A magnetic force microscopy based study on the formation of stripe domains in Permalloy (Ni80Fe20) thin films is presented. Our results show that the critical thickness for stripe domain initiation depended on the sputtering rate, the substrate temperature, and the film thickness. Beyond the stripe domain formation, an increase of the period of a highly ordered array of stripe domains was evident with increasing film thickness. Thin films sputtered at room temperature with thickness variation between ∼80 and ∼350nm exhibited square-root growth dependency on stripe domains periodicity from ∼150to∼380nm, respectively. Above a certain thickness, the domain period decreased and the periodicity deteriorated with the array becoming more random, which is a strong indicator of relatively high structural perpendicular anisotropy. To illustrate, Permalloy sputtered at 100°C initially showed linear dependence in stripe domain periodicity growth up until ∼650nm thick films. The magnetic stripe domain structure began breaking down for thicker Permalloy films. Our data also suggested that the perpendicular anisotropy responsible for the formation of stripe domains might have resulted from strain-caused magnetostriction and the thin-film microstructure shape effect.

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Abstract:We investigate a tapered, hybrid plasmonic waveguide which has previously been proposed as an optically efficient near-field transducer (NFT), or component thereof, in several devices which aim to exploit nanofocused light. We numerically analyze how light is transported through the waveguide and ultimately focused via effective-mode coupling and taper optimization. Crucial dimensional parameters in this optimization process are identified that are not only necessary to achieve maximum optical throughput, but also optimum thermal performance with specific application towards heat-assisted magnetic recording (HAMR). It is shown that existing devices constructed on similar waveguides may benefit from a heat spreader to avoid deformation of the plasmonic element which we achieve with no cost to the optical efficiency. For HAMR, our design is able to surpass many industry requirements in regard to both optical and thermal efficiency using pertinent figure of merits like 8.5% optical efficiency. 503-510 (2015). 15. C. Peng, "Efficient excitation of a monopole optical transducer for near-field recording," J. Appl. Phys. 112(4), 043108 (2012). 16. X. He, L. Yang, and T. Yang, "Optical nanofocusing by tapering coupled photonic-plasmonic waveguides," Opt.Express 19

We investigate the energy conversion process and subsequent thermal and bit-writing performance of a plasmonic near-field transducer (NFT) under steady-state operation within heat-assisted magnetic recording (HAMR) devices. The NFT is composed of metal-insulator-metal (MIM) layers that are designed to localize heating and produce optimal thermal gradients in order to relieve parasitic heating effects in the NFT. The thin-film MIM structure confines the electromagnetic energy in the down-track direction while cross-track confinement is achieved by tapering the insulator feature of the MIM. A comparative analysis using Gold and a number of novel Au alloys is undertaken. Modeled performance shows excellent thermal spot confinement (50 × 50 nm2) of temperatures above 650 K at an input laser power of 830 nm of less than 5 milliwatts. In addition, micromagnetic simulations using a stochastic Landau-Lifshitz-Bloch equation yield excellent signal to noise ratio with minimum jitter of under 2 nm when recording.

The dc Josephson effect is considered from the thermodynamic point of view. Universal thermodynamic equations, relating both bound and continuum contributions to the Josephson current with the normal electron scattering amplitudes are derived for the single mode case. To derive these equations we use and further develop the method of spatial separation between the superconducting and normal parts of the junction. We also use this method to find the Andreev bound states in structures containing superconducting components. The general thermodynamic formulas are applied to the calculation of the current in various Josephson-type structures. In particular, the crucial role of the continuum contribution is demonstrated, even for short junctions (where it is usually neglected). We also find structures where the bound states supporting the giant currents are well separated; thus they can, hopefully, be populated nonuniformly and such current can be measured.