Magnetic and magnetoelastic properties of UCo2Si2as studied by high-field magnetization and ultrasound measurements

Abstract

We investigated an antiferromagnet UCo${}_{2}$Si${}_{2}$ by use of magnetization and ultrasound measurements in pulsed magnetic fields up to 60 T. It is found that the crystal UCo${}_{2}$Si${}_{2}$, which has the antiferromagnet type-I magnetic structure in zero field below ${T}_{\mathrm{N}}$ $=$ 83 K, undergoes the metamagnetic phase transition to ferrimagnetic structure $++\ensuremath{-}$ type similarly to the UNi${}_{2}$Si${}_{2}$ with substitution of 10$%$--15$%$ Ni by Pd or UPd${}_{2}$Si${}_{2}$. Therefore, similar phase transitions take place in the compounds with expected essentially different strength of the 5$f$-$d$ electron hybridization. In UCo${}_{2}$Si${}_{2}$, the transition occurs when the magnetic field is applied along the $c$ axis at 45 T (at 1.5 K). The transition is extremely sharp and exhibits a small but non-negligible hysteresis. With increasing temperature, it becomes broader and vanishes at ${T}_{\mathrm{N}}$. In our ultrasound measurements, the metamagnetic transition appears as anomalies in the sound velocity and attenuation. Our analysis suggests that the low-temperature changes in the sound velocity and attenuation predominantly are determined by an exchange renormalization caused by the sound waves.