Low Frequency Field Modulation Differential Magnetometer; Applications to the De Haas-Van Alphen Effect

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Abstract
Low frequency field modulation techniques (FMT) for measurements of differential magnetic susceptibility are discussed and specific applications to the de Haas‐van Alphen effect are analyzed. The method utilizes a small ac modulating field which is superimposed on a large applied dc magnetic field. Differential changes in magnetization of the sample are synchronously detected with the aid of a suitable arrangement of pickup coils. The FMT is applicable to a wide variety of magnetic measurements and is particularly valuable for de Haas‐van Alphen or magnetic transition studies at high magnetic fields. Advantages of this technique include: simplicity, versatility, direct applicability to axial high field water‐cooled and superconducting solenoids or transverse magnets, high differential sensitivity (dσ/dB=3×10−6 emu/gG), convenient access to the sample environment, and use of standard commercially available electronic components. Details of the detection coil assembly, sample rotation devices, and low temperature accessories are presented along with a general discussion of the data processing techniques. Modifications for transverse field modulation and accurate orientation of the dc or modulation field with respect to the sample are also discussed.