Nuclear spin-lattice relaxation of 133Cs in CsFeCl3

The spin state of Fe2+ ion in CsFeCl3 is known as the singlet ground state presenting the magnetic order at only around the level crossing field, Bx, of 7.5 T and at low temperatures below 2.5 K. In order to study the magnetic fluctuations of Fe2+ spin of this material, the nuclear spin-lattice relaxation time, T1, of 133Cs is measured mainly at 4.2 K, i.e., at the paramagnetic phase, under the applied magnetic field up to 15 T. A drastic decrease of T1 around Bx is observed. We propose a new mechanism of T1 inherent in the level crossing based on the direct flip process between the nuclear spin and the exchange broadened electron spin system. (author)