Abstract
A study of magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys is reported. Amorphous Fe40Ni38Mo4B18, near its magnetic ordering temperature (600K) showed a magnetic entropy change ΔSM of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K) in a field change of 10 kOe. The decrease in ΔSM on partial crystallisation is attributed to the biphasic magnetic nature of the sample.
Highlights
The quest for new materials that would help us improve our life quality has always been an active area of research
The temperature change associated with a material which undergoes an adiabatic change in magnetic field is known as magnetocaloric effect (MCE) and materials exhibiting this property are called magnetocaloric materials
magnetocaloric materials (MCM) with first order phase transition (FOPT) (Gd5Si1.7Ge2.3, MnFeP0.45As0.55 etc.) shows hysteresis losses which will limit the performance of a refrigerator employing this material.[1]
Summary
The quest for new materials that would help us improve our life quality has always been an active area of research. The soft magnetic alloys are good candidates for MCE based cooling applications as they have large enough magnetisation and are relatively free of hysteresis.[3,4,5,6] Besides there are many reasons people opt for amorphous magnetic materials in their search for better MCM They show broad ∆SM peak around TC, which is a second order phase transition. Alloying provides an easy way of tuning TC They have good mechanical properties and high corrosion resistance and produce large RCP.[2] Recent studies on rare-earth free nanoparticles for magnetocaloric applications have shown that it is tangible to achieve near room temperature magnetic transitions by suitable combination of materials as well as the accompanied RCP of these systems are found to be greater than the benchmark material Gd.[7,8,9]. It even transcends alloys containing rare earth elements as well as several other Fe based amorphous alloys.[17,18,19,20,21,22]
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