Browsing by Author "Khedr, D.M"

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    A molecular-field study on the magnetocaloric effect in Er2Fe17
    (Elsevier, 6/25/2018) Khedr, D.M; Aly, Samy H; Shabara, Reham M; Yehia, Sherif
    A method, based on the molecular field theory of ferrimagnetism, and standard relations for the electronic and lattice heat capacities and entropies, is used to calculate the magnetocaloric effect (MCE) in Er2Fe17. This compound has a Curie temperature in the vicinity of room temperature and could be, therefore, of practical interest. The magnetization, magnetic, lattice, electronic and total entropies and specific heats, for different magnetic fields, have been calculated as function of temperature up to and beyond T-c. The magnetocaloric effect i.e. the isothermal magnetic entropy change Delta S-M and the adiabatic temperature change, Delta T-ad for different magnetic fields, have been studied in the temperature range 0 - 400 K. As an example of our results, the maximum isothermal magnetic entropy change Delta S-M in Er2Fe17 is in the range 5 - 6 J/kg K, for a magnetic field change of 80 kOe. The adiabatic temperature change, Delta T-ad has a maximum value in the range 1.5 - 2.1 K for Delta H = 80 kOe. For the purpose of comparison, a giant magnetocaloric bench-mark material, with first-order phase transition e.g. Gd5Si2Ge2 has a maximum Delta S-m and Delta T-ad (for a field change of 50 kOe) in the range 20-36 J/kg. K and 11-17 K respectively. Our results are in fair agreement with available results of other studies on this compound, in which more involved Hamiltonian was used e.g. taking crystal electric field into account.
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    On the magnetization process and the associated probability in anisotropic cubic crystals (vol 430, pg 103, 2017)
    (ELSEVIER SCIENCE BV, 2019-01) Khedr, D.M; Aly, Samy H; Shabara, Reham M; Yehia, Sherif
    We present a theoretical method to calculate specific magnetic properties, e.g. magnetization curves, magnetic susceptibility and probability landscapes along the [100], [110] and [111] crystallographic directions of a crystal of cubic symmetry. The probability landscape displays the evolution of the most probable angular orientation of the magnetization vector, for selected temperatures and magnetic fields. Our method is based on the premises of classical statistical mechanics. The energy density, used in the partition function, is the sum of magnetic anisotropy and Zeeman energies, however no other energies e.g. elastic or magnetoelastic terms are considered in the present work. Model cubic systems of diverse anisotropies are analyzed first, and subsequently material magnetic systems of cubic symmetry; namely iron, nickel and Cox Fe100−x compounds, are discussed. We highlight a correlation between magnetization curves and the associated probability landscapes. In addition, determination of easiest axes of magnetization, using energy consideration, is done and compared with the results of the present method.