Understanding YIG – the magnetic properties of an artificial garnet

14 November 2017

Researchers from the University of Oxford have for the first time mapped the magnetic interactions of an artificial garnet known as YIG (yttrium iron garnet). This understanding could pave the way for the ‘magnonics’ revolution, which offers an entirely new way to transfer data.

Fig. 1Fig. 1: a) Atomic structure of YIG. b) Atomic structure of metallic iron. c) A crystal of YIG

YIG is already used in a broad range of technological devices, from microphones to lasers. However, it is also a key candidate for magnonics – the process of transferring information via variations in a material’s magnetic properties. If YIG is to fulfil this potential, its magnetic properties, particularly at room temperature, need to be well understood.
Fig. 2Fig. 2: Left: Measured neutron scattering data on a crystal of YIG. The vertical axis is the amount of energy the neutron loses when scattering, and the horizontal axis is the amount of momentum lost by the neutron. Right: the computer model.

At the very lowest temperatures – near to absolute zero – YIG can be understood as a conventional ferromagnet (like a bar magnet made of iron), and existing measurements, made almost 40 years ago, are adequate. However, the complexities of YIG (shown alongside iron in Fig. 1) are much more difficult to understand in detail.

Dr Andrew Princep and a team from Oxford University (with colleagues from the ISIS neutron and muon source, the Paul Scherrer Institut in Switzerland, and the German research association INNOVENT) have now measured the microscopic forces that control the magnetic properties of YIG. The researchers used a large, flawless crystal of YIG (equivalent to over 60 carats), grown by INNOVENT. The measurements, which took more than 200 hours with the MAPS spectrometer at ISIS, entailed studying the interactions of neutrons with the magnetic fields of the crystal’s atoms.

Using sophisticated computer modelling techniques, the researchers moreover were able to fully reproduce the data (Fig. 2), which tell a complicated story about the magnetic interactions between iron atoms in YIG. These results can be used to understand and predict in detail the magnetic behaviour of YIG at room temperature, and bring the prospect of YIG magnonics one step closer.

A. J. Princep et. al. “The full magnon spectrum of yttrium iron garnet” NPJ Quant. Mat. DOI: 10.1038/s41535-017-0067-y