Magnetic and structural phase transitions in some orthocobaltites doped by Ba or Sr ions
I O Troyanchuk; N V Kasper; D D Khalyavin; A N Chobot; G M Chobot; H Szymczak
Журнал:
Journal of Physics: Condensed Matter
Дата:
1998-07-20
Аннотация:
It has been found that reduction of perovskite in vacuum leads to collapse of the ferromagnetic state without changes of cubic symmetry. (, Tb) oxygen deficit orthorhombic phases undergo phase transitions approximately at temperatures K, K and K. The first order antiferro-ferromagnet transition at is accompanied by a jump of conductivity, and the negative magnetoresistance reaches 25% in a field of 1 T. The magnetization data indicate a low-spin state of cobalt ions. Spontaneous magnetization develops at and disappears at . The first order transition from a semiconductive to quasi-metallic state occurs at with a drop of resistivity of more than one order of magnitude. The transitions are most pronounced at x = 0.25. It is supposed that the transition at results from oxygen vacancies ordering. The perovskites are metallic ferromagnets with an intermediate-spin state of Co ions. The properties of compounds drastically differ from those of apparently due to rare-earth and barium ions ordering.
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