Cr3+-substituted Ba nanohexaferrites as high-quality microwave absorber in X band

Abstract

Cr3+-ion-substituted Ba nanohexaferrites (NHFs) were prepared via a sol–gel auto-combustion approach. The structural, magnetic, and microwave properties of the products were investigated by X-ray diffractometry, transmission electron microscopy, vibrating sample magnetometry, and reflection/transmission measurements in a vector network analyzer. A single barium hexaferrite phase was verified from the X-ray diffraction patterns. An average particle size of 2 μm and hexagonal crystal shapes were observed by scanning electron microscopy. Hard ferromagnetic ordering was also observed in room-temperature M–H hysteresis curves. Magnetic measurements revealed that both the saturation magnetization and coercivity of the nanoparticles decreased as the Cr3+ content increased. The substitution of Cr3+ ions in the Ba NHFs shifted the matching frequency at which microwave absorption occurs from 14 to 12 GHz. In addition, the Cr3+-ion-substituted barium NHFs showed better microwave absorption capability (−41 dB) than a pure Ba hexaferrite sample (−33 dB).