Physical and Magnetic Properties of [Co/Pd] based Spin-Valves with Perpendicular Anisotropy for Spintronic Device Application

Ph.DDOCTOR OF PHILOSOPH

Magneto-optic Kerr effect in a spin-polarized zero-moment ferrimagnet

The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to the magnetisation of a magnetically ordered metallic sample; in metallic ferrimagnets with chemically distinct sublattices, such as rare-earth transition-metal alloys, it depends on the difference between the sublattice contributions. Here we show that in a highly spin polarized, fully compensated ferrimagnet, where the sublattices are chemically similar, MOKE is observed even when the net moment is strictly zero. We analyse the spectral ellipsometry and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a highly spin-polarized conduction band dominated by one of the two manganese sublattices which creates helicity-dependent reflectivity determined by a broad Drude tail. Our findings open new prospects for studying spin dynamics in the infra-red.Comment: 7 pages, 7 figure

Designing a fully compensated half-metallic ferrimagnet

Recent experimental work on Mn2RuxGa demonstrates its potential as a compensated ferrimagnetic half-metal (CFHM). Here we present a set of high-throughput ab initio density functional theory calculations and detailed experimental characterisation, that enable us to correctly describe the nominal Mn2RuxGa thin films, in particular with regard to site-disorder and defects. We then construct models that accurately capture all the key features of the Mn-Ru-Ga system, including magnetic compensation and the spin gap at the Fermi level. We find that electronic doping is neccessary, which is achieved with a Mn/Ga ratio smaller than two. Our study shows how composition and substrate-induced biaxial strain can be combined to design a ferrimagnetic half-metal with a compensation point close to room temperature

The zero-moment half metal: How could it change spin electronics?

The Heusler compound Mn2RuxGa (MRG) may well be the first compensated half metal. Here, the structural, magnetic and transport properties of thin films of MRG are discussed. There is evidence of half-metallicity up to x = 0.7, and compensation of the two Mn sublattice moments is observed at specific compositions and temperatures, leading to a zero-moment half metal. There are potential benefits for using such films with perpendicular anisotropy for spin-torque magnetic tunnel junctions and oscillators, such as low critical current, high tunnel magnetoresistance ratio, insensitivity to external fields and resonance frequency in the THz range

Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully compensated half-metallic Mn2RuxGa thin films

Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn2RuxGa in pulsed magnetic fields of up to 58T. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature (155K), where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673Ω−1 m−1 and the coercivity exceeds 9T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216kJm−3 and predict the magnetic resonances frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems

Directed Self-Assembly of Densely Packed Gold Nanoparticles

Directing the self-assembly of sub-10-nm nanoparticles has been challenging because of the simultaneous requirements to achieve a densely packed monolayer and rearrange nanoparticles to assemble within a template. We met both requirements by separating the processes into two steps by first forming a monolayer of gold nanoparticles on a suitable liquid subphase of anisole and then transferring it edgewise onto a silicon substrate with a prepatterned template comprising nanoposts and nanogratings. Doing so resulted in nanoparticles that assembled in commensuration with the template design while exhibiting appreciable template-induced strain. These dense arrays of nanostructures could either be directly applied or used as lithographic masks in applications for light collection, chemical sensing, and data storage

A facile approach for screening isolated nanomagnetic behavior for bit-patterned media

10.1088/0957-4484/25/22/225203Nanotechnology2522-NNOT