Spin ordering in a triangular X-Y antiferromagnet : CsFeCl3 and RbFeCl3

Magnetic-field- and pressure-induced quantum phase transition inCsFeCl3proved via magnetization measurements

“…Unlike the case of the spin dimer system, the gapped ground state originates from competition between the large easy-plane single ion anisotropy D(s z ) 2 and the exchange interactions. Field-induced AF ordering with H c has been confirmed in several experiments in fields between ∼ 4 T and ∼ 11 T at LTs below 2.6 K [35][36][37][38][39]. Neutron scattering experiments have revealed that the ground-state spin configuration is probably a 120…”

“…At P c ∼ 0.9 GPa, the zero-field ground state changes from a gapped state to a magnetically ordered state. Note that the H − T phase diagram of CsFeCl 3 in the pressure-induced ordered phase at P ≥ P c resembles that of the isomorphic compound RbFeCl 3 at ambient pressure [35]. RbFeCl 3 exhibits magnetic ordering in zero field owing to the relatively large exchange interactions as compared with the D term.…”

Quantum phase transition: Van Vleck antiferromagnet in a magnetic field

“…Actually this anisotropy does not change the position of critical field h s , but it also does not "desire" the establishment of collinear state, when s 1 → s 2 OZ. At the same time the account of exchange anisotropy of easy-plane type being taken into account, it permits to obtain such a behavior of magnetization that is close to linear and is observed in the studies [22,23,29,30]. For clarifying how well the linear dependence corresponds to m(h ), the magnetic susceptibility χ = dm /dh is shown in figure 2 for the same parameters as in figure 1.…”

“…As a result, the observed magnetization actually follows the linear field behavior [22,23,29,30]. In other words, this behavior of magnetization of the system (but not the proper sublattice magnetization) in the AFM phase turns out to be similar to the magnetization induced by the external field in Neel AFMs.…”

“…Then, at the transition point, the sublattices could magnetize, due to jump (in the presence of corresponding susceptibility singularity), and with further field growth the sublattice magnetic vectors would turn only. However, the experiment shows that transformation of the non-magnetic (singlet) state into the AFM state takes place continuously, i.e., this magnetic transformation is a phase transition of the IInd order [22,23,29,30]. The latter demonstrates that sublattice magnetizations appear and change from their initial zero value to maximal value also continuously.…”