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

The effect of high pressures P on the Neel temperature T-N , the crystal la ttice parameters, and the magnitude of the hyperfine magnetic field H-Sn at a nucleus of a diamagnetic tin atom was studied in pure and tin-doped orth oferrites RFeO3 (R = Nd, Lu). The dependence of these quantities on the geo metry of the exchange bonds, specifically, the angle and length of the chem ical bond Fe-O-Fe(Sn), was analyzed. It was established that under pressure the angular contribution decreases and the radial contribution increases T -N and H-Sn, the radial contribution being greater than the angular contrib ution in absolute magnitude. Numerical estimates were obtained for the angu lar and radial contributions to T-N and H-Sn. In lutecium orthoferrite, at P > 30 GPa anomalies indicating a possible phase transition were observed i n the behavior of the lattice parameters and the value of H-Sn. (C) 2000 MA IK "Nauka/Interperiodica".