Heat regenerating material particle, regenerator, refrigerator, superconducting magnet, nuclear magnetic resonance imaging device, nuclear magnetic resonance device, cryopump, and single-crystal pulling device of magnetic-field application type

A heat regenerating material particle comprising:

• a heat regenerating substance having a maximum value of specific heat at a temperature of 20 K or less of 0.3 J/cm3·K or more:
• and
• one metal element selected from the group consisting of calcium (Ca), magnesium (Mg), beryllium (Be), strontium (Sr), aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), and cobalt (Co),
• wherein the heat regenerating material particle includes a first region and a second region, the second region is closer to an outer edge of the heat regenerating material particle than the first region, and the second region has a higher concentration of the metal element than the first region,
• the first region and the second region contain the heat regenerating substance, and
• the heat regenerating substance contains a component in a form of an oxide or an oxysulfide.