Magnetic Properties of ZnO Nanoparticles

Abstract

In this work it is experimentally shown that capping ZnO nanoparticles with organic molecules leads to the appearance of magnetism at room temperature.The bonds between the molecules and the Zn atoms at the nanoparticle surface alter its electronic structure (as XANES and photoluminescence spectra demonstrate) arising magnetic moments with values that depend on the nature of the molecule. This result points out the possibility to observe magnetism at nanoscale in semiconductors without typical magnetic atoms (transition metals and rare earths).

Magnetism in Dopant-Free ZnO Nanoplates

“…Therefore, all of the experimental results support the existence of a magnetic moment in the nanoplates but not in bulk or nanowires of ZnO, and it is thought that the origin of the magnetic moment in the nanoplate is the modified electronic band structure due to the reduced dimension along the c-axis direction. This is consistent with the previous study by Garcia et al 28 in which modified surface electronic states of ZnO nanoparticle are responsible for a measurable magnetic moment in pure ZnO, In summary, it has been demonstrated that a magnetic moment can be induced into nominally nonmagnetic ZnO by reducing the dimension to a few nanometers along the c-axis direction. Size reduction of ZnO along the a-or b-axis direction results in the shape of a nanowire, which does not carry a magnetic moment.…”

Evidence of intrinsic magnetism in capped ZnO nanoparticles

“…Indeed, the observed variation in the XANES, magnetization and photoluminescence spectra through the TOPO-AMINE-THIOL is just the opposite to that previously reported on similar samples. 8 This result points out that the magnetic behavior is not associated with the electronegativity of the surrounding atoms, as previously proposed, 8 but to the particular structural arrangement of these bonds at the surface of the NPs.…”

“…The value of the saturation magnetization, ϳ2 memu/ g, is in agreement with the values previously reported although the dependence with the capping molecule is fairly different. 8 From Fig. 4͑d͒, where the magnetization curves at 5 K after subtracting the diamagnetic component are shown, it is observed that the paramagnetic contribution is fairly larger than the ferromagnetic one.…”

“…[2][3][4] Actually, several recent reports claimed the observation of ferromagnetism in semiconductor and insulating oxide nanostructures without any doping despite the diamagnetic character of the material in bulk. [5][6][7][8] Among these, we recently reported the observation of room-temperature ferromagnetism of ZnO nanoparticles ͑NPs͒ capped with different molecules. 8 This result was accounted in terms of the modification of the electronic structure induced by the capping molecule: the charge transfer at the bonds created between the NPs surface atoms and the molecules induce a modification of the NP electronic configuration that scaled with the appearance of the magnetic properties of the NPs.…”

A novel zinc(II) macrocycle-based synthesis of pure ZnO nanoparticles

“…ZnO nanoparticles have been extensively studied over the past decades because of their fascinating electrical [2], mechanical [3], optical [4], and piezoelectric properties [5]. ZnO nanoparticles have a wide range of applications such as gas sensors [6], dye-sensitized solar cells [7], ultra violet photodetectors [8], UV lasers [9], photocatalysts [10], piezoelectric transducers [11], and for biomedical applications [12].…”