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

Abstract

We report the magnetic properties of $A$-site spinel compound MnSc${}_2$Se${}_4$. The macroscopic magnetic measurements uncovers successive magnetic transitions at $T_{N1}$= 2.04 K, followed by two further transitions at $T_{N2}$=1.8 K and $T_{N3}$=1.6 K. Neutron powder diffraction reveals that both, $T_{N2}<T<T_{N1}$ and $T<T_{N3}$, 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${}_2{X}_4$ ($X$=S, Se) spinels.

Accepted in Phys. Rev. B