Suppression of simple antiferromagnetism in under high pressure

(Formula presented) appears successively in three magnetically ordered phases with decreasing temperature below (Formula presented) The intermediate phase, which exists in a temperature range of (Formula presented) at ambient pressure is the simple antiferromagnetic (AF1) phase. The temperature dependence of the electrical resistivity in this compound shows distinct anomalies at related magnetic-phase transitions at (Formula presented) and (Formula presented) We have measured the electrical resistance for current parallel to the c axis (Formula presented) in a (Formula presented) single crystal under high pressures up to 4.0 GPa. With increasing pressure, (Formula presented) increases and (Formula presented) decreases at rates of 8.6 K/GPa and (Formula presented) respectively, which yields gradual shrinking of the temperature range of stability of the AF1 phase. The critical pressure for suppression of simple antiferromagnetism in (Formula presented) has been determined as 3.2 GPa. On the other hand, (Formula presented) seems to be almost pressure independent. From these results, a more complete pressure-temperature magnetic phase diagram is constructed.