Abstract

The structure, magnetic and magnetocaloric properties of Nd2Fe17−xCox (x = 0; 1; 2; 3, 4) and Gd2Fe17-xCux (x = 0, 0.5, 1 and 1.5) solid solutions have been studied. For this purpose, these samples were prepared by arc melting and subsequent annealing at 1073 K for a 7 days. Structural analysis by Rietveld method on X-ray diffraction (XRD) have determined that these alloys crystallize in the rhombohedral Th2Zn17-type structure (Space group R¯3 m) and the substitution of iron by nickel and copper leads to a decrease in the unit cell volume. The Curie temperature (TC) of the prepared samples depends on the nickel and copper content. Based on the Arrott plot, these analyses show that Nd2Fe17-xCox exhibits a second-order ferromagnetic to paramagnetic phase transition around the Curie temperature. These curves were also used to determine the magnetic entropy change ∆SMax and the relative cooling power. For an applied field of 1.5 T, ∆SMax increase from 3.35 J/kg. K for x = 0 to 5.83 J/kg. K for x = 2. In addition the RCP increases monotonously. This is due to an important temperature range for the magnetic phase transition, contributing to a large ∆SMax shape. Gd2Fe17-xCux solid solution has a reduction of the ferromagnetic phase transition temperature from 475 K (for x = 0) to 460 K (for x = 1.5) is due to the substitution of the magnetic element (Fe) by non-magnetic atoms (Cu). The magnetocaloric effect was determined in the vicinity of the Curie temperature TC. By increasing the Cu content, an increase in the values of magnetic entropy (∆SMax) in a low applied field is observed.

Highlights

  • Much attention in this area has been focused on intermetallic compounds which are defined as solid phases containing two or more metals, possibly with one or more non-metallic elements, whose crystal structure differs from that of the constituent elements

  • The Curie temperature is the result of two effects: a magnetovolumic effect [53, 54] linked to Fe-Fe distances and an electronic effect linked to the filling of the 3d band of iron

  • The variation of the magnetic entropy ΔSM is evaluated by an indirect method whose the main objective is magnetic measurement, this method is based on magnetization isotherms as a function of the magnetic field applied for different temperatures

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Summary

Introduction

During the last decades and until now, the production of cold has mainly been ensured by the technique of compression/expansion of a refrigerant. Magnetic Skyrmions reason that researchers and manufacturers of refrigeration and heat pump have set out to search for a new refrigeration technology that is more respectful of the environment and less energy intensive, which is magnetic refrigeration (RM) This cold production technology, which is based on a physical phenomenon called the magnetocaloric effect (EMC), has considerable advantages over conventional techniques: absence of atmospheric pollutants, absence of noise and vibration, high reliability thanks to the use solid refrigerants rather than harmful gases and above all environmental protection and reduction of electricity consumption. In this regard, in order to get rid of harmful refrigerants, additional efforts have been turned towards the search for magnetocaloric materials. The substitution of Ni or Co by Fe atoms confirmed a extension of binaries Nd2Fe17 and GdFe17 in the Nd-Fe-Co and Nd-Fe-Co ternary systems, respectively and improved physical support properties and structural stability [28, 29]

Crystallographic study of the solid solution R2Fe17-xMx
Structural of the solid solution
Magnetic and manetocaloric properties of the solide solution R2Fe17-xMx
Magnetic properties
Magnetic and magnetocaloric properties of the solid solution Gd2Fe17-xCux
Conclusion
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