Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese-gallium nanoparticles

• Published in: Chinese physics B 2014-08, Vol.23 (8), p.95-98
• Main Authors: Feng, Jun-Ning, Liu, Wei, Geng, Dian-Yu, Ma, Song, Yu, Tao, Zhao, Xiao-Tian, Dai, Zhi-Ming, Zhao, Xin-Guo, Zhang, Zhi-Dong
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Coercive force; Coercivity; Decoupling; Exchange; Ferromagnetism; Joining; Nanoparticles; 二元化合物; 交流耦合; 反铁磁性; 矫顽力; 纳米颗粒; 被覆; 透射电子显微镜; 锰氧化物
• ISSN: 1674-1056; 2058-3834; 1741-4199
• DOI: 10.1088/1674-1056/23/8/087503

The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic （AFM） manganese-oxide shell and a ferromagnetic-like core of manganese-gallium （MnGa） compounds, are studied. The coreshell structure is confirmed by transmission electron microscope （TEM）. The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic （FI） DO22-type MnaGa, ferromagnetic （FM） Mn8Gas, and AFM DO19-type Mn3Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at low temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias （EB） effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe （1Oe = 79.5775 A·m^-1） and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively.