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Nanocavity optomechanical torque magnetometry and radiofrequency susceptometry


Nanophotonic optomechanical devices allow the observation of nanoscale vibrations with a sensitivity that has dramatically advanced the metrology of nanomechanical structures1,2,3,4,5,6,7,8,9 and has the potential to impact studies of nanoscale physical systems in a similar manner10,11. Here we demonstrate this potential with a nanophotonic optomechanical torque magnetometer and radiofrequency (RF) magnetic susceptometer. Exquisite readout sensitivity provided by a nanocavity integrated within a torsional nanomechanical resonator enables observations of the unique net magnetization and RF-driven responses of single mesoscopic magnetic structures in ambient conditions. The magnetic moment resolution is sufficient for the observation of Barkhausen steps in the magnetic hysteresis of a lithographically patterned permalloy island12. In addition, significantly enhanced RF susceptibility is found over narrow field ranges and attributed to thermally assisted driven hopping of a magnetic vortex core between neighbouring pinning sites13. The on-chip magnetosusceptometer scheme offers a promising path to powerful integrated cavity optomechanical devices for the quantitative characterization of magnetic micro- and nanosystems in science and technology.

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Figure 1: Split-beam nanocavity.
Figure 2: Measurement set-up and spectral response.
Figure 3: Magnetic hysteresis of the permalloy island.
Figure 4: Enhanced room-temperature magnetic susceptibility at Barkhausen steps.


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This work is supported by the Natural Science and Engineering Research Council of Canada, Canada Research Chairs, the Canada Foundation for Innovation and Alberta Innovates Technology Futures. Many thanks to A. Hryciw, M. Mitchell, M. Belov and D. Fortin for their technical contributions. We also thank the staff of the nanofabrication facilities at the University of Alberta and at the National Institute for Nanotechnology as well as the machinists at the University of Calgary Science Workshop for their technical support.

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Authors and Affiliations



P.E.B. and M.R.F. conceived and supervised the project. M.W. and N.L.-Y.W. designed and fabricated the devices. N.L.-Y.W. imaged the devices. M.W. set up the measurement equipment, including the fibre taper. M.W., N.L.-Y.W. and T.F. performed measurements on the device. M.W., N.L.-Y.W., T.F. and F.F. analysed the data. M.W. and N.L.-Y.W. prepared the figures. F.F. and T.F. contributed simulations to the manuscript. F.F. helped with the theoretical framework for the RF susceptibility mixing scheme in the supplementary material. J.E.L. provided guidance and technical assistance with the instrumentation and measurements. All the co-authors contributed to and proofread the manuscript.

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Correspondence to Mark R. Freeman or Paul E. Barclay.

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The authors declare no competing financial interests.

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Wu, M., Wu, NY., Firdous, T. et al. Nanocavity optomechanical torque magnetometry and radiofrequency susceptometry. Nature Nanotech 12, 127–131 (2017).

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