Magnetic computing defined
Magnetic computing – in the broadest sense – is about using magnetic signals (nanomagnets, domain walls) to represent and process information. Nowadays, when “information processing” and “electronics” is synonymous, this concept sounds rather exotic. However, before the triumphant era of CMOS logic devices, non-charge based computers were serious candidates for information processing – for example, ingenious magnetic computing circuits were invented by R. J. Spain [1–3]. It was Cowburn  who first realized that the properties of nanoscale, single-domain magnets – which are very different from large, multi-domain magnets – are well suited for digital computing.
This chapter deals with one approach to magnetic computing, nanomagnet logic (or NML) [5, 6]. In NML devices, binary information is represented by the state (magnetization direction) of single domain nanomagnets and the magnetically represented information is propagated and processed by magnetic dipole–dipole interactions. From the circuit architecture point of view, NML builds on the concept of “quantum-dot cellular automata”  – they both share the idea of representing binary signals by bistable nanosystems and processing them through field-interactions. For this reason, nanomagnet logic was formerly called “magnetic quantum-dot cellular automata” (QCA), or field-coupled computing.