Local structure, chemical bond parameters and hyperfine magnetic interactions of 57Fe and doped 119Sn atoms in the orthoferrites TlFeO3 and TlFe0.99Sn0.01O3

Moessbauer spectroscopy has been applied to study the magnetic hyperfine interactions of 57Fe and 119Sn probe atoms within TlFeO3 and TlFe0.99Sn0.01O3 ferrites. According to the magnetic measurements, the magnetic ordering temperature TN (= 560 K) for TlFeO3 is much lower than that for any other orthoferrites RFeO3 (R = rare earth). It is suggested that such difference in TN may be explained by different characteristics of the Tl-O and R-O chemical bonds involved and the induced competition with the Fe-O bonds. The effects of covalency and overlap distortion on the spin and charge densities at 57Fe nuclei are discussed in relation with the hyperfine interactions observed. By using cluster molecular orbital (MO) calculations, it was shown that the low value of the hyperfine magnetic field HFe(= 538 kOe) at 57Fe nuclei in TlFeO3 is strongly associated with a decrease of the covalent mixing parameter (bσ)2 0.048 and (bπ)2 = 0.009 values, which characterize the Fe-O bond covalence. It was elucidated that the value of super-transferred hyperfine field (HSTHF) at 119Sn nuclei in TlFe0.99Sn0.01O3 is sensitive mainly to the angle of the Sn-O-Fe bonds