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The defence will be in French.
Abstract: This thesis is about the thermodynamic study of the heavy-fermions materials CeRh1-xIrxIn5, with a primitive tetragonal structure. The pure compound at x = 0, CeRhIn5, shows an incommensurate antiferromagnetic phase AFM I at low temperature below 3.7 K. When a magnetic field is applied along the c axis, a phase transition occurs at high field around B* = 30 T to probably another incommensurate antiferromagnetic order, but with a different propagation vector, which disappears around 52 T [1]. At zero field, neutron diffraction measurements showed that AFM I coexists with a commensurate antiferromagnetic phase AFM C from x = 0.3 to x = 0.6 where the two phases vanish in a quantum critical point (QCP). Around this QCP, a superconducting dome emerges and reaches its maximum critical temperature at Tc (x = 0.5) = 0.8 K [2]. The superconductivity persists until the other pure compound at x = 1, CeIrIn5, which is paramagnetic at zero field. However, two phase transitions are observed under a magnetic field applied along the c axis [3]. The first one at Bc occurs approximately at 26 T and seems, according to unpublished data, to correspond to a rare case of transition from a paramagnetic to a commensurate antiferromagnetic phase AF C2 (different from AFM C) under magnetic field. The second is seen at Bm around 40 T but very few data are available. The rest of the series has hardly been studied under magnetic field. During this thesis, we explored its phase diagram using specific heat measurements under high steady magnetic fields (up to 35 T) and magnetic torque measurements under pulsed fields (up to 50 T) for compounds near the QCP (x = 0.4 ; 0.5 ; 0.6 ; 0.78 & 0.87) for temperatures between 300 mK and 5 K in order to understand the evolution of all these phases with doping. Our specific heat measurements show a new anomaly at low fields, hidden by the superconductivity at zero field, that has never been seen before in similar measurements, and the presence of the transition at Bc (to AF C2 phase) at lower field for x = 0.6 than for higher doped compounds, even if this phase does not appear in the zero field phase diagram of the series. Moreover, the torque measurements seem to show that AF 2, the phase appearing at Bc, could disappear at Bm , suggesting a dome in the H-T phase diagram. These results allow on one hand a better understanding about the behaviours of the magnetic phases up to high fields, and suggest, on the other hand, a slightly different phase diagram at zero field for the series than the one in the literature.
[1] S. Mishra et al., Phys. Rev. B 103, 045110 (2021)
[2] A. Llobet et al., Phys. Rev. Lett. 95, 217002 (2005)
[3] R. Kurihara et al., in Proceedings of the 29th International Conference on Low Temperature Physics (LT29) (Journal of the Physical Society of Japan, Sapporo, Japan (Hybrid), 2023)
