Aaron J. Rosenberg

Scanning SQUID susceptometers with sub-micron spatial resolution

Superconducting QUantum Interference Device (SQUID) microscopy has excellent magnetic field sensitivity, but suffers from modest spatial resolution when compared with other scanning probes. This spatial resolution is determined by both the size of the field sensitive area and the spacing between this area and the sample surface. In this paper we describe scanning SQUID susceptometers that achieve sub-micron spatial resolution while retaining a white noise floor flux sensitivity of ≈2μΦ0/Hz1/2. This high spatial resolution is accomplished by deep sub-micron feature sizes, well shielded pickup loops fabricated using a planarized process, and a deep etch step that minimizes the spacing between the sample surface and the SQUID pickup loop. We describe the design, modeling, fabrication, and testing of these sensors. Although sub-micron spatial resolution has been achieved previously in scanning SQUID sensors, our sensors not only achieve high spatial resolution but also have integrated modulation coils for flux feedback, integrated field coils for susceptibility measurements, and batch processing. They are therefore a generally applicable tool for imaging sample magnetization, currents, and susceptibilities with higher spatial resolution than previous susceptometers.

Magnetic coupling at rare earth ferromagnet/transition metal ferromagnet interfaces: A comprehensive study of Gd/Ni.

T. D. C. Higgs, S. Bonetti, ∗ H. Ohldag, N. Banerjee, X. L. Wang, A. J. Rosenberg, Z. Cai, J. H. Zhao, K. A. Moler, and J. W. A. Robinson † Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS, Cambridge, United Kingdom Department of Physics, Stanford University, Stanford, CA 94305, USA SLAC National Accelerator Laboratory, California 94025, USA State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA‡ (Dated: June 1, 2015)Thin film magnetic heterostructures with competing interfacial coupling and Zeeman energy provide a fertile ground to study phase transition between different equilibrium states as a function of external magnetic field and temperature. A rare-earth (RE)/transition metal (TM) ferromagnetic multilayer is a classic example where the magnetic state is determined by a competition between the Zeeman energy and antiferromagnetic interfacial exchange coupling energy. Technologically, such structures offer the possibility to engineer the macroscopic magnetic response by tuning the microscopic interactions between the layers. We have performed an exhaustive study of nickel/gadolinium as a model system for understanding RE/TM multilayers using the element-specific measurement technique x-ray magnetic circular dichroism, and determined the full magnetic state diagrams as a function of temperature and magnetic layer thickness. We compare our results to a modified Stoner-Wohlfarth-based model and provide evidence of a thickness-dependent transition to a magnetic fan state which is critical in understanding magnetoresistance effects in RE/TM systems. The results provide important insight for spintronics and superconducting spintronics where engineering tunable magnetic inhomogeneity is key for certain applications.

Electric coupling in scanning SQUID measurements

Scanning SQUID is a local magnetometer which can image flux through its pickup loop due to DC magnetic fields (

The response of small SQUID pickup loops to magnetic fields

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Scanning SQUID sampler with 40-ps time resolution

). Scanning SQUID can also measure a samples magnetic response to an applied current (

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3 : APS

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Determining the vibrations between sensor and sample in SQUID microscopy

) or voltage (

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO

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Scanning-SQUID investigation of spin-orbit torque acting on yttrium iron garnet devices

) using standard lock-in techniques. In this manuscript, we demonstrate that electric coupling between the scanning SQUID and a back gate-tuned, magnetic sample can lead to a gate-voltage dependent artifact when imaging

Imaging Spatially Varying Magnetic Order in Proximity Induced Magnetic Topological Insulator

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