Impurities, ferromagnetic

Parasitic ferromagnetism is a weak ferromagnetism that accompanies antiferromagnetism, eg, in a-ferric oxide [1309-37-1], a-Fe202. Possible causes include the presence of a smaU amount of ferromagnetic impurities, defects in the crystal, and slight deviations in the directions of the plus and minus spins from the original common axis. 

Magnetic Susceptibility Measurements. Magnetic susceptibilities were measured by the Faraday method and were accurate to 2%. Samples, usually as powders, were placed in a cylindrical Teflon boat having an internal volume of 0.30 cc. Measurements were made at 2963, 4357, 5724, 7077, and 8243 G, and at temperatures 77°-295°K. It was possible to correct for ferromagnetic impurities from any field dependent effects. 

The magnetic behaviour of compounds 1-4 in the temperature range 77-300K was studied (ref. 2), but the authors considered that ferromagnetic impurities, undetectable by chemical analysis, are the origin of part of the anomalous behaviour of some of the complexes. 

Traces of ferromagnetic impurities cause severe broadening of absorption peaks because of reduction of T2 relaxation times. Common sources are rust particles from tapwater, steel wool, Raney nickel, and particles from metal spatulas or fittings (Figure 3.16). These impurities can be removed by filtration. 

Erratic spectra from ferromagnetic impurities remove by filtration... 

Also, field distortion.s from ferromagnetic impurities are tolerable, and polymer-iron composites can be investigated fZim2. ... 

The magnetic susceptibility was found to be field independent for both CogSg and Ni3S2. This indicates the absence of any ferromagnetic impurity. In addition, the susceptibilities for both of these materials are temperature independent, and their respective values of 1.3x10 and 0.6x10" emu/g are consistent with Pauli paramagnetism. 

C-NMR-Spectroscopy C-NMR-spectroscopy can also provide valuable informa-hon on the structure and the bond type of the carbon nano tubes. Yet the full potential of the method cannot be exploited due to experimental problems. Most of all, the heterogeneity of the samples, their poor solubility in common NMR solvents and the presence of ferromagnetic impurities (catalyst particles) complicate the recording of instructive NMR spectra. 

ThCo is weakly paramagnetic with x - 1 X 10 8 m3/mol [see Buschow (1971) the measurements were not corrected for ferromagnetic impurities]. 

Results of Omejec and Ban (1971) deal with the whole 3d-series for both Si and Ge. They are, however, strongly affected by the low sensitivity of the measurements, and in some cases a contamination by ferromagnetic impurities is evident (for T = Fe, Co). The compounds with T = Cr, Ni, and Cu were found to be only weakly magnetic in the temperature range of 100-570 K. 

Traces of ferromagnetic impurities cause severe broadening of absorption peaks because of reduction of... 

Ehrlich and co-workers (160) measured the magnetic susceptibility of zirconium(III) trifluoride over the temperature range —183° to 20°C. They also observed a field dependence, but assumed that it was due to ferromagnetic impurities. After removing the field dependence by extrapolating to a value of of 1040 to 1260 x 10 c.g.s. units/mole was obtained which was only slightly temperature dependent. 

The Faraday microbalance used here has been described elsewhere [7], Details about the procedure we have followed to determine the magnetic susceptibility of the Rh/Ce02 catalysts are reported in refs. [3,8], The experimental values, which were corrected from the traces of ferromagnetic impurities (6-12 ppm), allowed us to determine the content of paramagnetic Ce3+ ions, and therefore the percentage of Ce4+ ions reduced to the 3+ oxidation state [8], The magnetic contribution of rhodium was considered to be negligeable (Maximum value to be expected 3.10" emu CGS at 298 K, to be multiplied by 12.56 to obtain SI units in m. g-l). 

In the study of the magnetism, we must always pay attention to the ferromagnetic impurity, especially for the study in a low concentration. This is one of the reasons why everyone in our field tends to use samples for which the molecular and crystal structure is elucidated by X-ray analysis. Carbenes are free from such a worry about ferromagnetic impurity, because we can easily know the origin of the observed magnetic moments by comparison before and after irradiation and/or those before and after annealing. This fact makes it possible to study the magnetism under frozen solution condition. 

In all calibrations with solid substances of supposedly known susceptibility the greatest care must be taken to avoid contamination with minute traces of ferromagnetic impurities, which may have a disastrous effect on the accuracy of any contemplated measurements. 

If the susceptibility seems to rise with increasing field the probability is that the calibrating agent contains a ferromagnetic impurity. 

Some very careful efforts were made to detect this expected effect. But the low susceptibilities and the ubiquitous trace of ferromagnetic impurity combined to make it difficult to examine this region. It may be said, however, that certainly no more than 10 per cent of the copper atoms can be considered as atomically dispersed. 

The concentration of the solutions appropriate for obtaining NMR spectra is in the range of 5-15% by weight about 1 mL of solution is needed to fill an NMR tube to the proper level, although as little as 0.6 mL can be used. The tube must be scrupulously clean and dry, and the solution must be free of undissolved solids arising from the sample itself or even dust. Furthermore, as a consequence of contact of the solute or the solvent with metals such as the iron in "tin" cans, trace amounts of ferromagnetic impurities may contaminate the solution the result is a spectrum that has only broad, weak absorptions. 

Plot of x -T and xT-T for (NH4)[Np02(02CH)2] (1). The data were corrected by subtraction of 2.8% of ferromagnetic impurity that can be identified as [Np02(02CH)(H20)] (3). The peak at 13 K is due to the residual by subtraction for correction. (Reproduced from Ref. 10 with permission of Transworld Research Network.)... 

If it is subtracted then Ueff = 2.535 Ub and 0p = -9K. The monoclinic sample contained a ferromagnetic impurity phase. After correction for fliis impurity term, this sample followed the Curie-Weiss behaviour with a moment close to the Ce ionic value and 0p=-7K. A large difference was found in comparison with the previously published magnetic data. The authors explain this difference by the existence of spurious phases in some of the annealed samples, the occurrence of a superimposed Pauli paramagnetic contribution which was not taken into account in the analysis, and a large anisotropy. 

V CH3C(S)S- 4 293 200- -77 1.87 1.72 -20 Gouy sign of 0p uncertain eight-coordination suggested probably ferromagnetic impurities 72P10... 

---