Spin stress contribution to the lattice dynamics of FePt.

Science Advances
A von ReppertM Bargheer

Abstract

Invar-behavior occurring in many magnetic materials has long been of interest to materials science. Here, we show not only invar behavior of a continuous film of FePt but also even negative thermal expansion of FePt nanograins upon equilibrium heating. Yet, both samples exhibit pronounced transient expansion upon laser heating in femtosecond x-ray diffraction experiments. We show that the granular microstructure is essential to support the contractive out-of-plane stresses originating from in-plane expansion via the Poisson effect that add to the uniaxial contractive stress driven by spin disorder. We prove the spin contribution by saturating the magnetic excitations with a first laser pulse and then detecting the purely expansive response to a second pulse. The contractive spin stress is reestablished on the same 100-ps time scale that we observe for the recovery of the ferromagnetic order. Finite-element modeling of the mechanical response of FePt nanosystems confirms the morphology dependence of the dynamics.

References

May 27, 1996·Physical Review Letters·E BeaurepaireJ Bigot
Mar 3, 2012·The Review of Scientific Instruments·D SchickM Bargheer
Mar 9, 2017·Nano Letters·Patrick W GranitzkaHermann A Dürr
May 31, 2017·Journal of Physics. Condensed Matter : an Institute of Physics Journal·A KocM Bargheer
Jan 28, 2018·Nature Communications·A H ReidH A Dürr
Sep 4, 2018·Structural Dynamics·Kevin BühlmannYves Acremann
Jan 4, 2019·Nature·C DornesS L Johnson

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Citations

Feb 4, 2021·Structural Dynamics·S P ZeuschnerM Bargheer

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Methods Mentioned

BETA
x-ray diffraction
electron diffraction
X-ray
scanning electron microscopy

Software Mentioned

tr
UXRD
MOKE
COMSOL

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