Correlating changes of the unit cell parameters and microstructure with magnetic properties in the CeFe11Ti compound

Highlights: • A comprehensive study of ThMn12-type Ce(Fe,Ti)₁₂ material system. • Twinned grains of CeFe₁₁Ti with misorientation angle of 58^∘± 2^∘. • Invar-type anomaly at the Curie temperature of CeFe₁₁Ti. • Reduction of anisotropy field of CeFe₁₁Ti under hydrostatic pressure in contrast to an increase for chemical expansion of CeFe₁₁TiHx. -- Abstract: The criticality of rare-earth elements and its impact on the permanent magnet market have initiated a search for alternative material systems, either to fill the magnetic performance gap between ferrites and Nd-Fe-B magnets or to even replace the existing benchmark systems. Ce-based systems are attractive due to the abundance of cerium, however the formation of secondary phases leads to challenges for Ce-based compounds. We investigated the formation and magnetic properties of ThMn₁₂-type Ce_1+xFe₁₁Ti samples for x = 0.15 and 0.20 compositions. Microstructural investigations reveal the formation of twin boundaries in the ThMn₁₂ grains with a misorientation angle of 58^∘± 2^∘. By varying the chemical composition and lowering the annealing temperatures, a grain refinement and reduction in twin boundary density was achieved. In addition, the magnetostrictive characteristic of CeFe₁₁Ti-phase was investigated. Around the Curie temperature, an M² behaviour is noted, in contrast to an M³ behaviour at lower temperatures. To probe the effect of unit cell compression and expansion on the magnetic properties, magnetic characterizations were carried out under hydrostatic pressure and after hydrogenation. A slight reduction is observed for the measured anisotropy field under 0.45 GPa hydrostatic pressure in the temperature interval of 10–300 K, which is consistent with the small increase detected for the hydrogenated compound.