Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet Ba3NiSb2O9

We report the results of magnetization and specific heat measurements on Ba 3 NiSb 2 O 9 , which is a quasi-two-dimensional spin-1 triangular-lattice antiferromagnet. We observed a nonclassical magnetization plateau at one-third of the saturation magnetization that is driven by spin frustration and quantum fluctuation. Exact diagonalization for a 21-site rhombic cluster was performed to analyze the magnetization process. Experimental and calculated results agree well.