Single crystal growth and magnetic anisotropy characterization of Ising-like antiferromagnets Na 4 M TeO 6 ( M = Co, Ni)

Abstract Large-sized single crystals of Na 4 M TeO 6 ( M = Co, Ni) were successfully grown using the flux method. The magnetic anisotropy and field-induced magnetic transitions were systematically investigated, and the distortion of the CoO 6 and NiO 6 octahedra was quantitatively analyzed. Both compounds are identified as strongly anisotropic Ising-like antiferromagnets. Na 4 CoTeO 6 exhibits a Néel temperature of 3.2 K with the b -axis as the easy axis, and field-induced spin-flip transitions are observed along all three crystallographic directions. The magnetic anisotropy constant is determined to be K (2 K) = 1.63(5) × 10 5 erg/cm 3 . In Na 4 NiTeO 6 , the Néel temperature is 5.9 K, also with the b -axis as the easy axis, while field-induced spin-flip transitions occur along both the a - and b -axes, yielding an anisotropy constant of K (2 K) = 1.63(4) × 10 4 erg/cm 3 . Structural analysis reveals that the Co 2+ ions in Na 4 CoTeO 6 exhibit larger bond-length and bond-angle distortions within the CoO 6 octahedra than the Ni 2+ ions in Na 4 NiTeO 6 . These results highlight the significant role of octahedral distortion in governing the strong magnetic anisotropy of the Na 4 MTeO 6 family.