Magnetic ordering in bulk MnSi crystals with chemically induced negative pressure

Abstract

MnSi crystals with chemically induced negative pressure (doped by less than 1% Ge) have been synthesized by the Czochralski method. X-ray powder diffraction has revealed that the samples are crystallized in the B20 structure, inherent to pure MnSi, without any impurity phases. The lattice constant a is slightly larger than that of undoped MnSi. The samples have a spiral spin structure with the wave vector |k|=0.385 nm−1 at low temperatures. The ordering temperature is enhanced up to TC=39 K. The critical field HC2 shows an increase of about 25% for the doped samples. Close to the critical temperature the A phase occurs. The temperature range of the A phase in the (H–T) phase diagram for the doped compound ranges from TA=27.5 K, characteristic for pure MnSi, to TC=39 K in the zero-field cooled (ZFC) regime of magnetization. The magnetic features of the (H–T) phase diagram of the compounds MnSi are reminiscent of those observed for the MnSi thin films on the Si substrate.