Crystal and magnetic structure of hexagonal RCo4Al intermetallic compounds (R=Y and Pr)

We report on the structural and magnetic properties of the YCo4Al and PrCo4Al intermetallic compounds. Both phases crystallize in the hexagonal CaCu5-type structure with P6/mmm space group. Neutron powder diffraction experiments demonstrate that the Al atoms preferentially occupy the 3g crystallographic site of the CaCu5 structure. Al substitution in RCo5 induces remarkable changes of the magnetic properties: a drastic decrease of the mean Co magnetic moment, the saturation magnetization, and the Curie temperature. The magnetic anisotropy field at room temperature has been measured on field-oriented powder using magnetization measurements. A spin reorientation transition was observed in PrCo4Al at low temperature by susceptibility measurements on a field-oriented sample. A detailed analysis of this phenomenon is completed by polar magnetic measurements and neutron thermodiffraction experiment. First-order magnetization process occurs in PrCo4Al up to 60 K at a critical field of about 6 T. r 2002 Elsevier Science B.V. All rights reserved.