Detecting interfacial defects at magnetic/non-magnetic junctions

Nature Physics, 2007

The development of semiconductor spintronics requires a reliable electronic means for writing, processing and reading information using spin-polarized carriers. Here, we demonstrate a fully electrical scheme for achieving spin injection, transport and detection in a single device. Our device consists of a lateral semiconducting channel with two ferromagnetic contacts, one of which serves as a source of spin-polarized electrons and the other as a detector. Spin detection in the device is achieved through a non-local, spinsensitive, Schottky-tunnel-barrier contact whose electrochemical potential depends on the relative magnetizations of the source and detector. We verify the effectiveness of this approach by showing that a transverse magnetic field suppresses the non-local signal at the detection contact by inducing spin precession and dephasing in the channel (the Hanle effect). The sign of the signal varies with the injection current and is correlated with the spin polarization in the channel as determined by optical Kerr rotation measurements.

Physical Review Letters, 2004

The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe=MgO=Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe=MgO interface. The voltage variation of the conductance points out the signature of an interfacial resonance state located in the minority band of Fe(001). When coupled to a metallic bulk state, this spin-polarized interfacial state enhances the band matching at the interface and therefore increases strongly the conductivity in the antiparallel magnetization configuration. Consequently, the tunnel magnetoresistance is found to be positive below 0.2 V and negative above. On the other hand, when the interfacial state is either destroyed by roughness-related disorder or not coupled to the bulk, the magnetoresistance is almost independent on the bias voltage.

Physical Review Letters, 2022

Journal of Physics D: Applied Physics

Scientific reports, 2017

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magneti...

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.

Journal of Magnetism and Magnetic Materials, 2019

We present an experimental observation of interfacial spin accumulation induced by anomalous Hall effect (AHE) in ferromagnets (FMs) in a multilayer structure of FM/YIG/Pt, where the direction of charge current injection in FM layer is perpendicular to the direction of voltage detection in Pt layer. In this structure, the magnon-mediated drag voltage (V drag) due to the interfacial spin accumulation induced by AHE, can be unambiguously separated from spin Seebeck voltage (V SSE) by sweeping or rotating the applied magnetic field. Field-dependent spin accumulation induced by AHE has been observed by comparison of nonlocal voltages between Ni/Cu/YIG/Pt and Pt/YIG/Pt samples. Furthermore, we demonstrate that the AHE voltage strongly depends on the spin polarization of conductivity and spin Hall angles of electrons with opposite spins in FMs. Our results show a prospect for FMs to be field-control spin generators via AHE, and provide a new viewpoint to realize the AHE.

Angewandte Chemie, 2013

Recently, nanoscale spin-crossover (SCO) particles have been the subject of great interest. The change in the 3d electronic configuration of the metal ion results in significant changes in the metal-ligand bond length and geometry, as well as in the molecular volume. Hence the spin switching process is accompanied by a remarkable change in the color, mechanical properties, dielectric properties, and magnetic susceptibility. The synthesis and investigation of these materials at reduced length scales is central not only to the exploration of fundamental effects of size reduction in these systems, but also for the development of new functional materials with applications, including guest molecule sensing, memory devices, and molecular switches. Until now, the observation of spin switching was essentially limited to the simple investigation of the temperature dependence of the magnetization or the optical absorption in a huge ensemble of nanoparticles with different degrees of size and shape dispersion. The development of methods for the detection of single SCO particles would thus be desirable not only from a fundamental perspective, but also for applications; however, such methods remain scarce. [2] In the field of nanoscale magnetic measurements, the state of the art is the micro-superconducting quantum interference device (micro-SQUID) and the nano-SQUID, which allow the detection of magnetization reversal in a few magnetic nanoparticles (or even a single one) through their deposition directly onto the microbridge Josephson junctions. However, for low noise operation, the Josephson junctions are normally made of a low temperature superconducting material such as Nb, Ti/Al, or Pd/Al bilayers. [3] Thus far, the working temperature of the system was limited to below a few tens of Kelvin. Consequently, the conventional micro-or nano-SQUID technique is not appropriate for studying magnetic properties in the room-temperature range.

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.

2011

Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4 nm. The sample with 0.75 nm thick Co showed an exchange coupling field (H ex ) exceeding 15 kOe at room temperature and 17.2 kOe at 5 K. With an increase of Co thickness, H ex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8 nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9-1.2 nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2 nm) in which the magnetization was in-plane. In addition, Hall effect measurements were carried out to observe the anomalous and planar Hall voltages and to quantify the perpendicular and in-plane components of magnetization. The sample with thicker Co layer (2.4 nm) showed an in-plane component of magnetization, whereas the sample with 0.75 nm Co showed no in-plane component. The high value of H ex observed in 0.75 nm Co samples can have important implications in spintronics and bit patterned media.