Candidate for a fully frustrated square lattice in a verdazyl-based salt

Frustrated spin systems prevent the formation of conventional magnetic order and can form an entangled spin state. A frustrated square lattice with only nearest-neighbor interactions is called a fully frustrated square lattice (FFSL) and expected to exhibit strong quantum fluctuations. Here, the authors present an experimental realization of an $S$=\textonehalf{} FFSL composed of a verdazyl-based salt. $A\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations indicate the formation of an FFSL with competing ferro- and antiferromagnetic nearest-neighbor interactions. The magnetic behavior demonstrates that the system forms a quantum valence-bond solid state. This material provides a way to realize a variety of $S$=\textonehalf{} FFSLs through the molecular design method, proposed here.