Yo Tokunaga

Here, the authors establish NaCdCo${}_{2}$F${}_{7}$ as a spin-orbit-entangled ${J}_{\mathrm{eff}}$=\textonehalf{} pyrochlore antiferromagnet, in which strong geometric frustration and bond disorder drive unconventional spin freezing. Despite the onset of a frozen state, persistent spin dynamics survive to the lowest temperatures, revealing an unusual coexistence of static and dynamic magnetism in a highly frustrated, disordered system.

We report the discovery of CePd3Pb2, a Ce-based intermetallic compound with strongly anisotropic magnetism. Ce ions form one-dimensional chains along the crystallographic b axis, and the low-temperature c-axis susceptibility exceeds the a- and b-axis susceptibilities by more than an order of magnitude, indicating strong Ising-like magnetic anisotropy. At low temperatures, CePd3Pb2 orders magnetically at TN = 1.1 K. For B //c, the magnetically ordered phase exhibits an unusual temperature--field phase diagram, in which an internal phase boundary terminates at a finite magnetic field rather than enclosing a separate ordered phase. Reflecting the strong magnetic anisotropy, the antiferromagnetic phase is much more robust against fields applied along the a and b axes, with critical fields more than an order of magnitude larger than that for B //c. These results establish CePd3Pb2 as a localized 4f magnet with quasi-one-dimensional Ce chains and giant Ising-like anisotropy.

We investigated electron-nuclear spin entanglement in the paramagnetic ground state of the Ho-based cubic compound HoCo 2 Zn 20 . From analyses of magnetization and specific heat data, we determined the cubic crystalline electric field (CEF) parameters, the magnetic exchange constant, and the hyperfine coupling constant between the 4 f magnetic moment and the Ho 165 nuclear spin. Our results show that the Γ 5 CEF ground state is split by the hyperfine coupling, with an energy width of 1.3 K at 0 T, and that the true paramagnetic ground state is a quasisextet arising primarily from entanglement between the f -electron effective spin S = 1 and the Ho 165 nuclear spin I = 7 / 2 . We further demonstrate that, depending on the CEF parameters, the paramagnetic ground state can switch to an electron-nuclear coupled dectet. These findings underscore the importance of accurately identifying the electron-nuclear level scheme for understanding the low-temperature properties of rare-earth compounds containing spin-active nuclei.

We report a random singlet ground state in the S = 1 2 Heisenberg pyrochlore antiferromagnet NaCdCu 2 F 7 . Cationic Na + / Cd 2 + disorder on the pyrochlore A site generates a broad distribution of Cu 2 + – F − – Cu 2 + exchange couplings, introducing intrinsic magnetic bond disorder. Despite strong antiferromagnetic interactions ( θ CW = − 72 K ) , no magnetic order or global spin freezing is observed in dc and ac susceptibility, specific heat, or Na 23 nuclear magnetic resonance to 120 mK, with muon spin relaxation experiments confirming persistent spin dynamics to 58 mK. T -linear specific heat, a Curie-like susceptibility tail, and power-law scaling with data collapse in χ ( T ) , M ( H ) , C mag / T , Na 23 ( 1 / T 1 T ) , and the muon spin polarization P ( t ) reveal a disorder-driven network of random singlets and orphan spins. Scaling across multiple bulk and local probes is consistent with a broad distribution of exchange energies, P [ J ] ∼ J − α . This behavior contrasts with previously studied Na A ″ B 2 F 7 pyrochlore fluorides, where magnetic bond disorder precipitates spin-glass freezing, underscoring the crucial role of strong S = 1 2 quantum fluctuations in NaCdCu 2 F 7 .