Ultrafast ferromagnetic fluctuations preceding magnetoelastic first-order transitions

Zhao Zhang; Yanna Chen; Dehong Yu; Richard Mole; Chenyang Yu; Zhe Zhang; Houbo Zhou; Xuexi Yan; Xinguo Zhao; Weijun Ren; Chunlin Chen; Shigeki Owada; Kensuke Tono; Michihiro Sugahara; Yue Cao; Osami Sakata; Michael J. Bedzyk; Bing Li; Fengxia Hu; Baogen Shen; Zhidong Zhang

arXiv · 2012.03186

Ultrafast ferromagnetic fluctuations preceding magnetoelastic first-order transitions

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Abstract

First-order magnetic transitions are of both fundamental and technological interest given that a number of emergent phases and functionalities are thereby created. Of particular interest are giant magnetocaloric effects, which are attributed to first-order magnetic transitions and have attracted broad attention for solid-state refrigeration applications. While the conventional wisdom is that atomic lattices play an important role in first-order magnetic transitions, a coherent microscopic description of the lattice and spin degrees of freedom is still lacking. Here, we study the magnetic phase transition dynamics on the intermetallic LaFe13-xSix, which is one of the most classical giant magnetocaloric systems, in both frequency and time domains utilizing neutron scattering and ultrafast X-ray diffraction. We have observed a strong magnetic diffuse scattering in the paramagnetic state preceding the first-order magnetic transition, corresponding to picosecond ferromagnetic fluctuations. Upon photon-excitation, the ferromagnetic state is completely suppressed in 0.9 ps and recovered in 20 ps. The ultrafast dynamics suggest that the magnetic degree of freedom dominates this magnetoelastic transition and ferromagnetic fluctuations might be universally relevant for this kind of compounds.

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Zhao Zhang, Yanna Chen, Dehong Yu, Richard Mole, Chenyang Yu, Zhe Zhang, Houbo Zhou, Xuexi Yan, Xinguo Zhao, Weijun Ren, Chunlin Chen, Shigeki Owada, Kensuke Tono, Michihiro Sugahara, Yue Cao, Osami Sakata, Michael J. Bedzyk, Bing Li, Fengxia Hu, Baogen Shen, Zhidong Zhang. 2020-12-06. Ultrafast ferromagnetic fluctuations preceding magnetoelastic first-order transitions. https://arxiv.org/abs/2012.03186

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