Suppression of simple antiferromagnetism inUNi2Si2under high pressure

Abstract

${\mathrm{UNi}}_{2}{\mathrm{Si}}_{2}$ appears successively in three magnetically ordered phases with decreasing temperature below ${T}_{\mathrm{N}}=124 \mathrm{K}.$ The intermediate phase, which exists in a temperature range of $43<T<103 \mathrm{K}$ 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 ${T}_{\mathrm{N}},$ ${T}_{1}=43 \mathrm{K}$ and ${T}_{2}=103 \mathrm{K}.$ We have measured the electrical resistance for current parallel to the c axis $(i\ensuremath{\Vert}c)$ in a ${\mathrm{UNi}}_{2}{\mathrm{Si}}_{2}$ single crystal under high pressures up to 4.0 GPa. With increasing pressure, ${T}_{1}$ increases and ${T}_{2}$ decreases at rates of 8.6 K/GPa and $\ensuremath{-}1.3 \mathrm{K}/\mathrm{G}\mathrm{P}\mathrm{a},$ respectively, which yields gradual shrinking of the temperature range of stability of the AF1 phase. The critical pressure for suppression of simple antiferromagnetism in ${\mathrm{UNi}}_{2}{\mathrm{Si}}_{2}$ has been determined as 3.2 GPa. On the other hand, ${T}_{\mathrm{N}}$ seems to be almost pressure independent. From these results, a more complete pressure-temperature magnetic phase diagram is constructed.