I.N. Rozantsev

Mössbauer-effect study of competitive exchange interactions in UNi1−xCoxGa solid solutions

Abstract Results of Mossbauer spectroscopy of 119 Sn atoms substituted on Ga sites in the UNi 1− x Co x Ga solid solutions are presented and discussed together with previously reported magnetization data in terms of evolution of magnetism between the antiferromagnet UNiGa and ferromagnet UCoGa. The Mossbauer spectra were analyzed by considering the hyperfine field transferred to the 119 Sn nucleus from the six nearest U magnetic moments and a weak signal due to anisotropic polarization of Sn 5p states. The low-temperature spectra for UNiGa and UCoGa are consistent with their ground-state magnetic structures. The nonmagnetic component observed for UNiGa persists in the spectra for x up to 0.4 which indicates the presence of antiferromagnetically coupled U moments. The nonmagnetic component emerging in the spectra for x around 0.77 is tentatively attributed to clusters of frustrated U magnetic moments surrounding the 119 Sn nuclei.

Influence of vacancies on the magnetic structure of UCuGe

Abstract The local magnetic moment configurations in the UCu x Ge ( x =0.90, 0.95 and 0.98) and UCuGe y ( y =0.90 and 0.95) non-stoichiometric intermetallic compounds were studied by means of Mossbauer spectroscopy in the temperature range 10–100 K. The 119 Sn nuclei in Sn atoms doped on the Ge sites were exploited as a local probe. The vacancies on the Ge sites in UCuGe y seem to have no considerable influence on the original magnetic structure of UCuGe. On the other hand, two ‘new’ magnetic moment configurations, which coexist at low temperatures with the original UCuGe magnetic structure, were observed in the Cu-deficient UCu x Ge compounds. The changes of the mutual orientation of the U magnetic moments in the ‘new’ (perturbed) magnetic structure is due to the vacancy-induced variations of the effective exchange fields, which determines also the temperature evolution of magnetization. The observed anomalous temperature dependence of the hyperfine magnetic field on the 119 Sn nuclei is qualitatively interpreted within the model of ‘melting’ of frustrated spins.

Competition between ferromagnetic and antiferromagnetic exchange interactions in the quasibinary U(Ge1-xSnx)2 compounds

Abstract The evolution of the magnetic ordering temperature T M and the low-temperature magnetic structure in the quasibinary compounds U(Ge 1− x Sn x ) 2 for 0.01≤ x ≤1 were studied by means of 119 Sn Mossbauer spectroscopy. These compounds are solid solutions between the ferromagnet UGe 2 ( T C =52 K) and the antiferromagnet USn 2 ( T N =75 K), both being collinear. The boundary compounds possess different easy-magnetization directions, the a - and c -axis, respectively. The minimum ordering temperature ( T min ≈36 K) has been found for x =0.58. The complex Mossbauer spectra observed for lower Sn concentrations could be attributed to the appearance of two non-collinear spin configurations characterized by a canting angle between pairs of U magnetic moments of 60 and 120°, respectively. When increasing the Sn concentration beyond x =0.58, the Mossbauer spectrum resembles that observed for USn 2 which is accompanied by a rapid increase of T M .