In recent years the composite spring exchange magnets have

In recent years, the composite spring exchange magnets have attracted considerable attentions due to the prediction for getting higher magnetic CC0651 product (BH)max[1]. Early in the 1990s, the concept of the exchange spring coupling behavior in composite magnets was proposed first. According to the exchange spring concept, exchange coupled composite permanent magnets can have magnetic properties by combining the high magnetic anisotropy of the hard phase and the high saturation magnetization of the soft phase, which are superior to those of single-phase magnets and exhibit high (BH)max[1], [2] and [3]. Previous studies of permanent magnets with high (BH)max mainly focus on alloy composites [4], [5], [6] and [7]. The alloy composites have a very high (BH)max but the cost of preparation is high and the corrosion resistance is poor. In contrast, the hard ferrites can overcome extracellular digestion shortcomings. It has low cost, excellent chemical stability, and corrosion resistance, but the (BH)max is low, which seriously hinders the applications. Hence, improving the (BH)max of hard ferrites is inevitable.