Surendra Singh

The interface structure and microstructure of ferrimagnetic rare earth-transition metal thin films control their magnetic properties, which are highly tunable near the compensation temperature and present significant opportunities for ultrafast magnetic switching in spintronic devices. We investigate the temperature-dependent longitudinal resistance (Rxx) and transverse (Hall) resistance (Rxy) measurements as a function of magnetic field applied perpendicular to the plane of the Gd/Co multilayer in pristine (as-deposited) and annealed states. Isothermal annealing at 573 K for varying times controlled the interface structure and morphology, which influenced the strong antiferromagnetic exchange interaction at the Gd-Co interfaces and consequently the electronic transport properties. The pristine Gd/Co multilayer showed a compensation temperature of 215 K, and we observed a sign reversal in the longitudinal resistance (magnetoresistance, MR) and anomalous Hall effect (AHE) across this temperature. X-ray scattering and polarized neutron reflectivity results reveal the formation of a Kagomé magnet alloy (GdCo2) phase at the interfaces upon annealing of the pristine Gd/Co multilayer, which influences the exchange interactions across the interfaces and reveals unconventional MR and complex AHE. In contrast to the pristine Gd/Co multilayer and ferromagnetic transition metals, the annealed Gd/Co multilayer displays unique MR and AHE properties. Our results demonstrate that RE-TM multilayer ferrimagnets offer a dynamic tool for fine-tuning interface exchange interactions and governing spin transport, ultimately contributing to advancements in antiferromagnetic spin devices.

PNR data for a Ni/Gd multilayer in front (a) and back (b) surface reflectivity modes are presented. The corresponding magnetization depth profiles in front (c) and back (d) modes indicate helical magnetization at interfaces at room temperature.

The quantum mechanical phenomena of frustrated total reflection of neutrons in periodic ternary (Ti/Ni/Si) superlattices have been investigated using the polarized neutron reflectivity (PNR) technique. We have experimentally demonstrated that periodic ternary superlattices can efficiently produce a resonant enhanced coherent neutron source with a smaller cross-sectional size, which can probe large-scale inhomogeneities in condensed matter. Using PNR experiments and simulations, we have also studied the applications of periodic ternary superlattices for a possible neutron bandpass filter in the wavelength ranges of 1–10 Å. A comparison of neutron bandpass filter applications for the periodic ternary systems with periodic binary systems is also carried out. The PNR results revealed that the periodic ternary superlattices, which show quantum resonant behaviors, provide a smaller bandwidth for the neutron bandpass filter applications. Our measurements suggest that such periodic superlattices may, therefore, be used for making neutron beams suitable for applications in biochemical and nanoscience research, as well as for studying the fundamental quantum behaviors of neutron beams.

The effects of Ag¹⁵⁺ (120 MeV) swift heavy ion (SHI) irradiation on the structural and morphological properties of epitaxial La_0.25Pr_0.375Ca_0.375MnO₃ (LPCMO) thin films were investigated by x-ray scattering and atomic force microscopy (AFM) techniques. LPCMO films of thickness ∼ 280 Å were irradiated with an Ag¹⁵⁺ ion beam at different fluences of 1 × 10¹¹, 5 × 10¹¹, and 1 × 10¹² ions cm⁻². XRD results suggested the development of the tensile stress along the out-of-plane direction of the LPCMO film upon ion irradiation, which increases on increasing the ion fluence. The morphology of the film was also modified with the irradiation and an increase in the fluence of the ion beam enhanced the in-plane height-height correlation length scale (grain size) with a loss of the fractal behaviours. The linear variation of microstrain with ion irradiation fluence in thin LPCMO film can be considered for a possible strain-driven application in modifying functional properties of such a phase separated complex oxide.