Li ions for degaussing: A Prussian blue analogue with FeIII and CuII ions bridged by CN ligands underwent a ferromagnetic transition induced by ferromagnetic interactions between the Fe and Cu ions (see picture). Li ions penetrating into this ferromagnetic framework eliminated the ferromagnetic interaction and effected the formation of a paramagnetic framework. The ferromagnetism was recovered by extracting the Li ions. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.