Ultrafast negative thermal expansion driven by spin disorder

Article

关键词: PHASE-TRANSITIONS;    MAGNETIC-MOMENTS;    DYNAMICS;    MAGNETOSTRICTION;    DEMAGNETIZATION;    GENERATION;    HOLMIUM;    PHONONS;    HEAT;   

DOI  :  10.1103/PhysRevB.99.094304

来源: SCIE

【 摘 要 】

We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium, and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion, which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho [Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign traveling through the heterostructure.

【 授权许可】

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