Magnetocaloric effect: From materials research to refrigeration devices

This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 (NZFAO) nanoparticles (NPs). The samples were successfully synthesized by the sol–gel method followed by annealing of the as-synthesized at 600, 800, 900, 1050, and 1200 °C. This approach yielded the formation of a highly crystalline structure with crystallite size ranging from 17 nm to 40 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, as well as energy disperse spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy, were used in order to determine the structural and morphological properties of the prepared samples. Rietveld XRD refinement reveals that Ni–Zn–Al ferrite nanoparticles crystallize in inverse cubic (Fdm) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core–shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni–Zn–Al ferrite samples may be promising for multifunctional diverse applications.

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Magnetic and spectroscopic properties of Ni–Zn–Al ferrite spinel: from the nanoscale to microscale

Detailed magnetization measurements in La_{5/8-y}Pr_{y}Ca_{3/8} MnO_{3}, including magnetic relaxation properties, demonstrate the dynamic nature of the phase separated state in manganites. The difference between the field-cooled-cooling and zero-field-cooled magnetization curves signals the existence in the latter of blocked metastable states separated by high energy barriers. Results of the magnetic viscosity show that the system becomes unblocked in a certain temperature window, where large relaxation rates are observed. We propose a simple phenomenological model in which the system evolves through a hierarchy of energy barriers, which separates the coexisting phases. The calculated magnetization curves using this model reproduce all the qualitative features of the experimental data. The overall results allowed us to construct an H-T phase diagram, where frozen and dynamical phase separation regions are clearly distinguished.

Dynamic phase separation in La_{5/8-y}Pr_{y}Ca_{3/8}MnO_{3}

pdf/magnetic-and-magnetocaloric-properties-of-la-0-6-ca-0-4-mno-3zwf7048mm.pdf

Magnetic and magnetocaloric properties of La 0.6 Ca 0.4 MnO 3 tunable by particle size and dimensionality

Structural, electrical and ethanol sensing properties of double-doping LaFeO3 perovskite oxides

Critical behavior in Sr-doped manganites La0.6Ca0.4−xSrxMnO3

In this work, our focus is upon the synthesis of material having useful and less expensive high frequency applications. For this purpose, we used the sol–gel method to elaborate the Cu-substituted CoFe2O4. The XRD analysis confirmed the single-phase cubic spinel structure with the Fd 3 - m space group. The grain size distribution was traced through different methods. It confirms the nano-metric size of the compound. To elaborate the electrical and dielectric properties of the prepared sample, impedance spectroscopy was invested. It demonstrated the relaxing nature of our material and indicated that the substitution of Fe by Cu on CoFe2O4 increases the ac conductivity and decreases the dielectric loss especially at higher frequencies; the low loss values indicate the potential of these ferrites for high frequency applications at temperatures close to the room temperature. The activation energy value was estimated based on the relaxation time and the conductance curves analysis, the found value is around 0.33 eV which confirms the semiconductor character of our compound and its capacity to achieve a significant gain in productivity. Moreover, this obtained value indicates the relationship between the electrical conductivity mechanism and the relaxation one.

Structural, dielectric, electrical and modulus spectroscopic characteristics of CoFeCuO4 spinel ferrite nanoparticles

Impact of CuO phase on magnetocaloric and magnetotransport properties of La 0.6 Ca 0.4 MnO 3 ceramic composites

Investigation studies of structural, electrical, dielectric, and optical of DyTi0.5 Mn0.5O3 multiferroic for optoelectronics applications

Detailed Investigation of Structural, Morphology, Magnetic, Electical and Optical Properties of the Half-Doped PerovsikteNd0.5Ba0.5FeO3

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