Negative thermal expansion and itinerant ferromagnetism in Mn${}_{1.4}$Fe${}_{3.6}$Si${}_3$

Abstract

We report the thermal expansion, critical behavior, magnetocaloric effect (MCE), and magnetoresistance ($MR$) on the polycrystalline Mn${}_{1.4}$Fe${}_{3.6}$Si${}_3$ compound around the ferromagnetic transition. A large negative volume thermal expansion (${\alpha }_{\mathrm{V}}\sim -20\times 10^{-6}$ K${}^{-1}$) is observed across the transition temperature with a strong anisotropic variation of lattice parameters in the $ab$-plane. The anisotropic magnetoelasticity arises from the competition between magnetic ordering and structural deformation which could be responsible for the large MCE ($\Delta S_{\mathrm{m}}\simeq -6$ J/Kg-K) across the magnetic transition in this compound. The large and negative $MR$ ($\sim -3\%$ in 80 kOe) is also observed at the transition temperature which can be attributed to the suppression of spin disorder. Further, the Rhodes-Wolfarth ratio (RWR $>1$) and identical field dependence of $MR$ and MCE isotherms indicate the itinerant character of the $3d$ electrons. The critical exponents determined from the analysis of magnetization and MCE are consistent with the quasi-two-dimensional (2D) Ising model with long range exchange interactions which decays as $J(r)\sim r^{-3.41}$. This unconventional quasi-2D Ising character with long-range interactions can be ascribed to strong $ab$-plane anisotropy and the delocalized $3d$ electrons in the studied compound.

9 pages, 8 figures, 1 table, J. Appl. Phys. (Accepted)

References in corpus (4)

• Fermi-liquid instabilities at magnetic quantum phase transitions
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• Element-resolved thermodynamics of magnetocaloric LaFe${}_{13-x}$Si${}_x$
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Cited by in corpus (1)

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