A pyroxene-based quantum magnet with multiple magnetization plateaus.

Pyroxenes (AMXO) consisting of infinite one-dimensional edge-sharing MO chains and bridging XO tetrahedra are fertile ground for finding quantum materials. Thus, here, we have studied calcium cobalt germanate (CaCoGeO) and calcium cobalt silicate (CaCoSiO) crystals in depth. Heat capacity data show that the spins in both compounds are dominantly Ising-like, even after being manipulated by high magnetic fields. On cooling below the Néel temperatures, a sharp field-induced transition in magnetization is observed for CaCoGeO, while multiple magnetization plateaus beneath the full saturation moment are spotted for CaCoSiO. Our analysis shows that these contrasting behaviors potentially arise from the different electron configurations of germanium and silicon, in which the 3d orbitals are filled in the former but empty in the latter, enabling electron hopping. Thus, silicate tetrahedra can aid the interchain superexchange pathway between cobalt(II) ion centers, while germanate ones tend to block it during magnetization.