An Experimental Evaluation of Quenched Fe-Ga Alloys: Structural Magnetic and Magnetostrictive Properties

This study examines the effect of quenching on Fe100-x-Gax (x – 20 & 25) alloys. The long range of D03 ordering causes a minor variation in unit cell, which reduces peak intensity. This existence of D03, coupled with the A2 phase, leads to a decrease in magnetostriction in the quenched 25 at.% Ga alloy, which promotes D03 ordering. An Fe-Ga alloy having 20 at.% Ga that has been quenched possesses the A2 phase, the production of D03 is a first-order transition. Continuous ordering attempts to suppress D03 in 25 at. % Ga alloys were ineffective. Quenched Fe80-Ga20 alloy's saturation magnetization is larger than Fe75-Ga25 alloy. This suggests that lowering the nonmagnetic element Ga promotes saturation magnetization. The rise in material flaws and dislocations is due to the increased Ga content and higher quenching temperature. In a single-phase region, Fe80-Ga20 has the greatest magnetostriction at 85 ppm. Magnetostriction diminishes as Ga content rises to 25%, the D03 structure is responsible for this drop

An Experimental Evaluation of Quenched Fe-Ga Alloys: Structural Magnetic and Magnetostrictive Properties

627-633This study examines the effect of quenching on Fe100-x-Gax (x – 20 & 25) alloys. The long range of D03 ordering causes a minor variation in unit cell, which reduces peak intensity. This existence of D03, coupled with the A2 phase, leads to a decrease in magnetostriction in the quenched 25 at.% Ga alloy, which promotes D03 ordering. An Fe-Ga alloy having 20 at.% Ga that has been quenched possesses the A2 phase, the production of D03 is a first-order transition. Continuous ordering attempts to suppress D03 in 25 at. % Ga alloys were ineffective. Quenched Fe80-Ga20 alloy's saturation magnetization is larger than Fe75-Ga25 alloy. This suggests that lowering the nonmagnetic element Ga promotes saturation magnetization. The rise in material flaws and dislocations is due to the increased Ga content and higher quenching temperature. In a single-phase region, Fe80-Ga20 has the greatest magnetostriction at 85 ppm. Magnetostriction diminishes as Ga content rises to 25%, the D03 structure is responsible for this drop

Structural and Magnetic Properties of Amorphous Tb-Dy-Fe-Co Thin Films

This paper reports the effect of film thickness (50, 200, 400 and 800 nm) on the structural and magnetic properties of amorphous Tb-Dy-Fe-Co alloy thin films. All the films are found to exhibit perpendicular magnetic anisotropy (PMA) irrespective of the film thickness. The PMA is found to decrease with increase in film thickness due to the decrease in the magnetic texture and anisotropy energy. While the coercivity deduced from the out-of-plane magnetization curve increases with increasing film thickness, the in-plane coercivity exhibits weak thickness dependence. The irreversibility point in the thermo-magnetic curves obtained from field-cooled and zero-field-cooled measurements along the out-of-plane direction is found to shift towards higher temperature compared to the measurements in in-plane directions, indicating the presence of strong PMA

Ferromagnetism in the multiferroic alloy systems BiFeO3-BaTiO3 and BiFeO3-SrTiO3: Intrinsic or extrinsic?

Among the different bulk alloys of the room temperature multiferroic compound BiFeO3, alloying with ATiO(3) (A = Ba, Sr, Pb) is interesting as they have been reported to induce ferromagnetism under certain conditions. While this makes them interesting as potential multiferroic magnetoelectric materials, there is a lack of clarity on the origin of ferromagnetism in these systems. We have performed a detailed magneto-structural analysis on two alloys, namely, BiFeO3-BaTiO3 and BiFeO3-SrTiO3, and found the systems' propensity for the formation of ferrimagnetic hexaferrite (BaFe12O19 and SrFe12O19) phases. Though insignificantly small to the extent of being undetectable by x-ray powder diffraction, we prove that the ferromagnetic character of the specimen is entirely due to spontaneous precipitation of the hexaferrite grains. While our results suggest that care should be exercised before attributing ferromagnetism in such alloy systems as intrinsic to the perovskite phase, the propensity for the spontaneous precipitation of the hexaferrite phase in these multiferroic alloy systems is encouraging as it provides an opportunity for designing selfgrown ferroelectric-ferromagnetic composites with good magnetoelectric coupling

Influence of substrate temperature on structure, microstructure and magnetic properties of sputtered Fe-Ga thin films

This paper reports the structure, microstructure and magnetic properties of Fe-Ga thin films deposited using DC magnetron sputtering technique on Si(100) substrate kept at different temperatures. Structural studies employing X-ray diffraction and TEM revealed the presence of only disordered A2 phase in the film. Columnar growth of nanocrystalline grains from the substrate was observed in the film deposited at room temperature. With increase in substrate temperature the grain size as well as surface roughness was found to increase. The magnetization of the films deposited at higher substrate temperatures were Found to saturate at lower magnetic held as compared to the room temperature deposited Film. Coercivity was found to decrease with increasing substrate temperature upto a minimum value of similar to 2 Oe for the film deposited at 450 degrees C and with further increase in substrate temperature it was found to increase. A maximum magnetostriction of 200 mu-strains was also observed for the film deposited at 450 degrees C. (C) 2015 Elsevier B.V. All rights reserve

Effect of sputtering parameters on the structure, microstructure and magnetic properties of Tb-Fe films

The effect of sputtering parameters such as gas pressure and power on the structure, microstructure and magnetic properties of sputtered Tb-Fe thin films was investigated. X-ray diffraction and transmission electron microscopy studies showed that all the films were amorphous in nature irrespective of the sputtering parameters. A fine island kind of morphology was observed at low sputtering power whereas large clusters were seen at higher sputtering power. While the composition of Tb-Fe films remained constant with increasing sputtering power, the magnetic behaviour was found to change from superparamagnetic to ferromagnetic. On the other hand, the increase in argon gas pressure was found to deplete the iron concentration in Tb-Fe thin films, which in turn reduced the anisotropy and Curie temperature. Annealing of the films at 773 K did not result in any crystallization and the magnetic properties were also found to remain unchanged. (C) 2015 Elsevier B.V. All rights reserved

Cellular Metals and Ceramics for Defence Applications (Review Paper)

Among cellular metals, aluminium foams are the most commonly produced, and provide a unique combination of properties such as: very low density, high energy absorption under static and dynamic compressions, blast amelioration, sound absorption, and flame resistance. Applications in automotive and defence sectors have been reported. Foams based on high melting point metals such as nickel and its alloys are also under active development throughout the world for applications requiring corrosion and oxidation resistance coupled with high temperature strength and relatively high thermal conductivity. Ceramic foams were developed elsewhere in the world primarily for biomedical applications, but are also suitable for defence applications for high temperature insulation. These cellular materials will provide new materials options to designers of aerospace, transport, and other defence systems.Defence Science Journal, 2011, 61(6), pp.567-575, DOI:http://dx.doi.org/10.14429/dsj.61.64

Understanding thickness dependent magnetic properties of Tb-Fe thin films

In this paper, we have attempted to understand the magnetic behaviour of Tb-Fe thin films grown with different thicknesses through detailed electron microscopy, magnetization measurements and magnetic domain imaging studies. Tb-Fe thin films over a range of thicknesses such as 50, 100, 200, 400, 600 and 800 nm were deposited on Sisubstrates using electron beam evaporation technique. Grazing incidence X-ray diffraction studies revealed that all the films were amorphous in nature. Microstructural studies using transmission electron microscopy showed columnar channel of voids extending from substrate to film surface. Magnetization measurements along the in-plane and out-of-plane direction indicated presence of out-of-plane magnetic anisotropy in all the films. Saturation magnetization and coercivity measured along the out-of-plane direction were found to vary with the thickness of the films. A very high coercivity of ~2000 mT was obtained for the film having thickness of 400 nm. Magnetic anisotropy calculations indicated a strong perpendicular magnetic anisotropy for the 400 nm thick film. The variation of magnetic anisotropy with film thickness was correlated with the magnetic domain patterns observed in the films using magnetic force microscopy