Successive Magnetic Orderings of Rectangular Components Caused by Conservation of Paraquadrupolar State in Magnetically Ordered Phase in TbCoGa₅

Abstract

We grew single crystals of TbCoGa 5 and measured their magnetic susceptibility, specific heat, and elastic constants. The result of the magnetic susceptibility measurement suggests that the c - and a b -components of the magnetic moments of Tb 3+ ions order independently at T N1 =36.2 K and T N2 =5.4 K, respectively. The magnetic entropy change indicates that the degeneracy of internal degrees of freedom is not fully lifted in the intermediate phase. In addition, the degeneracy of electric-quadrupolar (orbital) degrees of freedom exists in spite of the formation of magnetic order because the elastic constants show softening in the intermediate phase. It is considered that the magnetic ordering of the a b -component is suppressed by the existence of the degeneracy of quadrupolar degrees of freedom in TbCoGa 5 .