Andreas Kaidatzis

Tailoring the magnetic anisotropy of CoFeB/MgO stacks onto W with a Ta buffer layer

The emergence of perpendicular magnetic anisotropy (PMA) in CoFeB/MgO stacks deposited on W using a Ta buffer layer is studied as a function of Ta and CoFeB layer thickness and annealing temperature. It is shown that very thin Ta “dusting” layers (thickness between 0.3 and 1 nm) enhance PMA of CoFeB layers grown on top of W. We find that Ta thickness is a crucial factor affecting magnetic anisotropy and it needs to be scaled proportionally to CoFeB thickness for obtaining PMA. Stacks without Ta have in-plane anisotropy, verifying the “PMA-enhancing” role of Ta. The maximum effective PMA energy ( 3.6×106 erg/cm3) is obtained for a stack with 1.4 nm of CoFeB and 1 nm of Ta and after annealing at 350 °C. Besides, PMA can be obtained even at the as-deposited state for certain thicknesses. This W-based CoFeB/MgO system could enable the development of low power consumption, high density, and non-volatile magnetic memories.

Nanometer Scale Hard/Soft Bilayer Magnetic Antidots.

The effect of arrays of nanometer scale pores on the magnetic properties of thin films has been analyzed. Particularly, we investigated the influence of the out-of-plane magnetization component created by the nanopores on the in-plane magnetic behavior of patterned hard/soft magnetic thin films in antidot morphology. Its influence on the coupling in Co/Py bilayers of few tens of nanometer thick is compared for disordered and ordered antidots of 35-nm diameter. The combination of magneto-optical Kerr effect (MOKE) and first-order reversal curve (FORC) technique allows probing the effects of the induced perpendicular magnetization component on the bilayer magnetic behavior, while magnetic force microscopy (MFM) is used to image it. We found that ordered antidots yield a stronger out-of-plane component than disordered ones, influencing in a similar manner the hard layer global in-plane magnetic behavior if with a thin or without soft layer. However, its influence changes with a thicker soft layer, which may be an indication of a weaker coupling.

Torsional resonance mode magnetic force microscopy: enabling higher lateral resolution magnetic imaging without topography-related effects

We present experimental work that reveals the benefits of performing magnetic force microscopy measurements employing the torsional resonance mode of cantilever oscillation. This approach provides two clear advantages: the ability of performing magnetic imaging without topography-related interference and the significant lateral resolution improvement (approximately 15%). We believe that this work demonstrates a significant improvement to a versatile magnetic imaging technique widely used in academia and in industry.

Au and Ag sputter deposition on printer paper

We study metal-coated paper for low cost sensor applications. Sputter deposition is used to coat commercially available stationary printer paper with Au or Ag thin films. Two kinds of substrates are used: copy paper and glossy photo paper. The surface morphology, coating structure and electrical resistivity of the samples is studied. We find that after deposition of a nominally 100 nm thick metal layer the templates retain their initial morphology, which is fibre-like at the copy paper and flake-like at the photo paper. The metal-coated paper is conductive in both cases, with resistivity a few times higher than the bulk value. The photo paper samples have lower resistivity than the copy paper ones. Moreover, no observable resistivity variation is observed after 8 weeks of room temperature storage in a desiccator.