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15 Oct 2005

Volume 98, Issue 8, Articles (08xxxx)

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Diode effect in magnetic tunnel junctions with impurities

F. Kanjouri, N. Ryzhanova, N. Strelkov, A. Vedyayev, and B. Dieny

J. Appl. Phys. 98, 083901 (2005); http://dx.doi.org/10.1063/1.1997294 (4 pages) | Cited 5 times

Online Publication Date: 18 October 2005

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The influence on the I-V characteristics and tunnel magnetoresistance (TMR) of impurities embedded into the insulating barrier (math) separating the two ferromagnetic electrodes (math) of a magnetic tunnel junction was theoretically investigated. When the energy of the electron bound state at the impurity site is close to the Fermi energy, the current and TMR are strongly enhanced in the vicinity of the impurity. If the position of the impurity inside the barrier is asymmetric, e.g., closer to one of the math/math interfaces, the I-V characteristic exhibits a quasidiode behavior. The cases of a single impurity and of a planar random distribution of impurities were both studied.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
61.72.S- Impurities in crystals

Electron-spin-resonance analysis of magnetic ordering in Co58Mn20B10Si12 amorphous alloy

Chong Seung Yoon, Keum Jee Chung, Ji Won Kim, and Chang Kyung Kim

J. Appl. Phys. 98, 083902 (2005); http://dx.doi.org/10.1063/1.2089163 (5 pages) | Cited 1 time

Online Publication Date: 20 October 2005

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Electron-spin-resonance (ESR) spectroscopy was used to study the magnetic structure of the paramagnetic Co58Mn20B10Si12 amorphous alloy, produced by melt spinning. The room-temperature ESR spectrum consisted of two resonance peaks (g = 2.00 and g = 5.22). The resonance peak at g = 5.22 was tentatively attributed to a possible existence of Co2+ ion clusters in the amorphous alloy. It was also shown that the ESR data obtained at different temperatures were consistent with the magnetic measurement, proving that ESR can be a useful tool probing magnetic states in an amorphous metal alloy. Moreover, the ESR spectra from the thermally annealed alloy showed that the peak at g = 5.22 is sensitive to the annealing temperature, suggesting that this resonance peak can be used as a signature signal for a magnetic sensor.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
76.30.-v Electron paramagnetic resonance and relaxation
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
81.40.Gh Other heat and thermomechanical treatments

Magnetic properties of amorphous iron nitride films by ion-beam sputtering

Ranu Dubey and Ajay Gupta

J. Appl. Phys. 98, 083903 (2005); http://dx.doi.org/10.1063/1.2076443 (6 pages) | Cited 7 times

Online Publication Date: 20 October 2005

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Amorphous films of magnetic iron nitride have been prepared by reactive ion-beam sputtering. The amorphous microstructure is expected to have several advantages over the crystalline films in terms of high-frequency applications. Films of two different compositions have been prepared by varying the partial pressure of N2. The structural and magnetic properties of the films have been studied using x-ray scattering, Mössbauer spectroscopy, and magneto-optic Kerr-effect measurements. The films are found to transform into a mixture of nanocrystalline ε-Fe3N and α-Fe phases in the temperature range 473-523 K. Mössbauer measurements in the nanocrystalline specimens give the composition of the two samples as Fe0.83N0.17 and Fe0.87N0.13 and saturation magnetization as 176 and 191 emu/g, respectively. The films exhibit excellent surface smoothness, which may be attributed to their amorphous microstructure. The as-deposited films exhibit corecivity of about 54 Oe, which increases upon nanocrystallization. The observed behavior of the coercivity can be understood in terms of a random-anisotropy model taking into account the reduced dimensionality of the system.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
78.20.Ls Magneto-optical effects

Control of magnetic vortex chirality in square ring micromagnets

A. Libál, M. Grimsditch, V. Metlushko, P. Vavassori, and B. Jankó

J. Appl. Phys. 98, 083904 (2005); http://dx.doi.org/10.1063/1.2113407 (6 pages) | Cited 13 times

Online Publication Date: 24 October 2005

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We investigate the effect of a deliberately introduced shape asymmetry on magnetization reversal in small, square-shaped, magnetic rings. The magnetization reversal process is investigated using the diffracted magneto-optical Kerr effect combined with micromagnetic simulations. Experimentally we find that the reversal path is sensitive to small (±1°) changes in the direction of the applied field. Micromagnetic simulations that reproduce the measured zeroth- and first-order loops allow us to identify the reversal mechanisms as due to different intermediate states, namely, the so-called vortex and horseshoe states. Based on our results we are now able to prescribe a methodology for writing a vortex state with specific chirality in these asymmetric rings. Such control will be necessary if patterned arrays of this kind are to be used as magnetic storage elements.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects

Transition from ferromagnetism to antiferromagnetism in Ga1−xMnxN

Gustavo M. Dalpian and Su-Huai Wei

J. Appl. Phys. 98, 083905 (2005); http://dx.doi.org/10.1063/1.2115091 (4 pages) | Cited 12 times

Online Publication Date: 24 October 2005

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Using density-functional theory, we study the magnetic stability of the Ga1−xMnxN alloy system. We show that unlike Ga1−xMnxAs, which shows only ferromagnetic phase, Ga1−xMnxN can be stable in either ferromagnetic or antiferromagnetic phases depending on the alloy concentration. The magnetic order can also be altered by applying pressure or with charge compensation. A band-structure model is used to explain these behaviors.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Effect of electric/magnetic field on pinned/biased moments at the interfaces of magnetic superlattices

P. Padhan and W. Prellier

J. Appl. Phys. 98, 083906 (2005); http://dx.doi.org/10.1063/1.2123372 (4 pages) | Cited 2 times

Online Publication Date: 31 October 2005

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We have observed the pinned/biased moments in the superlattices consisting of a ferromagnetic (FM) SrRuO3 (SRO) and an antiferromagnetic (AFM) SrMnO3 (SMO) bilayer. The alternate stacking of SRO and SMO leading to a low-field positive magnetoresistance with enhanced hysteretic field-dependent magnetoresistance under the application of the out-of-plane magnetic field. We attribute these effects to the observed biased/pinned magnetic moments in the SRO layer in the vicinity of the interfaces. In addition, the biased/pinned moments can be oriented under the application of either the out-of-plane magnetic field or a combination of out-of-plane magnetic field and in-plane electric field. These results will bring new insights in the understanding of the coupling at the AFM/FM interface that can be useful for creating new exotic phenomena at the interfaces of the multilayer.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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