Benchmarking Cantilever Torque Magnetometry as a Platform for Characterizing Molecular Qubits: A Case Study on Ni(II) Complexes.

Precise and experimentally accessible determination of the electronic structure of transition metal complexes remains a challenge in the development of molecular qubits, particularly for leading candidates with integer spin. Existing techniques often require large-scale facilities and substantial sample quantities or offer limited spectral access and sensitivity to subtle anisotropies. Here, we demonstrate that cantilever torque magnetometry (CTM) overcomes these limitations by combining high sensitivity to magnetic anisotropy with wide sample compatibility, minimal sample demands, and true laboratory-scale accessibility. By exploiting the distinct temperature dependences of -tensor anisotropy and zero-field splitting (ZFS), CTM enables their experimental decoupling, yielding exceptionally precise bulk-mean value determination of spin Hamiltonian parameters from microgram-scale single crystals. The parameters extracted by CTM were found to be qualitatively consistent but quantitatively different from those determined using high-frequency electron paramagnetic resonance spectroscopy (∼1% for and ∼5-15% for ZFS), highlighting that perfect agreement between magnetometric and resonance techniques is not guaranteed. Our study establishes CTM as a powerful and broadly accessible complement to magnetic resonance methods, opening new routes for high-precision characterization of low-anisotropy spin systems in molecular quantum information science.