Metallurgy and magnetoresistance of the holmium-copper compounds

A comprehensive study of the rare earth-intermetallic system, holmium-copper, has been carried out. The metallurgical phase diagram of the Ho-Cu system has been determined, and it has been established that only three ordered compounds exist in the system, namely HoCu, HoCu2 and HoCu5. The crystallographic structures for the three compounds have been confirmed and significant differences in the intensities of diffracted X-radiation between previously reported values and the experimentally determined values are discussed. The magnetoresistivity of the three compounds was measured, as a function of temperature, in the range 2K to 300K, using applied magnetic fields of up to 8T. Experimental details are given. Analysis of the results has allowed the determination of the characteristic magnetic ordering temperatures exhibited by each compound. It has been found that HoCu exhibits a Neel temperature of 27K, and shows evidence of a further ordering transition at 12.5K. HoCu2 has a Neel temperature of 11.2K and HoCu5 has a Curie temperature of about 8K. HoCu2 has been found to exhibit metamagnetic behaviour, such that ferromagnetic order may be produced by the application of a magnetic field, as well as providing evidence of a second ordering temperature of about 8K. (author)