Thermal expansion study of the spin reorientation and magnetic phase transitions in the Ho(Co1−cRhc)2 compounds

Abstract The cubic Laves-phase compound HoCo 2 orders magnetically at 76 K. Its moment undergoes a reorientation with increasing temperature from 〈110〉 to 〈100〉 in the temperature interval 10 to 17 K. The substitution of Rh for Co does not vary the crystal field parameters to any appreciable extent, but does alter the value of the exchange interaction, so that the series Ho(Co 1− c Rh c ) 2 is particularly suitable for the investigation of the spin reorientation. The results of thermal expansion measurements on these compounds are presented and compared with theoretical investigations. It is shown that a single-ion Hamiltonian used in conjunction with suitably chosen crystal-field and exchange parameters can satisfactorily describe the spin reorientation transition. The ‘s-d’ model is used to determine magnetic and related parameters of the series and is found to account quite well for the changing character of the magnetic phase transition.