Y. Au

Nanoscale spin wave valve and phase shifter

We have used micromagnetic simulations to demonstrate a method for controlling the amplitude and phase of spin waves propagating inside a magnonic waveguide. The method employs a nanomagnet formed on top of a magnonic waveguide. The function of the proposed device is controlled by defining the static magnetization direction of the nanomagnet. The result is a valve or phase shifter for spin waves, acting as the carrier of information for computation or data processing within the emerging spin wave logic architectures of magnonics. The proposed concept offers such technically important benefits as energy efficiency, non-volatility, and miniaturization.

Resonant microwave-to-spin-wave transducer

We use time resolved scanning Kerr microscopy and analytical and numerical calculations to demonstrate coupling of uniform global microwave field to propagating spin waves for emerging magnonic architectures. The coupling is mediated by the local dynamic dipolar field produced by the magnetization of a resonantly driven all-metallic magnetic microwave-to-spin-wave transducer. The local dipolar field can exceed that of the incident microwave field by one order of magnitude. Our numerical simulations demonstrate the ability of the transducer to unidirectionally emit coherent exchange spin waves of nanoscale wavelengths with the emission direction programmed by the magnetic state of the transducer.

Excitation of propagating spin waves with global uniform microwave fields

We demonstrate a magnonic architecture that converts global free-space uniform microwaves into spin waves propagating in a stripe magnonic waveguide. The architecture is based upon dispersion mismatch between the narrow magnonic waveguide and a wide “antenna” patch, both patterned from the same magnetic film. The spin waves injected into the waveguide travel to distances as large as several tens of micrometers. The antennas can be placed at multiple positions on a magnonic chip and used to excite mutually coherent multiple spin waves for magnonic logic operations. This demonstration paves way for “magnonics” to become a pervasive technology for information processing.

Micromagnetic Simulations in Magnonics

We review the use of numerical micromagnetic simulations (“micromagnetics”) for investigations in magnonics, the study of spin waves and their quanta – magnons. We argue that, when used with suitable post-processing tools, micromagnetics provide the power and flexibility necessary both for interpretation of complex magnonic phenomena observed in realistic magnetic structures and devices and for prediction of novel effects. We foresee that the development of multiscale and multiphysics extensions of micromagnetic solvers will broaden both the scope of micromagnetic simulations in magnonics and the field of magnonics itself. For example, the extension of micromagnetics to solvers based on atomistic spin models will underpin application of the developed methodology to studies of phenomena involving both magnons and other fundamental excitations of the solid state. In a more distant perspective, it is highly intriguing to study spin waves in non-stationary conditions (i.e. in structures with time dependent material properties), such as those realized in experiments with samples under ultrafast optical pumping.

Phase-change devices for simultaneous optical-electrical applications

We present a viable pathway to the design and characterization of phase-change devices operating in a mixed-mode optical-electrical, or optoelectronic, manner. Such devices have potential applications ranging from novel displays to optically-gated switches to reconfigurable metamaterials-based devices. With this in mind, a purpose-built optoelectronics probe station capable of simultaneous optical-electrical excitation and simultaneous optical-electrical response measurement has been designed and constructed. Two prototype phase-change devices that might exploit simultaneous optical and electrical effects and/or require simultaneous optical and electrical characterisation, namely a mixed-mode cross-bar type structure and a microheater-based structure, have been designed, fabricated and characterized. The microheater-based approach was shown to be capable of successful thermally-induced cycling, between amorphous and crystalline states, of large-area phase-change devices, making it attractive for practicable pixel fabrication in phase-change display applications.