We identify the phase boundary between spiral spin and ferromagnetic phasesin Au$_2$Mn at a critical pressure of 16.4 kbar, as determined by neutrondiffraction, magnetization and magnetoresistance measurements. Thetemperature-dependent critical field at a given pressure is accompanied by apeak in magnetoresistance and a step in magnetization. The critical fielddecreases with increasing temperature and pressure. The critical pressureseparating the spiral phase and ferromagnetism coincides with the disappearanceof the magnetroresistance peak, where the critical field goes to zero. Thenotable absence of an anomalous Hall effect in the the ferromagnetic phase isattributable to the high conductivity of this material.
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