Environment-friendly bulk Fe16N2 permanent magnet: Review and prospective

•α″-Fe16N2 was viewed as a mystery material because of inconclusive arguments in 1990s, including many controversial reports at two specific symposia at MMM conferences.•Then the topic was largely dropped by the magnetic research community.•The key controversies around this material have been successfully addressed through our long and persistent effort from 2002 to 2012, which was reported at APS Marching Meeting 2010 and INTERMAG 2012.•Since then, α″-Fe16N2 has been picked up as one of the most promising rare-earth-free magnet candidates because of its usage of environment-friendly raw materials, its confirmed giant saturation magnetization and reasonably high magnetic anisotropy constant.•Iron nitride magnet is of great interest as a magnetic material for the applications at relatively low temperature (