Spin dynamics in bulk MnNiGa and Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn investigated by muon spin relaxation

TL;DR

This study uses muon spin relaxation and magnetometry to explore the magnetic dynamics of bulk MnNiGa and Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn, revealing slow dynamics near phase transitions and persistent low-temperature spin fluctuations, which inform the understanding of their topological magnetic states.

Contribution

It provides new insights into the bulk magnetic dynamics of MnNiGa and Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn, especially around phase transitions, aiding the understanding of their topological magnetic phases.

Findings

Slow decrease in dynamic frequency near higher temperature transitions.

Persistent spin dynamics over broad frequency range at low temperatures.

Behavior differs from typical critical slowing down in second order transitions.

Abstract

We report muon spin relaxation and magnetometry studies of bulk Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn and MnNiGa, two materials which have recently been proposed to host topological magnetic states in thin lamella (antiskyrmions for Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn and biskyrmions for MnNiGa), and show spin reorientation transitions in bulk. These measurements shed light on the magnetic dynamics surounding the two magnetic phase transitions in each material. In particular, we demonstrate that the behaviour approaching the higher temperature transition in both samples is best understood by considering a slow decrease in the frequency of dynamics with temperature, rather than the sharp critical slowing down typical of second order transitions. Furthermore, at low temperatures the two samples both show spin dynamics over a broad range of frequencies that persist below the spin reorienation transition. The dynamic behavior we identify gives new insight into the bulk magnetism of these materials that may help underpin the stabilization of the topologically non-trivial phases that are seen in thin lamellae.