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 $|\mathbf{k}|=0.385$ nm${}^{\ensuremath{-}1}$ at low temperatures. The ordering temperature is enhanced up to ${T}_{C}=39$ K. The critical field ${H}_{C2}$ 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 ${T}_{A}=27.5$ K, characteristic for pure MnSi, to ${T}_{C}=39$ 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.