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High-resolution alternating-field technique to determine the magnetocaloric effect of metals down to very low temperatures

The magnetocaloric effect or "magnetic Grüneisen ratio" $Γ_H=T^{-1}(dT/dH)_S$ quantifies the cooling or heating of a material when an applied magnetic field is changed under adiabatic conditions. Recently this property has attracted considerable interest in the field of quantum criticality. Here we report the development of a low-frequency alternating field technique which allows to perform continuous temperature scans of $Γ_H(T)$ on small single crystals with very high precision and down to very low temperatures. Measurements on doped YbRh$_2$Si$_2$ show that $Γ_H(T)$ can be determined with this technique in a faster and much more accurate way than by calculation from magnetization and specific heat measurements.