Nickel magnetization curves

For a system of nickel particles covering a certain size range, the magnetization curve will be composed of the Langevin functions of the individual particles (see also Becker (lie)) ... 

Three alumina supported nickel samples were prepared with nickel loading ranging from 8 to 25% and dispersion varying from 10 to 28%. The surface area and the pore size of the support, the metal loading, the dispersion of the samples, deduced from hydrogen chemisorption and from magnetization curves are reported in Table 1. 

Fig. 27. (left) The magnetization curves of precursor and the nickel ferrite nanoparticles calcined at (a) 723 (b) 773 (c) 823 and (d) 873 K which measured at room temperature in the range of approximately -15 to +15 kOe. Figure27. (right) the expanded field region around the origin for clear visibility of the readers, in the range of approximately -400 to +400 Oe. 

The chemical reductitMi of in IPECs PAA-PEI results in metal NPs. The magnetization curves of diy films of the obtained nanocomposites qualitatively resemble those of metallic nickel [81], suggesting that the reactitMi proceeds as follows ... 

Figure 20.17 Magnetization curves for single crystals of iron and nickel. For both metals, a different curve was generated when the magnetic field was applied in each of [100], [110], and [111] crystallographic directions.

Vibrating sample magnetometry (VSM), a technique that was described in detail by Van Stiphout [6], was performed with the unsupported mixed oxalates, which were decomposed in a 10% HyN2 flow at 400 °C. The magnetization of the sample was measured at 77 K as a function of the applied field strength (maximum 12 kOe). The size distribution of the nickel particles was obtained by fitting the thus measured magnetization curve with theoretical curves calculated for discrete particle sizes. 

An obvious refinement of the simple theory for cobalt and nickel and their alloys can be made which leads to a significant increase in the calculated value of the Curie temperature. The foregoing calculation for nickel, for example, is based upon the assumption that the uncoupled valence electrons spend equal amounts of time on the nickel atoms with / = 1 and the nickel atoms with J = 0. However, the stabilizing interaction of the spins of the valence electrons and the parallel atomic moments would cause an increase in the wave function for the valence electrons in the neighborhood of the atoms with / = 1 and the parallel orientation. This effect also produces a change in the shape of the curve of saturation magnetization as a function of temperature. The details of this refined theory will be published later. 

Fig. 15. Spontaneous magnetization vs. temperature, according to Weiss (655) theory, (a) Graphical solution. The value of M,/Mo is given by the intersection of the two curves, (b see facing page) Reduced-scale plot. The solid lines represent the Weiss field theory for J — 1/2, 1. The experimental (dashed) curves for iron and nickel fit more closely the theoretical curve for J = 1/2. (After Bozorth (92)).

Figure 6.2. Curves of magnetization for shock synthesized nickel ferrites and the precursor material, (a) Co-precipitated mixture of nickel oxide and ferric oxide (b) nickel ferrite synthesized by calcination (c,d) nickel ferrite synthesized by shock waves of 27.6 GPa and 23.4 GPa, respectively.

The thermal decompositions of nickel(II)-cobalt(II) oxalate solid solutions were studied using TG and TM [103], A series of the mixed binary Ni(II)-Co(II) oxalate samples was prepared at 25% (atom) intervals across the system. Physical mixtures were also prepared by mixing the pure end members. The DTG and DTM curves showed that the decomposition proceeds to completion in two overlapping stages. The kinetics of the individual steps were not studied. From the DTG curves, the authors stated that the physical mixtures behaved as individual oxalates, while the coprecipitate decomposed as a single entity. The TM curves showed that the products formed from the physical mixture and the coprecipitate were distinctly different. The magnetic behaviour of the product from the coprecipitate was consistent with the behaviour predicted for a Ni-Co alloy, but the products from the physically mixed oxalate do not show the transition temperature predicted for an alloy. The kinetics of decomposition of iron-nickel mixed oxalates have been studied by Doremieux et al. [104]. 

Figure 2.6 Magnetization of nickel-copper alloys as a function of composition (6). [Points are data for the catalysts of Figure 2.5 curve represents data of Ahern et al. (39) on metallurgical specimens.] (Reprinted with permission from Academic Press, Inc.)...

Curve 1 for nickel shows a maximum at about 4 nm, and curve 2 may also be at a maximum at around 10 nm. Recent data of Richardson and Koveal (300) (not shown in Fig. 18) also exhibit a maximum turnover rate at about 10 nm. They studied Ni/Si02 catalyst in the size range d of about 2.5 to 25 nm, and the Ni particle sizes were measured by magnetic methods. Also reported are results on H2 chemisorption (H/M). As d and Ms were known from the magnetic measurements, it was shown that H/Ms... 

It has been shown by Marian and others (Marian, 57 Ross, 58) that for solid solutions of copper in nickel, both Curie point and specific magnetization are linear with respect to concentration. Marian s data for the Curie points are shown in Fig. 50. The thermomagnetic curve for a homogeneous solid solution has the same shape and abrupt Curie point shown by a pure ferromagnetic substance except that the specific magnetization (tr ) at any given temperature is lower, and the... 

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