The Final Chapter In The Saga Of YIG

TL;DR

This paper provides the first comprehensive measurement of YIG's magnon spectrum across the entire Brillouin zone, revealing more complex magnetic interactions than previously modeled, which is crucial for advancing spintronic device design.

Contribution

It presents the first full magnon spectrum measurement of YIG using neutron scattering, challenging existing models and uncovering longer-range, more complex magnetic interactions.

Findings

Full magnon spectrum measured throughout the Brillouin zone.

Existing models fail to describe optical magnon modes.

Magnetic interactions are longer-ranged and more complex.

Abstract

The magnetic insulator Yttrium Iron Garnet can be grown with exceptional quality, has a ferrimagnetic transition temperature of nearly 600 K, and is used in microwave and spintronic devices that can operate at room temperature. The most accurate prior measurements of the magnon spectrum date back nearly 40 years, but cover only 3 of the lowest energy modes out of 20 distinct magnon branches. Here we have used time-of-flight inelastic neutron scattering to measure the full magnon spectrum throughout the Brillouin zone. We find that the existing model of the excitation spectrum, well known from an earlier work titled "The Saga of YIG", fails to describe the optical magnon modes. Using a very general spin Hamiltonian, we show that the magnetic interactions are both longer-ranged and more complex than was previously understood. The results provide the basis for accurate microscopic models of the finite temperature magnetic properties of Yttrium Iron Garnet, necessary for next-generation electronic devices.