M. Asif Iqbal

Structural, magnetic, and microwave properties of NdZn-substituted Ca 0.5 Ba 0.5 Fe 12 O 19 hexaferrites

AbstractnSubstitution of NdZn in Ca0.5Ba0.5−xNdxZnyFe12−yO19, (xxa0=xa00.00–0.10; yxa0=xa00.00–1.00) hexaferrites prepared by sol–gel method is investigated, and their effect on the microwave, structural, and magnetic properties is reported. The XRD patterns reveal single-phase M-type hexaferrite structure. The lattice parameters were found to increase by the substitution of NdZn. The increase in lattice parameters is due to the difference in ionic sizes of the cations involved. The average grain size was found between 16 and 29xa0nm by Scherer formula and was also confirmed by SEM and TEM. Magnetic behavior of selected sample was observed up to a magnetic field of 8T taken at temperature ranges from 4.2 to 373xa0K. The coercivity of the sample decreased from 2300 to 1210 Oe with increasing temperatures in a linear fashion up to 373xa0K. The grain boundaries, and the associated pinning fields, seem to have a resolute role in the magnetic behavior of these hexaferrites. Microwave measurements of the ferrite sample have been measured in the frequency range 0.5–12xa0GHz. The frequency dispersion of ferrites is credited to the phenomenon of natural magnetic resonance and domain wall pinning.Graphical Abstract

Electrical transport properties and temperature-dependent magnetization behavior of TbZn-substituted Ca0.5Ba0.5Fe12O19 hexaferrites

AbstractnSubstitution of TbZn in the series of Ca0.5Ba0.5−xTbxZnyFe12−yO19 (xxa0=xa00.00–0.10; Yxa0=xa00.00–1.00) hexaferrites prepared by sol–gel method and their effect on the structural, electrical and magnetic properties are investigated. Temperature-dependent magnetic behaviors of selected samples are observed up to the magnetic field of 8T taken over temperature ranges from 4.2 to 373xa0K. The coercivity of the samples decreases from 2740 to 1370xa0Oe with increasing temperatures in a linear fashion up to 373xa0K. The grain boundaries and the associated pinning fields seem to have an important role in the magnetic behavior of these hexaferrites. The resistivity of ferrite decreases from 24xa0×xa0108 to 15xa0×xa0108xa0Ω-m. The temperature dependence of resistivity and mobility exhibits the degenerate-type semiconductor-like behavior of these ferrites. The dielectric constant and dielectric loss decrease and show relaxation behavior at higher frequencies.Graphical Abstract

Content-based hierarchical Web cache

Web caches are deployed in order to quickly deliver the required information to user by placing data in proximity to users. Hierarchical Web caches are scalable, fault tolerant and enhance the degree of sharing. Typically data is either cached at each level or the most wanted data is cached at the leaf levels in the hierarchy. This strategy consumes much network bandwidth during the refreshment of data at each level and leads to poor hit ratio at upper levels by caching most popular data at leaf levels. In this paper we have proposed a content-based hierarchical Web cache. It characterizes hierarchy levels with respect to Web page contents. The highest, middle and contents respectively. A template is maintained at each level for assembling the page contents. This proposed strategy consumes less network bandwidth in refreshment and leads to moderate processing at each level. The performance evaluation also supports the hypothesis.