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首页> 外文期刊>Physical review >Intrinsic instability of the helix spin structure in MnGe and order-disorder phase transition
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Intrinsic instability of the helix spin structure in MnGe and order-disorder phase transition

机译：MnGe中螺旋自旋结构的内在不稳定性和有序无序相变

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摘要

The magnetic structure of the cubic helimagnet MnGe was studied by small-angle neutron scattering in a wide temperature range from 10 to 300 K. We show that MnGe undergoes a complex order-disorder phase transition covering more than 100 K above the critical temperature T_N = (130 ± 2) K. Moreover, the helical structure is intrinsically unstable below T_N, since the profile of the reflection at k_h, ～ 2 nm~(-1) associated with the spin helix can be described by the sum of Gaussian and Lorentzian contributions, indicating a stable helix and spin-helix fluctuations, respectively. The Gaussian behavior determines the system at low temperature, whereas the Lorentzian is negligible. With increasing temperature, however, the Lorentzian starts to contribute and dominates at T_N. The spin-helix fluctuations are accompanied by intensive spin excitations observed in small-angle neutron scattering as Q-independent scattering at Q ＜ k_h. The integral intensities of both the spin excitations and spin fluctuations obey exactly the same temperature law proportional to exp(T/T_α) with the activation temperature T_α = (80 ± 1) K. These two contributions coexist above T_N, being well distinguished up to J_(DM) = 150 K, where they are intermixed with and transform into diffuse scattering at T_(SR) = (175 ± 5) K. Above T_(SR) the diffuse scattering is well described by a Gauss law, ascribed to static short-range ferromagnetic inhomogeneities with an inverse correlation length κ ≈ 2 nm~(-1).
机译：通过小角度中子散射在10至300 K的宽温度范围内研究了立方直升机磁铁MnGe的磁性结构。我们证明MnGe经历了复杂的有序无序相变，覆盖了超过临界温度T_N = 100 K以上的情况。 （130±2）K。此外，在T_N以下，螺旋结构本质上是不稳定的，因为与自旋螺旋有关的k_h〜2 nm〜（-1）处的反射曲线可以用高斯和洛伦兹之和来描述。贡献，分别表示稳定的螺旋和自旋螺旋波动。高斯行为决定了系统在低温下的作用，而洛伦兹行为则可以忽略不计。但是，随着温度的升高，洛伦兹曲线开始发挥作用，并在T_N占主导地位。自旋螺旋涨落伴随着小角度中子散射中强烈的自旋激发，这是在Q ＜k_h时Q无关的散射。在活化温度T_α=（80±1）K时，自旋激发和自旋涨落的积分强度都遵循与exp（T /T_α）成正比的完全相同的温度定律。这两个贡献共存于T_N以上，直到达到J_（DM）= 150 K，在此处它们混合并转化为T_（SR）=（175±5）K的漫散射。在T_（SR）之上，高斯定律很好地描述了漫散射，归因于静态相关长度κ≈2 nm〜（-1）呈反比的短程铁磁不均匀性。

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  • 来源
    《Physical review》 |2014年第17期|174420.1-174420.6|共6页
  • 作者

    E. Altynbaev; S.-A. Siegfried; V. Dyadkin; E. Moskvin; D. Menzel; A. Heinemann; C. Dewhurst; L. Fomicheva; A. Tsvyashchenko; S. Grigoriev;

  • 作者单位

    Petersburg Nuclear Physics Institute, Gatchina, 188300 Saint Petersburg, Russia,Faculty of Physics, Saint Petersburg State University, 198504 Saint Petersburg, Russia;

    Helmholtz Zentrum Geesthacht, 21502 Geesthacht, Germany;

    Petersburg Nuclear Physics Institute, Gatchina, 188300 Saint Petersburg, Russia,Swiss-Norwegian Beamlines at the ESRF, Grenoble 38000, France;

    Petersburg Nuclear Physics Institute, Gatchina, 188300 Saint Petersburg, Russia,Faculty of Physics, Saint Petersburg State University, 198504 Saint Petersburg, Russia;

    Technische Universitaet Braunschweig, 38106 Braunschweig, Germany;

    Helmholtz Zentrum Geesthacht, 21502 Geesthacht, Germany;

    Institute Laue-Langevin, F-38042 Grenoble Cedex 9, France;

    Institute for High Pressure Physics, 142190, Troitsk, Moscow Region, Russia;

    Institute for High Pressure Physics, 142190, Troitsk, Moscow Region, Russia;

    Petersburg Nuclear Physics Institute, Gatchina, 188300 Saint Petersburg, Russia,Faculty of Physics, Saint Petersburg State University, 198504 Saint Petersburg, Russia;

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    magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.);

    机译：磁相边界（包括磁跃迁;超磁性等）;

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