Neutron probes of long-range ordering with suppressed dipolar moments in Ce₂Zn₁₇

Multipolar ordering has been observed in rare-earth compounds as a result of magnetic anisotropy in single-ion states and interactions. While a multipolar ground state escapes the direct neutron probe, excitation out of such an order still carries dipolar fluctuation, allowing the application of inelastic neutron scattering to unveil the microscopic interactions. Our recent neutron scattering experiments on the hexagonal metal Ce₂Zn₁₇ documented the lack of magnetic Bragg peaks and the presence of sharp magnons. The field- and polarization-dependence of the excitation spectrum suggested an order parameter with in-plane components S^x and S^y, while the fluctuation is predominantly of S^z component. In addition, the single-ion ground state inferred from crystal field measurements suggests a strong Ising anisotropy with a dipolar moment of S^z = 2.04µ_B and S^x, S^y ~ 0.05µ_B. The totality of these results strongly suggested a ground state with multipolar ordering in Ce₂Zn₁₇. We developed an effective spin Hamiltonian from the neutron-documented S(Q, ω), constrained by the evolution of T_N with magnetic field, in an attempt to explain the dominance of multipolar over dipolar ordering.