Effects of external pressure on the 5f-band metamagnetism in UCoAl

UCoAl exhibits below 16 K anisotropic 5f-band metamagnetism induced by magnetic fields as low as ∼1 T applied along the c axis of the hexagonal structure. No metamagnetic transition is observed in fields up to 40 T applied within the basal plane. The critical field of the metamagnetic transition ${\mathrm{B}}_{\mathrm{c}}$ is composition dependent within the homogeneity range. The metamagnetic transition is found to be very sensitive to external pressure. The value of ${\mathrm{B}}_{\mathrm{c}}$ increases with the rate ${\mathrm{dB}}_{\mathrm{c}}$ /dp=0.27 T/kbar, whereas the magnetization gained through the transition becomes reduced. The critical pressure of 24 kbar (corresponding to ∼2% volume contraction) for disappearance of metamagnetism in UCoAl has been estimated. Relations of UCoAl to 3d-band metamagnets are discussed.