Topochemical Crystal Transformation from a Distorted to a Nearly Perfect Kagome Cuprate

Single crystals are indispensable
for understanding the fundamental
properties of materials, although obtaining them are often challenging.
To investigate the magnetic properties of a kagome-lattice antiferromagnet,
we have performed a topochemical crystal transformation from a copper
mineral volborthite with a distorted kagome lattice into another copper
mineral vesignieite with an almost perfect kagome lattice. A millimeter-sized
crystal of vesignieite, which is difficult to prepare via direct chemical
reactions, has been successfully obtained. Magnetization measurements
on the crystals reveal a unique magnetic order with weak-ferromagnetic
moments lying within the kagome plane and successive anomalies in
the magnetization curve, which would give important information on
the magnetic order of the kagome-lattice antiferromagnet. The present
results demonstrate a novel route via the topochemical crystal transformation
in preparing a hard-to-obtain crystal.