Evidence for spiral magnetic order in the heavy fermion material CeRhIn5

The interplay between magnetism and superconductivity in heavy fermion materials has attracted much interest since the discovery of heavy fermion superconductivity. In several of the Ce based heavy fermion compounds, the behavior of the magnetic order can be understood qualitatively in terms of a simple picture, in which long-range RudermanKittel-Kasuya-Yosida ~RKKY! interactions between the Ce moments compete with short-range Kondo interactions. In this picture, both the RKKY and the Kondo interactions depend on a coupling constant J that can be tuned with pressure or chemical substitution. Since each of these interactions evolves differently with J, the nature of the ground state can change drastically with pressure or chemical substitution. Recent experimental work indicates that when the manybody Kondo effect dominates ~large J), the system undergoes a zero-temperature magnetic-nonmagnetic transition. In CeIn3 and CePd2Si2, both of which have antiferromagnetic ground states at ambient pressure, TN decreases monotonically with pressure and superconductivity develops close to the magnetic instability where TN vanishes. 3 Transport measurements indicate that these systems exhibit unusual nonFermi-liquid behavior near this point, supporting the idea that the physics of these materials is dominated by proximity to a quantum critical point, and it has been suggested that the superconductivity in these materials is mediated by spin fluctuations near this boundary. Recently a very interesting class of heavy fermion materials with the formula CemM nIn3m12n , where M is Rh or Ir, was studied. CeRhIn5 is an antiferromagnet at ambient pressure with TN53.8 K, and becomes a superconductor with Tc52.1 K above a critical pressure Pc;16 kbar. CeRhIn5 differs somewhat from other Ce based heavy fermion materials in that the magnetic-nonmagnetic transition where superconductivity develops is apparently a first-order transition. It has been suggested that CeRhIn5 exhibits twodimensional ~2D! magnetic character, thus the magnetic behavior and the origin of the superconductivity may be related to that of the cuprates. A detailed understanding of the magnetism is crucial in order to understand how the antiferromagnetism evolves into superconductivity. Here we report In nuclear quadrupolar resonance ~NQR! (I59/2) measurements at ambient pressure in a powder sample of CeRhIn5 in the paramagnetic and antiferromagnetic states. NQR is an ideal probe of the local magnetic fields in the unit cell as well as the dynamic behavior of the