Emerging High Coercivity and Huge Exchange Bias Effect in Single Phased Mn 1− x Ru x Co 2 O 4 Compounds

The inhomogeneous cationic distribution is an important factor determining physical properties, but it has seldom been observed in bulk. In Mn 1− x Ru x Co 2 O 4 , high‐resolution transmission electron microscopy images illustrate segregated cationic distributions in ball milled x = 0.3, x = 0.5. It facilitates magnetic phase separations and exchange couplings. Ball milled x = 0.3 is antiferromagnetic accompanied with frustrated moments with exchange bias field 14.8 kOe. The coercivity of ball milled x = 0.1 is very high, 16.5 kOe. In x = 0.2, 0.4, and 0.5, both enhanced coercivities and exchange bias effects are observed. These phenomena are related to exchange couplings. In samples with solid state reaction, high coercivities are obtained in x = 0.3 as 16.3 kOe and in x = 0.2 as 4.4 kOe, while low coercivities are observed in x ≤ 0.1 and x = 0.5. After being annealed at high pressure and high temperature, homogeneous samples without ionic segregations display low coercivity of 30 Oe. In Mn 1− x Ru x Co 2 O 4 , both the coercivity increment and the bias field are higher than those reported in multilayer interfaces or core/shell nanoparticles. This is due to the perfect interfaces between different magnetic phases in one compound. A new strategy toward high‐performance permanent magnets with high coercivities is presented.