Abstract
We have developed a scanning magnetic microscope (SMM) with25 µm resolution in spatial position for the magnetic features of room temperature objects. Themicroscope consists of a high-temperature superconductor (HTS) dc SQUID sensor,suspended in vacuum with a self-adjusting standoff, close spaced liquid nitrogen Dewar,X–Y scanning stage and a computer control system. The HTS SQUIDs were optimized for better spatialand field resolutions for operation at liquid nitrogen temperature. Measured inside a magnetic shield,the 10 pT Hz−1/2 typical noise of the SQUIDs is white down to frequencies of about 10 Hz, increasing up to about20 pT Hz−1/2 at 1 Hz. The microscope is mounted on actively damped platforms, which negate vibrations from theenvironment as well as damping internal stepper motor noises. A high-resolution video telescope anda 1 µm precision z-axis positioning system allow a close positioning of the sample under the sensor. Theability of the sensors to operate in unshielded environmental conditions with magneticfields up to about 15 G allowed us to perform 2D mapping of the local ac and dcsusceptibility of the objects.
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