | Cited 1 time

Online Publication Date: 16 August 2011

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The high interest in FeGa films is due to the high magnetostriction present in single crystal thin films. There is, however, significant reduction in the magnetostriction when grown using sputtering. The reduction is explained here using finite element analysis by considering the local magnetocrystalline and magnetoelastic behavior of the grains within the sample. It is shown that, if the saturation magnetostrictive constant for each grain in a polycrystalline structure is of the order of 400 ppm, this is reduced to less than 90 ppm when the crystallites are randomly orientated. Furthermore, the inherent stress due to the sample fabrication leads to an increase in the anisotropy field. This work suggests that, with low stress fabrication and aligning the in-plane orientation of the crystallites, the potential in unlocking FeGa as a thin film for sensory applications can be realised.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.80.+q Magnetomechanical effects, magnetostriction
02.70.Dh Finite-element and Galerkin methods
75.30.Gw Magnetic anisotropy

Simulation of fluid flow during protein crystal growth in magnetic fields

H. Okada, N. Hirota, S. Matsumoto, and H. Wada

J. Appl. Phys. 110, 043903 (2011); http://dx.doi.org/10.1063/1.3620744 (6 pages) | Cited 2 times

Online Publication Date: 16 August 2011

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We are developing a superconducting magnet system to grow high-quality protein crystals. The gravity-controlled environment, based on magnetic forces, can suppress thermal convection and may give rise to a variety of additional effects on the protein crystal growth. To design suitable magnetic force conditions for protein crystal growth in protein solutions, we are studying a gravity-controlled environment by magnetic forces in the crystal growth process by computer simulations. In this study, we derived a modified Navier-Stokes equation with gravity and static magnetic force and numerically solved the equation. The obtained results show that the temperature dependence of the magnetization modifies the levitation condition and the magnetic force gives rise to an unexpected change of fluid motion.
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87.50.cf Biophysical mechanisms of interaction
36.20.-r Macromolecules and polymer molecules
47.63.-b Biological fluid dynamics
87.14.E- Proteins
87.15.H- Dynamics of biomolecules
87.15.N- Properties of solutions of macromolecules

Quadratic magneto-optical Kerr effect in Co2MnSi

Georg Wolf, Jaroslav Hamrle, Simon Trudel, Takahide Kubota, Yasuo Ando, and Burkard Hillebrands

J. Appl. Phys. 110, 043904 (2011); http://dx.doi.org/10.1063/1.3622512 (5 pages)

Online Publication Date: 16 August 2011

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Quadratic magneto-optical Kerr effects (QMOKE) are investigated in epitaxial Co2MnSi thin films as a function of the post-deposition annealing temperature. We determine the amplitude of the QMOKE signal for different annealing temperatures, which provide various degrees of L21 crystal ordering, as manifested by X-ray diffraction. We observe that QMOKE is significantly present only when the L21 ordering phase is also present, and that the QMOKE signal increases with the higher degree of L21 ordering. Additionally, we notice that the linear magneto-optical Kerr effect (LMOKE) decreases with higher annealing temperature. A comparison of the linear and quadratic MOKE contributions shows the amplitudes are of similar magnitude. From these results, we conclude that the presence of QMOKE is linked to the higher degree of L21 ordering in Co2MnSi.
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78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
75.60.Nt Magnetic annealing and temperature-hysteresis effects

Conventional and inverse magnetocaloric effects in La0.45Sr0.55MnO3 nanoparticles

A. Rostamnejadi, M. Venkatesan, J. Alaria, M. Boese, P. Kameli, H. Salamati, and J. M. D. Coey

J. Appl. Phys. 110, 043905 (2011); http://dx.doi.org/10.1063/1.3614586 (7 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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The magnetocaloric effect of La0.45Sr0.55MnO3 nanoparticles was studied by dc magnetization measurements. A sample with mean particle size of about 140 nm exhibits both a conventional magnetocaloric effect around the Curie temperature (≈ 295 K) and a large inverse magnetocaloric effect around the antiferromagnetic-ferromagnetic transition temperature (≈ 200 K). The change of magnetic entropy increases monotonically with applied magnetic field and reaches the values of 5.51 J/kg K and − 2.35 J/kg K at 200 K and 295 K, respectively, in an applied field of 5 T. The antiferromagnetic-ferromagnetic transition is absent in a 36 nm size sample, which shows only a broad ferromagnetic transition around 340 K and a small change in magnetic entropy near room temperature. The results are discussed in terms of the entropy difference between the A-type antiferromagnetic ground state of La0.45Sr0.55MnO3 and the low moment ferromagnetic state. By comparing the results obtained on nanoparticles and bulk La0.45Sr0.55MnO3, one can conclude that the inverse magnetocaloric effect in a material showing the antiferromagnetic-ferromagnetic transition could be improved over a wide range of temperature by tuning the spin disorder in the antiferromagnetic state.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Out-of-plane anisotropy and low field induced magnetic domain reorientation in Al/Metglas-2605S2/Al trilayer sensors

E. C. Passamani, C. Larica, P. S. Moscon, P. Mendoza Zélis, and F. H. Sánchez

J. Appl. Phys. 110, 043906 (2011); http://dx.doi.org/10.1063/1.3622339 (7 pages)

Online Publication Date: 17 August 2011

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Local magnetism of Al/Metglas-2605S2/Al trilayer-like sensors prepared by dc sputtering has been studied at room temperature by both in-field and zero-field Mössbauer spectroscopy for a maximum field of 60 mT. Ferromagnetic domain reorientation from out-of-ribbon plane to in-plane, induced by low applied fields, was measured by monitoring the intensities of lines 2 and 5 in the Mössbauer sextet spectra obtained for different magnitudes of applied magnetic field. Coating the Metglas-2605S2 with Al layers of 20 μm thickness, a stress-field is induced, allowing to distinguish different in-plane magnetic anisotropy distributions along the ribbon length (∼4 mT) as well along its width (∼10 mT). Using a phenomenological model for the magnetization reversal, out-of-plane anisotropies ranging up to 3 kJ/m3 were estimated for the Metglas-2605S2 alloy ribbons. This anisotropy range is similar to that observed for the in-plane case previously reported. The methodology applied in this work can be used to determine native out-of-plane anisotropy distributions for different melt-spun ribbons. It also allows understanding magnetization reversal associated with the ferromagnetic domains reorientation caused either by induced stress or by applied magnetic field.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Suppression of ferromagnetism and metal-like conductivity in lightly Fe-doped SrRuO3

Jiyu Fan, Sicheng Liao, Wenqin Wang, Lei Zhang, Wei Tong, Langsheng Ling, Bo Hong, Yangguang Shi, Yan Zhu, Dazhi Hu, Li Pi, and Yuheng Zhang

J. Appl. Phys. 110, 043907 (2011); http://dx.doi.org/10.1063/1.3624764 (5 pages)

Online Publication Date: 18 August 2011

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The magnetic and electronic transport properties of the lightly doped SrRu1-x Fex O3 (x ≤ 0.15) have been studied. All the samples show a paramagnetic-ferromagnetic phase transition and hysteresis effect. With the increase of Fe, the temperature of magnetic phase transition decreases but coercive field increases indicting the existence of antiferromagnetic interaction and magnetic-crystalline anisotropy. In low temperature, all the doping samples exhibit an insulating behavior while metal feature appears only at x ≤ 0.10 samples. The induced disorder suppresses the itinerant property of Ru 4d electron due to Fe random occupation. As a result, the ferromagnetism is weakened and metal-insulator transition is suppressed.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions
75.30.Gw Magnetic anisotropy

Study of uniaxial magnetism and enhanced magnetostriction in magnetic-annealed polycrystalline CoFe2O4

Y. X. Zheng, Q. Q. Cao, C. L. Zhang, H. C. Xuan, L. Y. Wang, D. H. Wang, and Y. W. Du

J. Appl. Phys. 110, 043908 (2011); http://dx.doi.org/10.1063/1.3624661 (7 pages) | Cited 1 time

Online Publication Date: 19 August 2011

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Magnetic and magnetostrictive properties of magnetic-annealed polycrystalline CoFe2O4 were investigated. The magnetic hysteresis loops showed obvious uniaxiality with an induced easy direction parallel to the annealing field. Magnetic force microscopy study revealed that the domains were fixed by magnetic annealing. The uniaxial behavior was also observed in the magnetostrictive measurement, which showed a significantly enhanced magnetostriction of − 273 PPM when the external field was applied perpendicular to the annealing field direction. A physical mechanism for the effect of magnetic annealing on polycrystalline CoFe2O4 is developed, in which the induced uniaxiality is ascribed to the realignment of easy axes in polycrystals. The uniaxial behavior of magnetism and enhanced magnetostriction could be well explained by this model.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Exchange bias in magnetic nanoparticle capped with amorphous magnetic shell

Ha M. Nguyen, Chih-Hao Lee, Pai-Yi Hsiao, and Manh-Huong Phan

J. Appl. Phys. 110, 043909 (2011); http://dx.doi.org/10.1063/1.3624751 (7 pages)

Online Publication Date: 19 August 2011

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An extensive Monte Carlo (MC) simulation is performed to investigate exchange bias in a novel model of a nanoparticle consisting of a ferromagnetic (FM) core and an amorphous magnetic (AM) shell. The magnetic glassy ordering of the AM shell governed by random magnetic anisotropy (RMA) is shown to be responsible for the unidirectional anisotropy to the FM core. Our MC results show that, while the bias field and coercivity exhibit a strong dependence on RMA strength, which looks like that on the antiferromagnetic (AFM) thickness in traditional FM/AFM bilayers, they are independent of AM thickness. However, the bias field and coercivity abruptly change with increasing small core size and get saturated for a large enough core size. The cooling field and temperature dependencies show the peculiar sign inversion of the bias field. Our study supports the argument that the exchange bias observed in some magnetic nanoparticles or nanocrystallined alloys is not necessarily due to the presence of an AFM phase.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Study of valence band structure of Fe doped anatase TiO2 thin films

Komal Bapna, D. M. Phase, and R. J. Choudhary

J. Appl. Phys. 110, 043910 (2011); http://dx.doi.org/10.1063/1.3624775 (6 pages) | Cited 1 time

Online Publication Date: 19 August 2011

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We study the structural and electronic properties of Fe doped (4–8 at. %) and undoped TiO2 thin films deposited by pulsed laser deposition on Si(111) substrate. The films grow in single phase anatase structure of TiO2 as revealed by x-ray diffraction and Raman spectroscopy measurements. The Fe doped films reveal room temperature magnetic hysteresis behavior. We have probed the electronic environment of Fe in TiO2 matrix and its coupling to the cations, using photoelectron spectroscopy measurements. Photoelectron spectroscopic studies reveal the ionic state of Fe in TiO2, precluding the formation of Fe metal clusters. Valence band spectra of these films suggest that it primarily consists of O-2p derived state, however, Fe derived state is also observed in Fe doped films. Resonance photoelectron spectroscopy studies indicate that Fe ions are hybridized with Ti3+ defect states.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
81.15.Fg Pulsed laser ablation deposition

High coercive FePt and FePt-SiNx(001) films with small grain size and narrow opening-up of in-plane hysteresis loop by TiN intermediate layer

H. H. Li, K. F. Dong, Y. G. Peng, G. Ju, G. M. Chow, and J. S. Chen

J. Appl. Phys. 110, 043911 (2011); http://dx.doi.org/10.1063/1.3624910 (4 pages) | Cited 4 times

Online Publication Date: 22 August 2011

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The effects of a TiN intermediate layer on the epitaxial growth and magnetic properties of FePt films were investigated. It was found that 5 nm TiN can effectively block the diffusion of a CrRu underlayer into a FePt magnetic layer and the magnetic dead layer on the TiN layer was negligible. Compared with an FePt film grown on a MgO intermediate layer, FePt film grown on a TiN interlayer exhibited very high out-of-plane coercivity and very narrow opening-up of in-plane hysteresis loop. With doping 40 vol. % SiNx in FePt film the grain size was reduced to 5.5 nm and the magnetic properties, such as high out-of-plane coercivity and line-like in-plane hysteresis loop, were retained.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
68.55.aj Insulators
75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Giant magnetocaloric effect in antiferromagnetic borocarbide superconductor RNi2B2C (R = Dy, Ho, and Er) compounds

Lingwei Li, Katsuhiko Nishimura, Michiaki Kadonaga, Zhenghong Qian, and Dexuan Huo

J. Appl. Phys. 110, 043912 (2011); http://dx.doi.org/10.1063/1.3625250 (5 pages) | Cited 2 times

Online Publication Date: 22 August 2011

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The magnetocaloric effect (MCE) in antiferromagnetic borocarbide superconductor RNi2B2C (R = Dy, Ho, and Er) compounds have been investigated by measuring the temperature and field dependences of heat capacity. An inverse MCE was observed, which is attributed to the nature of the antiferromagnetic state under low magnetic field and at low temperatures for the present RNi2B2C compounds. A normal giant/large MCE was observed under higher magnetic field change, which is related to a field-induced first-order metamagnetic transition from antiferromagnetic to ferromagnetic state. For a field change of 5 T, the maximum values of magnetic entropy change (− ΔSMmax) reach 17.6, 17.7, and 9.8 J kg−1 K−1 for R = Dy, Ho, and Er, respectively. The corresponding values of maximum adiabatic temperature changes (ΔTadmax) are 9.7, 11, and 4.6 K. The present results indicated the antiferromagnetic borocarbide superconductor RNi2B2C compounds could be promising candidates for low temperature magnetic refrigeration.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Ee Antiferromagnetics
65.40.Ba Heat capacity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Nonvolatile, reversible electric-field controlled switching of remanent magnetization in multifunctional ferromagnetic/ferroelectric hybrids

A. Brandlmaier, S. Geprägs, G. Woltersdorf, R. Gross, and S. T. B. Goennenwein

J. Appl. Phys. 110, 043913 (2011); http://dx.doi.org/10.1063/1.3624663 (5 pages) | Cited 4 times

Online Publication Date: 23 August 2011

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In spin-mechanics, the magnetoelastic coupling in ferromagnetic/ferroelectric hybrid devices is exploited in order to realize an electric-voltage control of magnetization orientation. To this end, different voltage-induced elastic strain states are used to generate different magnetization orientations. In our approach, we take advantage of the hysteretic expansion and contraction of a commercial piezoelectric actuator as a function of electrical voltage to deterministically select one of two electro-remanent elastic strain states. We investigate the resulting magnetic response in a nickel thin film/piezoelectric actuator hybrid device at room temperature, using simultaneous magneto-optical Kerr effect and magnetotransport measurements. The magnetic properties of the hybrid can be consistently described in a macrospin model, i.e., in terms of a single magnetic domain. At zero external magnetic field, the magnetization orientation in the two electro-remanent strain states differs by 15°, which corresponds to a magnetoresistance change of 0.5%. These results demonstrate that the spin-mechanics scheme indeed enables a nonvolatile electrically read- and writable memory bit where the information is encoded in a magnetic property.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.Dj Domain structure; hysteresis
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Structural, optical and magnetic properties of polycrystalline BaTi1−xFexO3 ceramics

N. V. Dang, T. D. Thanh, L. V. Hong, V. D. Lam, and The-Long Phan

J. Appl. Phys. 110, 043914 (2011); http://dx.doi.org/10.1063/1.3625235 (7 pages) | Cited 3 times

Online Publication Date: 23 August 2011

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Polycrystalline BaTi1−xFexO3 ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi1−xFexO3 samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02–0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.72.sd Impurity concentration
61.72.up Other materials
75.85.+t Magnetoelectric effects, multiferroics
75.50.Dd Nonmetallic ferromagnetic materials
78.30.Hv Other nonmetallic inorganics

Studying the force characteristics of a high temperature superconducting linear synchronous motor

Luhai Zheng and Jianxun Jin

J. Appl. Phys. 110, 043915 (2011); http://dx.doi.org/10.1063/1.3625266 (5 pages)

Online Publication Date: 23 August 2011

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A single-sided high temperature superconducting (HTS) linear synchronous motor (HTSLSM) with an HTS bulk magnet array as its secondary has been developed. A field-cooled magnetization system has also been developed to obtain the magnet array with alternate magnetic poles. In order to identify the performance and force characteristics of the HTSLSM, an equivalent 3D finite element analysis (FEA) model has been built up to analyze its field distributions and cogging force characteristics, and an experimental system has been constructed to measure its thrust and normal force characteristics. The traits of the thrust and the normal force have been extracted by comprehensive experiments, including the trends versus different exciting currents, different air gap lengths and variable magnetic poles. The analysis and experimental results are fundamental to the electromagnetic optimum design and control scheme evaluation for the HTSLSM.
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84.50.+d Electric motors
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
02.70.Dh Finite-element and Galerkin methods

Oxygen partial pressure effect on the thermal stability of Nd-123 superconductor thin films

S. B. Yan, Y. Y. Chen, L. Cheng, and X. Yao

J. Appl. Phys. 110, 043916 (2011); http://dx.doi.org/10.1063/1.3618675 (5 pages) | Cited 1 time

Online Publication Date: 24 August 2011

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The effect of oxygen partial pressure on the thermal stability of Nd-123 superconductor thin films was investigated by means of high temperature in situ microscopy. It was found that the thermal stability of Nd-123 films decreases as the oxygen partial pressure increases. We attribute the thermal stability suppression to the increased growth rate of Nd-422 and a high concentration difference ratio. Under the assumption of quasi-equilibrium, a simplified model for peritectic melting of RE-123 was suggested.
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68.60.Dv Thermal stability; thermal effects
74.78.-w Superconducting films and low-dimensional structures

Magnetic behavior of Fe(Se,Te) systems: First-principles calculations

Hongliang Shi, Zhong-Bing Huang, John S. Tse, and Hai-Qing Lin

J. Appl. Phys. 110, 043917 (2011); http://dx.doi.org/10.1063/1.3624759 (7 pages)

Online Publication Date: 24 August 2011

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The magnetic behaviors in Fe(Se,Te) systems have been investigated systematically using density functional calculations. At the experimental lattice parameters, the ground state is found to be in the double stripe magnetic phase for FeTe but in the single stripe magnetic phase for FeSe and FeSe0.5Te0.5, and there is no preference in the different easy axes of magnetization. Substitution of Se by Te enlarges the size of the Fermi surface in FeSe0.5Te0.5, resulting in a stronger nesting effect and thus enhancing the superconductivity. It is found that the double stripe order in FeTe1-xSex changes to the single stripe order when x> 0.18. Spiral calculations on FeSe0.5Te0.5 show that the lowest energy is at the commensurate point math = (0.5,0.5), accompanied by additional local minima at two incommensurate points near math = (0.5,0.5). This observation is consistent with the experimentally observed positions of low energy magnetic excitations. Geometry optimization calculations show that the tetragonal cell relaxes to orthorhombic and monoclinic cells for FeSe and FeTe, respectively, but remains unchanged for FeSe0.5Te0.5.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
74.20.Pq Electronic structure calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Time dependence of interlayer coupling in Pd(50 Å)/Co(tCo Å)/Pd(54 Å)/Co(tCo Å)/Pd(50 Å) multilayer with perpendicular anisotropy

F. S. Wen, F. Zhang, Y. F. Lü, J. Y. Xiang, W. Li, Y. F. Lu, Z. Y. Liu, B. Xu, D. L. Yu, J. L. He, and Y. J. Tian

J. Appl. Phys. 110, 043918 (2011); http://dx.doi.org/10.1063/1.3626066 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2011

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Time-dependent ferromagnetic (FM)-antiferromagnetic (AFM) interlayer coupling transition has been found in Pd(50 Å)/Co(tCo Å)/Pd(54 Å)/Co(tCo Å)/Pd(50 Å) multilayer. During exposure to the air, saturation magnetic moment and coercivity both drop with time; moreover, a shift of the minor loop center for AFM coupling also decreases with time. During exposure of the sample to the air, as one possibility, the observed time-dependent FM-AFM interlayer coupling transition and decrease of AFM coupling strength may result from absorption of gaseous elements, which can induce reduction of Pd-polarization and a decrease of saturation magnetic moment; another possibility may be the alloying of the Co/Pd interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Switchable voltage control of the magnetic coercive field via magnetoelectric effect

Jing Wang, Jing Ma, Zheng Li, Yang Shen, Yuanhua Lin, and C. W. Nan

J. Appl. Phys. 110, 043919 (2011); http://dx.doi.org/10.1063/1.3626748 (5 pages) | Cited 3 times

Online Publication Date: 24 August 2011

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Switchable voltage modulation of the magnetic properties is reported in different multiferroic bilayers with magnetic films grown on pre-poled ferroelectric substrates, based on the magneto-optical Kerr effect observations. The dynamic voltage control of the magnetic coercive field (Hc) is dependent not only on the materials properties of each ferroic layer, but also on the bias voltage history. The Hc versus electric field behaviors essentially track the dependence of the piezostrains of the substrates on the bias voltage. The observations demonstrate that Hc in such multiferroic bilayers can be controlled by voltage via strain-mediated magnetoelectric coupling and that the Hc change is not an artifact due to a heating effect.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
77.80.-e Ferroelectricity and antiferroelectricity

Magnetic and elastic properties of CoFe2O4- polydimethylsiloxane magnetically oriented elastomer nanocomposites

P. Soledad Antonel, Guillermo Jorge, Oscar E. Perez, Alejandro Butera, A. Gabriela Leyva, and R. Martín Negri

J. Appl. Phys. 110, 043920 (2011); http://dx.doi.org/10.1063/1.3624602 (8 pages) | Cited 1 time

Online Publication Date: 25 August 2011

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Magnetic elastic structured composites were prepared by using CoFe2O4 ferromagnetic and superparamagnetic nanoparticles as fillers in polydimethylsiloxane (PDMS) matrixes, which were cured in the presence of a uniform magnetic field. Cobalt-iron oxide nanoparticles of three different average sizes (between 2 and 12 nm) were synthesized and characterized. The smallest nanoparticles presented superparamagnetic behavior, with a blocking temperature of approximately 75 K, while larger particles are already blocked at room temperature. Macroscopically structured-anisotropic PDMS-CoFe2O4 composites were obtained when curing the dispersion of the nanoparticles in the presence of a uniform magnetic field (0.3 T). The formation of the particle’s chains (needles) orientated in the direction of the magnetic field was observed only when loading with the larger magnetically blocked nanoparticles. The SEM images show that the needles are formed by groups of nanoparticles which retain their original average size. The Young’s moduli of the structured composites are four times larger when measured along the oriented needles than in the perpendicular direction. Magnetization (VSM) and ferromagnetic resonance curves of the structured composites were determined as a function of the relative orientation between the needles and the probe field. The remanence magnetization was 30% higher when measured parallel to the needles, while the coercive field remains isotropic. These observations are discussed in terms of the individual nanoparticle’s properties and its aggregation in the composites.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.41.+e Polymers, elastomers, and plastics
75.50.Tt Fine-particle systems; nanocrystalline materials
62.20.de Elastic moduli
75.50.Cc Other ferromagnetic metals and alloys
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetism in antiferromagnetic NiO-based thin films

Yuan-Hua Lin, Bin Zhan, Ce-Wen Nan, Rongjuan Zhao, Xiang Xu, and M. Kobayashi

J. Appl. Phys. 110, 043921 (2011); http://dx.doi.org/10.1063/1.3626053 (4 pages) | Cited 1 time

Online Publication Date: 25 August 2011

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Polycrystalline NiO-based thin films with Li or/and transition metal ions (V, Cr, Mn, Fe, Co, Cu, Zn) doping have been prepared by a sol-gel spin-coating method. Magnetization measurements reveal that V-, Fe-, and Mn-doped NiO thin films show obvious room-temperature ferromagnetic behaviors and ferromagnetic properties can be enhanced by the Li co-doping. Microstructure and X-ray core-level photoemission spectra analysis indicate that the ferromagnetism was not from the impurity TM metal cluster and may be ascribed to double exchange coupling effects via Li-induced holes.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
61.72.up Other materials
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Coexistence of exchange bias effect and giant magnetoresistance in a Ni/NiO nanogranular sample

L. Del Bianco, F. Spizzo, M. Tamisari, and A. Castiglioni

J. Appl. Phys. 110, 043922 (2011); http://dx.doi.org/10.1063/1.3626063 (5 pages)

Online Publication Date: 25 August 2011

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We have studied the coexistence of exchange bias (EB) effect and spin-dependent magnetotransport in a Ni/NiO nanogranular sample by measuring the magnetization (M) and the magnetoresistance (MR) versus the magnetic field (H) in the 5-250 K temperature (T) range, both in zero-field-cooling (ZFC) and field-cooling (FC) conditions. The sample consisted of Ni nanocrystallites (mean size ∼13 nm) dispersed in a NiO matrix; the Ni volume fraction was ∼33%, above the percolation threshold for electrical conductivity, as revealed by the low resistivity (order of 10−3 Ωm) and by its growth with increasing T. The EB and magnetotransport phenomena appear strictly intertwined: the FC M(H) and MR(H) loops exhibit a similar horizontal shift, corresponding to an exchange field of ∼460 Oe at T = 5 K, which decreases with increasing T and disappears at ∼200 K. Both the EB and the magnetotransport properties have been explained, considering the presence of a structurally disordered component of the NiO matrix around the Ni nanocrystallites, whose spin-glass-like magnetic character rules the interface exchange interaction with the Ni phase and the spin-dependent conductivity.
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75.30.Et Exchange and superexchange interactions
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Ns Metal-nonmetal contacts

Analytical description of a system of two interacting identical uniaxial ferromagnetic particles

Iulian Petrila and Alexandru Stancu

J. Appl. Phys. 110, 043923 (2011); http://dx.doi.org/10.1063/1.3626465 (4 pages)

Online Publication Date: 26 August 2011

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In this paper, we present an analytical method to study the magnetization processes of two magnetic particles with ferromagnetic or antiferromagnetic coupling by using a modified expression for the anisotropy free energy. By considering a system consisting of two uniaxial particles, coupled by a simple exchange interaction, we describe analytically: the particles orientations, switching points and hysteresis loops for different ferromagnetic or antiferromagnetic couplings and for different orientations of the applied field.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

The effect of magnetostatic coupling on spin configurations in ultrathin multilayers

M. Tekielak, R. Gieniusz, M. Kisielewski, P. Mazalski, A. Maziewski, V. Zablotskii, F. Stobiecki, B. Szymański, and R. Schäfer

J. Appl. Phys. 110, 043924 (2011); http://dx.doi.org/10.1063/1.3626747 (11 pages) | Cited 1 time

Online Publication Date: 26 August 2011

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(Co/Au)N ultrathin multilayers with perpendicular and in-plane magnetic anisotropy were studied experimentally using a combination of ferromagnetic resonance, magneto-optical magnetometry and microscopy (with both in-plane and out-of-plane magnetization-sensitive longitudinal and polar Kerr effects), and magnetic force microscopy (MFM). Three-dimensional magnetization distributions were reconstructed from micromagnetic simulations complemented by the measured magnetic parameters of the multilayers and observations by Kerr microscopy and MFM. It is shown that, in the reorientation phase transition (RPT) zone – the range of anisotropy characterized by 0 < Q < 1 (the ratio of the anisotropy energy to be gained by magnetization along the easy axis perpendicular to the sample surface, and the magnetostatic energy of a uniformly magnetized layer along the surface normal) – the three-dimensional magnetization distributions consist of alternating pairs of vortices and half-antivortices, both with in-plane magnetized cores and elliptical cross-sections. It is shown that an increase in N leads to a significant increase in the saturation field as well as changes in the hysteresis loop shape, domain structure size, and geometry. We demonstrate by simulations and prove by experimentation that, in multilayers with Q < 1, an increase in N induces the nucleation of out-of-plane magnetized domains, which then triggers magnetostatic interlayer coupling and RPT onset to out-of-plane magnetization states. We report on the observations of large micrometer-sized metastable domains (connected with the vortex cores) with the in-plane magnetization modulated by submicrometer-sized out-of-plane domains with sizes defined mainly by magnetostatics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Optimum condition for magnetic properties of two-phase soft magnetic alloys

Kai-Yuan He

J. Appl. Phys. 110, 043925 (2011); http://dx.doi.org/10.1063/1.3622583 (5 pages)

Online Publication Date: 26 August 2011

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It is well-known that the optimum condition to obtain the highest permeability and lowest coercive force for a soft magnetic material is that both K and λs are very small. In this paper, it is suggested that this optimum condition is sufficient only for the single phase soft magnetic material. For the material containing two phases, in order to obtain the best magnetic properties, a new condition must be added; the difference in the magnitude of the saturation magnetization of the two phases, ΔMS, should be very small. Only when the K, λs, and ΔMS are all very small can the best soft magnetic properties be obtained. A model describing the hindrance of the domain well motion by the ΔMS effect is suggested. Some examples in the nanocrystalline soft magnetic alloys are used to demonstrate the existence of the ΔMS effect.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
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