Effect of Particle Size on the Magnetic Properties of Ni Nanoparticles Synthesized with Trioctylphosphine as the Capping Agent

Abstract

Magnetic cores of passive components are required to have low hysteresis loss, which is dependent on the coercive force. Since it is well known that the coercive force becomes zero at the superparamagnetic regime below a certain critical size, we attempted to synthesize Ni nanoparticles in a size-controlled fashion and investigated the effect of particle size on the magnetic properties. Ni nanoparticles were synthesized by the reduction of Ni acetylacetonate in oleylamine at 220 °C with trioctylphosphine (TOP) as the capping agent. An increase in the TOP/Ni ratio resulted in the size decrease. We succeeded in synthesizing superparamagnetic Ni nanoparticles with almost zero coercive force at particle size below 20 nm by the TOP/Ni ratio of 0.8. However, the saturation magnetization values became smaller with decrease in the size. The saturation magnetizations of the Ni nanoparticles without capping layers were calculated based on the assumption that the interior atoms of the nanoparticles were magnetic, whereas the surface-oxidized atoms were non-magnetic. The measured and calculated saturation magnetization values decreased in approximately the same fashion as the TOP/Ni ratio increased, indicating that the decrease could be mainly attributed to increases in the amounts of capping layer and oxidized surface atoms.

Nickel‐containing magnetoceramics from water vapor‐assisted pyrolysis of polysiloxane and nickel 2,4‐pentanedionate

“…Since the hysteresis loss is dependent on the coercivity, a decrease in the size of Ni nanocrystallites can effectively decrease the hysteresis loss. In fact, the critical sizes for spherical Ni particles to exhibit superparamagnetism have been estimated to be below 20 nm, which is not much smaller than our results (see Section 3.2). It suggests that the SiOC–Ni samples could show almost zero coercivity by choosing the pyrolysis temperature more precisely to control the nanocrystallite size.…”

Stable Zero‐Valent Nickel Nanoparticles in Glycerol: Synthesis and Applications in Selective Hydrogenations

“…Actually, both materials exhibited narrow hysteresis at 2 K (coercive fields of 64 Oe and 89 Oe for NiA dispersed in glycerol and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 NiA(s), respectively), together with moderate remanence magnetizations (0.66 and 2.15 emu/g for NiA dispersed in glycerol and NiA(s), respectively), showing a weak ferromagnetic behavior. The saturation magnetization of NiA(s) (31 emu/g) is slightly lower than that reported for bulk nickel (54 emu/g) [32] ). Data corresponding to NiA(s) is in agreement with that reported for cubic nickel nanocrystals.…”

Anisotropic Nanoporous Nickel Obtained through the Chemical Dealloying of Y2Ni7 for the Comprehension of Anode Surface Chemistry of Ni‐MH Batteries

“…For np‐Ni, the experimental value corrected from the residual yttrium hydroxide content is M s,np‐Ni =39.9 Am 2 kg −1 . T. Ishizaki et al . have established a relationship between the saturation magnetization and the crystallite size for nickel samples assuming a spherical shape.…”