Abstract
We present experimental evidence about the magnetocaloric tuning effect in one-dimensional nanostructure fibers mixed-valence manganite as synthesized by electrospinning techniques and under heat treatments of 973, 1073 and 1173 K. The stoichiometry obtained is La0.7Ca0.23Sr0.07MnO3 and Rietveld refinement indicates a single-phase with an orthorhombic (Pnma) crystal structure. Scanning and transmission electron microscopy observations indicate coalescence in granular colonies of La0.7Ca0.23Sr0.07MnO3 nanoparticles to conform nanofibers. Magnetic entropy change is tuned due to heat treatments at 1173 K with maximum values of 1, 1.82 and 2.51 J/kgK for applied external magnetic fields of μ0H = 1, 2 and 3T, respectively, with a maximum magnetic entropy difference at a Curie temperature of 293 K (furthermore, second-order magnetic phase transition was observed). Additionally, for a magnetic field, ~μ0H = 3 T values of 49, 95 and 143 J/kg for 973, 1073 and 1173 K heat-treated samples were obtained.
Highlights
The development of a new cooling technology referred as magnetic refrigeration, is based on the magnetocaloric effect (MCE), considered an intrinsic property of magnetic materials
The maximum value of magnetic entropy change occurs near magnetic phase transition temperature, and strongly depends of the magnetic field magnitude [3]
The electrospinning technique is picked to fabricate 1D nanostructure specially for ceramic nanofibers, due to its fast and low-cost route to achieve a one-dimensional nanostructure with a specific shape and chemical parameters [7]
Summary
The development of a new cooling technology referred as magnetic refrigeration, is based on the magnetocaloric effect (MCE), considered an intrinsic property of magnetic materials. When estimating MCE two parameters are considered: the isothermal entropy change and the adiabatic temperature gradient. Both take place when an external magnetic field is applied and removed from a magnetic material. The variation of the external applied magnetic field and its interaction with the magnetic material, change the magnetic contribution of total entropy and originate the magnetocaloric effect as described by the authors of [2]. R1-xAxMnO3 manganites are ideal materials candidates for the development of magnetic refrigeration technology, due to their substantial MCE values, preparation forms, low cost, chemical stability, and tuning of magnetic transition temperatures [11,12]. We present magnetocaloric effect in La0.7Ca0.23Sr0.07MnO3 nanofibers fabricated by the electrospinning technique along with extensive characterization using X-ray diffraction, scanning and transmission electron microscopy and vibrating sample magnetometry
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