Mahmud Khan

Effect of ionic size compensation by Ag+ incorporation in homogeneous Fe-substituted ZnO: studies on structural, mechanical, optical, and magnetic properties

Substituting an ion of different size from that of the host element introduces lattice strain and defects. However, this mismatch may be significantly reduced by substituting an additional ion with a compensating size relative to the dopant. Such a double substitution might offer better solubility irrespective of the local distortions as well as the formation of defects in the valence states. Fe-substituted ZnO has been widely reported with conflicting results primarily arising from lack of chemical and structural homogeneity originating from preparation techniques, compositional fluctuations, and equivocal comprehension of actual solubility limits of the dopants. In this study, Ag ion has been incorporated in Fe-substituted ZnO to compensate the ionic size of Zn1−x[Fe0.8Ag0.2]xO (0 ≤ x ≤ 0.03125) by determining the solubility limit of the homogeneous material and their corresponding structural, mechanical, optical and magnetic properties have been investigated thoroughly. Co-substitution rearranges the lattice and leads to better crystal structures with tunable properties related to the amount of substitution.

Anisotropy induced anomalies in Dy1−xTbxAl2

The Dy1−xTbxAl2 alloys have been investigated by X-ray powder diffraction, heat capacity, and magnetic measurements. All samples exhibit cubic Laves phase crystal structure at room temperature but at TC, DyAl2 and TbAl2 show tetragonal and rhombohedral distortions, respectively. First order phase transitions are observed below TC (at the spin-reorientation transition, TSR) in the alloys with 0.15 ≤ x ≤ 0.35. These transitions are signified by sharp heat capacity peaks and corresponding anomalies in the magnetization and ac magnetic susceptibility data. The observations are interpreted by taking into consideration the differences in easy magnetization directions of DyAl2 and TbAl2. Due to the competing magnetic structures, the anisotropy-related instability and magnetic frustrations are prominent in the Dy1−xTbxAl2 alloys at certain concentrations resulting in the first order transitions.

Controlling the microstructure and associated magnetic properties of Ni0.2Mn3.2Ga0.6 melt-spun ribbons by annealing

Here we report on the structural and magnetic properties of Ni0.2Mn3.2Ga0.6 melt-spun ribbons. The as-spun ribbons were found to exhibit mixed cubic phases that transform to non-cubic structure upon annealing. Additionally, an amorphous phase was found to co-exist in all ribbons. The SEM images show that minor grain formation occurs on the as-spun ribbons. However, the formation of extensive nano-grains was observed on the surfaces of the annealed ribbons. While the as-spun ribbons exhibit predominantly paramagnetic behavior, the ribbons annealed under various thermal conditions were found to be ferromagnetic with a Curie temperature of about 380 K. The ribbons annealed at 450 °C for 30 minutes exhibit a large coercive field of about 2500 Oe. The experimental results show that the microstructure and associated magnetic properties of the ribbons can be controlled by annealing techniques. The coercive fields and the shape of the magnetic hysteresis loops vary significantly with annealing conditions. Exchang...