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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Vortex circulation control in mesoscopic ring magnets

M. Kläui, J. Rothman, L. Lopez-Diaz, C. A. F. Vaz, J. A. C. Bland, and Z. Cui

Appl. Phys. Lett. 78, 3268 (2001); http://dx.doi.org/10.1063/1.1361282 (3 pages) | Cited 72 times

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We present a simple method to control the direction of the circulation of the magnetization in mesoscopic ring magnets, using a uniform magnetic field only. The method is based on the nucleation free switching which occurs when the rings switch from the near-saturated state, referred to as the “onion state,” to the flux-closed vortex state. Two possible onion states, forward or reverse magnetized, are possible for a given direction of the magnetic field. Going from the forward or the backward onion state, both local scanning Kerr microscopy measurements and micromagnetic simulations show that the clockwise or the counterclockwise vortex state, respectively, can be selected due to asymmetric pinning of the two domain walls that are present in the onion state. © 2001 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Structural and magnetic properties of GaMnAs layers with high Mn-content grown by migration-enhanced epitaxy on GaAs(100) substrates

J. Sadowski, R. Mathieu, P. Svedlindh, J. Z. Domagała, J. Bak-Misiuk, K. Światek, M. Karlsteen, J. Kanski, L. Ilver, H. Åsklund, and U. Södervall

Appl. Phys. Lett. 78, 3271 (2001); http://dx.doi.org/10.1063/1.1370535 (3 pages) | Cited 32 times

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Ferromagnetic GaMnAs containing up to 10% Mn has been grown by migration-enhanced epitaxy at a substrate temperature of 150 °C. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.90 Å, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition-dependent density of point defects. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.3% is broken. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.66.Fn Inorganic compounds

Tantalum oxide as an alternative low height tunnel barrier in magnetic junctions

P. Rottländer, M. Hehn, O. Lenoble, and A. Schuhl

Appl. Phys. Lett. 78, 3274 (2001); http://dx.doi.org/10.1063/1.1374223 (3 pages) | Cited 31 times

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Magnetic tunnel junctions with a barrier of tantalum oxide were prepared by plasma oxidation of sputter-deposited tantalum. They show magnetoresistance ratios of 2.5% at room temperature and 4% at low temperatures. The material exhibits low barrier heights of ∼0.4 eV. This makes it possible to substantially increase the barrier thickness, compared to a barrier of aluminum oxide. The resulting decrease of coupling between the ferromagnetic layers is easily seen. Tantalum oxide appears to be a candidate for use as a tunnel barrier of spin-dependent tunneling devices. © 2001 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
81.65.Mq Oxidation
52.77.-j Plasma applications

Negative thermal expansion and magnetic properties of Y2Al3Fe14−xMnx compounds

Yanming Hao, Yan Gao, Bowen Wang, Jingping Qu, Yangxian Li, Jifan Hu, and Jiachun Deng

Appl. Phys. Lett. 78, 3277 (2001); http://dx.doi.org/10.1063/1.1371968 (3 pages) | Cited 19 times

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The structure and magnetic properties of Y2Al3Fe14−xMnx (x = 0–12) compounds have been investigated by means of x-ray diffraction and magnetization measurements. The Y2Al3Fe14−xMnx compounds have a hexagonal Th2Ni17-type structure. Their unit-cell volumes increase slowly with increasing x first, then increases rapidly with the further increase of x. This implies that there exists a positive spontaneous volume magnetostriction in the magnetic state of Y2Al3Fe14−xMnx compounds. X-ray diffraction of the Y2Al3Fe11Mn3 compound from 150 to 300 K shows that there appears a negative coefficient of thermal expansion, math ≈ −7.5×10−5/K, from 185 to 200 K. The Curie temperature and the saturation magnetization of these compounds show a rapid drop with increasing x. © 2001 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.De Thermal expansion; thermomechanical effects
75.80.+q Magnetomechanical effects, magnetostriction
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.Bb Fe and its alloys

Separation of reversible domain-wall motion and magnetization rotation components in susceptibility spectra of amorphous magnetic materials

S. S. Yoon and C. G. Kim

Appl. Phys. Lett. 78, 3280 (2001); http://dx.doi.org/10.1063/1.1374519 (3 pages) | Cited 6 times

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The reversible susceptibility spectra are measured for rectangular Co66Fe4NiB14Si15 samples with various easy-axis angles, α, relative to the sample axis. A phenomenological method is proposed for the reversible spectra to separate the relaxation processes of domain-wall motion and magnetization rotation. The separation provides a method for measuring the static susceptibilities and the relaxation frequencies for the two reversible magnetization processes. The α and the longitudinal stress dependence show that the separated spectra with relaxation frequencies near 360 kHz and 1.6 MHz correspond to relaxations of domain-wall motion and to magnetization rotation, respectively. © 2001 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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