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  Feng, H.L.; Reehuis, M.; Adler, P.; Hu, Z.; Nicklas, M.; Hoser, A.; Weng, S.-C.; Felser, C.; Jansen, M.: Canted ferrimagnetism and giant coercivity in the nonstoichiometric double perovskite La₂Ni_1.19Os_0.81O₆. Physical Review B 97 (2018), p. 184407/1-9

10.1103/PhysRevB.97.184407
Open Accesn Version

Abstract:
The nonstoichiometric double perovskite oxide La2Ni1.19Os0.81O6 was synthesized by solid-state reaction and its crystal and magnetic structures were investigated by powder x-ray and neutron diffraction. La2Ni1.19Os0.81O6 crystallizes in the monoclinic double perovskite structure (general formula A2B B'O6) with space group P21/n, where the B site is fully occupied by Ni and the B' site by 19% Ni and 81% Os atoms. Using x-ray absorption spectroscopy an Os4.5+ oxidation state was established, suggesting the presence of about 50% paramagnetic Os5+ (5d(3), S = 3/2) and 50% nonmagnetic Os4+ (5d(4), J(eff) = 0) ions at the B' sites. Magnetization and neutron diffraction measurements on La2Ni1.19Os0.81O6 provide evidence for a ferrimagnetic transition at 125 K. The analysis of the neutron data suggests a canted ferrimagnetic spin structure with collinear Ni2+-spin chains extending along the c axis but a noncollinear spin alignment within the ab plane. The magnetization curve of La2Ni1.19Os0.81O6 features a hysteresis with a very high coercive field, HC = 41 kOe, at T = 5 K, which is explained in terms of large magnetocrystalline anisotropy due to the presence of Os ions together with atomic disorder. Our results are encouraging to search for rare-earth-free hard magnets in the class of double perovskite oxides.