A 4 K to 20 K rotational-cooling magnetic refrigerator capable of 1 mW to 'gt' 1 W operation

The low-temperature, magnetic entropy of certain single-crystal paramagnetic materials, eg DyPO4 changes dramatically as the crystal rotates in a magnetic field. A new magnetic refrigerator design based on the anisotropic nature of such materials is presented. The key advantages of the rotational-cooling concept are: a single, rotary motion is required; magnetic field shaping is not a problem because the entire working material is in a constant field; and the size of the refrigerator is smaller than other comparable magnetic refrigerators because the working material is entirely inside the magnet at all times. The main disadvantage of the rotational-cooling concept is that small-dimension single crystals are required. (author)