Evolution Of The Magnetic Field-Temperature Phase Diagram In Uas1-Xsex

The evolution of the magnetic field-temperature phase diagram of UAs1-xSex with x in the range of 0-0.1 is studied by means of magnetocaloric and specific-heat measurements. Our interest is focused on the high-temperature phase transitions and especially on the point, where the paramagnetic (P) and two ordered phases meet. For undoped UAs these two ordered states are the ferrimagnetic (Fi) and the type-I antiferromagnetic phases. According to Sinha et al. [Phys. Rev. Lett. 45, 1028 (1980)] the antiferromagnetic phase transition is in the vicinity of a Lifshitz point. Furthermore, Kuznietz et al. [J. Magn. Magn. Mater. 61, 246 (1986)] showed that an incommensurate phase (IC) emerges between the type-I (or type-IA) antiferromagnetic and paramagnetic phases in the case of UAs1-xSex with 0 < x < 0.15 in zero magnetic field. The results reported in this paper show the existence of a T-Fi/IC(B) line that separates the ferrimagnetic region from a phase, which cannot be identified on the basis of our thermodynamic measurements. However, one may assume it is the IC phase, consistent with the above mentioned zero field results. The T-Fi/IC(B) line merges with the order-disorder line at point (B-p, T-p), where the critical line (IC/P) meets with two first order transitions lines: Fi/P and Fi/IC. This point can be considered as an analog of a Lifshitz point. A simple phenomenological description of the phase transitions near this special point is provided.