Structure and unusual magnetic properties in the itinerant electron system Hf0.8Ta0.2(Fe1−xCox)2

The crystal structure and magnetization of Hf0.8Ta0.2(Fe1−xCox)2 are investigated by X-ray powder diffraction and magnetization measurements. The compounds exhibit the Laves C14 structure for <F>x=0.0</F>–0.2 and the C15 structure for <F>x≥0.3</F>. The structural transition from C14 to C15 leads to an anomaly of the unit cell volume between <F>x=0.2</F> and 0.3. When <F>x=0.0</F>, the compound undergoes a magnetic phase transition from ferromagnetic to paramagnetic state via the antiferromagnetic state, in which a field-induced metamagnetic transition is observed. When <F>x=0.1</F> and 0.2, the compounds exhibit unusually small saturation moments, which are considered as antiferromagnetism (with weak ferromagnetic impurities) and weak ferromagnetism or ferrimagnetism, respectively. The formation of the AFM state is associated with a small bond length of Fe atom in the 6h site. When <F>x≥0.3</F>, the compounds exhibit a ferromagnetic to paramagnetic transition, which can be explained by itinerant electron metamagnetism. [Copyright &y& Elsevier]