Small magnetic moment and superconductivity in URu2Si2 Original Research Article

One of the most puzzling properties observed in URu2Si2 has been the large jump of specific heat around 17 K for small magnetic moments. This specific heat jump is attributed to the quadrupolar order rise around 17 K instead of the dipolar order. Neutron experiments showed about 0.03μB at low temperatures whereas no evidences were found in NMR experiments for static magnetic order. These experiments suggest that Bragg peaks observed in the neutron experiments are not really due to static magnetic order but due to quasi-static ones. However, new NMR experiments clearly show the internal field below 17 K, corresponding to the appearance of magnetic moments of 0.2μB. The intensity of the signal is small, suggesting that a small portion of the sample is magnetic while the other portions are non-magnetic. We present a scenario, consistent with these experiments, based on the assumption that the sample is a mixture of dipolar and quadrupolar phases, and also taking account of quasi-static magnetic fluctuations. We also discuss the pressure effects in the sample.