The portable magnet could make possible sensitive, high-resolution NMR devices that can be taken to an archaeological dig to identify artifacts and to a factory to detect contamination in products. It could be used in doctors' offices to spot blood clots, bacteria, or cancer proteins in a patient's blood. It could also allow portable NMR machines to monitor the production of drugs and chemicals in-line instead of taking chemical samples to NMR labs for analysis.

Casanova and his colleagues have tweaked a well-known magnet design known as a Halbach array, a special arrangement of many permanent magnets that focuses magnetic fields only on one side of the array. One common design is a Halbach cylinder, which has an intense magnetic field inside the cylinder. This is what the researchers start with. As they describe in a paper posted online in the journal Angewandte Chemie, they first stack three rings of samarium cobalt to make the cylinder. The cylinder's outside diameter is 35 millimeters; the inside diameter of 15 millimeters is large enough to hold a standard NMR tube.

Each magnet ring is made of trapezoid-shaped pieces with gaps in between. These gaps are filled with rectangular pieces that move in and out by up to two millimeters. The researchers measure the inhomogeneity in the magnetic field created by the Halbach rings. Then, with the aid of sophisticated computer simulations, they calculate how much they need to move each of the rectangular pieces to adjust the magnetic field and smooth out inhomogeneities.

Even better magnets might be possible by fine-tuning the design, the researchers say. While the magnet's field strength is 0.7 tesla right now, increasing the outer diameter of the magnet should make it possible to generate 1.5 tesla, the researchers say. What is more, using magnets made of other materials such as neodymium, as much as two tesla could be generated.