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Abstract: Heusler alloys feature both regular and inverse magnetocaloric effects (MCE) near room temperature as they undergo two different transitions. A temperature scaling methodology to obtain self-similar field dependent curves for materials exhibiting one first-order transition has been previously presented. In this paper, this methodology is modified and extended to obtain self-similar curves for a Ni51Mn32.8In16.8 Heusler alloy undergoing two transitions near room temperature. Using this method, the collapsed curve reflects the cluster compositions in the mixed-state regions. The results of characterizing the dual transitions of Heusler alloys and establishing a new model will allow the data to be better analyzed and thus more easily predicted. [Copyright &y& Elsevier]

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χirr, decay coefficient,S, fluctuation field,hf, and activation volume,V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient,Smax, and the fluctuation field,hf, as a function of temperatureT.The peak of both temperature curves are identical and occur at a critical temperatureTkof ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier,hfis studied forT

The latent heat linked with the first-order transformation of a NiMnIn Heusler alloy has been studied through direct measurements of the adiabatic temperature change, ΔTad, during magnetization process. The experimental procedure used guarantees independent data points and negates any contribution of hysteretic losses to the magnetocaloric effect. Thus, the differences between the magnitudes of ΔTad measurements during the magnetization with the initial temperature change directions from low-to-high and high-to-low are solely attributed to the latent heat exchange, which accompanies the irreversible structural first-order transformation. An estimate of the latent heat inducing such differences is about 0.292 J/g. [ABSTRACT FROM AUTHOR]

The adiabatic temperature change (ΔT) during the magnetization and demagnetization processes of bulk gadolinium is directly measured for several applied magnetic fields in the temperature range 285 K to 305 K. In low magnetic fields, the measurements of ΔT display two maxima at 293.8 K and 291.5 K with an inflection point between 289 K and 293 K. The height of the second peak is more pronounced at low applied magnetic fields and diminishes in high fields. The occurrence of a second ΔT maximum is indicative of the complex spin dynamics in Gd and is related to the presence of metastable states near the Curie temperature. [ABSTRACT FROM AUTHOR]

The phenomenon of negative remanent magnetization (NRM) has been observed experimentally in a number of heterogeneous magnetic systems and has been considered anomalous. The existence of NRM in homogenous magnetic materials is still in debate, mainly due to the lack of compelling support from experimental data and a convincing theoretical explanation for its thermodynamic validation. Here we resolve the long-existing controversy by presenting experimental evidence and physical justification that NRM is real in a prototype homogeneous ferromagnetic nanoparticle, an europium sulfide nanoparticle. We provide novel insights into major and minor hysteresis behavior that illuminate the true nature of the observed inverted hysteresis and validate its thermodynamic permissibility and, for the first time, present counterintuitive magnetic aftereffect behavior that is consistent with the mechanism of magnetization reversal, possessing unique capability to identify NRM. The origin and conditions of NRM are explained quantitatively via a wasp-waist model, in combination of energy calculations.