Spin waves in Dirac semimetal Ca$_{0.6}$Sr$_{0.4}$MnSb$_2$ investigated with neutrons by the diffraction method

TL;DR

This study uses neutron diffraction to detect and analyze spin waves in the Dirac semimetal Ca$_{0.6}$Sr$_{0.4}$MnSb$_2$, revealing magnetic interactions and their temperature dependence without energy analysis, enabling efficient characterization of magnetic excitations.

Contribution

It introduces a novel high-throughput neutron diffraction method to study magnetic excitations in small crystals without energy analysis, applied to a Dirac semimetal.

Findings

Detected inelastic spin waves in a small crystal sample.

Refined spin Hamiltonian parameters including inter-plane interactions.

Observed softening of the spin gap near the Neel temperature.

Abstract

We report neutron diffraction measurements of Ca$_{0.6}$Sr$_{0.4}$MnSb$_2$, a low-carrier-density Dirac semimetal in which the antiferromagnetic Mn layers are interleaved with Sb layers that host Dirac fermions. We have discovered that we can detect a good quality inelastic spin wave signal from a small (m ~ 0.28 g) single crystal sample by the diffraction method, without energy analysis, using a neutron diffractometer with a position-sensitive area detector; the spin-waves appear as diffuse scattering that is shaped by energy-momentum conservation. By fitting this characteristic magnetic scattering to a spin-wave model, we refine all parameters of the model spin Hamiltonian, including the inter-plane interaction, through use of a three-dimensional measurement in reciprocal space. We also measure the temperature dependence of the spin waves, including the softening of the spin gap on approaching the Neel temperature, $T_N$. Not only do our results provide important new insights into an interplay of magnetism and Dirac electrons, they also establish a new, high-throughput approach to characterizing magnetic excitations on a modern diffractometer without direct energy analysis. Our work opens exciting new opportunities for the follow-up parametric and compositional studies on small, ~0.1 g crystals.