ISSN:
1090-6509
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract Mössbauer spectroscopy is used to study the hyperfine magnetic fields at tin 119Sn ions introduced as an isomorphic impurity in the lattices of the orthoferrites RFeO3. The large reduction in the field H Sn hf (4.2 K) observed when R is changed from La to Lu correlates with the drop in the Néel point and indicates that the exchange interactions are decreasing over this series. A crystal chemical analysis of the structural series with the general formula ABO3 shows that the ideal structure of cubic perovskite can be converted to a rhombohedral hematite-corundum structure by simple rotation of the [BO6] octahedra if the B-O interionic distances remain unchanged. The rhombic distortions are associated with a reduction in the B-O-B bond angle from θ =180° in perovskite to ∼132° in hematite. The rare earth orthoferrites RFeO3 follow the same mechanism for structural transformations and the LaFeO3-LuFeO3 series occupies an intermediate position (157°〉θ〉142°) between the extreme members of the series mentioned above. A reduction in the bond angle leads to weakening of the Fe-O-Fe exchange interaction, which shows up as a drop in the Néel temperature and in the hyperfine magnetic field at the nucleus. An analysis of theoretical models shows that for a suitable choice of the exchange and transfer parameters, the angular variation in the parameters of the exchange interaction is described fairly well by the Moskvin theory over a rather wide range of angles θ. The contributions to the fields H Sn hf and H Fe hf from the t 2g -and e g -orbitals of neighboring paramagnetic ions in the orthoferrites and orthochromites are examined.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1134/1.558833
