Abstract
A field and/or temperature hysteresis is more than just an interesting incomprehensibility that occurs in materials with a first-order magnetic transition. Indeed, the reversibility of the magnetocaloric effect (MCE), being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, the polymer matrix composites with MnAs powder as reinforcing material were obtained and its MCE by direct method was studied. The influence of composite preparation process on the MCE was investigated. It was found that the MCE of bulk MnAs shows strong temperature hysteresis caused by magnetostructural transition from paramagnetic to ferromagnetic state, which also leads to an irreversible MCE at cooling at first magnetization. The reversible MCE of bulk MnAs in field 12.5 kOe is ΔT ∼ 0.4 K. It was shown that Mn-based polymeric composite cured in aligned magnetic field presents a reinforcement of the MCE temperature hysteresis. Thus, the MCE value in aligned composite is less than the value of the MCE in the bulk MnAs. It was shown that the decreasing of linear size of MnAs grains in the polymeric composite leads to sharp decreasing of the MCE to value of 0.05 K. It was established that the optimal properties, such as giant MCE and low temperature hysteresis, are found for composite hardened under pressure of 10 kBar. In this composite an increase of reversible MCE (compared to the bulk MnAs) till to the value of ΔT ∼ 1.2K was observed.
Highlights
The composite material which is made of metallic and polymeric material by certain processes, can retain the advantages of the original components, overcome some shortcomings and show some new properties
The reversibility of the magnetocaloric effect (MCE), being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, it is necessary to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices
It was found that the MCE of bulk MnAs shows strong temperature hysteresis caused by magnetostructural transition from paramagnetic to ferromagnetic state, which leads to an irreversible MCE at cooling at first magnetization
Summary
The composite material which is made of metallic and polymeric material by certain processes, can retain the advantages of the original components, overcome some shortcomings and show some new properties. A composite material is a multi-phase system consisted of matrix material and reinforcing material. Electromagnetic functional materials develop most rapidly and are used most commonly as the functional composite materials. These composite materials can be processed into magnetic products with the required shape and the certain mechanical properties by the general forming methods (such as compression molding, laminating, etc.) of polymeric materials. In order to obtain a good overall performance, we must increase the amount of filler or enhanced material as much as possible, control the interface of composite materials and make composite materials have better process ability [2]
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