MAGNETIC-PROPERTIES OF THE S = 1/2 ANTIFERROMAGNETIC TRIANGULAR LATTICE LINIO2

We measured susceptibility, resistivity and specific heat of the S = 1/2 antiferromagnetic triangular lattice LiNiO2. In addition to the formerly recognized characteristic temperatures T(N1)(approximately 210 K) and T(N2)(approximately 20 K), we found another characteristic temperature T(N3)(approximately 70 K) from the susceptibility measurement, at which three-dimensional short-range order presumably sets in at the expense of the planar frustration. In the range between T(N1) and T(N3), an exponentially increasing susceptibility with decreasing temperature was disclosed, which is believed to be one of the characteristic features of the planar frustration in this system. The specific heat results revealed that the magnetic entropy gradually decreases from R 1n 2 without any pronounced anomalies corresponding to a long-range magnetic order down to 0.4 K. The nature of the ordering process LiNiO2 is discussed by referring these characteristic temperatures.