Magnetic order and exchange coupling in the frustrated diamond-lattice antiferromagnet MnSc2Se4

We report the magnetic properties of the A-site spinel compound MnSc2Se4. The macroscopic magnetic measurements uncover 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 suppressed due to the chemical pressure of the X ion in MnSc2X4 (X = S, Se) spinels.