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The series of alloys (GdxTb5−x)Si4 (x=0,2.5,3,3.5,4,4.5,5) and (GdxPr5−x)Si4 (x=4,4.25,4.5) have been prepared. Their room temperature crystal structure has been established, and dc magnetization and ac magnetic susceptibility have been measured in the temperature range from 4.2 to 550 K and in dc magnetic fields up to 50 kOe. The magnetocaloric effect has been calculated from the magnetization data and, for one of the alloys, from the heat capacity data. The magnetocaloric effect values from the two different measurements are in excellent agreement. The (GdxTb5−x)Si4 alloys exhibit magnetocaloric effects in low magnetic fields (<20 kOe) comparable to that of Gd metal and, therefore, they represent a new class of promising magnetic refrigerant materials.

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A wide class of magnetic molecular materials - molecular clusters with high magnetic moment containing 3d transition metals (such as `Fe8', `Mn12ac', etc) - have been considered from the point of view of their use as refrigerants in low-temperature regions. The consideration was made in the framework of the model based on the Langevin theory of a superparamagnet. The magnetic entropy change caused by a change in an external magnetic field was calculated for various magnetic clusters. The estimations made show that the magnetic molecular clusters could be promising materials for magnetic refrigeration in low-temperature regions (below about 20 K).

Articles you may be interested inComparison of the order of magnetic phase transitions in several magnetocaloric materials using the rescaled universal curve, Banerjee and mean field theory criteria J. Appl. Phys. 117, 17D144 (2015) The field dependence of the adiabatic temperature change ⌬T ad of second order phase transition materials is studied, both theoretically and experimentally. Using scaling laws, it is demonstrated that, at the Curie temperature, the field dependence of ⌬T ad is characterized by H 1/⌬ . Therefore, as the magnetic entropy change ⌬S M follows a H ͑1−␣͒/⌬ power law, these two dependencies coincide only in the case of a mean field model. A phenomenological construction of a universal curve for ⌬T ad is presented, and its theoretical justification is also given. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory ͑extrapolations in field or temperature͒, for enhancing the resolution of the data and as a simple screening procedure for the characterization of materials.

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