Ishfaq Ahmad Shah

Realization of magnetostructural coupling by modifying structural transitions in MnNiSi-CoNiGe system with a wide Curie temperature window

The magnetostructural coupling between structural and magnetic transitions leads to magneto-multifunctionalities of phase-transition alloys. Due to the increasing demands of multifunctional applications, to search for the new materials with tunable magnetostructural transformations in a large operating temperature range is important. In this work, we demonstrate that by chemically alloying MnNiSi with CoNiGe, the structural transformation temperature of MnNiSi (1200 K) is remarkably decreased by almost 1000 K. A tunable magnetostructural transformation between the paramagnetic hexagonal and ferromagnetic orthorhombic phase over a wide temperature window from 425 to 125 K is realized in (MnNiSi)1−x(CoNiGe)x system. The magnetic-field-induced magnetostructural transformation is accompanied by the high-performance magnetocaloric effect, proving that MnNiSi-CoNiGe system is a promising candidate for magnetic cooling refrigerant.

INFLUENCE OF ION BEAM IRRADIATION ON STRUCTURAL, MAGNETIC AND ELECTRICAL CHARACTERISTICS OF Ho-DOPED AlN THIN FILMS

Holmium (Ho)-doped AlN thin films of thicknesses 60, 90 and 300 nm were grown in pure nitrogen atmosphere via RF magnetron sputtering. The deposited thin films were irradiated with protons at a dose of 5×1014 ions/cm2 and the effects of irradiation on structural, magnetic and electrical characteristics of thin films were investigated. Rutherford backscattering spectroscopy (RBS) confirmed the presence of Al, N and Ho in prepared samples. X-ray diffraction analysis showed that crystallinity of the thin films was enhanced after irradiation and thicker films were more crystalline. Atomic force microscopy (AFM) revealed that the surface roughness and porosity of the thin films were increased after irradiation. Magnetic measurements showed that diamagnetic AlN:Ho thin films can be transformed into paramagnetic and ferromagnetic ones via suitable irradiation. The increase in carrier concentrations after irradiation was responsible for tuning the electrical and magnetic characteristics of thin films for applications in various high voltage microelectronic and magnetic devices.

Inducing the magnetic character in reduced graphene oxide through incorporation of Fe2O3 nanoparticles

A chemical two-step approach based on solvothermal technique has been adopted to synthesize the reduced graphene oxide (rGO)/Fe2O3 hybrid materials. The rGO was prepurified by acidic treatment, followed by sensitization to attach the desired functional groups. The structural, compositional, morphological and magnetic analyzes of the prepared samples were carried out using various characterization techniques. The fabricated rGO/Fe2O3 heterostructures were confirmed by X-ray diffraction analysis and Fourier transform infrared spectroscopy. Raman spectroscopy evidenced the fabrication of multilayer graphene and scanning electron microscopy was carried out to study the morphology of the prepared samples. The average particle size of Fe2O3 nanoparticles (NPs) loaded on rGO was found to be ∼20 nm, as was observed during transmission electron microscopy. Thermogravimetric analysis of rGO/Fe2O3 hybrid structures was performed to investigate their thermal behaviors. It was evidenced that the incorporation of Fe2O3 NPs into rGO enhanced its thermal stability. Vibrating sample magnetometry showed that ferromagnetic character was induced in rGO due to involvement of Fe2O3 NPs. The rGO/Fe2O3 hybrid structures can be considered as a competent material for fabrication of various magnetic devices.

Effect of Sb-doping on martensitic transformation and magnetocaloric effect in Mn-rich alloys*

We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn50Ni40Sn Sb x (x = 1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure with the space group at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases. The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn50Ni40Sn Sb x alloys are attractive candidates for applications in solid-state refrigeration.