Study of Low-Temperature Excitation and Phase Transition in the Frustrated Systems by Nuclear and Electronic Heat Capacities.

通过核热、电子热容和磁化率的测量，获得了受挫磁系统的基态和相变信息，对于自旋S=3/2的VX_2(X：Br，Cl)，估算出反映低温磁相的自旋缩减率为40%。与时间尺度为10^-13秒的核衍射实验得到的70%的缩减值相比，这个值有很大的不同。结果表明，系统和动力学观测对于理解受挫系统的基态是必要的，对于处于共振价键态的费米液体来说，热容与低温的线性关系是可望的。然而，VX_2的热容不显示T^1项。这一点在S=1/2的受挫系统中是可能的。在LiNiO_2的热容测量中，不仅观察到热容的线性关系，而且还观察到任何相变的痕迹：磁化率测量表明，在T_&lt；N1&gt；=240K和T_&lt；n2&gt；=15K有连续相变的可能性，这是三角形反铁磁的一个特征。在最近的超导研究中，强调了共振价键态在带有电子空穴的CuO_2平面上起重要作用。我们已经开始研究有机自由基晶体中的共振价键态，与具有3d电子的无机化合物相比有一些显着的特点。作为第一个例子，给出了未成对电子系统三苯基verdazyi的磁性行为。

Information of the ground state and phase transition in frustrated magnetic systems has been obtained by the measurements of nuclear and electronic heat capacity, and magnetic susceptibility.The spin reduction which reflects the magnetic phase at low temperatures is estimated to be 40% for spin s=3/2 of VX_2(X:Br,Cl). This value makes a significant difference when compared with the reduction of 70% obtained from the nuclear diffraction experiment with the time scale of the order 10^<-13> sec.. It is revealed that systematic and dynamical observations are necessary for understanding the ground state of frustrated systems.The linear dependence of the heat capacity on low-temperatures is expected for the Fermi liquid in the resonating valence bond state. The heat capacity of VX_2, however, does not show the T^1 term. The crucial check of this is possible with the frustrated system with s=1/2. Not only the linear dependence of the heat capacity, but also any trace of the phase change is observed in the heat capacity measurements for LiNiO_2: the magnetic susceptibility measurements indicate the possibility of the successive phase transitions at T_<N1>=240K and T_<N2>=15K, which is a feature of the triangular antiferromagnet.In the recent study of the superconductivity, the resonating valence bond state is stressed to play an important role in the CuO_2 plane with the electronic holes. We have begun investigating the resonating valence bond state also in the crystal of organic free radical which has some remarkable points when compared with inorganic compounds with the 3d electron. The magnetic behavior of the unpaired electron system ,triphenylverdazyi, is given as the first example.