Microwave absorption enhancement, magnetic coupling and ab initio electronic structure of monodispersed (Mn1−xCox)3O4 nanoparticles

Abstract

Monodispersed manganese oxide (Mn_1−xCo_x)₃O₄ (0 ≤ x ≤ 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to 100 °C, without any inertia gas for protection. The influences of the Co dopant content on the critical reaction temperature required for the nanoparticle formation, electronic band structures, magnetic properties, and the microwave absorption capability of (Mn_1−xCo_x)₃O₄ are comprehensively investigated by means of both experimental and theoretical approaches including powder X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), super conductivity quantum interference device (SQUID) examination, and first-principle simulations. Co is successfully doped into the Mn atomic sites of the (Mn_1−xCo_x)₃O₄ lattice, which is further confirmed by EELS data acquired from one individual nanoparticle. Therefore, continuous solid solutions of well-crystallized (Mn_1−xCo_x)₃O₄ products are achieved without any impurity phase or phase separation. With increases in the Co dopant concentration x from 0 to 0.5, the lattice parameters change systemically, where the overall saturation magnetization at 30 K increases due to the more intense coupling of the 3d electrons between Mn and Co, as revealed by simulations. The microwave absorption properties of the (Mn_1−xCo_x)₃O₄ nanoparticles are examined between 2 and 18 GHz. The maximum absorption peak −11.0 dB of the x = 0 sample is enhanced to −11.5 dB for x = 0.2, −12.7 dB for x = 0.25, −15.6 dB for x = 0.33, and −24.0 dB for x = 0.5 respectively, suggesting the Co doping effects. Our results might provide novel insights into the understanding of the influences of metallic ion doping on the electromagnetic properties of metallic oxide nanomaterials.