Rento Ohsugi

Structural and magnetic properties of L10-FePd/MgO films on GaAs and InP lattice mismatched substrates

Structural and magnetic properties of epitaxial L10-FePd/MgO films on GaAs and InP lattice mismatched substrates are investigated at different MgO and FePd growth temperatures. While c-axis lattice constants of MgO and FePd show similar values on both substrates, the remanent magnetization becomes larger on GaAs than that on InP. Since the ratio of FePd (002) tetragonal ordered phase and FePd (200) cubic disordered phase follows similar growth temperature dependence to the remanent magnetization and the long range chemical order parameter, the perpendicular magnetic anisotropy grown on the lattice-mismatched semiconductors is strongly affected by formation of the disordered phase.

MgO Layer Thickness Dependence of Structure and Magnetic Properties of L10-FePt/MgO/GaAs Structures

We investigated the MgO layer thickness dependences of the structure and magnetic properties of L10-FePt/MgO/GaAs structures. To examine how the crystallinity and growth morphology of the MgO layer affect the L10-FePt layer, two kinds of preparation method were employed for MgO deposition: electron beam (EB) evaporation and sputter deposition. The MgO layer deposited by EB evaporation included a large strain because of the cube-on-cube epitaxial relationship despite a large lattice mismatch between MgO and GaAs. For the MgO layer prepared by sputtering, on the other hand, an amorphous MgO layer was initially grown on the GaAs substrate. Subsequently, a crystalline MgO layer was grown in the (001) direction. In the case of the EB-deposited MgO, as the MgO layer thickness increased, the degree of chemical order of the L10-FePt layer increased from 55 to 81% owing to the improvement of the crystallinity of the MgO layer. The improvement of chemical order also led to the increase in the remanent magnetization of L10-FePt from 84 to 98%.

Comparison of electrical and optical detection of spin injection in L10-FePt/MgO/GaAs hybrid structures

We have investigated comparative experiments for spin injection into semiconductor in an ordered L10-FePt/MgO/n-GaAs hybrid structure using electrical and optical detection methods. Spatial-resolved Kerr rotation microscope image clearly demonstrates accumulation of perpendicularly oriented spins in an n-GaAs channel at zero magnetic field. On the other hand, electrical three-terminal Hanle measurement shows shorter spin lifetime than that of the optical measurement. It suggests that the spin lifetime obtained from three-terminal Hanle method originates from spins at the MgO/GaAs interface but not in the bulk GaAs channel.

Bias dependence of spin injection/transport properties of a perpendicularly magnetized FePt/MgO/GaAs structure

We demonstrate injection and transport of perpendicularly spin-polarized electrons in an FePt/MgO/n-GaAs structure. Spin-polarized electrons were injected from a perpendicularly magnetized FePt layer into an n-GaAs layer through a MgO barrier and detected by spatially resolved Kerr rotation microscopy. By measuring the Hanle effect, we reveal that the injected/extracted spin polarizations drastically vary with bias voltages. A spin lifetime of 3.5 ns is obtained that is consistent with the result from pump–probe measurements. This direct observation of perpendicularly polarized spin injection and lateral transport is one step toward realizing future spintronic devices.

Three-Terminal Electrical Spin Injection into GaAs from Perpendicularly Magnetized L10-FePt

All electrical spin injection and detection into a semiconductor channel from a ferromagnetic electrode with perpendicular magnetization is one of the important techniques for spintronics devices. For a spin field effect transistor [1] and a spin vertical cavity surface emitting laser [2], a perpendicular magnetized spin injector enables us to operate those potential devices at zero magnetic field. The electrical spin injection from perpendicular spin polarizer has been already investigated by the optical detection [3, 4, 5]. However, its electrical detection is still challenging and is inevitable for the development of future spintronic devices. We previously reported the preparation of perpendicularly magnetized FePt / MgO / GaAs structure [6]. In this study, we investigated electrical spin injection and detection in a perpendicularly magnetized FePt / MgO / n-GaAs structure by three-terminal (3T-) Hanle effect [7].