Chiral Properties of Structure and Magnetism in Mn 1-x Fe x Ge Compounds: When the Left and the Right are Fighting, Who Wins? S. V. Grigoriev, 1,2 N. M. Potapova, 1 S.-A. Siegfried, 3 V. A. Dyadkin, 4,1 E. V. Moskvin, 1,2 V. Dmitriev, 4 D. Menzel, 5 C. D. Dewhurst, 6 D. Chernyshov, 4 R. A. Sadykov, 7,8 L. N. Fomicheva, 7 and A.V. Tsvyashchenko 7 1 Petersburg Nuclear Physics Institute, 188300 Gatchina, Saint-Petersburg, Russia 2 Saint-Petersburg State University, Ulyanovskaya 1, 198504 Saint-Petersburg, Russia 3 Helmholtz Zentrum Geesthacht, Geesthacht 21502, Germany 4 Swiss-Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000 Grenoble, France 5 Institut fu ¨r Physik der Kondensierten Materie, TU Braunschweig, Braunschweig 38106, Germany 6 Institute Laue-Langevin, 38042 Grenoble Cedex 9, France 7 Institute for High Pressure Physics, Russian Academy of Sciences, 142190 Troitsk, Moscow, Russia 8 Institute for Nuclear Research, Russian Academy of Sciences, 117312 Moscow, Russia (Received 3 March 2013; published 13 May 2013) Magnetic susceptibility measurements have shown that the compounds Mn 1-x Fe x Ge are magnetically ordered through the whole range of concentrations x ¼½0:0; 1:0. Small-angle neutron scattering reveals the helical nature of the spin structure with a wave vector, which changes from its maximum (jkj¼ 2:3 nm 1 ) for pure MnGe, through its minimum (jkj! 0) at x c  0:75, to the value of jkj¼ 0:09 nm 1 for pure FeGe. The macroscopic magnetic measurements confirm the ferromagnetic nature of the compound with x ¼ x c . The observed transformation of the helix structure to the ferromagnet at x ¼ x c is explained by different signs of chirality for the compounds with x>x c and x<x c . We used x-ray diffraction and polarized neutron scattering to evaluate the crystallographic chirality  c and the magnetic chirality  m of the FeGe single crystals. Similar to previous observations for FeSi-based compounds, FeGe demonstrates left- (right-)handed crystalline chirality acompained by right (left) handedness of the magnetic helix ( c  m ¼1). At variance, MnSi related compounds show the opposite behavior ( c  m ¼ 1). Since the magnetic chirality  m relates to the sign of the Dzyaloshinskii-Moriya interaction (DMI), for the same geometrical arrangement ( c ) the sign of DMI can be set by the proper choice of the transition metal. DOI: 10.1103/PhysRevLett.110.207201 PACS numbers: 75.30.Cr, 61.05.F, 75.40.s, 75.50.Bb The crystalline and magnetic structures of MnSi and doped monosilicides of Mn and Fe (Mn 1-x Fe x Si, Mn 1-x Co x Si, and Fe 1-x Co x Si) are very well established nowadays. All these compounds have the same B20 type cubic noncentrosymmetric crystallographic structure described by the chiral P2 1 3 space group. The chiral Dzyaloshinskii-Moriya (DM) interaction stabilizes the spi- ral spin structure in these systems below T c [1,2]. Systematic studies [3–7] have shown that the sense of the structural chirality (left or right) rigorously determines the sense of the magnetic chirality via the sign of the DM interaction. However, the relation between two chiralities is found to be different for various B20 compounds. For Mn- based compounds (Mn 1-x Fe x Si and Mn 1-x Co x Si) the crys- talline and magnetic chiralities have the same sense, while for the Fe-based ones (Fe 1-x Co x Si) the chiralities are oppo- site to each other [3–7]. One can conclude that the two types of compounds, Mn and Fe based, posses different signs of the DM interaction for the crystals of the same chirality. An intriguing experiment for proof of this hypothesis would be the change of the chirality sense in the Mn 1-x Fe x Si family by changing the Mn to Fe ratio. Unfortunately, the pure FeSi is not magnetically ordered, so the Mn 1-x Fe x Si family shows the spin ordering only in a narrow range of x 2 ½0; 0:17, and further Fe doping leads to magnetic disorder. A good candidate to follow the change of the magnetic chirality is the Mn 1-x Fe x Ge family with B20 structure. The pure compounds (FeGe [8] and MnGe [9–11]) and, as we show in this Letter, all Mn 1-x Fe x Ge monogermanides are magnetically ordered. Here, we report on the experimental evidence for magnetic transition in the Mn 1-x Fe x Ge com- pounds, where the helix chirality can be altered by mixing the two types of magnetic atoms (Fe and Mn). We used x-ray diffraction [12,13] and polarized neutron scattering [14,15] to evaluate the crystallographic chirality  c and the magnetic chirality  m of the FeGe single crystal. A single crystal with the size of 1  1  1 mm 3 was measured with neutrons and, afterwards, it was polished to 50 m and investigated using x-ray diffraction. The experiment was done using synchrotron radiation with ( ¼ 0:7  A) at the Swiss-Norwegian Beam Line BM1A of the ESRF (Grenoble, France) with the PILATUS@SNBL diffractometer. The protocol similar to that used in Refs. [5–7] has been applied for the data analysis. The FeGe sample was identified as having P2 1 3 symmetry with the structural parameters u Fe ¼ 0:1358ð3Þ PRL 110, 207201 (2013) PHYSICAL REVIEW LETTERS week ending 17 MAY 2013 0031-9007= 13=110(20)=207201(5) 207201-1 Ó 2013 American Physical Society