Field-induced antiferromagnetism and upper critical field in pressure-induced superconductor CeRhIn₅

An antiferromagnet CeRhIn₅ is well known to be changed into a superconductor by applying pressure P. Its electronic state is also clarified to be changed at the critical pressure P_c ≃ 2:5 GPa under magnetic fields. We measured the low-temperature electrical resistivity of CeRhIn ₅ in magnetic fields up to 17 T and at pressures up to 2.45 GPa, and constructed phase diagrams. At P = 2:45 GPa, which is close to P_c ≃ 2:5 GPa, there are four kinds of phases, namely, the paramagnetic, superconducting, super-conducting and antiferromagnetic, and antiferromagnetic phases in the temperature vs magnetic field phase diagram. The antiferromagnetic phase is found to be induced in the superconducting phase under magnetic fields and expanded in magnetic fields higher than the upper critical field in superconductivity. Interestingly, the anisotropy of the upper critical field in CeRhIn₅ is found to be different from that in a similar non-magnetic heavy-fermion superconductor CeCoIn₅, revealing the anisotropic paramagnetic suppression of the upper critical field.