Magnetic Phase Diagram of MnSi near Critical Temperature Studied by Neutron Small Angle Scattering

The magnetic phase diagram of MnSi near the critical temperature T N =29.5 K has been studied by neutron small angle scattering at KENS. It has been found that the anomalous new phase predicted by various methods to exist around at 28 K and 2 kOe is the paramagnetic phase where the magnetic correlations exhibit the same characteristics as those found at 29.5 K and zero magnetic field. This phenomenon, together with the sharp decrease of the magnetic phase boundary at T N and the substantial increase of the satellite Q vector at this temperature, has been found not to be interpreted by the current theories.