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21 Feb 2013

Volume 113, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt
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back to top Magnetism and Superconductivity

Thermal properties, magneto- and baro-caloric effects in La0.7Pb0.3MnO3 single crystal

A. V. Kartashev, E. A. Mikhaleva, M. V. Gorev, E. V. Bogdanov, A. V. Cherepakhin, K. A. Sablina, N. V. Mikhashonok, I. N. Flerov, and N. V. Volkov

J. Appl. Phys. 113, 073901 (2013); http://dx.doi.org/10.1063/1.4792044 (6 pages)

Online Publication Date: 15 February 2013

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The results of heat capacity, thermal dilatation and T-p phase diagram studies on the La0.7Pb0.3MnO3 single crystal are reported. Direct measurements of intensive magnetocaloric effect are performed by means of adiabatic calorimeter. Barocaloric effect is determined using data of heat capacity and susceptibility to hydrostatic pressure. Caloric efficiency of manganite in the vicinity of ferromagnetic phase transition is discussed and compared with that of other magnetic materials.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
81.30.Dz Phase diagrams of other materials
65.40.Ba Heat capacity
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Investigation of magnetic properties and microwave characteristics of obliquely sputtered NiFe/MnIr bilayers

Nguyen N. Phuoc, Wee Tee Soh, Guozhi Chai, and C. K. Ong

J. Appl. Phys. 113, 073902 (2013); http://dx.doi.org/10.1063/1.4792496 (6 pages)

Online Publication Date: 15 February 2013

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A comprehensive investigation of the magnetic properties and high frequency characteristics of NiFe/MnIr bilayers with regards to oblique deposition angle was conducted in conjunction with an analysis based on the Landau-Lifshitz-Gilbert equation. It was found that exchange bias can be significantly enhanced with the variation of oblique deposition angle, which is interpreted in terms of the formation of inclined columnar structure of the films often observed in samples fabricated by this oblique deposition technique. Moreover, the uniaxial magnetic anisotropy field and the resonance frequency are increased with the increasing of oblique deposition angle. The variations of effective Gilbert damping factor and the frequency linewidth with oblique deposition angle are also presented and discussed in details.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Revisiting magnetic stripe domains — anisotropy gradient and stripe asymmetry

Jeffrey McCord, Burak Erkartal, Thomas von Hofe, Lorenz Kienle, Eckhard Quandt, Olga Roshchupkina, and Jörg Grenzer

J. Appl. Phys. 113, 073903 (2013); http://dx.doi.org/10.1063/1.4792517 (5 pages)

Online Publication Date: 15 February 2013

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The thickness dependent generation of magnetic stripe domains in NiFe films is investigated by in-depth magnetic domain and micromagnetic analysis, as well as complementary analysis of the microstructure by x-ray diffraction and transmission electron microscopy. A gradient of perpendicular magnetic anisotropy with film thickness is found. Micromagnetic simulations show that the anisotropy gradient results in an asymmetric stripe domain configuration. Columnar grain coarsening and texture development with thickness are derived from the microstructural investigations. The variations correspondingly lead to the gradient of magnetic anisotropy and to an asymmetric magnetic stripe domain structure.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.jm Texture
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure

Dependence of the switching current density on the junction sizes in spin transfer torque

Chun-Yeol You and Myung-Hwa Jung

J. Appl. Phys. 113, 073904 (2013); http://dx.doi.org/10.1063/1.4792728 (5 pages)

Online Publication Date: 19 February 2013

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We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape.
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75.78.Cd Micromagnetic simulations
75.60.-d Domain effects, magnetization curves, and hysteresis
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Effect of barium-deficiency on the structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2−x◻xMnO3 (0 ≤ x ≤ 0.15)

R. M'nassri, W. Cheikhrouhou-Koubaa, N. Chniba Boudjada, and A. Cheikhrouhou

J. Appl. Phys. 113, 073905 (2013); http://dx.doi.org/10.1063/1.4792730 (7 pages)

Online Publication Date: 19 February 2013

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Structural, magnetic, and magnetocaloric properties of La0.6Sr0.2Ba0.2-x◻xMnO3 (0 ≤ x ≤ 0.15) where ◻ is a barium deficiency have been investigated by X-ray diffraction and magnetic measurements. Our samples were synthesized using the solid-state reaction method at high temperatures. Structural studies show that our samples are single phase and crystallize in the rhombohedral system with R math c space group. Magnetization measurements as a function of temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature TC shifts to lower values with increasing barium-deficiency. The Arrott plots show that the phase transition is of second order. The effect of barium deficiency on the magnetocaloric properties has been investigated. The values of the maximum of the magnetic entropy change, |−ΔSmax|, under a magnetic field change of 3.5 T are found to be 2.9, 2.92, 3.31, and 3.34 J/kg K for x = 0.0, 0.05, 0.1, and 0.15, respectively.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.gd Entropy

Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing

P. J. Metaxas, P.-J. Zermatten, R. L. Novak, S. Rohart, J.-P. Jamet, R. Weil, J. Ferré, A. Mougin, R. L. Stamps, G. Gaudin, V. Baltz, and B. Rodmacq

J. Appl. Phys. 113, 073906 (2013); http://dx.doi.org/10.1063/1.4792216 (10 pages)

Online Publication Date: 19 February 2013

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Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]m nanoplatelets, which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, Hret, which acts against the applied field, H. We show that Hret depends not only on the array geometry but also on the relative orientation of H and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement, and domain wall roughness that is dependent on the applied field polarity.
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81.05.Bx Metals, semimetals, and alloys
81.07.-b Nanoscale materials and structures: fabrication and characterization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetocaloric effect in inhomogeneous ferromagnets

N. G. Bebenin, R. I. Zainullina, and V. V. Ustinov

J. Appl. Phys. 113, 073907 (2013); http://dx.doi.org/10.1063/1.4792306 (7 pages)

Online Publication Date: 19 February 2013

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The article is devoted to the theoretical study of magnetocaloric effect in imhomogeneous ferromagnets in vicinity of magnetic phase transitions of first and second orders as well as in vicinity of tricritical and critical points. In the frame of Landau theory the formulae for the magnetic field induced entropy change are derived. The theory is compared with the experimental data obtained on single crystals of La0.7Ba0.3MnO3 (second order transition) and La0.7Ca0.3MnO3 (first order transition).
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Dd Nonmetallic ferromagnetic materials
71.70.Di Landau levels
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

The competing spin orders and fractional magnetization plateaus of the classical Heisenberg model on Shastry-Sutherland lattice: Consequence of long-range interactions

L. Huo, W. C. Huang, Z. B. Yan, X. T. Jia, X. S. Gao, M. H. Qin, and J.-M. Liu

J. Appl. Phys. 113, 073908 (2013); http://dx.doi.org/10.1063/1.4792504 (6 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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The competing spin orders and fractional magnetization plateaus of the classical Heisenberg model with long-range interactions on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating spin ordering sequence observed in TmB4 and other rare-earth tetraborides. The simulation reproduces the experimental 1/2 magnetization plateau at low temperature by considering multifold long range interactions. It is found that more local long range interactions can be satisfied in the 1/2 plateau state than those in the 1/3 plateau state, leading to the stabilization of the extended 1/2 plateau. The phase boundaries in the magnetic field at zero temperature are determined, demonstrating the simulation results. When the energies of the Neel state and the collinear state are degenerated, the former state is more likely to be stabilized due to the competitions among the local collinear spin orders. The present work provides a comprehensive proof of the phase transitions to the Neel state at nonzero temperature, in complimentary to the earlier predictions for the Fe-based superconductors.
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75.10.Hk Classical spin models
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Control of magnetic loss tangent of hexaferrite for advanced radio frequency antenna applications

Jaejin Lee, Yang-Ki Hong, Woncheol Lee, Gavin S. Abo, Jihoon Park, Won-Mo Seong, and Won-Ki Ahn

J. Appl. Phys. 113, 073909 (2013); http://dx.doi.org/10.1063/1.4793089 (6 pages)

Online Publication Date: 21 February 2013

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We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.
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84.40.Ba Antennas: theory, components and accessories
75.50.Gg Ferrimagnetics
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Ge1−xMnx heteroepitaxial quantum dots: Growth, morphology, and magnetism

J. Kassim, C. Nolph, M. Jamet, P. Reinke, and J. Floro

J. Appl. Phys. 113, 073910 (2013); http://dx.doi.org/10.1063/1.4792221 (7 pages)

Online Publication Date: 21 February 2013

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Heteroepitaxial Ge1-xMnx quantum dots (QDs) were grown on Si (001) by molecular beam epitaxial co-deposition, with x = 0 to 0.10, in order to explore the interaction between Mn content, surface morphological evolution, and magnetism. Morphological evolution typical of the Ge/Si (001) system was observed, where the effect of Mn on surface morphology is surprisingly minimal at low Mn content, with no obvious surface morphological indicators of second phase formation. As the Mn content increases, secondary phase formation becomes evident, appearing to heterogeneously nucleate on or within Ge QDs. Still higher Mn concentrations lead to extensive second phase formation interspersed with an array of Ge QDs. Although ferromagnetism up to 220 K is observed, likely arising from intermetallic precipitates, there is no clear evidence for room-temperature ferromagnetism associated with a dilute magnetic solution phase.
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81.05.Cy Elemental semiconductors
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.07.Ta Quantum dots

A simple formulation for magnetoresistance in metal-insulator granular films with increased current

M. A. S. Boff, B. Canto, M. N. Baibich, and L. G. Pereira

J. Appl. Phys. 113, 073911 (2013); http://dx.doi.org/10.1063/1.4793272 (4 pages)

Online Publication Date: 21 February 2013

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We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa's model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.
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81.05.Rm Porous materials; granular materials
72.25.-b Spin polarized transport
73.50.Dn Low-field transport and mobility; piezoresistance
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Reducing the writing field of L10-FePt by graded order parameter

Zhihong Lu, Junbo Guo, Zhanghua Gan, Yong Liu, Rui Xiong, G. J. Mankey, and W. H. Butler

J. Appl. Phys. 113, 073912 (2013); http://dx.doi.org/10.1063/1.4791583 (5 pages)

Online Publication Date: 21 February 2013

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The dependence of the magnetic properties of epitaxial Fe50Pt50 films on order parameter (S) was investigated. It was demonstrated that the magnetic anisotropy could be tuned by controlling S which can be controlled by the growth temperature. Based on this result, two kinds of multilayered structures, each with a 13 nm fully ordered Fe50Pt50 layer as the bottom layer, were built: (1) 4-layered structure with S decreasing layer by layer from bottom to top; (2) graded structure with S changing more continuously along the thickness. The magnetic properties of the films were characterized using vibrating sample magnetometry. It was found that both structures have their easy axis perpendicular to the film; the anisotropy fields of the 4-layered film and the graded film are 53 kOe and 37 kOe, respectively. These values are much lower than that of the fully ordered uniform Fe50Pt50 film (about 73 kOe). The results suggest that it may be possible to reduce the writing field of Fe50Pt50 by gradually changing the order parameter.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

A flow simulation study of protein solution under magnetic forces

Hidehiko Okada, Noriyuki Hirota, Shinji Matsumoto, and Hitoshi Wada

J. Appl. Phys. 113, 073913 (2013); http://dx.doi.org/10.1063/1.4792650 (8 pages)

Online Publication Date: 21 February 2013

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We have developed a superconducting magnet system generating magnetic forces able to compensate gravity and suppress convection of diamagnetic protein solution from which protein crystals precipitate. A simulation model has been proposed to elucidate the motion of protein solutions and search for the optimal conditions of the crystal formation process. This model incorporates general, non-uniform magnetic forces as external forces, while the previous models involve only simple, uniform magnetic forces. The simulation results indicate that the vertical component can suppress the convection of protein solution, while the horizontal component induces minimal convection. We, therefore, need to take into account the both components when considering the formation of protein crystals under magnetic forces.
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87.14.E- Proteins
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