Spintronic properties in 3D and 2D magnets : uncompensated magnetism and emergent properties
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[EMBARGOED UNTIL 12/01/2026] This thesis investigates spintronic phenomena in both bulk and two-dimensional geometrically frustrated magnetic systems, unified by the theme of exploring unconventional magnetism, static and dynamic magnetic correlations, and emergent spin textures. The first part of the work focuses on the bulk intermetallic compound nickel monosilicide (NiSi), which has never yielded magnetic ground state in literature. Using neutron scattering techniques, we reveal a non-collinear uncompensated antiferromagnetic ground state with a weak ferromagnetic component with very high transition temperature of TN ≥ 700 K. This distinct magnetic structure is responsible for intriguing magnetic and transport properties that persist up to room temperature, making NiSi a promising candidate for spintronic applications. In the second part, we transition to two-dimensional frustrated magnets, where artificial honeycomb lattices were fabricated using a self-assembled diblock copolymer approach, enabling access to nanoscopic element sizes beyond photolithographic limits. We use extensive neutron scattering techniques to investigate static and dynamic behavior of a magnetic (Py) 2D honeycomb lattice. We observe here that this system hosts a highly degenerate ground state that persists against high magnetic fields. We also observe strong dynamic behavior in this system where the kinetics is mediated by magnetic charge defects arising at the vertices of the Py honeycomb lattice. An important finding from this work is that while the relaxation time of the magnetic charge defects for a thicker lattice (8.5 nm Py) increases with the increase in temperature, that for a thinner, 6 nm Py honeycomb lattice is temperature indenpendent down to the lowest temperature. This suggests quantum mechanical nature of the kinetics observed. Finally, substituting Permalloy with Neodymium surprisingly results in similar dynamic behavior, despite bulk Neodymium being an antiferromagnet below TN = 20 K and paramagnetic beyond this temperature. The kinetics could no longer be explained by migration of magnetic charge defects, it can rather be explained by formation of vortex-type micro-spin profile quasiparticles. These vortex-like magnetic quasiparticles resemble meron-like excitations and align with emerging concepts in topological spin textures. Their presence in non-magnetic hosts and realization of magnetization in special confined geometries suggests potential for low-power spintronic applications. The final chapter of this thesis further explores the static correlations in these quasiparticles by utilizing Small Angle Neutron Spectroscopy which confirms the existence of these particles in the confined geometry of the 2D Nd honeycomb lattice.
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Ph. D.