Magnetic properties of polycrystalline cobalt nanoparticles

Abstract

The energy diagram of stationary magnetization states existing in polycrystalline cobalt nanoparticles in the range of diameters 20 ≤ D ≤ 60 nm has been calculated by means of numerical simulation. It is shown that in polycrystalline cobalt nanoparticles in the range of diameters D ≥ 32 nm only vortex states with low average magnetization are present, whereas mostly quasi-uniform states are realized in nanoparticles with diameter D ≤ 24 nm. Thus, the effective single-domain diameter of polycrystalline cobalt nanoparticles is estimated to be Dc = 24 nm. It is approximately two times smaller than the actual single-domain diameter of monocrystalline cobalt nanoparticle, Dc0 = 45 nm. The hysteresis loops of a dilute assembly of polycrystalline cobalt nanoparticles in the range of diameters D ≤ Dc are characterized by a coercive force that is approximately 2.5 times less compared with that of the randomly oriented assembly of monocrystalline cobalt nanoparticles.

Cation and anion topotactic transformations in cobaltite thin films leading to Ruddlesden-Popper phases

“…The weak FM signal from the BM phase measured in the XMCD spectrum (Figure 3(b) blue curve) was not detected in the magnetization-temperature plot in Figure 4(b), mainly due to the detection sensitivity difference between the two measurements. In addition to the insulating properties, the NP phase displayed FM properties with a nearly constant magnetization value of 847 emu cm -3 up to the highest measurement temperature of 370 K. This magnetization value was normalized to the estimated volume of all the Co nanoparticles (i.e., 23% of the total NP film volume, based on XA spectra fitting results), and the measured MS of these Co nanoparticles corresponds well to the reported value for metallic Co (i.e., MS = 1352 emu cm -3 compared to MS ~1400 emu cm -3 , [67,68] respectively). The high TC value in the NP sample is also consistent with the presence of FM Co nanoparticles embedded within an insulating matrix.…”

Impact of aligned carbon nanotubes array on the magnetostatic isolation of closely packed ferromagnetic nanoparticles

“…Ross et al assumed that M S ¼ 1100 emu/cm 3 for massive of Co NPs [52]. To calculate the magnetization distribution in Co NPs, it is usually assumed that the saturation magnetization of Co NPs is M S ¼ 1400 emu/cm 3 , the exchange constant is given by A ¼ 1.3 10 6 erg/cm and the uniaxial anisotropy constant is K ¼ 4.3 10 6 erg/cm 3 [53,54]. As for the exchange constant A, it depends less on temperature, but for nanoscale layers or nanoparticle arrays its value may depend on the method by which it is measured.…”

Skyrmion formation in nanodiscs using magnetic force microscopy tip

“…Magnetic characterization of the representative sample was carried out using a vibrating sample magnetometer with an in-plane magnetic field up to 2 T. The obtained value of the magnetization saturation was about M s = 1.3 MA/m, which is slightly lower than the bulk value of the M s for cobalt (1.4 MA/m) [26]. We expect that the M s does not strongly depend on the number of trilayer repetition.…”