Study of Higher Energy Spin Dynamics in Frustrated MnCr2S4 Using Inelastic Neutron Scattering

Frustrated spinel compound MnCr2S4 shows two consecutive transitions at T_c = 65 K to a ferrimagnetic state and at T_YK = 5 K to the Yafet-Kittel (YK) phase. Ultrasound and magnetization experiments on MnCr2S4 revealed a series of field-driven phase transitions too. In analogy to the quantum-lattice gas models it was proposed that the zero field phase below T_YK and the field-induced phases can be described as exotic spin superfluid and spin supersolid states of quantum nature, respectively. With our preliminary powder INS measurements at OSIRIS, we successfully observed presence of low energy excitation modes up to 5 meV and its thermal evolution. However, it also looks that the low-energy modes observed at 50 K near 2-3 meV energy transfer move to higher energy sides (above 5 meV) with decreasing temperature below 50 K. However, due to the maximum energy (5 meV) transfer limitation of the OSIRIS instrument for a clean signal without background scattering, we could not verify that. Hence, to study such thermal evolution towards higher energy sides and by that to acquire more systematic and comprehensive picture, we need further detailed zero-field INS measurements on MnCr2S4 powder with transfer energy >5 meV on MERLIN. Completion of these measurements will provide details of the spin excitation spectra emerging from the exotic spin-superfluid magnetic ground state and ferrimagnetic phase above, and will allow to determine precisely the ingredients of the spin Hamiltonian.