John Michael David Coey, known as Michael Coey (1945-2025), was a Northern Irish experimental physicist who worked on magnetism and spintronics. Born in Belfast, he read natural sciences at Cambridge and took his doctorate at the University of Manitoba in 1971, then spent seven years at the CNRS in Grenoble before joining Trinity College Dublin in 1978, where he founded and led Ireland's main magnetism research group and held the Erasmus Smith's Professorship from 2007 to 2012. With his student Sun Hong he discovered the rare-earth magnetic compound Sm2Fe17N3. He wrote the textbook Magnetism and Magnetic Materials, published more than five hundred papers, and was elected a fellow of the Royal Society in 2003.