Premartensitic phenomena in the ferro-and paramagnetic phases of Ni_ {2} MnGa
Premartensitic phenomena in the ferro-and paramagnetic phases of Ni_ {2} MnGa
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DOI：
10.1103/physrevb.56.14360
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发表时间：
1997-12
影响因子：
3.7
通讯作者：
U. Stuhr;P. Vorderwisch;V. Kokorin;P. Lindgård
中科院分区：
文献类型：
--
作者：
U. Stuhr;P. Vorderwisch;V. Kokorin;P. Lindgård
在Heusler合金的铁磁相和顺磁相中研究了低能声子${\mathrm{Ni}}_{2}\mathrm{MnGa}.$，样品呈现马氏体相变，相变温度${T}_{M}\ensuremath{\approx}284\mathrm{K},$仅比居里温度低约80k。因此，可以研究铁磁和顺磁状态下的预马氏体现象。当温度接近${T}_{M}.$时，（\ensuremath{\xi}\ensuremath{\xi} 0） ${\mathrm{TA}}_{2}$ -声子分支在$\ensuremath{\xi}\ensuremath{\approx}1/3$处表现出强烈但不完全的软化，这种软化的温度依赖性在居里温度下发生变化，这可以用磁化对朗道自由能的额外贡献来解释。在最强声子软化的波矢量处出现一个中心峰。第二个具有相同温度行为的弹性峰出现在$\ensuremath{\xi}\ensuremath{\approx}0.17.$，讨论了这些弹性前驱体与低温结构的关系。
Low-energy phonons were studied in the ferromagnetic and paramagnetic phases of the Heusler alloy ${\mathrm{Ni}}_{2}\mathrm{MnGa}.$ The investigated sample shows a martensitic phase transformation with a transition temperature ${T}_{M}\ensuremath{\approx}284\mathrm{K},$ only about 80 K below the Curie temperature. Therefore, premartensitic phenomena could be studied in the ferromagnetic as well as in the paramagnetic state. The (\ensuremath{\xi} \ensuremath{\xi} 0) ${\mathrm{TA}}_{2}$-phonon branch shows a strong but incomplete softening at $\ensuremath{\xi}\ensuremath{\approx}1/3$ in the premartensitic phase when the temperature approaches ${T}_{M}.$ The temperature dependence of this softening changes at the Curie temperature which can be explained by an additional contribution of the magnetization to the Landau free energy. At the wave vector of the strongest phonon softening a central peak occurs. A second elastic peak, with the same temperature behavior, appears at $\ensuremath{\xi}\ensuremath{\approx}0.17.$ The relation of these elastic precursors to the low-temperature structure is discussed.