Lecturer, Department of Applied Physics, The University of Tokyo
Researcher, Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST)
Realization of magnetization reversal by carrier-spin-injection into nano-scale ferromagnetic alloy semiconductors
In spintronics, ferromagnetism is an indispensable property in designing non-volatile memories, magnetoresistance devices, and so on. Control of the magnetization orientation in ferromagnetic substances without using an external magnetic field is crucial for low-power consumption and high-density integration in future spintronics devices. To pursue this goal, we are studying optical/electrical spin-injection magnetization reversal in III-V-based magnetic alloy semiconductors (III-V-MAS). III-V-based magnetic alloy semiconductors show ferromagnetic ordering mediated by the exchange interactions between carriers and magnetic atoms. The exchange interaction offers opportunities to manipulate the magnetism and the magnetization reversal by controlling the carrier number and spin.
We are trying to perform spin-injection magnetization reversal by optical and electrical means. In optical spin-injection experiments, when the spin-polarized holes are generated in a III-V-based magnetic alloy semiconductor (Ga, Mn)As thin film with circularly polarized light, the magnetization is rotated in the direction along the hole spin polarization (Fig. 1a). From time-resolved magneto-optical effect measurements using a fs-Ti:sapphire laser, the signal of photoinduced magnetization rotation rises very rapidly within the pulse width (150 fs) immediately after the excitation (Fig. 1b). This indicates the possibility of ultrafast photoinduced magnetization rotation. On the other hand, in electrical control experiments (Fig. 2a), partial magnetization reversal has been observed when spin-polarized holes are injected into a free layer in (Ga, Mn)As-based tunnel magnetoresistance device (Fig. 2b). The observed reversal current density (middle of 105 A/cm2) is significantly lower than the value reported in ferromagnetic metals. These results indicate that III-V-based magnetic alloy semiconductors can be used as spin-injection magnetization reversal materials.
Our goals have been to establish optical/electrical spin-injection magnetization reversal and to reduce further the optical intensity and reversal current density in III-V-based magnetic alloy semiconductors. Moreover, the control of magnetization reversal dynamics is an interesting subject.
