The quantum physics of electron spins and photons


DMI modulation with current.

We find the Dzyaloshinskii-Moriya interaction (DMI) that emerges at heavy metal/ferromagnetic metal interfaces can be modulated with current.
The DMI increases with increasing current with a rate that agrees with what is predicted by the model based on the spin Doppler effect.
The results imply that the interfacial DMI may partly originate from equilibrium spin current which can be modulated externally.

Current induced modulation of interfacial Dzyaloshinskii-Moriya interaction
N. Kato, M. Kawaguchi, Y.-C. Lau, T. Kikuchi, Y. Nakatani, M. Hayashi
Phys. Rev. Lett. 122, 257205 (2019).

A giant acoustic planar Hall effect observed.

We find a planar-Hall like transverse voltage develops in magnetic thin film when surface acoustic waves (SAW) are excited in feromagnetic thin films.
The sign of the field angle dependent transverse voltage does not depend on the SAW propagation direction but its size is more than an order of magnitude larger than its electronic counterpart (i.e. planar Hall effect).
These results imply that acoustic current can generate magneto-galvanic effects similar to the electric and thermo-electric currents but the effect can be significantly larger.

Unidirectional planar Hall voltages induced by surface acoustic waves in ferromagnetic thin films
T. Kawada, M. Kawaguchi, M. Hayashi
Phys. Rev. B 99, 184435 (2019).

Studies on the DMI and spin orbit torque at the Ir/Co interface published.

The DMI of the Ir and Co interface is found to be similar in magnitude with that of the Pt and Co interface.
The sign of the Ir/Co DMI is the same with that of the Pt/Co interface.
Ir has small a spin Hall angle of 0.01 but acts as a good spin sink, which can be exploited for engineering spin orbit torque in spin orbit heterostructures.

Dzyaloshinskii-Moriya interaction and spin-orbit torque at the Ir/Co interface
Y. Ishikuro, M. Kawaguchi, N. Kato, Y.-C. Lau, M. Hayashi
Phys. Rev. B 99, 134421 (2019).

Our paper on the spin Hall effect in Co-Ga alloy is published.

Spin Hall angle of ~0.05 is found in an alloy formed from elements with relatively small spin spin orbit coupling.
First principle calculations show that hybridization of the Co 3d and Ga 4p orbitals contribute to the large spin Hall effect in this alloy.

Spin Hall effect from 3d-4p hybridized orbitals
Y.-C. Lau, H. Lee, G. Qu, K. Nakamura, M. Hayashi
Phys. Rev. B 99, 064410 (2019).

Hana Hirose won the JSAP young scientist presentation award!

Hana Hirose won the 45th young scientist presentation award for her presentation at the 79th Japan Applied Physics Society (JSAP) autumn meeting.
Presentation title: "Material dependence of interfacial spin-momentum locked bands in metallic heterostructures."

Our paper was selected as a featured article!

Circular photogalvanic effect in Cu/Bi bilayers
H. Hirose, N. Ito, M. Kawaguchi, Y. C. Lau, M. Hayashi
Appl. Phys. Lett. 113, 222404 (2018).

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Spin orbit induced photocurrent found in Bi/Cu bilayer.

Irradiation of circularly polarized light in the visible range generates a helicity dependent photocurrent in Cu/Bi bilayers.
The effect can arise from a spin momentum locked band at the Cu/Bi interface.

Circular photogalvanic effect in Cu/Bi bilayers
H. Hirose, N. Ito, M. Kawaguchi, Y. C. Lau, M. Hayashi
Appl. Phys. Lett. 113, 222404 (2018).

Spin orbit torque detected optically!

The spin orbit torque of W/CoFeB/MgO and Pt/CoFeB/MgO heterostructures are studied using magneto-optical Kerr effect. Signals from the current induced torque and current induced heating are separated using a double modulation scheme.

Optical Detection of Spin-Orbit Torque and Current-Induced Heating
Y. Marui, M. Kawaguchi, M. Hayashi
Appl. Phys. Express 11, 5 093001 (2018).

Hana Hirose won the Best presentation award!

Hana Hirose won the Best presentation award at the Condensed Matter Physics Summer School.

Our paper on the resistance of chiral domain walls is published.

Resistance associated with chiral domain walls is studied. Contributon form the anomalous Hall effect dominates the domain wall resistance, but we also find effects that can be attributed to the chiral magnetoresistance.

Domain-Wall Resistance in Cofeb-Based Heterostructures with Interface Dzyaloshinskii-Moriya Interaction
Y. Ishikuro, M. Kawaguchi, Y. C. Lau, Y. Nakatani, M. Hayashi
Appl. Phys. Express 11, 5 073001 (2018).

Our paper on the spin Hall magnetoresistance in Pt/Co bilayers is published.

An anomalously large spin Hall magnetoresistance (SMR) is found in Co/Pt bilayers. The effective spin Hall angle derived from the SMR approaches 0.4, indicating that the measured SMR includes contribution from other spin dependent effect.

Anomalous Spin Hall Magnetoresistance in Pt/Co Bilayers
M. Kawaguchi, D. Towa, Y. C. Lau, S. Takahashi, M. Hayashi
Appl. Phys. Lett. 112, 5 202405 (2018).