100 research outputs found

    Theoretical and experimental study of high-pressure synthesized B20-type compounds Mn1x_{1-x}(Co,Rh)x_xGe

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    The search and exploration of new materials not found in nature is one of modern trends in pure and applied chemistry. In the present work, we report on experimental and \textit{ab initio} density-functional study of the high-pressure-synthesized series of compounds Mn1x_{1-x}(Co,Rh)x_xGe. These high-pressure phases remain metastable at normal conditions, therewith they preserve their inherent noncentrosymmetric B20-type structure and chiral magnetism. Of particular interest in these two isovalent systems is the comparative analysis of the effect of 3d3d (Co) and 4d4d (Rh) substitution for Mn, since the 3d3d orbitals are characterized by higher localization and electron interaction than the 4d4d orbitals. The behavior of Mn1x_{1-x}(Co,Rh)x_xGe systems is traced as the concentration changes in the range 0x10 \leq x \leq 1. We applied a sensitive experimental and theoretical technique which allowed to refine the shape of the temperature dependencies of magnetic susceptibility χ(T)\chi(T) and thereby provide a new and detailed magnetic phase diagram of Mn1x_{1-x}Cox_xGe. It is shown that both systems exhibit a helical magnetic ordering that very strongly depends on the composition xx. However, the phase diagram of Mn1x_{1-x}Cox_xGe differs from that of Mn1x_{1-x}Rhx_xGe in that it is characterized by coexistence of two helices in particular regions of concentrations and temperatures.Comment: 12 pages, 11 figure

    Hidden quantum phase transition in Mn1x_{1-x}Fex_{x}Ge: evidence brought by small-angle neutron scattering

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    The magnetic system of the Mn1x_{1-x}Fex_{x}Ge solid solution is ordered in a spiral spin structure in the whole concentration range of x[0÷1]x \in [0 \div 1]. The close inspection of the small-angle neutron scattering data reveals the quantum phase transition from the long-range ordered (LRO) to short range ordered (SRO) helical structure upon increase of Fe-concentration at x[0.25÷0.4]x \in [0.25 \div 0.4]. The SRO of the helical structure is identified as a Lorentzian contribution, while LRO is associated with the Gaussian contribution into the scattering profile function. The scenario of the quantum phase transition with xx as a driving parameter is similar to the thermal phase transition in pure MnGe. The quantum nature of the SRO is proved by the temperature independent correlation length of the helical structure at low and intermediate temperature ranges with remarkable decrease above certain temperature TQT_Q. We suggest the xx-dependent modification of the effective Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism to explain the quantum critical regime in Mn1x_{1-x}Fex_{x}Ge.Comment: 6 pages, 4 figure

    Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation

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    We have studied by muon spin resonance ({\mu}SR) the helical ground state and fluctuating chiral phase recently observed in the MnGe chiral magnet. At low temperature, the muon polarization shows double period oscillations at short time scales. Their analysis, akin to that recently developed for MnSi [A. Amato et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field distribution induced by the Mn helical order at the muon site. The refined muon position agrees nicely with ab initio calculations. With increasing temperature, an inhomogeneous fluctuating chiral phase sets in, characterized by two well separated frequency ranges which coexist in the sample. Rapid and slow fluctuations, respectively associated with short range and long range ordered helices, coexist in a large temperature range below TN_{N} = 170 K. We discuss the results with respect to MnSi, taking the short helical period, metastable quenched state and peculiar band structure of MnGe into account.Comment: 13 pages, 11 figure
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