Pressure-induced Jahn-Teller suppression and simultaneous high-spin to low-spin transition in the layered perovskite CsMnF4

The interplay between the orbital ordering and the spin state in Jahn-Teller Mn3+ governing the optical, magnetic, and transport properties in the layered CsMnF4 perovskite is investigated. Such electronic effects are strongly coupled to the lattice and thus can be modified by external pressure. However, there is very little understanding of the structural conditions which are required to attain spin crossover in connection with the electronic structure of Mn3+. The distortion, spin state, and tilting of (MnF6)(3-) octahedra in the insulating ferromagnet CsMnF4 are jointly studied by high-pressure optical spectroscopy. The insulating character of CsMnF4 allowed us to explore the electronic structure associated with the 3d levels of Mn3+ in the 0-46 GPa pressure range, an information which is obscured in most oxides due to metallization at high pressure. We show that the spin-crossover transition, related to the spin change, S = 2 -> 1, in Mn3+, takes place at 37 GPa with the simultaneous suppression of the axially elongated distortion associated with the Jahn-Teller effect. The wide stability pressure range of the Jahn-Teller distortion and high-spin state is explained in terms of crystal-field models including the Jahn-Teller stabilization energy. On this basis, we discuss the interplay between spin transition and Jahn-Teller effect comparing present findings with other results attained in Mn3+, Ni3+, and Co3+ systems.