M.R. Said

Critical exponents of (Fe,Mn)3Si

Abstract The magnetic phase transitions in Fe 3− x Mn x Si alloys are investigated by measuring the magnetisation as a function of magnetic field and temperature. The magnetisation measurements have been carried out on three samples with x =1.15, 1.3 and 1.5. The ferromagnetic transition temperature ( T C ), critical amplitude and critical exponents ( β , γ and δ ) have been determined by using Arrot plots, Kouvel–Fisher methods and scaling plots of the reduced magnetisation and reduced magnetic field. The values of β , γ and δ are discussed and compared with the results of various theoretical models.

Magnetization study of high-temperature superconductor

The DC susceptibility under zero-field-cooled and field-cooled conditions, hysteresis loop and isothermal remanent magnetization measurements have been carried out on a powdered sample of . The temperature and field dependence of the critical current density and the pinning-force density , and the irreversibility field were obtained from the hysteresis loops. An exponential-like dependence of the critical current on both temperature and applied field was observed over the temperature range 85 - 115 K in fields up to 0.6 T. The time-dependent magnetization data were analysed within the Anderson - Kim flux creep model. Derived potential barrier heights were found to increase with increasing temperature over the range 85 - 105 K.

Local environmental effects in Fe(Al, Co) SYSTEM

Abstract The local environmental effects have been used to calculate the magnetic moments carried by Fe and Co atoms, in FeAl1−xCox (0.31 ≤ x ≤ 0.45). A good agreement has been observed between the calculated values of the magnetic moments and those obtained from both 57Fe-Mossbauer spectroscopy and static magnetization measurements.

Spin-glass resistivity of pseudobinary (Tb, Y)Ag and (Gd, Y)Ag compounds

Abstract In both series of compounds, spin-glass (SG) ordering is evidenced by the onset of magnetization irreversibilities at T g , which in (Tb, Y)Ag is known to be accompanied by long-range antiferromagnetic (AFM) order with T N = T g . Electrical resistivity (ϱ) versus temperature ( T ) data for each compound when corrected for the phonon contribution (derived from ϱ versus T for nonmagnetic YAg), show a constant high- T value (ϱ HT ) down to T g , where there is a rapid descent to a low- T residual value (ϱ 0 ). From a reasonable estimate of the paramagnetic scattering contribution to to ϱ HT , the chemical-disorder component (ϱ CD is determined. Assumed to be temperature independent, ϱ CD is then subtracted from ϱ O to obtain the component of topological magnetic disorder (ϱ MD ). In both Tb x Y 1- x Ag and Gd x Y 1- x Ag, the differences between the changes of ϱ MD and ϱ CD with decreasing x indicate a progressive development of SG order out of a gradual breakdown of AFM order.

A local environmental effect in the Co(AlFe) system

Abstract 57Fe-Mossbauer spectroscopy (MS) measurements at room and liquid nitrogen (LN) temperature were recorded for Co Al1−xFex (0.05 ⩽ x ⩽ 0.5) system. The MS shows a splitting for x ⪖/ 0.2 at room temperature and for x ⩾ 0.05 at LN temperature. The average magnetic moments per formula unit (FU) were calculated within a simple local environmental model for the three possible atomic site occupancy of this system, i.e. B21, B22, and B23, CsCl-type structure. The contribution to the magnetic moments by Fe and Co atoms were also calculated and compared with values estimated using the hyperfine field values as obtained from the present MS and previous magnetization results.