Nonlinear magnetic susceptibility measurements at GPa-level pressures

The second nonlinear susceptibility, χ⁽²⁾, reflects magnetic domain formation. At zero DC field, the temperature dependence of χ⁽²⁾ can be obtained through that of the third-harmonic AC susceptibility, χ_3ω. Generally, the magnitude of χ_3ω is at most a few percent of the linear component, χ_1ω, connected with the linear susceptibility, χ⁽⁰⁾. At GPa-level pressures generated using a diamond anvil cell, the detection of χ_3ω becomes more difficult, because of the small amount of measurement sample. We propose an effective method of measuring χ_3ω using a superconducting quantum interference device magnetometer and a statistics average technique. The experimental results for an inorganic chiral magnet, Cr_1/3NbS₂, indicate the efficiency of this technique and demonstrate that magnetic signals of the order of 10^-9 emu can be detected.