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1 May 2000

Volume 87, Issue 9, pp. 4051-7146

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Evaluation of vacuum bonded GaAs/Si spin-valve transistors

K. Dessein, H. Boeve, P. S. Anil Kumar, J. De Boeck, J. C. Lodder, L. Delaey, and G. Borghs

J. Appl. Phys. 87, 5155 (2000); http://dx.doi.org/10.1063/1.373280 (3 pages) | Cited 4 times

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In this article a new type of spin-valve transistor, a hybrid GaAs/Si device, is presented. In this device the Si emitter is replaced by a GaAs emitter launcher structure. The integration of the GaAs with the Si was done by means of a room temperature vacuum bonding technique. By using a soft NiFe/Au/Co spin-valve structure as metal base, a 63% change in collector current is obtained at room temperature for a saturation field of 30 Oe. The corresponding in-plane magnetoresistance is only 1%. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

a-Si buffer layer for improvement of crystallographic and magnetoresistance characteristics of Co/Cu multilayers

Yutaka Shimizu, Koichi Nishimura, Hiroyuki Saito, Shigeki Nakagawa, and Masahiko Naoe

J. Appl. Phys. 87, 5158 (2000); http://dx.doi.org/10.1063/1.373281 (3 pages)

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Co/Cu multilayers deposited on an amorphous Si (a-Si) buffer layer revealed good crystallinity and lower resistivity than ones deposited on other buffer layers. The periodicity and the sharpness at the interface between each layer were not as good as those in the multilayer with a Ni–Fe buffer. Therefore, the multilayer with a Si buffer exhibited smaller resistivity ρ but slightly smaller change of resistivity Δρ. The annealing process improved the periodicity and the sharpness at the interface in the Co/Cu multilayer with a Si buffer, and the value of the magnetoresistance ratio in the multilayer with a Si buffer (17.1%) became larger than that with Ni–Fe (15.5%). © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing

Effect of silicon crystal structure on spin transmission through spin electronic devices

Duncan R. Loraine, David I. Pugh, Hartmut Jenniches, Randall Kirschman, Sarah M. Thompson, Will Allen, Chitnarong Sirisathikul, and John F. Gregg

J. Appl. Phys. 87, 5161 (2000); http://dx.doi.org/10.1063/1.373282 (3 pages) | Cited 5 times

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Spin injection into and spin transport through silicon spacer layers in iron/silicon/cobalt structures has been investigated. Ultrahigh vacuum evaporated silicon spacers of varying crystal quality from amorphous to epitaxial of thicknesses from 10 to 200 Å were shown to improve their electrical conduction with increasing crystallinity, but no spin dependent transport was observed through the structure. Silicon and iron interdiffusion was also observed at the interfacial region. Device quality silicon was studied using 460 and 540 μm doped silicon wafers of resistivity 0.1 and 1 Ω cm, respectively, polished on both sides, onto which were deposited iron and cobalt layers. Sharp metal-semiconductor interfaces were achieved in this way, but no spin dependent transport, putting an upper limit on the spin diffusion length in device quality silicon wafers. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Ns Metal-nonmetal contacts
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.47.De Giant magnetoresistance

Hot-electron attenuation lengths in ultrathin magnetic films

R. P. Lu, B. A. Morgan, K. L. Kavanagh, C. J. Powell, P. J. Chen, F. G. Serpa, and W. F. Egelhoff

J. Appl. Phys. 87, 5164 (2000); http://dx.doi.org/10.1063/1.373417 (3 pages) | Cited 17 times

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Ballistic electron emission microscopy (BEEM) is used to measure hot-electron transport across magnetic metal multilayers. Room temperature measurements in air have been carried out on Au/M/Si(100), Au/M/Au/Si(100), and Au/M/PtSi/Si diodes, that were sputter deposited at 175 or 300 K, where M is Co, Fe, Ni, Cu, or Ni81Fe19. Plots of log BEEM current versus M thickness are linear giving hot-electron (1.5 eV) attenuation lengths (ALs), for Au/M/Si diodes (M=Co, Fe, Ni81Fe19, and Ni) of 0.3, 0.5, 0.8, and 1.3 nm, respectively (with typical standard uncertainties of ±10%). Magnetic metal sandwich diodes, (Au/M/Au/Si) show larger ALs, 0.8 and 2.1 nm, for M=Co and Ni81Fe19, respectively. PtSi interlayers improve the surface roughness but have little effect on the AL while low temperature depositions increase the AL. We presume that the increases in the AL are due to better microstructure, less silicide reaction, or to changes in elastic scattering at interfaces. © 2000 American Institute of Physics.
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73.61.At Metal and metallic alloys
75.70.Ak Magnetic properties of monolayers and thin films
68.35.B- Structure of clean surfaces (and surface reconstruction)

Giant magnetoresistance of Fe/Cu/Fe(001) trilayers grown directly on GaAs(001)

T. L. Monchesky, R. Urban, B. Heinrich, M. Klaua, and J. Kirschner

J. Appl. Phys. 87, 5167 (2000); http://dx.doi.org/10.1063/1.373283 (3 pages) | Cited 7 times

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The giant magnetoresistance of crystalline Fe/Cu/Fe(001) epitaxial structures characterized by scanning tunneling microscopy are presented. Fe/Cu/Fe(001) trilayers capped with Au are grown directly on GaAs(001) using a new procedure for producing pure Fe layers with As-free Fe surfaces on GaAs(001). The temperature dependence of the magnetoconductance and sheet resistance measured from 4 to 300 K is modeled by the Boltzmann equation assuming that the mean free paths in the crystalline epitaxial layers are equal to those in bulk materials. The results of the simple model suggest that the coefficient of the specular scattering at the Fe/GaAs interface is R=0.45, while the scattering at the outer Au interface is diffuse. Spin asymmetry scattering at the metallic interfaces is ΔT=∣T↑−T↓∣=0.34, Tavg=(T↑+T↓)/2=0.79. The sheet resistance was best modeled using a low temperature mean free path of 25 nm in the Fe layer. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetization-controlled spin transport in DyAs/GaAs layers

J. M. Mao, M. E. Zudov, R. R. Du, P. P. Lee, L. P. Sadwick, and R. J. Hwu

J. Appl. Phys. 87, 5170 (2000); http://dx.doi.org/10.1063/1.373284 (3 pages)

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Electrical transport properties of DyAs epitaxial layers grown on GaAs have been investigated at various temperatures and at magnetic fields up to 12 T. The measured magnetoresistances show two distinct peaks at fields around 0.2 and 2.5 T which are believed to arise from the strong spin-disorder scattering occurring at the phase transition boundaries induced by the external magnetic field. An empirical magnetic phase diagram is deduced from the temperature dependence of magnetoresistance, and the anisotropic transport properties are also presented for various magnetic field directions with respect to the current flow. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Solution to the Boltzmann equation for layered systems for current perpendicular to the planes

W. H. Butler, X.-G. Zhang, and J. M. MacLaren

J. Appl. Phys. 87, 5173 (2000); http://dx.doi.org/10.1063/1.373285 (3 pages) | Cited 8 times

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Present theories of giant magnetoresistance (GMR) for current perpendicular to the planes (CPP) are based on an extremely restricted solution to the Boltzmann equation that assumes a single free electron band structure for all layers and all spin channels. Within this model only the scattering rate changes from one layer to the next. This model leads to the remarkable result that the resistance of a layered material is simply the sum of the resistances of each layer. We present a solution to the Boltzmann equation for CPP for the case in which the electronic structure can be different for different layers. The problem of matching boundary conditions between layers is much more complicated than in the current in the planes (CIP) geometry because it is necessary to include the scattering-in term of the Boltzmann equation even for the case of isotropic scattering. This term couples different values of the momentum parallel to the planes. When the electronic structure is different in different layers there is an interface resistance even in the absence of intermixing of the layers. The size of this interface resistance is affected by the electronic structure, scattering rates, and thicknesses of nearby layers. For Co–Cu, the calculated interface resistance and its spin asymmetry is comparable to that measured at low temperature in sputtered samples. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
73.20.At Surface states, band structure, electron density of states

A simple treatment of the “scattering-in” term of the Boltzmann equation for multilayers

X.-G. Zhang and W. H. Butler

J. Appl. Phys. 87, 5176 (2000); http://dx.doi.org/10.1063/1.373286 (3 pages) | Cited 2 times

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We present a simple approximation for treating anisotropic scattering within the semiclassical Boltzmann equation for current in plane geometry in magnetic multilayers. This approximation can be used to qualitatively account for the forward scattering that is neglected in the lifetime approximation, and requires only one additional parameter. For the case of a bulk material its effect is a simple renormalization of the scattering rate. The simplicity of this term has allowed quick and simple solution to the Boltzmann equation for magnetic multilayers using realistic band structures. When we use the band structures for Cu∣Co multilayers obtained from first-principles calculations, we find an increase in the resistance of the multilayer, compared to the solution without the scattering-in term, due to the higher scattering rates needed to fit the same bulk conductivities. The giant-magnetoresistance ratio is also changed when the vertex corrections are included. © 2000 American Institute of Physics.
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73.61.-r Electrical properties of specific thin films
72.10.Bg General formulation of transport theory
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
05.60.-k Transport processes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
75.47.De Giant magnetoresistance

Magnetic structure and giant magnetoresistance in granular metals

D. Kechrakos and K. N. Trohidou

J. Appl. Phys. 87, 5179 (2000); http://dx.doi.org/10.1063/1.373287 (3 pages) | Cited 3 times

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The effect of dipolar interactions on the giant magnetoresistance (GMR) of a granular metal is studied numerically. The equilibrium magnetic configuration of the system is obtained by classical Monte Carlo simulation and the conductance is calculated using the real space Kubo–Greenwood formula and a single band tight-binding Hamiltonian. The numerical results are compared with experimental finding. © 2000 American Institute of Physics.
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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.)
75.47.De Giant magnetoresistance
75.40.Mg Numerical simulation studies
75.10.Dg Crystal-field theory and spin Hamiltonians
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.20.At Surface states, band structure, electron density of states
75.30.Gw Magnetic anisotropy

Ab initio calculations of giant magnetoresistance

J. Binder, P. Zahn, and I. Mertig

J. Appl. Phys. 87, 5182 (2000); http://dx.doi.org/10.1063/1.373288 (3 pages) | Cited 5 times

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We present ab initio calculations of the giant magnetoresistance in magnetic multilayers. The electronic structure of the multilayers is calculated by spin density functional theory using a screened Korringa–Kohn–Rostoker method. The scattering of nanostructural defects in the multilayers is described by means of a Green’s function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasiclassically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). Since we consider ferromagnetic systems a two current model is applied. Trends of residual resistivities and giant magnetoresistance ratios are discussed for Co/Cu multilayers with 3d transition metal defects. © 2000 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Bb Fe and its alloys

Electronic scattering from Co/Cu interfaces: In situ measurement, comparison with microstructure, and failure of semiclassical free-electron models

William E. Bailey, Shan X. Wang, and Evgueni Yu. Tsymbal

J. Appl. Phys. 87, 5185 (2000); http://dx.doi.org/10.1063/1.373289 (3 pages) | Cited 3 times

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We show that novel thickness-dependent film conductance measurements, taken in situ during deposition of NiO/Co/Cu/Co spin valves and compared with thickness-dependent microstructural characterization, indicate a qualitative failure of widely accepted semiclassical free-electron models of giant magnetoresistance (GMR). Both in situ Auger electron spectroscopy covering experiments and ex situ x-ray diffraction measurements of peak intensity for Co/Cu/Co films indicate that the defect concentration does not vary noticeably as a function of thickness. The microstructural measurements suggest that the bulk scattering parameters ρ and λ should be considered to be constant within each layer, and that the surface scattering parameter p does not change between layers. Under these constraints, it becomes difficult to fit even qualitatively the highly asymmetric scattering behavior measured during the formation of Co/Cu vs Cu/Co interfaces. Calculations incorporating realistic band structure resolve the observed inconsistency between free-electron model calculations and experiment. The asymmetry in scattering is understood here to arise simply from the higher density of unfilled d states in Co compared with Cu. © 2000 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.25.+i Surface conductivity and carrier phenomena
68.35.Ct Interface structure and roughness
79.20.Fv Electron impact: Auger emission
73.20.At Surface states, band structure, electron density of states
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