THE PHASE-DIAGRAM OF RBFECL3 IN A MAGNETIC-FIELD PERPENDICULAR TO THECHAIN DIRECTION

The temperature dependence of,the position and line width of antiferro magnetic Bragg peaks were measured at different applied magnetic field s up to 1.4 T by means of elastic neutron scattering. Three different types of temperature dependences were observed that can be attributed to the commensurate-incommensurate, commensurate-paramagnetic, and inc ommensurate-paramagnetic phase transitions. Below 0.3 T the transition goes from commensurate to incommensurate. Between 0.3 and 0.5 T a pha se boundary was observed, but there is some doubt as to whether the st ructure at temperatures below this boundary is commensurate. Between 0 .5 and 1.2 T the phase transition goes directly from commensurate to p aramagnetic at around 2.5 K. For fields higher than 1.3 T and temperat ures above 1.5 K no commensurate phase could be identified. But above 1.2 T and still at 1.4 T there exists an incommensurate phase. Based o n these temperature dependences at different magnetic fields, phase bo undaries in the H-T phase space are proposed and compared with the pha se diagram obtained by previous susceptibility measurements.