Effective staggered field for strongly anisotropic moments on the low-symmetry site in Ce₂Pd₂Pb

We studied magnetic-field responses of a low-symmetrical site, i.e., an orthorhombic site in a tetragonal crystal, in Ce₂Pd₂Pb, which exhibits a strong axial moment in the cerium site. Considering two orthogonalized local-coordinate systems on the cerium site, the field responses of the moment can be expressed as a product of the external field and spatial variation of the g factor and be regarded as the responses of an effective staggered field for the isotropic pseudospin sp=1/2 state. We obtained H-T phase diagrams of Ce₂Pd₂Pb under the fields H(100) and H(110) from thermodynamic measurements and identified magnetization plateaus for several phases. Assuming the effective staggered field, we can explain the specific heat of Ce₂Pd₂Pb under high fields. The result indicates that a partially ordered state in which one-half of the total cerium moments contributes to the long-range order is realized for H(110), where the staggered component becomes maximum. Furthermore, a slight incline of the field results in a change in the ordering nature of the partially ordered phase, demonstrating the controllability of the effective staggered field.