Magnetic order and exchange couplings in the frustrated diamond lattice antiferromagnet MnSc$_2$Se$_4$

TL;DR

This study investigates the magnetic phase transitions and exchange interactions in the frustrated diamond lattice antiferromagnet MnSc$_2$Se$_4$, revealing complex magnetic orders and the impact of chemical substitution on spin dynamics.

Contribution

It provides detailed experimental insights into the magnetic structures and exchange couplings in MnSc$_2$Se$_4$, highlighting the effects of Se substitution on magnetic excitations.

Findings

Successive magnetic transitions at 2.04 K, 1.8 K, and 1.6 K.

Identification of collinear and helical magnetic structures.

Suppression of spin-wave energies due to Se substitution.

Abstract

We report the magnetic properties of $A$-site spinel compound MnSc$_2$Se$_4$. The macroscopic magnetic measurements uncovers successive magnetic transitions at $T_{\rm{N1}}$= 2.04 K, followed by two further transitions at $T_{\rm{N2}}$=1.8 K and $T_{\rm{N3}}$=1.6 K. Neutron powder diffraction reveals that both, $T_{\rm{N2}} < T < T_{\rm{N1}}$ and $T <T_{\rm{N3}}$, orders are associated with the propagation vector $k$=(3/4 3/4 0), while the magnetic structures are collinear amplitude modulated and helical, respectively. Using neutron powder spectroscopy we demonstrated the effect of substitution of S by Se on the magnetic exchange. The energy range of the spin-wave excitations is supressed due to the chemical pressure of the $X$- ion in MnSc$_2X_4$ ($X$=S, Se) spinels.