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Magnetic materials are indispensable in modern day society. The vast majority of energy generation and conversion involves some kind of magnetic material, and several other applications such as data storage also use them. Despite this there are relatively few types of magnetic materials in use today, which is due to the difficulty of finding new materials that have the necessary properties. In this thesis synthesis of new magnetic materials is performed using a variety oftechniques in an attempt to identify a structured approach to finding crystal structures suited for further development.

Three approaches for developing new magnetic materials were used. Targeted substitutions of Mn was done in AlCoCrFeMn_xNi and Mn₃Co₂₀B₆, where Mn provided significant contributions to the magnetic moment, at the cost of stability of the ferromagnetic structures. A new system was identified using theoretical screening, Mn₂Co₃Ge, which was successfully synthesised. Application of the substitution method revealed properties in the system favourable for magnetic refrigeration. New systems were also discovered in synthesis attempts of Mn₂Co₃Ge and Ce-based magnets, but these materials were ferrimagnetic, or canted anti-ferromagnetic, resulting in low magnetisation.

Varying degrees of success were seen in creating magnetic materials with these approaches. Theoretical screening is likely to become an incredibly powerful tool in the future as more understanding of systems is gained. Complementing the theoretical screening method with the newly discovered structures could be a promising avenue for developing new applicable materials. Substitution of elements will remain an extremely powerful tool for tuning properties and by combining it with theoretical screening will likely be key to discovering new applicable magnet systems in the future.