Coexistence of normal and inverse magnetocaloric effect in inhomogeneous Ni₉₅Cr₅ layers

Abstract

Understanding of the coexistence of normal and inverse magnetocaloric effects (MCE) makes it promising for use in magnetic cooling applications. This study discusses the selection of Ni95Cr5 layers and their expected magnetocaloric effects for an extended temperature range (200 - 800 K). These layers offer a wide range of suitable magnetic ordering temperatures as a function of thicknesses. A modified phenomenological model was used to estimate the entropy changes (∆SM) at non-cryogenic and cryogenic ordering temperatures. The ΔS values increase somewhat with increasing thickness due to enhanced magnetization values. Under adiabatic magnetic field variation, normal and inverse MCE are computed near the ferromagnetic-paramagnetic and spin glass transition temperatures, respectively. Based on their ∆Smax values (= -0.06 to 0.11 J/kg-K) and relative cooling power (RCP = 7.6 to 15.5 J/kg) at the smallest magnetic field of 0.5 kOe, which are comparable to other MCE layer materials. The current study demonstrates that adjusting thickness, in addition to Cr doping, can externally regulate soft magnetic and magnetocaloric properties to create diverse magnetic ground states for future MCE and inverse MCE functionalities.

Analytical modeling of magnetocaloric effect in dense nanoparticle systems

“…NiCr alloys demonstrate a unique compositional dependence on T C , achieving values around room temperature with slight Cr doping, which render them suitable for MCE applications. [ 14 ] Recently, the coexistence of normal and inverse MCE in Ni 100‐x Cr x nanocrystalline thin films [ 15 ] with adjusting thickness and normal MCE in (Fe 70 Ni 30 ) 100−x Cr x nanoparticles [ 13 ] was reported. Inspired by these studies, we selected the interacting Ni 100‐x Cr x (0 ≤ x ≤ 15) DNS to investigate MCE properties using two different types of analytical models: the hyperbolic tangent and Gaussian‐distribution models.…”