Structures and magnetic properties of Tm1−yYyMn1−xCoxO3

The structure and magnetic properties of Tm 1− y Y y Mn 1− x Co x O 3 with 0 ≦ x ≦ 0.5 and 0 ≦ y ≦ 0.3 were investigated by X-ray diffraction, specific heat and magnetization measurements. Thulium manganite TmMnO 3 prepared by solid-state synthesis at ambient pressure is hexagonal and antiferromagnetic with a Nèel temperature T N of 86 K. The substitution of Y for Tm in TmMnO 3 does not greatly affect the fundamental hexagonal structure. The magnetization and specific heat measurement results for Tm 1− y Y y MnO 3 can be qualitatively explained in terms of the dilution effect of Tm by Y. On the other hand, the structure of TmMn 1− x Co x O 3 changes gradually from hexagonal to orthorhombic with the substitution of Co for Mn; hexagonal and orthorhombic phases coexist in samples for x ≦ 0.3 whereas TmMn 0.6 Co 0.4 O 3 is almost a single orthorhombic phase. The magnetization of TmMn 0.6 Co 0.4 O 3 in a field of 250 Oe increases rapidly at about 60K with decreasing temperature. The difference between zero-field-cooled (ZFC) and field-cooled (FC) magnetizations increases remarkably at about 60 K. Moreover, the temperature dependences of the ZFC and the FC magnetizations exhibit peaks at about 40 and 30K, respectively. Thus, TmMn 1− x Co x O 3 exhibits complex magnetic properties.