NATURE OF THE PRESSURE-INDUCED MAGNETIC PHASE-TRANSITION IN THE ITINERANT-ELECTRON ANTIFERROMAGNET YMN2 - A MICROSCOPIC VIEW

The Sn-119 high-pressure Mossbauer-effect technique on 0.5 at. % Sn-11 9-doped YMn2 has been used to investigate, on a microscopic level, the nature of the pressure-induced magnetic-to-nonmagnetic phase transiti on in the itinerant-electron antiferromagnet YMn2. We find, in contras t to the temperature-induced first-order magnetic phase transition at T(N) and at ambient pressure, a strong but continuous reduction of the ordered Mn local magnetic moment in the range 0 less-than-or-equal-to p < 0.3 GPa, which reveals a pressure-induced second-order phase tran sition. In the same pressure range, we observe a change of the nature of the spin fluctuations from transversal (0 less-than-or-equal-to p < 0.3 GPa) to longitudinal at higher pressures. We further show evidenc e for short-range magnetic order in the pressure-induced nonmagnetic s tate (0.3 less-than-or-equal-to p less-than-or-equal-to 4 GPa).