Angle-resolved magnetization study of the multipole ordering in PrFe ₄P ₁₂

Field-orientation dependences of the magnetization M(H, θ) and the ordering temperature T _A(H, θ) of the low-field phase (A-phase) of the filled skutterudite compound PrFe ₄P ₁₂ have been studied in detail at low temperatures down to 0.3 K, by means of angle-resolved magnetization measurements. Both M(H, θ) deep inside the A-phase and T _A(H, θ) show a smooth angular variation with a cubic anisotropy when H is rotated within the (001) and (110) planes. The results strongly suggest that the order parameter of the A-phase is of scalar (Γ ₁ ⁺) type which, together with the (1, 0, 0) ordering vector, preserves the cubic symmetry. The magnitude of the cubic anisotropy term in the magnetization in the ordered state at low temperatures is found to vary with H and exhibits a sign reversal at ∼2:3 T.