NMR Study of the Successive Phase Transitions in C\lowercaseuB₂O₄

Abstract

Nuclear magnetic resonance (NMR) experiments on copper metaborate CuB2O4 are performed in order to study the successive phase transitions which includes the transition from the paramagnetic to the commensurate weak ferromagnetic phase at TN = 21 K and further transition to the incommensurate helix phase at T * ∼ 10 K. 11 B-NMR spectra obtained for three crystal orientations (B [001], [110], [100]) were split into several lines below TN and changed into more complicated line shapes below T * . The results of the angular dependence of the spectrum in the commensurate phase and the nuclear spin-lattice relaxation rate T −1 1 are also discussed.

Magnetic successive phase transitions of probed by -NMR technique

“…As shown in our previous paper [8], the spectrum forms a sharp line above T N and splits into several lines below T N . Further, below T Ã , it becomes broad with continuous intensity between some peaks, which is a characteristic feature for incommensurate phase.…”

Spin Dynamics in Copper Metaborate CuB2O4 Studied by Muon Spin Relaxation

“…We also examined temperature dependence of λ in H LF =0.35 T. Quite small peaks of λ are observed at T N and T * in addition to T L , and T * and T L are lowered by magnetic field. The peak of λ at T * is consitent with the NMR result under ∼0.5 T. 11) In conventional magnets with a long-range order, the local fields are static in the ordered phase. However, in CuB 2 O 4 , the local fields are quasi-static in the weak ferromagnetic phase, whereas the fluctuating component becomes dominant at lower temperatures and persists even at 0.3 K. Such a thermal evolution is rather anomalous.…”

“…NMR measurement, which is a powerful method to study spin dynamics, has been performed for CuB 2 O 4 . 10,11) However, the dynamic behavior in zero field is still unclear because of the quite large relaxation rate and necessity of applying magnetic fields in NMR method. The muon spin relaxation (µSR) method is an-other powerful technique to study both magnetic order and spin dynamics in magnetic fields and zero field.…”

11B-NMR study of low-temperature phase transition in CuB2O4

“…The copper metaborate CuB 2 O 4 is one such magnet. This material has been studied using several experimental methods, such as magnetic susceptibility [1], specific heat [2], electron spin resonance (ESR) [3,4], neutron diffraction [5][6][7], muon spin relaxation (µSR) [6], nonlinear optics [8], nuclear magnetic resonance (NMR) [9] and so on. Under a zero magnetic field, the successive phase transitions occur as follows.…”

“…For the convenience of the discussion below, the B-T phase diagram of CuB 2 O 4 is shown in figure 1. The diagram has been determined under a magnetic field applied along the a-axis through experiments that have already been reported [6,[8][9][10].…”