Topics that shape the future
- Closer look at research results -

It originally started as a student's graduation and master's thesis research. The research theme was to join two prefabricated superconducting bulk bodies while keeping them in a superconducting state via an intermediate layer, but the student's master's thesis research suggested that "if we do this on only one side, we might be able to grow the joint part as a bulk body," which is what sparked the idea.
The project that was adopted this time aims to establish a method for growing the bulk magnets grown from these materials, and to establish a method for reproducibly producing high-temperature superconductor bulk magnets that can be used for NMR in the future.

NMR is a device that places a sample in an extremely strong magnetic field and analyzes the molecular structure of a substance through the phenomenon of nuclear magnetic resonance. Since it can obtain detailed information on molecular structures and chemical reactions in a non-destructive manner, its applications are expanding to many fields, including medicine, pharmaceuticals, chemistry, food, and materials. One familiar example is the MRI (Magnetic Resonance Imaging) diagnostic device found in hospitals, which can be considered a type of NMR that focuses on image depiction.
NMR is used in various industrial fields, but it has a major weakness in its operation. This is the large size of the device and the use of a large amount of liquid helium. Currently, in order to operate the superconducting magnet that is the core of the device, it is necessary to create an extremely low temperature environment close to absolute zero, which means that NMR has to be a huge device with high maintenance costs.

We say that materials are "grown," but bulk magnets of superconductors are usually made by growing crystals using small single crystals as "seeds." First, let us explain the conventional method of growing bulk magnets. Conventional magnets grow three-dimensionally, horizontally (sideways) and vertically (downwards), from a small seed crystal placed at the top of the pellet as a nucleus, so only simple shapes such as cylindrical shapes can be grown. Another issue is that it takes an extremely long time to grow large magnets. For example, it takes about one month to make one with a diameter of 100 mm, but the lack of reproducibility in the growth process means that "we don't know if it will be usable until we make it." While it is required to generate a strong magnetic field for NMR with even a hundred millionth of a percent of magnetic field disturbance, conventional bulk magnets, which have a mixture of horizontal and vertical growth, have difficulty achieving this extremely high homogeneity. On the other hand, in the method we are currently researching, the "Single-Direction Melt Growth (SDMG) method," existing bulk materials are cut into thin plates and used as large "seed substrates." This makes it easy to maintain homogeneity as the bulk grows in only one vertical (upward) direction, and since it is not dependent on the size in the radial (horizontal) direction, in principle the growth time does not change with increasing size, and growth can be completed in a short period of a few days. Another advantage is that it is possible to directly grow bulks of various shapes, including the ring shape required for NMR applications.

As mentioned above, the conventional method has a three-dimensional growth direction, which results in variations in quality. As a result, the area where the magnetic field is generated (trapped magnetic field), which should ideally be concentric, ends up being less circular, such as rectangular, and there is variation depending on the finished product. On the other hand, with our developed method, even when we tried products of various diameters, the trapped magnetic field was distributed in a form that was extremely close to concentric, and they all demonstrated high magnetic field performance. This shows the possibility of developing high-temperature superconductor bulk magnets with high reproducibility.

As I mentioned earlier, if NMR that does not use liquid helium is realized, the power consumption of the device will be greatly reduced. Furthermore, if a tabletop-sized device can be completed and made versatile, we may see a future in which multiple NMR devices are installed on production lines for food, organic synthesis, pharmaceuticals, etc., which could greatly contribute to improving product safety and quality. I envision a future in which the use of magnetic resonance devices will be greatly expanded after we establish technology that reduces power consumption and leads to a carbon-neutral world without relying on fossil fuels.