EVIDENCE OF A FIRST ORDER MAGNETIC PHASE TRANSITION IN FeI2 BY NEUTRON SCATTERING.

Neutron scattering by magnetic Bragg reflections in FeI//2 is found to exhibit a sharp discontinuity at T//c equals 8. 95 K. At this temperature the order parameter abruptly falls from 0. 83 to zero revealing an unsuspected first order transition. This result is discussed in the light of renormalization-group predictions for phase transitions in systems with n greater than equivalent to 4. It is also pointed out that this behavior could be an indication of the possible existence of a different magnetic structure above T//c.