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1 May 2010

Volume 107, Issue 9, Articles (09xxxx)

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back to top Magnetism and Superconductivity

Frequency response of magnetoelectric 1–3-type composites

K. H. Lam, C. Y. Lo, and H. L. W. Chan

J. Appl. Phys. 107, 093901 (2010); http://dx.doi.org/10.1063/1.3399703 (5 pages) | Cited 4 times

Online Publication Date: 3 May 2010

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A three-phase magnetoelectric (ME) composite consisting of Pb(Zr,Ti)O3 rods embedded in a matrix of Terfenol-D/epoxy (TDE) pseudo 1–3 composites has been fabricated. Besides the large ME effect, its frequency response under a magnetic bias field has been studied. It was found that the resonance shifts to lower frequency with increasing bias field. Due to the magnetomechanical characteristics of the TDE pseudo 1–3 medium, the composite shows a similar trend in ME performance. Magnetic-field dependence of the frequency shift provides a means to tune the performance of ME sensors based on the composite.
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81.05.Qk Reinforced polymers and polymer-based composites
75.85.+t Magnetoelectric effects, multiferroics
75.80.+q Magnetomechanical effects, magnetostriction

Multiferroic properties in Ba0.93Bi0.07Ti1−xMnxO3 ceramics

C. H. Wang, S. L. Yuan, S. Y. Yin, Z. M. Tian, and P. Li

J. Appl. Phys. 107, 093902 (2010); http://dx.doi.org/10.1063/1.3402285 (4 pages) | Cited 1 time

Online Publication Date: 3 May 2010

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Nominal composition of Ba0.93Bi0.07Ti1−xMnxO3 (x = 0, 0.02, and 0.04) ceramics have been prepared by a modified Pechini method. X-ray diffraction analysis reveals that the samples are pure perovskite BaTiO3 (BTO) structure with no trace of impurity phase. The cell volume of the composites increases monotonously with the increase in Mn content, which indicates that Mn ions have been incorporated into the lattice of Ba0.93Bi0.07TiO3. The samples are experimentally confirmed to show ferromagnetic (FM) and ferroelectric behaviors simultaneously at room temperature. The temperature dependent magnetic behaviors show complex magnetic interactions including FM, antiferromagnetic, and paramagnetic. These results suggest that the dopant Bi and Mn help BTO transit from pure ferroelectric to multiferroic materials and the magnetic behaviors can be explained by the bound magnetic polaron model with inhomogeneity of Mn dopant distribution.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Ee Antiferromagnetics
75.85.+t Magnetoelectric effects, multiferroics
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials

Quasiparticle density of states measurements in clean superconducting AlMn alloys

G. C. O’Neil, D. R. Schmidt, N. A. Tomlin, and J. N. Ullom

J. Appl. Phys. 107, 093903 (2010); http://dx.doi.org/10.1063/1.3369280 (6 pages) | Cited 2 times

Online Publication Date: 6 May 2010

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Aluminum doped with Manganese (AlMn) forms a superconducting alloy with the transition temperature suppressed by the added manganese. We present quasiparticle density of states (DOS) measurements on superconducting AlMn alloys made by current-voltage measurements on normal-metal/insulator/superconductor tunnel junctions. The DOS remains Bardeen-Cooper-Schrieffer-like with a reduced gap, matching the predictions of Kaiser. However, we measure additional subgap states not predicted by Kaiser, and demonstrate that these subgap states will harm some potential applications.
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71.20.Gj Other metals and alloys
74.20.Pq Electronic structure calculations
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.20.Fg BCS theory and its development
71.30.+h Metal-insulator transitions and other electronic transitions

Extraction of the tunnel magnetocapacitance with two-terminal measurements

Yin-Ming Chang, Kai-Shin Li, Hongbo Huang, Mean-Jue Tung, Shi-Yuan Tong, and Minn-Tsong Lin

J. Appl. Phys. 107, 093904 (2010); http://dx.doi.org/10.1063/1.3407509 (4 pages) | Cited 3 times

Online Publication Date: 6 May 2010

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The tunnel magnetocapacitance (TMC) of the magnetic tunnel junction has been investigated with a series of complex impedance spectra measured at varying magnetic field. To avoid the circuit complication in the four-terminal measurement with high frequency operation, two-terminal approach was developed by elimination of spin independent contribution apart from the junction area. A subsequent fitting process based on the difference spectra analysis gave the TMC ratio of −0.43% with the opposite dependence on the field as compared to the tunnel magnetoresistance (TMR) of 30.67%. This technique would be applied in the further development and integration of spintronics devices.
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75.85.+t Magnetoelectric effects, multiferroics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

The critical current density, irreversibility line, and flux pinning properties of Ba2CaCu2O4(O,F)2 high-Tc superconductor

P. M. Shirage, Y. Tanaka, and A. Iyo

J. Appl. Phys. 107, 093905 (2010); http://dx.doi.org/10.1063/1.3369446 (6 pages) | Cited 2 times

Online Publication Date: 6 May 2010

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The high-Tc superconductor of Ba2CaCu2O4(O,F)2 (F-0212) is an appealing material for application as it has a simple crystal structure with a highest Tc of 108 K. We have derived the intragrain critical current density (Jc), irreversibility field (Birr), flux pinning properties, etc., for the polycrystalline samples from under doping (Tc = 82 K) to slightly-over doping (Tc = 106 K) from the dc magnetization hysteresis loops. The Jc and Birr properties were found to improve rapidly as the doping state changes from under doping to slightly-over doping. Here we show that property of the spacing is crucial to enhance Birr as well as its thickness. An anisotropy factor for under doped Ba2CaCu2O4F2 was reckoned to 118 from a three-dimensional-two-dimensional crossover field of about 0.28 T. The double logarithmic plot of irreversibility field versus [1−(T/Tc)] analysis hints that the flux line melting model is adopted. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field bmax = 0.2 agree with surface pinning mechanism with closely spaced pins.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.72.U- Doping and impurity implantation

Effect of Bi doping on magnetic and magnetocaloric properties of La0.7−xBixSr0.3MnO3 (0 ≤ x ≤ 0.4)

S. K. Barik and R. Mahendiran

J. Appl. Phys. 107, 093906 (2010); http://dx.doi.org/10.1063/1.3407523 (6 pages) | Cited 5 times

Online Publication Date: 6 May 2010

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We investigated the effect of Bi doping on magnetic and magnetocaloric properties of La0.7−xBixSr0.3MnO3 (x = 0.0–0.4). It is shown that the low temperature ground state changes from a ferromagnet (x = 0) to a charge-ordered antiferromagnet for x = 0.4. While the paramagnetic-ferromagnetic (PM-FM) transition is second-order in x ≤ 0.25, it changes into first-order for x = 0.3 which is at the magnetic phase boundary. The changes in the magnetic ground state affect magnetic entropy. The magnitude of the isothermal magnetic entropy (|ΔSM|) at the FM Curie temperature increases from 4.56 J/kg K for x = 0 to a maximum value of 5.02 J/kg K for x = 0.05 and then decreases to nearly zero for x = 0.4 at the charge order transition. In contrast to x ≤ 0.25, the ΔSM of x = 0.3 is magnetic history dependent and its temperature dependence exhibits a clear step at TCO = 260 K followed by a plateau between 240 and 185 K. Although |ΔSM| = 3.1 J/kg K of x = 0.3 is small compared to other compositions, it has a high relative cooling power (325 J/kg) which is desirable for magnetic refrigeration over a wide temperature. The unusual magnetic and magnetocaloric properties of x = 0.3 are attributed to the existence of short-range charge-orbital (CO) correlations in the PM state. It is suggested that harnessing competition between FM spin ordering and CO correlations may provide a strategy to enhance magnetic refrigeration capacity over a wide temperature range.
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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.)
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys

Magnetoelectric effect in lead-free BNKLBT ceramic/terfenol-D continue fiber composite laminates

C. Y. Lo, S. H. Choy, S. W. Or, and H. L. W. Chan

J. Appl. Phys. 107, 093907 (2010); http://dx.doi.org/10.1063/1.3385413 (4 pages)

Online Publication Date: 6 May 2010

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A magnetostrictive-piezoelectric laminated composite has been developed by sandwiching a lead-free BNKLBT ceramic plate polarized in the thickness direction between two terfenol-D continuous fiber composite plates. This lead-free magnetoelectric (ME) laminated composite has a large ME voltage sensitivity of 2.5 V/Oe at the resonance frequency of 130.9 kHz under a low magnetic bias field (HBias) of 0.6 kOe. This work shows the potential of BNKLBT lead-free ceramics in ME sensing application.
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75.85.+t Magnetoelectric effects, multiferroics
77.84.Cg PZT ceramics and other titanates
81.05.Mh Cermets, ceramic and refractory composites

The influence of magnetic anisotropy on magnetoelectric behavior in conical spin ordered multiferroic state

Xiaoyan Yao, Veng Cheong Lo, and Jun-Ming Liu

J. Appl. Phys. 107, 093908 (2010); http://dx.doi.org/10.1063/1.3407541 (5 pages)

Online Publication Date: 6 May 2010

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For the magnetism-driven multiferroic materials, the magnetic anisotropy plays an essential role in the magnetoelectric behavior. To understand the influence of magnetic anisotropy on multiferroic state resulting from the conical spin order, we have performed Monte Carlo simulation on a three-dimensional classical Heisenberg model in spinel lattice. The single-ion anisotropy from the easy-axis type to the easy-plane type is considered in the system, and the corresponding magnetoelectric behavior is investigated under a rotating external magnetic field (h). It is revealed that the magnetic anisotropy drags the orientation of conical spin structure slightly away from the direction of h, and distorts the conical spin structure as well. The balance between h and the anisotropy results in the anisotropic magnetoelectric properties during the rotation of h.
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75.85.+t Magnetoelectric effects, multiferroics
75.10.Jm Quantized spin models, including quantum spin frustration
75.30.Gw Magnetic anisotropy
77.80.-e Ferroelectricity and antiferroelectricity

ac losses and field and current density distribution during a full cycle of a stack of superconducting tapes

Weijia Yuan, A. M. Campbell, and T. A. Coombs

J. Appl. Phys. 107, 093909 (2010); http://dx.doi.org/10.1063/1.3371190 (12 pages) | Cited 8 times

Online Publication Date: 6 May 2010

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Starting from an existing model by Clem et al. , this paper has analyzed how the current density and magnetic field distribution of a stack of superconducting tapes with ac transport currents or applied fields will change in a full cycle. This paper assumes when the ac current or field starts to change in the other direction, a new penetrated region will begin to penetrate from the superconductor surface. If we assume Jc is constant in the critical region, this paper demonstrates that the Claassen formula ( 7 ) can be used to calculate the exact ac losses. If Jc depends on local Bz, we can use Eq. ( 9 ) to quickly predict the ac losses. This approach does not need to calculate a complete ac cycle. This saves considerably computation time while gives a result which is in close agreement with that calculated from a complete ac cycle. The calculation method can be applied for calculating a superconducting pancake coil if the coil radius is much larger than the tape width.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
84.71.Ba Superconducting magnets; magnetic levitation devices
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Influence of nano-oxide layer on the giant magnetoresistance and exchange bias of NiMn/Co/Cu/Co spin valve sensors

Anoop Gupta, Senthilnathan Mohanan, Michael Kinyanjui, Andrey Chuvilin, Ute Kaiser, and Ulrich Herr

J. Appl. Phys. 107, 093910 (2010); http://dx.doi.org/10.1063/1.3407569 (5 pages) | Cited 3 times

Online Publication Date: 6 May 2010

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NiMn is an interesting material for achieving a high exchange bias in spin valve systems. We investigated the influence of a nano-oxide layer (NOL) inserted in the pinned Co layer on the magnetotransport properties of NiMn/Co/Cu/Co spin valve sensors. The samples were annealed at 350 °C for 10 min to achieve the antiferromagnetic L10 ordered structure of NiMn. The NOL has been characterized by small angle x-ray reflectivity, transmission electron microscopy (TEM), and energy filtered TEM. The inclusion of the NOL leads to an increase in the giant magnetoresistance (GMR) by 20 % indicating a high degree of specular reflection at the NOL. For NOL positions close to the NiMn/Co interface, a decrease in the exchange bias field (Hex) is observed. The best combination of high GMR value and large Hex was found when the NOL was inserted in the center of the pinned Co layer.
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75.47.De Giant magnetoresistance
81.40.Gh Other heat and thermomechanical treatments
75.50.Ee Antiferromagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

The electronic structure and spin polarization of Fe3−xMnxSi and Fe3−yMnSiy alloys

Bothina Hamad, Jamil Khalifeh, Ibrahim Abu Aljarayesh, Claude Demangeat, Hu-Bin Luo, and Qing-Miao Hu

J. Appl. Phys. 107, 093911 (2010); http://dx.doi.org/10.1063/1.3388640 (7 pages) | Cited 8 times

Online Publication Date: 6 May 2010

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First principle calculations using supercell approach and coherent potential approximation (CPA) are performed to investigate the electronic and magnetic structures of Fe3−xMnxSi and Fe3−yMnSiy alloys, where x,y = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.5, 1.75, and 2.25. Using supercell calculations we obtained a metallic behavior for x = 0, 0.25, and 0.5 in Fe3−xMnxSi alloys with spin polarizations of 24%, 39%, and 93%, respectively. The behavior starts to be half-metallic at x = 0.75 with a small direct band gap that increases for higher concentrations of Mn. Among the half-metallic systems, only those of L21 structure at x = 1 and 2 possess indirect band gaps along Γ-X symmetry line. The change of Si concentration in Fe3−yMnSiy structures retrieve the metallic behavior for all concentrations except y = 1.25 that shows a half-metallic behavior with a direct band gap of 0.27 eV. We obtained a good agreement between supercell and CPA calculations for the values of the magnetic moment and the trends of the formation energies, which reveals the validity of the supercell approach in predicting the magnetic structure and the energetics of doped Heusler alloys.
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71.20.Be Transition metals and alloys
71.15.-m Methods of electronic structure calculations
72.25.Ba Spin polarized transport in metals
75.30.Cr Saturation moments and magnetic susceptibilities

Electric-field control of strain-mediated magnetoelectric random access memory

Jia-Mian Hu, Zheng Li, Jing Wang, and C. W. Nan

J. Appl. Phys. 107, 093912 (2010); http://dx.doi.org/10.1063/1.3373593 (10 pages) | Cited 18 times

Online Publication Date: 6 May 2010

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A strain-mediated magnetoelectric random access memory with electric-field-writing is presented, which consists of a magnetic tunnel junction (MTJ) in intimate contact with a ferroelectric (FE) layer. The calculations show that the magnetization vector in the free layer of the MTJ unit can switch in-plane by 90° upon applying an appropriate electric field to the FE layer, as compared to the common 180° reversal induced by magnetic field or spin-current. A perfect interface between the FE layer and the MTJ is assumed. The free layers used for illustration include either (001)-oriented or polycrystalline magnetic films of Fe–Co alloy, CoFe2O4 (CFO), Ni, and Fe3O4. Among them, the (001)-oriented FeCo and CFO films with positive magnetocrystalline anisotropy constant (i.e., K1>0) show an abrupt magnetization switching, while a gradual magnetization switching takes place in the (001)-oriented Ni and Fe3O4 films with K1<0 as well as the polycrystalline films. Such electric-field-induced in-plane magnetization switching can result in a remarkable change in the MTJ’s electric resistance. In particular, hysteretic dependence of the device resistance on the applied electric field is obtained for the cases of the (001)-oriented FeCo and CFO free layers that exhibit the abrupt magnetization switching, whereby a nonvolatile information storage process can be achieved. The influence of the shape of the free layer on both magnetization and resistance switching features is discussed.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Spin polarization decay in magnetic tunnel junctions with semimetal-inserted layers

Kyoung-Il Lee, Jong Wook Roh, Kiyoung Lee, Joonyeon Chang, Kyung-Ho Shin, Mark Johnson, and Wooyoung Lee

J. Appl. Phys. 107, 093913 (2010); http://dx.doi.org/10.1063/1.3415540 (4 pages) | Cited 1 time

Online Publication Date: 6 May 2010

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Magnetic tunnel junctions (MTJs) were fabricated with a thin layer of semimetallic bismuth inserted between the tunnel barrier and the top ferromagnetic electrode. The tunneling magnetoresistance (TMR) was measured on a set of samples for which the thickness of the inserted layer varied from 0 to 20 nm. The TMR decreased with an exponential decay length that was found to be ΛBi = 4.1 nm = 0.48 λF,Bi, where λF,Bi is the Fermi wavelength measured in comparable Bi films. This result is in remarkably good agreement with the decay length previously measured in MTJs with inserted copper layers, λCu = 0.58 λF,Cu, even though the values of λF differ by an order of magnitude. It thereby gives a confirmation that the characteristic length scale of the tunneling density of states is the Fermi wavelength. Measurements of TMR as a function of bias voltage show a large asymmetry and the peak TMR is shifted to a nonzero value.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport

Electron spin resonance in CuCrS2 chrome-copper disulphides synthesized by different methods

Galina Abramova, Anatolii Pankrats, German Petrakovskii, Julia C. E. Rasch, Martin Boehm, Aleksandr Vorotynov, Vasilii Tugarinov, Rita Szumszak, Asya Bovina, and Viktor Vasil’ev

J. Appl. Phys. 107, 093914 (2010); http://dx.doi.org/10.1063/1.3374679 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2010

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The electron spin resonance (ESR) in CuCrS2 disulphides is found to be strongly dependent on a synthesis method used. At a temperature of 300 K, a polycrystalline CuCrS2 sample is paramagnetic with a g-value of 1.95 at 40 K, it undergoes the magnetic transition. In the temperature range 4.2–290 K, a single-crystal sample prepared by a chemical vapor transport method exhibits the ESR features typical of a ferromagnet. It is shown that these features are related to the presence of a small amount of the single-crystal CuCr2S4 impurity in the CuCrS2 single crystal.
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76.30.-v Electron paramagnetic resonance and relaxation
75.50.Pp Magnetic semiconductors
61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)

Magnetic properties of granular CoCrPt:SiO2 films as tailored by Co+ irradiation

Stefan Tibus, Thomas Strache, Felix Springer, Denys Makarov, Hartmut Rohrmann, Thomas Schrefl, Jürgen Fassbender, and Manfred Albrecht

J. Appl. Phys. 107, 093915 (2010); http://dx.doi.org/10.1063/1.3393960 (5 pages) | Cited 2 times

Online Publication Date: 6 May 2010

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We report on an approach to tailor the magnetic exchange in a conventional granular CoCrPt:SiO2 recording medium by irradiation with Co+ ions. Irradiation at low fluences enhances the intergranular exchange resulting in a narrowing of the switching field distribution (SFD). The modification of magnetic exchange coupling was evidenced by measuring the angular dependence of the switching field and is supported by an increase in the magnetic domain size. Further, micromagnetic simulations of a granular magnetic medium confirm the correlation between intergranular exchange and SFD. At high fluences, however, the irradiation damages lead to the degradation of the magnetic layer as magnetic anisotropy and saturation magnetization decrease. Ion irradiation simulations suggest that this is caused by strong intermixing at the grain and layer interfaces.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
61.82.-d Radiation effects on specific materials

Ferromagnetic resonance and magnetoelastic demodulation in thin active films with an uniaxial anisotropy

A. Klimov, Yu. Ignatov, N. Tiercelin, V. Preobrazhensky, P. Pernod, and S. Nikitov

J. Appl. Phys. 107, 093916 (2010); http://dx.doi.org/10.1063/1.3382911 (6 pages) | Cited 1 time

Online Publication Date: 7 May 2010

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The results of experimental and theoretical studies of ferromagnetic resonance (FMR) and magnetoelastic excitations near the spin reorientation transition (SRT) in an uniaxial TbCo2/FeCo layered nanostructure and a La0.7Sr0.3MnO3 film are reported. Experimental dependences of the amplitude of the reflected microwave signal versus the external magnetic field strength are presented in comparison with the theoretical ones. An increase in FMR reflectivity in the vicinity of SRT is clearly demonstrated. Low frequency magnetoelastic excitation of flexural vibrations of the samples by means of modulated microwave electromagnetic field is observed experimentally using a laser beam deflection technique. The increase in amplitude of vibrations at modulation frequency under combined FMR and SRT conditions is observed in agreement with the theory.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

Interlayer exchange coupling and current induced magnetization switching in magnetic tunnel junctions with MgO wedge barrier

Witold Skowroński, Tomasz Stobiecki, Jerzy Wrona, Karsten Rott, Andy Thomas, Günter Reiss, and Sebastiaan van Dijken

J. Appl. Phys. 107, 093917 (2010); http://dx.doi.org/10.1063/1.3387992 (4 pages) | Cited 3 times

Online Publication Date: 7 May 2010

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Current induced magnetization switching and interlayer exchange coupling (IEC) in sputtered CoFeB/MgO/CoFeB exchange-biased magnetic tunnel junctions with an extremely thin (0.96–0.62 nm) MgO wedge barrier is investigated. The IEC is found to be ferromagnetic for all samples and the associated energy increases exponentially down to a barrier thickness of 0.7 nm. Nanopillars with resistance area product ranging from 1.8 to 10 Ω μm2 and sizes of 0.13 μm2 down to 0.03 μm2 and tunneling magnetoresistance values of up to 170% were prepared. We found, that the critical current density increases with decreasing MgO barrier thickness. The experimental data and theoretical estimations show that the barrier thickness dependence of the spin transfer torque can largely be explained by a reduction in the tunnel current polarization at very small barrier thickness.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Jk Magnetization reversal mechanisms
75.76.+j Spin transport effects
72.25.-b Spin polarized transport
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.-y Studies of specific magnetic materials

Structural, electronic, and magnetic properties of Co doped SnO2 nanoparticles

Aditya Sharma, Abhinav Pratap Singh, P. Thakur, N. B. Brookes, Shalendra Kumar, Chan Gyu Lee, R. J. Choudhary, K. D. Verma, and Ravi Kumar

J. Appl. Phys. 107, 093918 (2010); http://dx.doi.org/10.1063/1.3415541 (7 pages) | Cited 7 times

Online Publication Date: 7 May 2010

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We present a detailed study on the structural, electronic, and magnetic properties of chemically synthesized Sn1−xCoxO2 (x = 0.00 to 0.05) nanoparticles. X-ray diffraction and transmission electron microscope measurements were performed to analyze the crystal structure and morphology of Sn1−xCoxO2 nanoparticles. The energy dispersive x-ray analysis measurements were performed to check the possible presence of any impurity elements in the nanocrystals. The near edge x-ray absorption fine structure (NEXAFS) experiments at Sn M5,4-edge and Co L3,2-edge were performed to probe the local environment of Sn and Co ions in the SnO2 matrix. The NEXAFS at Co L3,2-edge, along with multiplet calculations, indicate that the Co is substituted at the Sn site in SnO2 matrix with +2 charge state and do not form metallic clusters and other oxide phases. The ferromagnetic nature of these materials was confirmed by x-ray magnetic circular dichroism and room temperature magnetization hysteresis loop measurements.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Lf Electronic structure of magnetic nanoparticles
78.20.Ls Magneto-optical effects
61.66.Fn Inorganic compounds

The Ho2MnRuO7 pyrochlore oxide: Magnetic structure versus magnetic frustration

M. Retuerto, M. J. Martínez-Lope, C. de la Calle, R. Martínez-Coronado, M. García-Hernández, J. A. Alonso, and M. T. Fernández-Díaz

J. Appl. Phys. 107, 093919 (2010); http://dx.doi.org/10.1063/1.3393994 (7 pages) | Cited 2 times

Online Publication Date: 7 May 2010

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A pyrochlore-like phase of composition Ho2MnRuO7 has been synthesized by a soft-chemistry procedure followed by thermal treatments at moderate temperatures up to 900 °C for 12 h in air. It has been characterized by x-ray diffraction and neutron powder diffraction (NPD), as well as dc and ac susceptibilities. As in the parent Ho2Mn2O7 oxide, the magnetic Mn and Ru ions statistically occupy the 16c sites in a cubic unit cell with space group Fdmathm, which define a potentially frustrated three-dimensional array of corner sharing (Mn,Ru)4 tetrahedra. The dc and ac magnetic susceptibilities of Ho2MnRuO7 display a sharp increase near 60 K. In addition, the field-cooled and zero-field-cooled curves diverge below 30 K. The ac data present frequency variability below 60 K and broad frequency dependent maxima at lower temperatures ( ∼ 30 K), suggesting a spin-glass like behavior similar to Ho2Mn2O7. However, a low-temperature NPD study of the magnetic structure unveils an antiferromagnetic coupling of two subsets of Mn4+/Ru4+ spins, indicating that the magnetic frustration is partially relieved by the random distribution of Mn and Ru over the 16c sites; at lower temperatures there is a polarization of the Ho3+ magnetic moments, which also participate in the magnetic structure. Under an external magnetic field the Ho moments become totally polarized, giving a saturation magnetization at 2 K of 10.8 μB/f.u. at 5 T.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
81.40.Gh Other heat and thermomechanical treatments
75.50.Lk Spin glasses and other random magnets
75.30.Cr Saturation moments and magnetic susceptibilities

Cluster spin glass behavior in Bi(Fe0.95Co0.05)O3

Qingyu Xu, Shengqiang Zhou, D. Wu, Marc Uhlarz, Y. K. Tang, Kay Potzger, M. X. Xu, and Heidemarie Schmidt

J. Appl. Phys. 107, 093920 (2010); http://dx.doi.org/10.1063/1.3406150 (4 pages) | Cited 8 times

Online Publication Date: 10 May 2010

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The static and time-dependent magnetic properties of Bi(Fe0.95Co0.05)O3 have been investigated by dc and ac magnetization measurements. Cluster spin glass has been confirmed to be the ground state due to the frustration of the interaction between the ferromagnetic clusters by canted antiferromagnetically arranged Fe spins (Tc>350 K) and by ferrimagnetically arranged Co and Fe spins (Tc ∼ 250 K). Two freezing temperatures Tf of about 260 and 100 K have been clearly identified from the abrupt change in magnetization relaxation. The higher Tf is related to the canted antiferromagnetically arranged Fe spins, and the lower Tf is related to the ferrimagnetically arranged Co and Fe spins. The cluster spin glass behavior with two freezing temperatures has been confirmed by ac susceptibility measurements.
Show PACS
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
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