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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetic scattering in Fe–Cr multilayers in the ferromagnetic state at low temperatures

R. S. Patel, A. K. Majumdar, A. F. Hebard, and D. Temple

J. Appl. Phys. 93, 7684 (2003); http://dx.doi.org/10.1063/1.1555753 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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We report here an interpretation of the electrical resistivity (ρ) below 15 K of two Fe–Cr multilayers (30 layers of 20 Å Fe/10 and 12 Å Cr) produced by Xe ion-beam sputter deposition. These multilayers have a negative giant magnetoresistance (GMR) of ∼21% at 4.2 K and Hsat=13 kOe. Very high-resolution resistance measurements (better than 3 ppm) were made down to 2.3 K at every (100±10) mK. Excellent results were obtained when the ρ(T) data in the ferromagnetic state (H=Hsat) were fitted to an equation containing the residual resistivity [ρ(0)], electron–phonon interband s–d scattering (Bloch–Wilson integral) and a magnetic BT2 term, where B is proportional to s–d interaction strength responsible for the electron–magnon s–s scattering. The value of B is found to be typically (9±2)×10−5 μΩ cm K−2 compared to the much smaller value of 1.5×10−5 μΩ cm K−2 for bulk crystalline Fe. The fits without the magnetic term are distinctly inferior as seen from their residuals plotted against T. However, the data in the antiferromagnetic state could be fitted very well with only the lattice term and ρ(0). We have restricted our analysis to T⩽15 K in order to avoid electron–magnon s–d scattering which dominates above 20 K and is very difficult to estimate. Thus magnetic scattering in 3d metals are best interpreted at low temperatures even for these magnetic multilayers. © 2003 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
63.20.kk Phonon interactions with other quasiparticles
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
63.20.K- Phonon interactions
75.30.Ds Spin waves

Multiple magnetic transitions and large magnetoresistance of Y0.8Dy0.2Mn6Sn6 compound

Shao-ying Zhang, Jin-lei Yao, Li-gang Zhang, Lu Li, Bao-gen Shen, and Tao Zhu

J. Appl. Phys. 93, 7687 (2003); http://dx.doi.org/10.1063/1.1540148 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Magnetic transitions and magnetoresistance of HfFe6Ge6-type Y0.8Dy0.2Mn6Sn6 compound have been investigated in the temperature range of 5–375 K. It was found that the compound displays paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. At low temperatures, the strong exchange interaction between the Dy and Mn sublattices results in ferrimagnetism. The metamagnetic transition from the antiferro- to ferrimagnetic state can be induced by a fairly small threshold field (⩽7 kOe). The magnetic transition is accompanied by a large magnetoresistance effect of about −29% and −7% at 5 and 293 K, respectively. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.20.En Metals and alloys
75.50.Ee Antiferromagnetics

Anomalous magnetoresistance behavior of CoFe nano-oxide spin valves at low temperatures

J. O. Ventura, J. B. Sousa, M. A. Salgueiro da Silva, P. P. Freitas, and A. Veloso

J. Appl. Phys. 93, 7690 (2003); http://dx.doi.org/10.1063/1.1540149 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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We report magnetoresistance curves of CoFe nano-oxide specular spin valves of MnIr/CoFe/nano-oxidized CoFe/CoFe/Cu/CoFe/nano-oxidized CoFe/Ta at different temperatures from 300 to 20 K. We extend the Stoner–Wolfarth model of a common spin valve to a specular spin valve, introducing the separation of the pinned layer into two sublayers and their magnetic coupling across the nano-oxide. We study the effect of different coupling/exchange (between the antiferromagnetic layer and the bottom sublayer) field ratios on the magnetization and magnetoresistance, corresponding with the experimentally observed anomalous bumps in low temperature magnetoresistance curves. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Multilayer configuration for experiments of spin precession induced by a dc current

L. Berger

J. Appl. Phys. 93, 7693 (2003); http://dx.doi.org/10.1063/1.1555771 (3 pages) | Cited 21 times

Online Publication Date: 9 May 2003

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Until now, most predictions about spin precession induced by a CPP dc current have concerned a simple “asymmetric” configuration consisting of a free magnetic layer and of a thicker pinned magnetic layer. In the present work, we propose a different configuration where the precessing free magnetic layer is sandwiched between two thicker pinned magnetic layers having opposite magnetizations. In this “antisymmetric” configuration, the spin current and accumulation arising from expansion/contraction are nearly three times as large as in the asymmetric configuration, for given current and layer thickness. Moreover, both interfaces of the free magnetic layer are now active to generate drive torques. This should result in a reduction of the critical current density needed for spin oscillations, by a factor of about six. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetization-orientation dependence of the superconducting transition temperature and magnetoresistance in the ferromagnet-superconductor-ferromagnet trilayer system

J. Y. Gu, Chun-Yeol You, J. S. Jiang, and S. D. Bader

J. Appl. Phys. 93, 7696 (2003); http://dx.doi.org/10.1063/1.1540150 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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The superconducting transition temperature (Tc) of a ferromagnet-superconductor-ferromagnet film system is predicted to exhibit a dependence of the magnetization orientation of the ferromagnetic layers. We have grown CuNi/Nb/CuNi films via magnetron sputtering and verified experimentally that the Tc is slightly higher in the case that the mutual magnetization direction of the two CuNi layers is antiparallel (AP) compared to the parallel (P). We also find that an ∼25% resistance change occurs near Tc in CuNi(5 nm)/Nb(18 nm)/CuNi(5 nm) when the two CuNi layers change their magnetization directions from P to AP. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.10.+v Occurrence, potential candidates
74.62.Yb Other effects
75.50.Cc Other ferromagnetic metals and alloys

Magnetoresistance in magnetic multilayers with the nano-oxide layer

Sui-Pin Chen, Ching-Ray Chang, and Chih-Huang Lai

J. Appl. Phys. 93, 7699 (2003); http://dx.doi.org/10.1063/1.1555772 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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From the linear response Boltzmann transport equation in the relaxation-time approximation, we investigate the structure consisting of magnet–metal–magnet multilayers inserted by the nano-oxide layer. Moreover, we propose a modified Boltzmann transport equation with the appropriate boundary conditions in multilayers instead of solving the complicated coupled equations. We find that the nano-oxide layer causes the decrement of the diffusive scattering effect and the increment of the reflective effect, and the magnetoresistance ratios vary with different positions of the nano-oxide layer. The theoretical results are reasonable in agreement with the experimental data. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Mg Numerical simulation studies

Magnetoresistance effect in Ag–Fe3O4 and Al–Fe3O4 composite films

Jen-Hwa Hsu, Shang-Yi Chen, Wen-Ming Chang, T. S. Jian, Ching-Ray Chang, and Shan-Fan Lee

J. Appl. Phys. 93, 7702 (2003); http://dx.doi.org/10.1063/1.1540151 (3 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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The Agx–(Fe3O4)1−x and Agx–(Fe3O4)1−x composite films were prepared by dc sputtering on Si(100) substrates. The x-ray diffraction results show that the films contain essentially only the cubic inverse spinal phase from Fe3O4 and face-centered cubic phase from Ag or Al. The transmission electron microscopy images indicate that the metal granules are randomly distributed with Fe3O4 grains. The resistivity determined from the four-probe method decreases rapidly with increasing metal content. At x≒0.5, a percolation occurs. The conducting path is formed from metal granules in series with Fe3O4 grains. The magnetoresistance (MR) is defined to be {R(H=0.8 T)−R(H=0)}/R(H=0). It has been found that MR is isotropic and the appearance of Ag granules has significant impact on the MR effect. Furthermore, a positive MR region appears with 0.011<x<0.1 in Agx–(Fe3O4)1−x. On the contrary, the incorporation of Al granules does not have the same effect on MR as in Agx–(Fe3O4)1−x. A slow increase of MR with Al content might be due to Coulomb blockade. The extra contribution to MR in Agx–(Fe3O4)1−x can be attributed to spin injection from Fe3O4 into Ag granules so that spin accumulation in Ag granules impedes the current causing a larger resistance under a field. © 2003 American Institute of Physics.
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75.47.Pq Other materials
72.25.Hg Electrical injection of spin polarized carriers
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.23.Hk Coulomb blockade; single-electron tunneling
73.61.-r Electrical properties of specific thin films
81.15.Cd Deposition by sputtering
68.55.Nq Composition and phase identification

Surface spin-flop transition in epitaxial Co/Re superlattices

T. Charlton and D. Lederman

J. Appl. Phys. 93, 7705 (2003); http://dx.doi.org/10.1063/1.1557957 (3 pages)

Online Publication Date: 9 May 2003

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Two hcp [Co/Re]x superlattices were grown simultaneously on (11math0) Al2O3 single crystal substrates, where the number of bilayers x=20 and 21. The film growth was epitaxial in nature with the [0001] of the substrate aligned with the [0001] of the superlattice. The film interface roughness and thickness were determined by x-ray reflectivity to be σ=4.4 Å, tRe=8 Å, tCo=20 Å for x=20 and tCo=16 Å for x=21. The Co layers were antiferromagnetically coupled with an easy axis along the [0001]. As expected, the 20-bilayer superlattice exhibited both surface and bulk spin-flop transitions, while in the 21-bilayer superlattice only the bulk spin-flop transition was observed by magneto-optic Kerr effect measurements. The magnetoresistance (MR) with H∥[0001] shows an extended plateau around H=0 with H⊥I, where H is the applied magnetic field and I the sensing current. The layer-by-layer magnetization profile was found using energy minimization techniques and the MR was calculated using an empirical model. The calculations compare favorably with the MR data allowing the separation of anisotropic magnetoresistance and giant magnetoresistance components to the MR. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
75.50.Ee Antiferromagnetics
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
75.70.Rf Surface magnetism
78.66.Bz Metals and metallic alloys

Role of oxygen exposure in different positions in the synthetic spin valves

Kebin Li, Guchang Han, Jinjun Qiu, Ping Luo, Zaibing Guo, Yuankai Zheng, and Yihong Wu

J. Appl. Phys. 93, 7708 (2003); http://dx.doi.org/10.1063/1.1555773 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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The magnetoresistance (MR) properties of a basic Ta/NiFe/IrMn/CoFe/Ru/CoFe/Cu/CoFe/Cu/Ta synthetic spin valve (SV) system have been systematically studied by using O2-soaked layers in five different positions. It is found that about 10% of MR ratio enhancement can be achieved without sacrificing other merits of SVs when the O2-soaking dose is controlled in the vicinity of 10−3 Pa s. It is probably due to improvement of the spin-dependent scattering (increasing the spin-dependent transmission coefficient and reducing the diffusion scattering coefficient) after O2 soaking either within the pinned layers or within the spacer layer. © 2003 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
72.25.Mk Spin transport through interfaces
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.65.Mq Oxidation
75.30.Et Exchange and superexchange interactions
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