Generation of strong magnetic field using 60 mmφ superconducting bulk magnet and its application to magnetron sputtering device

To make a practical application of a superconducting bulk magnet (SBM), it is necessary that the SBM generates a strong and stable magnetic field in a working space and the magnet can be handled without any special care that would be needed because of the use of a superconductor. To satisfy these requirements, we have designed a portable and user-friendly magnet system consisting of a small air-cooled type refrigerator and a bulk superconductor. By using the stress-controlling magnetization technique, we could achieve a magnetic flux density of 8.0 T on the bulk surface and 6.5 T over the vacuum chamber surface of the refrigerator, when a 60 mmφ Gd-Ba-Cu-O bulk superconductor reinforced with a 5 mm thick stainless steel ring was magnetized by field cooling in 8.5 T to 27 K. We have confirmed that the bulk magnet system coupled with a battery is quite portable and can be delivered to any location by using a car with an electric power outlet in the cabin. We have constructed a magnetron sputtering device that employs a bulk magnet system delivered from the place of magnetization by this method. This sputtering device exhibits several unique features such as deposition at a very low Ar gas pressure because the magnetic field is 20 times stronger than that obtained by a conventional device in the working space.