Electronic specific heat coefficient and magnetic entropy of icosahedral Mg-RE-Zn (RE=Gd, Tb and Y) quasicrystals

The low-temperature specific heat for non-magnetic Mg42Y8Zn50 quasicrystal has been investigated to get information on the electronic structure. The electronic specific heat coefficient gamma is estimated to be 0.63 mJ mol-1 K-2, which is about 70% of the value expected from the free-electron model. This small gamma value strongly suggests the existence of a pseudogap of the electronic density of states in the vicinity of the Fermi level. The low-temperature specific heats of icosahedral Mg42Gd8Zn50 and Mg42Tb8Zn50 quasicrystals, which exhibit spin-glass behaviour, have also been investigated. The specific heat of Mg42Gd8Zn50 exhibits a broad maximum at a temperature that is a few kelvins above the spin freezing temperature Tf determined by AC susceptibility measurements. The magnetic entropy at Tf for the Mg42Gd8Zn50 quasicrystal reaches about 30% of the theoretical value of R ln 8, being comparable to those of crystalline spin-glass systems such as magnetically dilute AuFe and CuMn alloys. The magnetic specific heat of Mg42Tb8Zn50 quasicrystal is smaller than that of Mg42Gd8Zn50, suggesting the splitting of the ground state due to the local electrostatic field.