Electronic properties and the appearance of magnetism in the (Tb 1− xY x)Co 2 compounds

Abstract

We present experimental results obtained from low temperature specific heat and magnetic measurements on the (Tb 1− x Y x )Co 2 pseudo-binary system. Two main concentration ranges are distinguished: i) 0⩽x⩽0.8, ii) 0.8⩽x⩽1.0 . The first of these corresponds to the ferrimagnetic alloys with decreasing Curie temperatures and mean cobalt moment when x increases. The density of states at the Fermi level N( E F), determined from specific heat measurements, show values of the same order of magnitude for x ⩽ 0.6. This little change of N( E F) over such a large concentration range is due to the location of E F in the 3d Co sub-band with small contributions from the 4d of Y and 5d or the Tb electrons. The concentration range 0.8⩽ x⩽1.0 corresponds to the onset of ferrimagnetism. Here high γ values are observed, favouring the Stoner condition for magnetism of cobalt sub-band, plus enhancement effects due to spin glass behaviour which appears to be untypical: instead of T, a T 3 2 behaviour is observed for the magnetic specific heat at low temperatures. This may be due to the existence of spin waves in a spin glass regime as predicted by recent theories.