VP15-06 Improving Reciprocating SQUID Magnetometry by Explicit Response Linearization
Creators: Plamen Stamenov
Publisher: name: IEEE
Year: 2025

Contemporary magnetometry is widely used by physicists, chemists and material scientists as a routine technique for sample characterization of both bulk and thin film materials. Its most popular modality: the SQUID-based, superconducting second-order gradiometer magnetometry has become the de facto standard. A decade ago, the go-to systems were primarily extraction-style, operating at low frequencies (~ 1 Hz), e.g. the popular by QD MPMS system. Lately, higher frequency (many 10ns of Hz), shorter linear drives, such as the one of the MPMS3 SQUID-VSM, by the same vendor, are gaining popularity. An overall higher sample throughput demands different design solutions and the benefits must be paid by compromises elsewhere: e. g. shorter maximal translation span and narrower gradiometers, yielding increased sample geometry- and position-dependent systematic errors. Here, we focus on the analysis of the temporal spectral components produced by the rather non-linear Point Spread Function (PTF) [1] and formulate a strategy for the minimization of the same for any particular choice of sample geometry restrictions. While at frequencies over few 10ns of Hz the main source of interference is mains-power induction, a typical large amplitude oscillation of the sample is generating primarily even harmonics of the drive frequency, whose low-frequency spectrum is overlapping with typical digital communication interference as shown on the figure. Following drive waveform modification, only the second harmonic survives, significantly enhancing the filtering possibilities and thus diminishing the noise and interference pickup. This methodology is applicable to both small-amplitude VSM-type oscillations and large-amplitude, low frequency sample reciprocation, necessitated by the mass of certain custom probe types, such as FMR rods [2] and liquid sample mounts.References: [1] P. Stamenov and J.M.D. Coey, Rev. Sci. Instr. 77, 015106 (2006) [2] J. M. O’Reilly and P. Stamenov, Rev. Sci. Instr. 89, 044701 (2018)
Contemporary magnetometry is widely used by physicists, chemists and material scientists as a routine technique for sample characterization of both bulk and thin film materials. Its most popular modality: the SQUID-based, superconducting second-order gradiometer magnetometry has become the de facto standard. A decade ago, the go-to systems were primarily extraction-style, operating at low frequencies (~ 1 Hz), e.g. the popular by QD MPMS system. Lately, higher frequency (many 10ns of Hz), shorter linear drives, such as the one of the MPMS3 SQUID-VSM, by the same vendor, are gaining popularity. An overall higher sample throughput demands different design solutions and the benefits must be paid by compromises elsewhere: e. g. shorter maximal translation span and narrower gradiometers, yielding increased sample geometry- and position-dependent systematic errors. Here, we focus on the analysis of the temporal spectral components produced by the rather non-linear Point Spread Function (PTF) [1] and formulate a strategy for the minimization of the same for any particular choice of sample geometry restrictions. While at frequencies over few 10ns of Hz the main source of interference is mains-power induction, a typical large amplitude oscillation of the sample is generating primarily even harmonics of the drive frequency, whose low-frequency spectrum is overlapping with typical digital communication interference as shown on the figure. Following drive waveform modification, only the second harmonic survives, significantly enhancing the filtering possibilities and thus diminishing the noise and interference pickup. This methodology is applicable to both small-amplitude VSM-type oscillations and large-amplitude, low frequency sample reciprocation, necessitated by the mass of certain custom probe types, such as FMR rods [2] and liquid sample mounts.References: [1] P. Stamenov and J.M.D. Coey, Rev. Sci. Instr. 77, 015106 (2006) [2] J. M. O’Reilly and P. Stamenov, Rev. Sci. Instr. 89, 044701 (2018)