  Using modern crystal structure prediction program (CALYPSO), we searched many
experimentally synthesizable low-energy structures with perfect or nearly
perfect easy-axis magnetocrystalline anisotropy energy (MAE) in manganese
nitride, including MnN, Mn2N, Mn3N2, Mn5N2, Mn4N, respectively, which are the
more frequently studied stoichiometries by experimental researchers. MnN (
I-42d) shows giant MAE with values of E001=1006, E010=0, E100=920 ueV/atom
(same hereinafter), respectively. One perfect easy-axis MAE in Mn3N2 (P42/mmc)
with correspondent values of E010=E100=12 is observed, the other nearly perfect
easy-axis MAE one (Ibam) with respective values of E001=324 and E010=345 is
observed. Four almost totally perfect easy-axis MAE structures are obtained in
Mn2N, including P4/mmm with individual E001=249 and E100=250, Pccm with
E001=E100=62, P4/nmm with E001=58 and E100=60, Imma with E001=108 and E100=109,
respectively. Three structures including one perfect candidates are found in
Mn4N, including Fmmm with individual E001=126 and E010=121, I4/mmm with
E010=127 and E100=133, I4/mmm with E001= E100=169, respectively. Too many
valuable structures are deserved to be further studied by both theoretical and
experimental scientists. The present study might attract close attention to
these several compounds.
