Transport properties of electrodeposited Ni films on GaAs(110) (original) (raw)
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Thickness dependence of Hall transport in Ni1.15Mn0.85Sb thin films on silicon
Physical Review B, 2004
Highly spin polarized Heusler alloys, NiMnSb and Co 2 MnSi, attract a great deal of interest as potential spin injectors for spintronic applications. Spintronic devices require control of interfacial properties at the ferromagnet:semiconductor contact. To address this issue we report a systematic study of the ordinary and anomalous Hall effect, in Ni 1.15 Mn 0.85 Sb films on silicon, as a function of film thickness. In contrast to the bulk stoichiometric material, the Hall carriers in these films become increasingly electron-like as the film thickness decreases, and as the temperature increases from 50 K toward room temperature. High field Hall measurements confirm that this is representative of the majority transport carriers. This suggests that current injected from a NiMnSb:semiconductor interface may not necessarily carry the bulk spin polarization. The films also show a low temperature upturn in the resistivity, which is linked to a discontinuity in the anomalous Hall coefficient. Overall these trends indicate that the application of Heusler alloys as spin injectors will require strictly controlled interfacial engineering, which is likely to be demanding in these ternary alloys.
On the Role of Interfaces on Spin Transport in Magnetic Insulator/Normal Metal Heterostructures
Adv. Mater. Interfaces, 2019
spin-polarized currents. In recent years, however, the flow of pure spin currents has received much interest [1,2] in the quest of novel and low-energy consumption devices. [3] A key discovery was reported in 2013, when Nakayama et al. [4] and Hahn et al. [5] found out a new kind of magnetoresistance that appears in a nonmagnetic metal (NM) when placed in contact with a ferromagnetic insu-lator (FMI). It turned out that the resistance of the NM varies with the direction in which the FMI is magnetized. The observed effect relies on two ingredients. [6] The first one, so-called spin Hall effect (SHE), in which a charge current (J C), due to spin-orbit coupling, creates a flow of spins (J S) perpendicular to J C and produces a spin accumulation at sample edges with a polarization (σ) which is normal to both J C and J S (Figure 1a,b,e). The charge-to-spin current conversion is given by the spin Hall angle θ SH of the NM layer. Additionally, the created J S is converted back to J C by the inverse spin Hall effect (ISHE) which is the reciprocal effect to SHE, in which a spin current generates a transverse charge current. This is thus a second-order effect in θ SH that lowers the base resistivity of the NM layer with respect to its Drude resis-tivity. The second ingredient is the transport of spins across the NM/FMI interface, which is quantified by the spin-mixing interfacial conductance (G ↑↓). When a charge current is applied along the NM, the transverse spin current may be absorbed by the FMI depending on the direction of σ with respect to the direction of the magnetization (M) of the FMI. When σ is parallel to M, the spin current cannot be absorbed via spin transfer torque into the FMI and thus the electrical resistance of the NM layer remains unaltered; in contrast, when σ is perpendicular to M, spin torque occurs and J S is partially absorbed into the FMI (spin excitations) producing a loss of spin accumulation in the metal and thus a reduction of J C which is equivalent to an increase of resistance. Therefore, the resistance of the NM depends on the direction of M of the neighboring FMI, which can be controlled by appropriate external magnetic field, thus giving rise to the so-called spin Hall magnetoresistance (SMR) [4,7] (Figure 1a,b and Figure 2 (central panel)). Angular-dependent magnetore-sistance measurements (ADMR) and field-dependent magne-toresistance may allow observation of SMR. The magnitude of the observed SMR is determined by θ SH and G ↑↓. Spin currents have emerged as a new tool in spintronics, with promises of more efficient devices. A pure spin current can be generated in a nonmagnetic metallic (NM) layer by a charge current (spin Hall effect). When the NM layer is placed in contact with a magnetic material, a magnetoresistance (spin Hall magnetoresistance) develops in the former via the inverse spin Hall effect (ISHE). In other novel spin-dependent phenomena, such as spin pumping or spin Seebeck effect, spin currents are generated by magnetic resonance or thermal gradients and detected via ISHE in a neighboring normal metal layer. All cases involve spin transport across interfaces between nonmagnetic metallic layers and magnetic materials; quite commonly, magnetic insulators. The structural, compositional, and electronic differences between these materials and their integration to form an interface, challenge the control and understanding of the spin transport across it, which is known to be sensitive to sub-nanometric interface features. Here, the authors review the tremendous progress in material's science achieved during the last few years and illustrate how the spin Hall magnetoresistance can be used as a probe for surface magnetism. The authors end with some views on concerted actions that may allow further progress.
Journal of Applied Physics, 2018
The photo-induced inverse spin Hall effect (ISHE) experiments are conducted in heavily doped n-GaAs epitaxial layers by measuring the transverse electric current generated through the diffusion of optically injected spin orientations over a temperature range of 10-300 K. ISHE origin of the measured signal is confirmed through meticulous checks including the characteristic dependence of magnitude of signal on the angle of incidence. The measured value of ISHE current (I ISHE) is observed to fall with the increase in temperature. Furthermore, the value of spin current density is theoretically estimated by solving the spin diffusion equation with appropriate boundary conditions for an epitaxial layer. It is shown that by near resonant excitation and subsequent solution of diffusion equation, the spin Hall angle (c) and spin Hall conductivity (r SH) can be estimated, provided the effective life time of spin polarized electrons(s S) is known independently. By using the numerically calculated value of s S , the proposed method is implemented to estimate the values of c and r SH. It is found that the fall in the values of I ISHE at high temperatures is not governed by r SH , rather by a rapid decrease in the values of s S. In fact, r SH is seen to increase with the temperature, which is compared with existing literature. The present work provides the necessary insight into material parameters which are essential for the development of advanced spin-photonic semiconductor devices.
Transport characteristics of magnetite thin films grown onto GaAs substrates
Magnetite thin films with a preferred ͑111͒ orientation have been deposited by reactive dc magnetron sputtering from a pure Fe target onto ͑100͒ GaAs substrates at 400°C. The films show a clear Verwey transition in both the magnetization and sheet resistance as functions of temperature. For films deposited onto semiconducting n-type GaAs substrates, we have obtained asymmetric current-voltage (I -V) characteristics with a Schottky diodelike behavior in forward bias. Activation energy plots of the I -V data as a function of temperature indicate a barrier height of 0.3-0.4 eV. This does not take into account the contribution from tunneling across the narrow depletion layer in these junctions, so should be considered a lower bound to the actual Schottky barrier height. Our work points to the potential integration of half-metallic magnetite with GaAs-based heterostructures for spin-electronic devices.
Spin-polarized electron transport in ferromagnet/semiconductor hybrid structures (invited)
Journal of Applied Physics, 2001
Two major problems in spin electronics remain to be solved: room temperature spin injection at a source and spin detection at a drain electrode. The lateral size of magnetic contacts and the presence of a potential barrier at the interface are believed to have a key influence on the efficiency of both of these processes. We therefore aimed to clarify these issues by studying spin-polarized transport across epitaxially grown single crystal Fe ͑001͒/GaAs nanoclusters and at the Schottky barrier formed at Ni 80 Fe 20 /GaAs interfaces. We observed a negative contribution to the magnetoresistance of an ultrathin ͑2.5 ML͒ discontinuous epitaxial Fe film as occurs in tunnel magnetoresistance. This result suggests that spin transport via GaAs is possible on the nanoscale. In the continuous NiFe/ GaAs structures, circularly polarized light was used to create a population of spin-polarized electrons in the GaAs substrate and spin-polarized electron transport across the interface at room temperature was detected as an electrical response associated with the field-dependent photocurrent. Surprisingly, highly efficient spin transmission is observed at room temperature, indicating that there is no significant loss of spin polarization for electrons crossing the interface. This result unambiguously demonstrates that spin detection is possible at room temperature in a continuous ferromagnet/semiconductor contact in the presence of the Schottky barrier.
Applied Physics Letters, 2019
We utilize spin Hall magnetoresistance (SMR) measurements to experimentally investigate the pure spin current transport in thin film heterostructures of nickel ferrite (NiFe 2 O 4 ,NFO) and the normal metals (NM) Ta and Pt. We grow (001)-oriented NFO thin films by pulsed laser deposition on lattice-matched magnesium gallate (MgGa 2 O 4) substrates, thereby significantly improving their magnetic and structural properties. We perform SMR measurements at room temperature in patterned Hall bar structures for charge currents applied in the [100]-and [110]-direction of NFO. We find that the extracted SMR magnitude for NFO/Pt heterostructures depends crucially on the Pt resistivity of the investigated Hall bar structure. We further study this resistivity scaling of the SMR effect at different temperatures for NFO/Pt. Our results suggest that the spin mixing conductance of the NFO/Pt interface and the Pt resistivity depend on the interface quality and thus a correlation between these two quantities exists.
Spin-dependent electron transport at the ferromagnet/semiconductor interface
Journal of Applied Physics, 1999
A search for spin-dependent electron transport at the ferromagnet/semiconductor interface has been made by measuring the bias dependence of a photon excited current through the interface. A circularly polarized laser beam was used to excite electrons with a spin polarization perpendicular to the film plane. In samples of the form 3 nm Au/5 nm Ni 80 Fe 20 /GaAs ͑110͒, a significant transport current was detected with a magnitude dependent on the relative orientation of the spin polarization and the magnetization vector. At perpendicular saturation, the bias dependence of the photocurrent is observed to change in the range 0.7-0.8 eV when the helicity is reversed.
Point contact spin spectroscopy of ferromagnetic MnAs epitaxial films
Physical Review B, 2003
We use point contact Andreev reflection spin spectroscopy to measure the transport spin polarization of MnAs epitaxial films grown on (001) GaAs. By analyzing both the temperature dependence of the contact resistance and the phonon spectra of lead acquired simultaneously with the spin polarization measurements, we demonstrate that all the point contacts are in the ballistic limit. A ballistic transport spin polarization of approximately 49% and 44% is obtained for the type A and type B orientations of MnAs, respectively. These measurements are consistent with our density functional calculations, and with recent observations of a large tunnel magnetoresistance in MnAs/AlAs/(Ga,Mn)As tunnel junctions.
Spin-Hall conductivity and electric polarization in metallic thin films
Physical Review B, 2013
We predict theoretically that, when a normal metallic thin film (without bulk spin-orbit coupling, such as Cu or Al) is sandwiched by two insulators, two prominent effects arise due to the interfacial spin-orbit coupling: a giant spin-Hall conductivity due to the surface scattering and a transverse electric polarization due to the spin-dependent phase shift in the spinor wave functions. PACS numbers: 72.25.Ba,75.70.Tj, Spin-orbit interaction, transferring angular momentum between electronic spins and orbital motion, has extended the boundary of the field of spintronics towards a full-electric manipulation of spins without using magnets. By coupling the charge and spin currents, spinorbit interaction has left its signature in bulk metals 1-3 and semiconductors 4-8 by the so-called spin-Hall effect, 9 which catches much attention in academia and industry due to its interesting physics and potential applications.