**4. Key challenges of modern permanent magnets**

Design and development of permanent magnets have challenges for the intrinsic and extrinsic magnetic effects due to mechanical, thermal and chemical parameters [1]. The challenges like metallurgical processing, microstructural changes and phase stability understanding are important for the development of good permanent magnets [17, 18]. The basic properties of the magnets such as remanent magnetization and coercivity are dependent on microstructure [7]. The parameters like room temperature (*BH*)max, *M*s and *H*c, *J* diminish rapidly with increasing temperature. The fine grain size also has effect on the coercivity at high temperature [19]. Further, the packaging of magnet in operating environment should be thermodynamically stable, so that magnets will be physically stable (resistant to corrosion, decomposition or oxidation). Again, challenges differ from one another on the selection of material system, which show simultaneous high magnetization and high coercivity at any given time and environment.
