Effect of high pressures on exchange and hyperfine interactions in rare-earth orthoferrites

The effect of high pressures P on the Néel temperature TN, the crystal lattice parameters, and the magnitude of the hyperfine magnetic field HSn at a nucleus of a diamagnetic tin atom was studied in pure and tin-doped orthoferrites RFeO3 (R = Nd, Lu). The dependence of these quantities on the geometry of the exchange bonds, specifically, the angle and length of the chemical bond Fe-O-Fe(Sn), was analyzed. It was established that under pressure the angular contribution decreases and the radial contribution increases TN and HSn, the radial contribution being greater than the angular contribution in absolute magnitude. Numerical estimates were obtained for the angular and radial contributions to TN and HSn. In lutecium orthoferrite, at P > 30 GPa anomalies indicating a possible phase transition were observed in the behavior of the lattice parameters and the value of HSn.