Magnetic properties of ultrafine nickel particles

Abstract

Ultrafine nickel particles have intriguing physical and chemical properties, which are interesting both in fundamental and applied research. The size of the particle was controlled by gas pressure. X-ray diffraction studies showed that fine Ni particles have fcc crystal structure and are coated with thin Ni oxide on the surface. Electron micrographs showed a spherical particle shape, forming a long chain. Size dependence of magnetic properties were studied. The specific magnetic moment drastically decreases when reducing the diameter d of particles <15 nm. The coercivity Hc also approaches zero when d is about 15 nm. Therefore, we can suppose that the critical size for superparamagnetism at room temperature is about 15 nm. According to the superparamagnetic formula KV=25 kT, the value of the magnetic anisotropy constant can be determined, K = −5.8 × 105 (erg/cc). It is found to be larger than bulk Ni [K=−3.4–5.1 × 104 (erg/cc)], the same as Fe particles. The maximum of coercivity at room temperature is about 250 Oe, that is less than the theory value for the coherent rotation model, Hc = 4 K/3Ms=1600 Oe. The mechanism of reversal magnetization can be understood by the sphere chain model. The critical diameter of the single domain is about 65 nm. Curie temperature Tc obviously decreases for 9-nm average diameter particles rather than bulk. It may be in connection with the lattice contraction.

Size Dependence of Structures and Properties of Magnetic Materials

“…Other low-dimensional nanocrystals, i.e. Ni nanorods [109,110] and nanoparticles [110,111], Gd [112], Fe 3 O 4 [113], and MnFe 2 O 4 [114] nanoparticles have been studied. Their structures and properties are determined by various techniques like magnetometry, spin-polarized photoemission, the magneto-optical Kerr effect, and acsusceptometry experiments, as well as more improved methods such as the ferromagnetic resonance, the conversionelectron Mössbauer spectroscopy, X-ray magnetic circular dichroism, the resonance magnetic X-ray spectroscopy, the magnetic force microscopy, etc.…”

“…Between this transition and the normal T N ( ) = 961 K, the spins of -Fe 2 O 3 are in (111) basal plane except for a slight spin canting out of the plane [259], which induces a small net weak FM moment. Whilst below T M 0 the spins are aligned AFM along [111] axis. The Morin transition arises from a competition between the local ionic anisotropy term from spin-orbit coupling and the long-range dipolar anisotropy term [260,261].…”

Preparation and magnetic properties of nanoscale ɛ-Fe3N particles

“…It can also be ascribed to the surface characteristic of particles. As all known that T c is related directly proportionally to an exchange interaction which is related to the atomic distance and structure [28]. The fraction of the atoms distributed in the surface layer increases with decreasing the particle size.…”

Properties of nanocrystalline iron–nickel alloys fabricated by galvano-static electrodeposition

“…Many synthesis techniques have been developed. Examples are gas condensation [2][3][4][5][6][7], ball-milling [8][9][10], chemical processing [11,12], sol-gel technique [13], sputtering [14][15][16], rapid solidification [17], devitrification of amorphous alloys [18][19][20][21] and electrodeposition [22][23][24][25][26]. As early as 1923, Geisen and Dehlinger reported the electrochemical synthesis of brass [27].…”