Crystal Field Analysis of Single-Ion Magnets Based on Tb3+, Tm3+, and Yb3+ Squarates from Neutron Experiments and First-Principles Calculations

Crystal field analysis of single-ion magnets was performed using inelastic neutron scattering (INS) experiments and complete active space (CAS) calculations for deuterated lanthanide squarate complexes (Ln-sq(D); Ln = Tb, Tm, and Yb). In Tb-sq(D), spin excitation signals were observed around 70-100 cm-1 in the INS results. The energy gaps between ground and excited states were estimated to be in the range of 87-115 cm-1 from the CAS calculations, and the results were comparable to those from the INS results. Tm-sq(D) and Yb-sq(D) also exhibited weak spin excitation bands, in rough agreement with the energy gaps obtained from the computational analysis. The order of the energy gaps is: ΔE(Tb-sq) < ΔE(Tm-sq) < ΔE(Yb-sq). The moderate D4d compression in the current Ln-sq family appears to induce significant crystal field splitting for prolate ions while to preserve the inherent strong anisotropy of oblate ions. Thanks to the use of a higher-resolution instrument, the ground-state manifold was clearly identified in Tb-sq(D) and Tm-sq(D), but not in Yb-sq(D). This difference arises from the distinction between non-Kramers or Kramers ion. This result was also reproduced with the CAS calculation. Therefore, a complementary and valid results were obtained regarding the crystal field splitting in Ln-sq.