Structural and magnetic characterization of CeTa7⁢O19 and YbTa7⁢O19 with a two-dimensional pseudospin-1/2 triangular lattice

Triangular lattice antiferromagnets are prototypes for frustrated magnetism and may potentially realize novel quantum magnetic states such as a quantum spin-liquid ground state. A recent work suggests NdTa7⁢O19 with rare-earth triangular lattice is a quantum spin-liquid candidate and highlights the large family of rare-earth heptatantalates as a framework for quantum magnetism investigation. In this paper, we report the structural and magnetic characterization of CeTa7⁢O19 and YbTa7⁢O19. Both compounds are isostructural to NdTa7⁢O19 with no detectable structural disorder. For CeTa7⁢O19, the crystal field energy levels and parameters are determined by inelastic neutron scattering measurements. Based on the crystal field result, the magnetic susceptibility data could be well fitted and explained, which reveals that CeTa7⁢O19 is a highly anisotropic Ising triangular-lattice antiferromagnet (𝑔𝑧⁡/𝑔𝑥⁢𝑦∼3) with very weak exchange interaction (J∼0.22 K). For YbTa7⁢O19, millimeter-sized single crystals could be grown. The anisotropic magnetization and electron spin resonance data show that YbTa7⁢O19 has a contrasting in-plane magnetic anisotropy with 𝑔𝑧⁡/𝑔𝑥⁢𝑦∼0.67 similar as that of YbMgGaO4. The above results indicate that CeTa7⁢O19 and YbTa7⁢O19 with pseudospin-1/2 ground states might either be quantum spin-liquid candidate materials or find applications in adiabatic demagnetization refrigeration due to the weak exchange interaction.