Naganivetha Thiyagarajah

Designing a fully compensated half-metallic ferrimagnet

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

Giant spontaneous Hall effect in zero-moment Mn2RuxGa

Here the authors report on the temperature, Ru concentration and substrate-induced strain dependence of the transport properties of MRG at or near the compensation point . Two sets of samples by co-sputtering from and Mn2Ga and Ru targets: (i) where the Ru concentration is constant at x ~ 1 and the strain (Δc/a) is varied from 1 .8% to 3 .6% and (ii) where the strain is constant at ~1 .9% and x is varied from 0 .62 to 1.1. The spontaneous Hall effect (SHE) of the samples are measured in a physical properties measurement system, with a maximum applied field of 12 T and a temperature range of 400 K to 10 K . We show that there is a temperature Tcomp, in most of the samples, depending both on x, and (Δc/a) where the overall magnetization is perfectly compensated.

Tunnelling magnetoresistance of the half-metallic compensated ferrimagnet Mn2RuxGa

Tunnel magnetoresistance ratios of up to 40% are measured between 10u2009K and 300u2009K when the highly spin-polarized compensated ferrimagnet, Mn2RuxGa, is integrated into MgO-based perpendicular magnetic tunnel junctions. Temperature and bias dependences of the tunnel magnetoresistance effect, with a sign change near −0.2u2009V, reflect the structure of the Mn2RuxGa interface density of states. Despite magnetic moment vanishing at a compensation temperature of 200u2009K for x≈0.8, the tunnel magnetoresistance ratio remains non-zero throughout the compensation region, demonstrating that the spin-transport is governed by one of the Mn sub-lattices only. Broad temperature range magnetic field immunity of at least 0.5u2009T is demonstrated in the same sample. The high spin polarization and perpendicular magnetic anisotropy make Mn2RuxGa suitable for applications in both non-volatile magnetic random access memory cells and terahertz spin-transfer oscillators.

Perpendicular exchange bias effect in sputter-deposited CoFe/IrMn bilayers

CoFe/IrMn bilayers with perpendicular magnetization for various IrMn layer thicknesses exhibit unusual two-step hysteresis loops with both positive and negative loop shifts. Observed at room temperature in the as-grown state, they provide direct evidence of large antiferromagnetic domain formation at the IrMn interface. The exchange bias field reaches 100u2009mT with an IrMn layer thickness of 4u2009nm after field annealing at 200u2009°C–300u2009°C in 800u2009mT, which is at least three times as large as the coercivity, and may be useful for reference layers of spin-valves or magnetic tunnel junctions with perpendicular magnetic anisotropy.

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.

Giant spontaneous hall effect in zero-moment Mn 2 Ru x Ga

Cubic ferromagnetic Heusler compounds which can exhibit higher spin polarization at the Fermi level than any binary 3d ferromagnetic alloy, are promising materials for applications in spin-valves and MTJs. [1] We have previously reported on the growth of cubic Mn 2 Ru x Ga (MRG), [2] which is the first experimental realization of a zero-moment compensated ferrimagnet, that shows signs of half-metallicity, as predicted by de Groot and van Leuken. [3]. In MRG the Mn occupies two inequivalent crystallographic positions; 4a and 4c. Perfect compensation is achieved when the two inequivalent Mn sublattices have equal and opposite magnetizations.

Magnetization Switching and Hall Effect in Co/Pd-Based Pseudospin-Valves With Perpendicular Magnetic Anisotropy

Magnetoresistance (MR), extraordinary Hall effect (EHE), planar Hall effect (PHE), and low-frequency noise are measured on pseudospin-valves based on Co/Pd multilayers with perpendicular magnetic anisotropy. In unpatterned films, a current-in-plane MR of 3.8% was obtained with a Cu spacer layer thickness of 2.0 nm. Large anomalous peaks observed in EHE and PHE in the narrow range of field where switching occurs are associated with multidomain magnetization during the reversal process. Magnetic field-and time-dependent noise indicates that the magnitude of the noise is directly related to magnetization switching in this system.