Novel Oxides: Preparation in Bulk & Thin-film form & Investigations for Multifunctional Properties

Among the available wide repository of oxide materials; some of the oxides containing transition metal elements have found growing interest among researchers in recent years, due to the observed unusual properties in these novel oxides, resulting from the contributions from the unique nature of the outer d-electrons of transition metals.

The researchers have made detailed studies in the field of multiferroic oxide solid-solutions that are pseudo-perovskites and composites. Even at present, there are ongoing works in the lab (Magnetics & Advanced Ceramics Lab) on investigating the origin of multiferroicity by controlled doping of transition elements at B-site of some well-known non-Pb based perovskites.

In this current proposal, the researchers investigate in detail two specific broad categories of novel contemporary oxide systems that have caught the intense research interest among the community, internationally.

1.Topological Insulators: In the past few years a new state of matter has emerged in literature, classified as “topological insulators (TI)”. These materials are insulating in the bulk and have exotic metallic states on their surfaces formed by topological effects when placed next to a vacuum or an ‘ordinary’ insulator. An ideal TI with bulk insulating property and time-reversal symmetry protected surface conducting properties could be the materials of future that are of potential interest for various applications including multiferroicity, spintronics etc.

Prior studies on slenide, telluride TIs reveal several limitations in these small gap semiconducting chalcogenides. The oxide or Heusler alloy TI systems are theoretically predicted to be lucrative as they can be used as cost effective and highly stable (against surface oxidation and degradation) TIs with bulk insulating and non-degrading conducting surface states.

Work in the area of Au/RBiO3/Pt hetero-junctions (R= (Y/Ba)): With above background, the researchers prepared a series of thin-films of (Y/Ba)BiO3 and studied their magneto-transport behavior in detail. Although the capacitance vs. magnetic field measurements revealed no typical signatures of topological insulator behavior in the BBO films, they observed a magnetic field dependent resistive switching (RS) behavior in the BBO films.The role of temperature and magnetic field on switching characteristics of BBO thin films were explored. The results revealed that the magnetic field can be a control parameter of the resistive switching behavior in Au/BBO/Pt hetero-junction, and a potential for magnetic field controlled RS devices useful in neuromorphic applications is indicated.

Work in the area of Half Heusler YPdBi films: Among the various predicted Heusler alloy based topological insulators, YPdBi stands in the border between the trivial and topological insulator states. The deposition parameters are successfully optimised to obtain aligned crystal growth of YPdBi (~ 100 nm) along (220) and (440) plane direction. Hall bar patterning of the deposited YPdBi thin film samples was done using photolithography. A typical Magneto-resistance measurement of the device at 2K temperature, using physical property measurement system (PPMS) is shown. Sharp drop in resistance around zero magnetic field is clearly observed, which can be understood in terms of weak antilocalization (WAL) effect, a typical signature of TI.