Suchergebnisse

Surface morphology and magnetic properties of ferromagnetic Heusler alloy Co2FeSi thin films and their multi-layers with anti-ferromagnetic Ir50Mn50, which find applications in spintronic devices were investigated. The sputtering process flow for large area deposition of thin films on 3 inch size thermally oxidized single crystal Si(100)/SiO2 substrates have been developed by optimizing the sputtering geometry and other process parameters. A uniform film composition, thickness, smooth surface, good crystallinity and magnetic properties have been achieved in the films over 3-inch size wafers. The isotropic magnetic properties such as saturation/remanent magnetizations, coercivity were achieved in Co2FeSi films deposited on 3-inch size Si(100)/SiO2 wafers with 15 nm Cr buffer layer. An exchange bias anisotropy has been established in Co2FeSi/IrMn multilayer by magnetic annealing process using in-house made magnetic annealing set up. A maximum exchange bias anisotropy field, Hex of 178 Oe and low coercivity, Hc of 85 Oe has been achieved in the Co2FeSi/IrMn multilayer stacks suitable for magnetic tunnel junctions for spintronic applications.

Heusler type alloys Ni50Mn25+xGa25-x (x=2,3,4 and 5) based on near stoichiometric Ni2MnGa compositions were directionally solidified using modified Bridgman method. The alloys thus prepared were characterized for their chemical composition, crystal structure, microstructure, phase transformation, magnetic and magneto-mechanical properties. The directionally solidified Ni50Mn30Ga20 alloy rod exhibited maximum magnetocrystalline value of 95 kJm-3 and lowest detwinning stresses for martensite phase of about 5MPa. The reversible room temperature magnetic field induced strain of 0.2% under external magnetic field of 0.6T and 0.05kN bias load was obtained for the directionally solidified Ni50Mn30Ga20 alloy.

(100-x) Na0.5Bi0.5TiO3 (NBT)-(x) NiFe2O4 (NFO)(x = 0, 20, 40, 60, 80 and 100) composites are synthesized using conventional solid state reaction method. Crystal structure studies are performed by using X-ray Diffraction technique (XRD) and the Rietveld analysis of XRD patterns confirms the co-existence of cubic (NFO) and rhombohedral (NBT) symmetry with Fd- 3m and R3c space groups, respectively. Micro-structural study reveals the formation of combination of composite phases and its inter-coupling grains. The average grain sizes and area percentage of each phase for the composites are calculated using Image J software. The Magnetisation versus Magnetic field (M-H) hysteresis loops show soft magnetic behavior of composites with variation in Saturation magnetization (MS) and Coercivity (HC). A maximum MS (34 emu/g) and low HC (15 Oe) is obtained for (80) NFO - (20) NBT composite.The Polarization – Electric field (P-E) analysis shows that the maximum saturation polarization (PS) is obtained for (60)NBT-(40)NFO sample and is attributed to the leakage current generated by conductive NFO phase. The coupling between the ferrite and ferroelectric phase is studied based on the magnetoelectric voltage coefficient(αME). The maximum (αME) of 1.82 mV/cm-Oe is obtained for (80)NBT -(20)NFO sample and this is almost 80% higher than the previously published literature on NBT-NFO composites. This can be attributed to the uniform distribution of grains with each ferroelectric phase surrounded by ferrite phase as shown in the morphological study.

The effect of Fe on the martensitic transitions, magnetic and inverse magnetocaloric effect in Ni47Mn40-xFexIn13 ribbons (x = 1, 2, 3 and 5) has been investigated. All the ribbon compositions under study have shown the presence of austenite phase at room temperature. The variation of martensitic transition with the increase in Fe-content is non-monotonic. The thermal hysteresis of the martensitic transition increased with the increase in Fe-content. The martensitic transitions shifted to lower temperatures in the presence of high magnetic fields. A maximum magnetic entropy change (∆SM) of 50 Jkg-1K-1 has been achieved in the Ni47Mn38Fe2In13 (x = 1) ribbon at 282 K for an applied field of 5 T.

In this report, glass forming ability, structure and soft magnetic properties of melt spun ribbons of (Fe1-xCox) 88-yVyZr7B4Cu1alloys with compositions x0.1y2, x0.1y4 and x0.1y6 & x0.35y2, x0.35y4 and x0.35y6 have been investigated. All alloys were found to be fully amorphous after melt spinning. Annealing of amorphous ribbons of x0.1 series alloys leads to the formation of bcc α-Fe(Co) phase and Fe2Zr phase in the amorphous matrix, while annealing of amorphous ribbons of x0.35 series alloys, leads to the formation of only bcc α-Fe(Co) phase in the amorphous matrix. High precision lattice parameter calculation revealed that V addition influences the phase formation in low Co containing x0.1 alloys. It leads to low volume fraction of bcc α-Fe(Co) phase and promotes Fe2Zr phase. A higher Co content increases the Curie temperature of amorphous phase, while V addition decreases the TC of amorphous phase in both x0.1 and x0.35 series of alloys. Saturation magnetization (Ms) of x0.35 alloys are higher than of x0.1 alloy due to higher Co content and the Ms decreases with increasing V content due to its non-magnetic nature. Coercivity was found to be increased with annealing in x0.35 alloys due to the low volume fraction formation of bcc α-Fe(Co) phase and Fe2Zr phase. The coercivity decreases with increasing V addition in x0.35 alloys as spun ribbons and a lowest coercivity of 0.13 Oe has been obtained in x0.35y6 alloy which is one of the lowest among FeCoZrBCu alloys reported.