Ising spin ladders of orthopyroxene CoGeO${}_3$

We present thermodynamic and spectroscopic measurements for an orthopyroxene CoGeO${}_3$ with magnetic Co${}^{2+}$ ions that form quasi-one-dimensional ladders. We show that non-collinear magnetic order below $T_N$=32 K can be stabilized by a strong local easy-axis anisotropy of $j_{\text{eff}}=1\mathrm{/}2$ moments, which is induced by ligand octahedra distortions. Extraction of a magnetic Hamiltonian from inelastic neutron scattering measurements supports this interpretation and allows us to establish an effective magnetic model. The resulting exchange Hamiltonian justifies CoGeO${}_3$ as a realization of an Ising spin ladder compound.