C. L. Prajapat

New thorium–bismuth oxide solid solutions with oxygen vacancy induced tunable ferromagnetism

A combined X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, and magnetic and electron paramagnetic resonance (EPR) study on defect-induced magnetism in Th1−xBixO2−δ (0 ≤ x ≤ 0.3) solid solutions is presented in this paper. The solid solutions were prepared through a solid-state reaction route. The XRD patterns of the solid solutions suggest Bi dissolution up to 30 at% in the ThO2 matrix. The EXAFS study at the Bi and Th L3 edges indicates the formation of oxygen vacancies near Bi sites with an increasing trend with the Bi at% in the solid solutions. The magnetic measurements in field cooled (FC) and zero field cooled (ZFC) mode indicate an interesting observation involving ferromagnetic ordering with Curie temperature at around 70 K. The possibility of a spin glass-like phase was conclusively ruled out by a memory effect test experiment. The EPR studies revealed the presence of two different signals at g ∼ 2.05 and 2.25 due to the paramagnetic oxygen vacancy () and ferromagnetic resonance (FMR). The constant increase in intensity of the FMR signal with increasing doping level corroborates well with the increasing saturation magnetization value in magnetic measurements. By lowering the measurement temperature, this FMR signal showed an increase in its intensity along with continuous broadening and shift of the resonance field position to the lower field, which further signifies the presence of ferromagnetic ordering due to the paramagnetic oxygen vacancy in the Th1−xBixO2−δ solid solution.

Oxygen vacancy induced magnetism in (Th0.9Bi0.1)O1.95 solid solution

We present a magnetic study on Bi doped ThO2. EPR study revealed a clear signature of oxygen vacancies as a result of doping Bi. Interestingly, we also observe clear indication of a ferromagnetic behavior in the Bi doped ThO2. FC and ZFC measurements clearly indicate the ferromagnetic ordering at low temperature. The magnetism presumably originates from the oxygen vacancies created by doping lower valent cations into ThO2.

Optimization and characterization of cobalt & gadolinium films using X-ray scattering

Optimization of deposition parameters of Cobalt and Gadolinium films on Si substrates by a dc magnetron sputtering system was performed to obtain good quality of films. The structural properties of these films have been studied by x-ray scattering techniques such as, X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXRD) and X-ray reflectometry (XRR). From Co/Gd bilayer film we observed small Co Oxide layer on top of the Co film which reduces the possibility of making CoGd alloying at interfaces.

Micro-structural characterization of low resistive metallic Ni germanide growth on annealing of Ni-Ge multilayer

Nickel-Germanides are an important class of metal semiconductor alloys because of their suitability in microelectronics applications. Here we report successful formation and detailed characterization of NiGe metallic alloy phase at the interfaces of a Ni-Ge multilayer on controlled annealing at relatively low temperature ∼ 250 °C. Using x-ray and polarized neutron reflectometry, we could estimate the width of the interfacial alloys formed with nanometer resolution and found the alloy stoichiometry to be equiatomic NiGe, a desirable low-resistance interconnect. We found significant drop in resistance (∼ 50%) on annealing the Ni-Ge multilayer suggesting metallic nature of alloy phase at the interfaces. Further we estimated the resistivity of the alloy phase to be ∼ 59μΩ cm.

Effect of annealing on structure and magneto-transport properties of Fe/Au multilayer

We have studied the effect of annealing on magnetotransport in Fe/Au multilayers grown on Si substrate by sputtering. The multilayer interface structure was studied by specular and off-specular x-ray reflectometry whereas macroscopic magnetic properties are studied using SQUID magnetometer. We observed a reduction in magnetoresistance on annealing film at low temperature of 100 and 150°C. Reduction in magnetoresistance is attributed to increase in interface roughness as observed in x-ray reflectivity measurements.

Fe/Au Multilayers: Structure and Magnetoresistance

We have measured the magnetoresistance (MR) in two sets of Fe/Au multilayers, with varying (1) Fe layer thickness, tFe = 3–10 nm, and (2) Au layer thickness tAu = 5–15 nm, grown on Si substrates by sputtering. The multilayer interface structure and magnetic properties were studied by polarized neutron reflectometry (PNR). The study was undertaken to understand the correlation between structure of these multilayers and their magneto‐transport properties.