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    Öğe
    Effect of Ho substitution on structural, magnetic and magnetocaloric properties of Co(CrFe)O4
    (Springer, 2021) Kivrak, Burak; Gulkesen, Semiramis; Ayas, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, structural, magnetic and magnetocaloric properties of Ho-substituted Co(CrFe)O-4 spinel compounds produced by the sol-gel method were investigated. The Ho concentration in Co(CrFe)O-4 spinel structure was changed from 0 to 20% by 5% steps. It is observed that the Ho3+ ions create a new phase HoCrO3/HoFeO3 in the host spinel lattice. SEM images of samples indicate that the average particle size increases with Ho content. The paramagnetic to ferro-/ferrimagnetic phase transition temperature increases from 312 to 344 K with Ho content. While the fluctuation in saturation magnetization of samples was detected at low temperature, it almost becomes a linear change with the Ho content. The maximum magnetic entropy change under 7 T magnetic field was found as - 1.39, - 1.50, - 1.20, - 0.98 and - 0.91 J/kgK for Ho-free, 5, 10, 15 and 20 wt% Ho content in CoCrFeO4 spinel structure, respectively.
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    Öğe
    Room-temperature magnetocaloric effect in Fe-substituted CoCr2O4 spinels
    (Springer Heidelberg, 2021) Gulkesen, Semiramis; Tumen, Kutluhan Utku; Akyol, Mustafa; Ekicibil, Ahmet
    In this study, structural, magnetic and magnetocaloric properties of Co(Cr1-xFex)(2)O-4 (x=0.0, 0.25, 0.50, 0.75 and 1.0) cubic spinel compounds produced by solgel method were investigated. The cubic crystal structure of CoCr2O4 has not disrupted by Fe substitution, but the lattice parameter increases with increasing Fe content due to bigger ionic radii of Fe3+ ions than Cr3+ ions. The magnetic transition temperature of CoCr2O4 (96 K) is increased to 312 K when 50% Fe is substituted with Cr in CoCr2O4 structure. The maximum magnetic entropy change values are-0.88 J/kgK,-1.27 J/kgK and-1.39 J/kgK under 7 T magnetic field for x=0.0, 0.25 and 0.5 in Co(Cr1-xFex)(2)O-4, respectively. The relative cooling power values are enhancedx5 when 50% Fe3+ ions are substituted with Cr3+ ions in CoCr2O4. Therefore, the CoFeCrO4 sample might be a potential material for magnetic refrigerant applications due to its considerable high magnetization values, having room-temperature magnetic transition temperature, highest magnetic entropy change and relative cooling power compared to other samples.