Second-order nature of the spin-reorientation phase transition in SmCrO3

The spin-reorientation phase transition in SmCr${\mathrm{O}}_3$ at $T\simeq 33°$K is studied using acoustic-velocity and specific-heat measurements. Although the reorientation occurs within a narrow temperature region (∼ 1°K) the acoustic data show clearly that the process is a continuous one, involving two second-order phase transitions. All the observed effects, including those induced by externally applied magnetic fields are satisfactorily accounted for using a phenomenological model with magnetoelastic coupling terms. The thermal anomaly associated with the spin reorientation is also observed and used to calculate the uniaxial energy of the chrome spin system.