Quantum Magnetization Plateau in Spin-1 Triangular-Lattice   Antiferromagnet Ba$_3$NiSb$_2$O$_9$
  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. 
Yutaka Shirata, Hidekazu Tanaka, Toshio Ono, Akira Matsuo, Koichi   Kindo and Hiroki Nakano
cond-mat.str-el