Magnetic Sensing Potential of Fe₃O₄ Nanocubes\nExceeds That of Fe₃O₄ Nanospheres

Abstract

This paper highlights the relation\nbetween the shape of iron oxide\n(Fe₃O₄) particles and their magnetic sensing\nability. We synthesized Fe₃O₄ nanocubes and\nnanospheres having tunable sizes via solvothermal and thermal decomposition\nsynthesis reactions, respectively, to obtain samples in which the\nvolumes and body diagonals/diameters were equivalent. Vibrating sample\nmagnetometry (VSM) data showed that the saturation magnetization (<i>M</i>_s) and coercivity of 100–225 nm cubic\nmagnetic nanoparticles (MNPs) were, respectively, 1.4–3.0 and\n1.1–8.4 times those of spherical MNPs on a same-volume and\nsame-body diagonal/diameter basis. The Curie temperature for the cubic\nFe₃O₄ MNPs for each size was also higher than\nthat of the corresponding spherical MNPs; furthermore, the cubic Fe₃O₄ MNPs were more crystalline than the corresponding\nspherical MNPs. For applications relying on both higher contact area\nand enhanced magnetic properties, higher-<i>M</i>_s Fe₃O₄ nanocubes offer distinct advantages\nover Fe₃O₄ nanospheres of the same-volume or\nsame-body diagonal/diameter. We evaluated the sensing potential of\nour synthesized MNPs using giant magnetoresistive (GMR) sensing and force-induced remnant magnetization\nspectroscopy (FIRMS). Preliminary data obtained by GMR sensing confirmed\nthat the nanocubes exhibited a distinct sensitivity advantage over\nthe nanospheres. Similarly, FIRMS data showed that when subjected\nto the same force at the same initial concentration, a greater number\nof nanocubes remained bound to the sensor surface because of higher\nsurface contact area. Because greater binding and higher <i>M</i>_s translate to stronger signal and better analytical sensitivity,\nnanocubes are an attractive alternative to nanospheres in sensing\napplications.