A new spin gapless semiconductors family: Quaternary Heusler compounds G. Z. Xu, E. K. Liu, Y. Du, G. J. Li, G. D. Liu, W. H. Wang and G. H. Wu EPL, 102 1 (2013) 17007 Published online: 16 April 2013 DOI: 10.1209/0295-5075/102/17007