Pressure- and Field-Tuning the Magnetostructural Phases of Mn3O4: Raman   Scattering and X-Ray Diffraction Studies
  We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of single crystal Mn3O4, combined with temperature- and field-dependent x-ray diffraction studies, revealing the novel magnetostructural phases in Mn3O4. Our temperature-dependent studies showed that the commensurate magnetic transition at T2=33K in the binary spinel Mn3O4 is associated with a structural transition from tetragonal to orthorhombic structures. Field-dependent studies showed that the onset and nature of this structural transition can be controlled with an applied magnetic field, and revealed evidence for a field-tuned quantum phase transition to a tetragonal spin-disordered phase for H||[1-10]. Pressure-dependent Raman measurements showed that the magnetic easy axis direction in Mn3O4 can be controlled---and the ferrimagnetic transition temperature increased---with applied pressure. Finally, combined pressure- and magnetic-field-tuned Raman measurements revealed a rich magnetostructural phase diagram---including a pressure- and field-induced magnetically frustrated tetragonal phase in the PH phase diagram---that can be generated in Mn3O4 with applied pressure and magnetic field. 
M. Kim, X.M. Chen, X. Wang, C.S. Nelson, R. Budakian, P. Abbamonte,   and S.L. Cooper
cond-mat.str-el