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Magnetic Phase Transitions and Spin Density Distribution in the Molecular Multiferroic System GaV4S8



Rebecca L Dally, William D. Ratcliff, Lunyong Zhang, Heung-Sik Kim, Markus NMN Bleuel, J. W. Kim, Kristjan Haule, David Vanderbilt, Sang-Wook Cheong, Jeffrey W. Lynn


We have carried out neutron diffraction and small angle neutron scattering measurements on a high quality single crystal of the cubic lacunar spinel multiferroic, GaV4S8, as a function of magnetic field and temperature to determine the magnetic form factor for the single electron that is located on the tetrahedrally coordinated V4 molecular unit. Our results are in good agreement with the structural transition at 44 K from cubic to rhombohedral symmetry where the system becomes a robust ferroelectric, while long range magnetic order develops below 13 K in the form of an incommensurate cycloidal magnetic structure, which can transform into a Neel-type skyrmion phase in modest applied magnetic field. Below 5.9(3) K, the crystal enters a ferromagnetic phase, and we find the magnetic order parameter indicates a long range ordered ground state with an ordered moment of 0.23(1) υB per V ion. The Bragg intensities for a series of peaks in the ferroelectric-paramagnetic phase have been measured to determine the magnetic form factor, and the intensities are consistent with a model of the single spin being uniformly distributed across the V4 molecular unit, rather than residing on the single apical V ion. In the magnetically ordered state, polarized neutron measurements are important since both the cycloidal and ferromagnetic order parameters are clearly coupled to the ferroelectricity, causing the structural peaks to be temperature and field dependent. For the ferromagnetic ground state, the spins are locked along the [1,1,1] direction by a surprisingly large anisotropy.
Physical Review X


skyrmion, multiferroic, polarized neutron scattering, form factor


, R. , Ratcliff, W. , Zhang, L. , Kim, H. , , M. , , J. , Haule, K. , Vanderbilt, D. , Cheong, S. and Lynn, J. (2020), Magnetic Phase Transitions and Spin Density Distribution in the Molecular Multiferroic System GaV<sub>4</sub>S<sub>8</sub>, Physical Review X, [online], (Accessed October 24, 2021)
Created July 6, 2020, Updated September 21, 2020