Neutron Scattering Study on Yttrium Iron Garnet for Spintronics

TL;DR

This study uses neutron scattering to analyze the magnetic structure and excitations of yttrium iron garnet, providing insights into spin current propagation crucial for advancing spintronics and magnonics.

Contribution

It offers a detailed momentum- and energy-resolved characterization of yttrium iron garnet's magnetism and introduces measurement of magnon polarization as a fundamental property affecting spin current.

Findings

Refined crystal and magnetic structure of yttrium iron garnet.

Measured magnetic excitations over four decades of energy.

Determined magnon polarization directions and their role in spin current.

Abstract

Spin current -- a flow of the spin degree of freedom in matter -- has vital importance in spintronics. Propagation of the spin current ranges over a whole momentum space; however, generated spin currents are mainly detected in the long-wavelength limit. To facilitate practical uses of spintronics and magnonics, microscopic understanding of the spin current is necessary. We here address yttrium iron garnet, which is a well-employed ferrimagnet for spintronics, and review {\it in re} the momentum- and energy-resolved characteristics of its magnetism. Using {\it unpolarized} neutrons, we refined its detailed crystal and magnetic structure, and examined magnetic excitations through four decades (10~$\mu$eV-100~meV) using chopper spectrometers in J-PARC, Japan. We also measured mode-resolved directions of the precessional motion of the magnetic moment, i.e., magnon polarization, which carries the spin current in insulators through {\it polarized} neutron scattering, using a triple-axis spectrometer in ILL, France. The magnon polarization is a hitherto untested fundamental property of magnets, affecting the thermodynamic properties of the spin current. Our momentum- and energy-resolved experimental findings provide an intuitive understanding of the spin current and demonstrate the importance of neutron scattering techniques for spintronics and magnonics.