Parallel pumping for magnon spintronics: Amplification and manipulation of magnon spin currents on the micron-scale

Magnonics and magnon spintronics aim at the utilization of spin waves and magnons, their quanta, for the construction of wave-based logic networks via the generation of pure all-magnon spin currents and their interfacing with electrical charge transport. The promise of efficient parallel data processing and low power consumption renders this field one of the most promising research areas in spintronics. In this context, the process of parallel parametric amplification, i.e., the conversion of microwave photons into magnons at one half of the microwave frequency, has proven to be a versatile tool. Its beneficial and unique properties, such as frequency and mode-selectivity, the possibility to excite spin waves in a wide wavevector range and the creation of phase-correlated wave pairs, render it one of the key methods of spin-wave generation and amplification. The application of parallel parametric amplification to micro- and nanostructures is an important step towards the realization of magnonic networks. This is motivated not only by the fact that amplifiers are an important tool for the construction of any extended logic network but also by the unique properties of parallel parametric amplification, such as a phase-dependent amplification. Recently, the successful application of parallel parametric amplification to metallic microstructures has been reported. It has been demonstrated that parametric amplification provides an excellent tool to generate and to amplify spin waves in these systems. In particular, the amplification greatly benefits from the discreteness of the spin-wave spectra. This opens up new, interesting routes of spin-wave amplification and manipulation. In this Review, we give an overview over the recent developments and achievements in this field.