Buddhadev Kanrar

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.

Preparation, characterization and thermal behavior of K2U4O13-Rb2U4O13 solid solutions

Abstract The preparation and characterization of (K1−xRbx)2U4O13 solid solutions has been studied for the x values in the range of 0 − 1. The solid solutions were prepared by heating K2U4O13 and Rb2U4O13 in required stoichiometry at about 600–700 ℃ for about 50 h in air atmosphere. The XRD patterns of the products suggest formation of the solid solutions in full composition range of Rb2U4O13 and K2U4O13. The cell volume of the crystal unit cell of solid solutions changes linearly with Rb atom % in (Rb + K) present in the solid solutions and follows Vegards law. The solid solutions when heated in Ar/He atmospheres at 900 ℃ produce corresponding low valent uranate solid solutions (K1−xRbx)2U4O12 or their mixtures.