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A new class of rare-earth-free permanent magnets is proposed. The parentcompound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result offirst principles theory combined with experimental synthesis andcharacterisation. The theory is based on a high-throughput/data-mining searchamong materials listed in the ICSD database. From ab-initio theory of thedefect free material it is predicted that the saturation magnetization is 1.71T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curietemperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized andcharacterised with respect to structure and magnetism. The crystal structurewas found to be the MgZn$_2$-type, with partial disorder of Co and Ge on thecrystallographic lattice sites. From magnetization measurements a saturationpolarization of 0.86 T at 10 K was detected, together with a uniaxialmagnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curietemperature of $T_{\rm C}$ = 359 K. These magnetic properties makeCo$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet,and since we can demonstrate that magnetism depends critically on the amount ofdisorder of the Co and Ge atoms, a further improvement of the magnetism ispossible. From the theoretical works, a substitution of Ge by neighboringelements suggest two other promising materials - Co$_3$Mn$_2$Al andCo$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on$T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in theMgZn$_2$ structure type, form a new class of rare-earth free permanent magnetswith very promising performance.

Data-driven design of a new class of rare-earth free permanent magnets