Magnetic coupling in 3D-hierarchical MnO2 microsphere
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The development of new routes for the synthesis of the magnetic nanostructures with low cost, simple and rapid growth has inspired as alternative materials in a wide range of applications. In this report, 3D-hierarchical MnO2 microspheres with an ultrathin nanosheet structure have been synthesized by microwave heating method. X-ray diffraction analysis exhibit the microcrystalline nature of microspheres and (211) is the major pattern with the highest intensity. High purity and surface adsorbed oxygen species have been detected by valance state of microspheres. The magnetic properties of microsphere α-MnO2 investigated experimentally and combined with density functional theory (DFT) calculations, suggest the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interaction in their nanostructures. The observed FM state is arising from noncollinear magnetic field that tilts two AFM Mn spins consequently, which make a distortion through intermediate oxygen ion in the crystal structure. While, the canted angle between two Mn sublattices lead them to a weak FM state. Similarly, the superexchange interaction is also responsible for magnetic ordering in the adjacent O ion, that can help to exchange magnetic information by direct electron hops of Mn–Mn chain. This is further confirmed from our DFT calculations. They may be found the strong potential for alternative materials other than partially oxidized metal nanoparticles.
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