Magnetic ordering and irreversible magnetization between ZFC and FC states in RCo 5Ga 7 compounds

Abstract

The magnetic properties of RCo 5Ga 7 (R=Y, Tb, Dy, Ho and Er) compounds which crystallize in the ScFe 6Ga 6-type structure have been studied. The compounds with R=Y, Tb, Dy, Ho and Er display behaviour similar to semiconductors. The Co transition metal sublattice is ferrimagnetic with a very low spontaneous magnetization. The ferrimagnetic ordering observed for R=Y, Tb, Dy, Ho and Er is due to the transition metal sublattice with transition temperatures at about 295 K. At low temperatures, the magnetic ordering for R=Tb, Dy, Ho and Er is due to the rare-earth sublattice, which is ferromagnetic with a Curie temperature below 5 K. By fitting the linear part of the inverse magnetization, the effective magnetic moment of the R ion is found to be close to its expected theoretical value, with paramagnetic Curie temperatures below 5 K. Due to the paramagnetic nature of the R sublattice above 60 K, the ferrimagnetic ordering temperature of the Co sublattice does not vary with the type of rare-earth ion. The irreversibility of the magnetization of YCo 5Ga 7, as measured in zero-field cooled (ZFC) and field cooled (FC) states, is attributed to movement of domain walls. Application of a large enough applied field completes the movement of the domain wall from the low-temperature to the high-temperature one at 5 K. With a very low magnetic field 100 Oe, the difference between the ZFC and the FC shrinks.