Piezomagnetism in the Ising ferromagnet URhGe

Piezomagnetism, deformation linear in magnetic fields, is an interesting response that is allowed only in materials, which break time-reversal symmetry. However, the most classical example of time-reversal-symmetry breaking, the ferromagnet, has never been known to exhibit piezomagnetism for more than half a century after the first prediction. Here, the authors found the overlooked piezomagnetism in the ferromagnet URhGe. They observed unconventional $V$-shaped field-induced deformation using optical-fiber-based strain-gauge technique. Unique monodomain switching of Ising-like magnetization in URhGe is key to this ferromagnetic piezomagnetism.