Spin dynamics in copper metaborate $CuB_2 O_4$ studied by muon spin relaxation

TL;DR

This study uses muon spin relaxation to explore static and dynamic magnetic properties of copper metaborate, revealing persistent spin fluctuations down to very low temperatures and suggesting possible origins such as exchange frustration and soliton dynamics.

Contribution

It provides detailed insights into the magnetic phases of CuB$_2$O$_4$ and identifies persistent spin fluctuations at low temperatures, highlighting the complex magnetic behavior of the material.

Findings

Static magnetic fields dominate in the weak ferromagnetic phase.

Fluctuating magnetic components become dominant in the incommensurate helix phase.

Spin fluctuations persist down to 0.3 K, indicating dynamic behavior at very low temperatures.

Abstract

Copper metaborate CuB$_2$O$_{4}$ was studied by muon spin relaxation measurements in order to clarify its static and dynamic magnetic properties. The time spectra of muon spin depolarization suggest that the local fields at the muon site contain both static and fluctuating components in all ordered phases down to 0.3 K. In the weak ferromagnetic phase (20 K~$>T>$~9.3 K), the static component is dominant. On the other hand, upon cooling the fluctuating component becomes dominant in the incommensurate helix phase (9.3K > T > 1.4K). The dynamical fluctuations of the local fields persist down to 0.3K, where a new incommensurate phase (T < 1.4K) is expected to appear. This result suggests that spins fluctuate even at T \to 0. We propose two possible origins of the remnant dynamical spin fluctuations: frustration of the exchange interactions and the dynamic behavior of the soliton lattice.