Spin glass behavior and magnetic boson peak in a structural glass of a magnetic ionic liquid

Maiko Kofu,Kazuhiro Akutsu,Takeshi Ueki,Seiko Ohira-Kawamura,Ryuta Watanuki,Osamu Yamamuro,Masato Matsuura,Kenji Nakajima,Toshiro Sakakibara

doi:10.1038/s41598-021-91619-z

Abstract

Glassy magnetic behavior has been observed in a wide range of crystalline magnetic materials called spin glass. Here, we report spin glass behavior in a structural glass of a magnetic ionic liquid, C4mimFeCl4. Magnetization measurements demonstrate that an antiferromagnetic ordering occurs at TN = 2.3 K in the crystalline state, while a spin glass transition occurs at TSG = 0.4 K in the structural glass state. In addition, localized magnetic excitations were found in the spin glass state by inelastic neutron scattering, in contrast to spin-wave excitations in the ordered phase of the crystalline sample. The localized excitation was scaled by the Bose population factor below TSG and gradually disappeared above TSG. This feature is highly reminiscent of boson peaks commonly observed in structural glasses. We suggest the “magnetic” boson peak to be one of the inherent dynamics of a spin glass state.

Highlights

Glassy magnetic behavior has been observed in a wide range of crystalline magnetic materials called spin glass
We report a new type of spin glasses (SGs) material, a magnetic ionic liquid (MIL), C 4mimFeCl4 (1-butyl-3-methylimidazolium tetrachloroferrate), that is nonmetallic, contains only one kind of magnetic element, and is completely vitrified without mechanical treatment
We have investigated the magnetic properties of C4mimFeCl4 in both the structural glass and crystal states by magnetization and neutron scattering measurements

Summary

Introduction

Glassy magnetic behavior has been observed in a wide range of crystalline magnetic materials called spin glass. We have investigated the magnetic properties of C4mimFeCl4 in both the structural glass and crystal states by magnetization and neutron scattering measurements. It is noted that the magnetic diffuse peak in the structural glass appears near the magnetic Bragg peaks in the crystalline sample, suggesting a similar local spin configuration in both the SG state and AFM phase (Supplementary SI-6).

Results

Conclusion