Control of Chirality of Transition-Metal Monosilicides by the Czochralski Method

The crystallographic and magnetic chirality of the B20 (space group P2${}_{1}$3) solid solutions Fe${}_{1\ensuremath{-}x}$Co${}_{x}$Si and pure MnSi grown by the Czochralski method has been studied by means of the single crystal x-ray diffraction and the small-angle diffraction of polarized neutrons. To test the possibilities to control the crystal handedness, first, we have grown a series of MnSi crystals and one series of Fe${}_{1\ensuremath{-}x}$Co${}_{x}$Si samples with $x=0,0.10,0.15,0.20,0.25,0.30,0.50$ using a right-handed crystal as a seed. Second, we have grown another series of MnSi and Fe${}_{1\ensuremath{-}x}$Co${}_{x}$Si samples again of different concentrations using a left-handed crystal as a seed. In $90%$ of the cases the grown sample has been found to be enantiopure and to inherit the crystallographic chirality of its seed crystal. In $10%$ of the cases undefined circumstances flip the chirality over for the next progeny or produce a racemic sample. The magnetic chirality of these compounds has been shown to be rigorously related to their crystallographic handedness, but in the opposite way for MnSi and for Fe${}_{1\ensuremath{-}x}$Co${}_{x}$Si.