Brajesh Kumar Mani | Searcharxiv

arXiv2025

Intralayer antiferromagnetism in two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

For the van der Waals magnet Fe$_3$GeTe$_2$, although a ferromagnetic ground state has been reported, there are also reports of complex magnetic behavior suggesting coexistence of ferromagnetism and antiferromagnetism due to the intricate interaction between Fe$^{+3}$ and Fe$^{+2}$ ions in this system. The exact nature of the interactions and the origin of antiferromagnetism are still under debate. Here, we report the observation of signature of ferromagnetic and antiferromagnetic couplings between different Fe-ions in the anomalous Hall effect measured for devices of mechanically exfoliated Fe$_3$GeTe$_2$ nano-flakes of thicknesses ranging from\,$\sim$\,15-20 layers. The temperature-dependent anomalous Hall effect data reveal two sharp step-like switchings at low temperature ($T\lesssim150\,$K). Our detailed analyses suggest the step-like sharp switchings in anomalous Hall resistance are due to the magnetization reversal behavior of different Fe-ions in individual layers of Fe$_3$GeTe$_2$. The experimental results can be explained by considering an intra-layer antiferromagnetic coupling between Fe$^{+3}$ and Fe$^{+3}$ ions, whereas intra-layer ferromagnetic coupling between Fe$^{+3}$ and Fe$^{+2}$ in the system. Our experimental results and the analyses are supported by the first-principles calculations for energetics and intralayer as well as interlayer exchange coupling constants.

cond-mat.mtrl-sci↗

arXiv2025

Theoretical and Experimental Investigations of High-Performance Sr2CoNbO6-delta Double Perovskite for IT-SOFC Cathode Applications

Enhancing the transport of oxygen anions in the cathode while maintaining surface stability is essential for improving the performance of intermediate-temperature solid oxide fuel cells (IT-SOFCs). This study investigates a novel cathode material candidate, Sr2CoNbO6-delta (SCNO), using density functional theory, molecular dynamics, and experimental characterization. The redox active Co cation at B-site and less reducible Nb cation at the B'-site together enhance both surface stability and electrocatalytic performance. SCNO is observed to have a higher concentration of oxygen vacancies and increased oxygen diffusivity on the surface. The surface stability of SCNO is further improved when simulated under compressive strain due to the GDC electrolyte substrate. These findings offer new insights into controlling Sr segregation in SCNO, contributing to a better understanding of its enhanced oxygen reduction reaction (ORR) activity and high surface stability. Subsequently, SCNO was synthesized to evaluate its potential as a cathode material in SOFCs. To assess its performance, symmetric cells with uniform dense thin films of varying thicknesses (40 and 80 nm) were fabricated using the pulsed laser deposition technique. Electrochemical impedance spectroscopy and distributed relaxation time analysis indicate that bulk oxygen ion diffusion is a limiting factor for the ORR in SCNO. The polarization resistance for the 40 and 80 nm dense thin film symmetric cells ranged between 0.329 - 0.241 ohm cm2 and 1.095 - 0.438 ohm cm2, respectively, within the temperature range of 773 - 973 K in an air atmosphere. The full cell configuration of NiO-GDC|GDC|SCNO demonstrated a significantly high peak power density of 0.633 W/cm2 at 973 K. This theory-guided design and experimental study suggest that SCNO is a promising candidate for IT-SOFC cathode materials.

cond-mat.mtrl-sci↗