Structural and magnetic transitions in the crystalline approximant Cd 6Sm

Abstract

Electrical resistivity, specific heat, magnetic susceptibility, and magnetization of the crystalline approximant Cd 6Sm are investigated in a temperature range 1.8-300 K. Both structural and magnetic transitions are clearly evidenced. A sharp structural phase transition is observed at T c = 179 K in the electrical resistivity as well as in the specific heat, which is attributed to orientational ordering of the Cd 4 tetrahedron located at the center of the icosahedral cluster. In addition, three successive magnetic transitions are found at T M1 = 12.5, T M2 = 10.2, and T M3 = 6.5 K. The anomaly at T M1 is attributed to an antiferromagnetic transition, whereas those at T M2 and T M3 are to ferrimagnetic transitions. The observation of the ferrimagnetic orders indicates that (pseudo) icosahedra made of localized Sm spins have a nonzero net magnetic moment, and the moments of the magnetic clusters form a long-range magnetic order. © 2012 American Physical Society.