Magnetic ordering in bulk MnSi crystals with chemically induced negative pressure

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.