Research overview

Non-uniform magnetisation across interface

(Published)

Anomalous Hall effect (AHE), which arises when a current is passed through a ferromagnetic material subjected to a perpendicular magnetic field, is proportional to the magnetization of the sample. Additional hump-like features in AHE are often attributed to the presence of non-trivial spin textures leading to topological Hall effect (THE). However, several recent reports have emphasized in context of ferromagnetic SrRuO3 based heterostructures that the sample inhomogeneity can also result in THE-like features. In order to investigate this issue in general for any ferromagnetic heterostructure, we have considered a phenomenological model to calculate the changes in the shape of hysteresis loop due to various interfacial effects. These changes in the magnetization have been accounted for by considering that the interdomain magnetic coupling parameter varies exponentially with the distance from the interface along the growth direction of the heterostructure. In case of symmetric interfaces on both sides of a ferromagnet, we have considered the variation a Gaussian function. We have found that the additional AHE contribution due to the net change in magnetization in such cases are akin to experimentally observed THE, even though we have not considered any topological quantity explicitly in our model. Thus, we propose another situation with nonuniform magnetization profile that may be used to explain additional features in AHE, which might not necessarily be intrinsic THE.


Interface engineering of quantum material (Broad discussion)

Heterostructures of transition metal oxide perovskites (ABO3, B: transition metal) have provided for a plethora of emergent phenomena arising from charge transfer, strain, symmetry breaking, polar catastrophe, etc. By tuning the various materials and parameters associated with a heterostructure, we can arrive at completely novel emergent physics that are absent in the bulk counterparts. For instance, a well-studied system in this regard is the LaAlO3/SrTiO3 heterostructure,  where a polarity compensation at the interface leads to various phenomena like 2D electron gas, interfacial ferromagnetism and even superconductivity. Our aim is to design and study such phenomena by studying films in ultra thin film limit where quantum effects predominate using pulsed laser deposition technique supported by by transport and spectroscopic measurements.