Free paramagnetic moment

The Cu+ ion, for instance, has a Sd structure. It is diamagnetic in all its compounds. The Cu + ion, however, has a 3d structure and its paramagnetic moment corresponds to the presence of one free electron. Thus the oxidation state of copper in one of its compounds can be found by measuring its paramagnetic susceptibility. Indeed the magnetic criterion of unpaired spin is so well established that, unless a compound is paramagnetic, the existence of an unpaired electron can be discounted. 

In the case of a dense system of randomly oriented moments, the field distribution can be assumed to have Gaussian shape. Truly random orientation is certainly fidfilled for a nuclear moment system (except at extremely low temperatures, which are out of the reach of jxSR). For electronic moments it is strictly true only for a free paramagnet. This field distribution is added to Bapp and in summary Bp is distributed. The width of this field distribution can be characterized by its second moment, the so called polycrystalline Van Vleck moment, originally derived for nuclear moments ... 

Because of interaction between the paramagnetic moment and that from nuclear spin, very small concentrations of free radicals can be detected by their influence on the hyperfine structure of electron spin resonance spectra (ESR). This technique is now much employed in free radical studies. Concentrations of the latter down to 1 in 10 M may be detected by ESR, but many free radicals are not sufficiently long-lived to attain even this concentration. Sometimes spin-trapping techniques are employed whereby highly unstable free radicals are reacted with suitable diamagnetic molecules to form relatively long-lived radical species. 

In SmRu2Si2, the effective paramagnetic moment is only 0.54/ig. It corresponds to 7 = 5/2 ground level for free Sm and a low lying excited level with 7 = 7/2. At the temperatures above 15 K the magnetic susceptibility as a function of temperature follows the Van Vleck function for the free Sm ion (Hiebl et al. 1983). In SmRu2Ge2 a small part of samarium moments 0.23(10) /Xg orders magnetically below 10 K (Felner and Nowik 1985). 

We can see that the paramagnetic moments and saturation moments seem to agree very well with the free-ion values. The observed differences are certainly due to the sample quality. These samples are quite difficult to prepare free from (ferromagnetic) impurities (metallic Gd, for example) and of perfect stoichiometry. All authors are aware of these problems and make the necessary caveats on the validity of their results. 

CfN, CfAs, CfSb. Only susceptibility measurements are available (Nave et al. 1986). The preparation and measurements of these compounds require admirable experimental skill. CfN is a ferromagnet (Tq = 25 K), CfAs and CfSb are antiferro-magnets with Neel temperatures of 17.5 and 25 K, respectively. The paramagnetic moments are practically identical with the free-ion value, which is 10.26/Ib- The susceptibility curves show the typical features of isotropic-exchange compounds. 

US-ThS Lam and Aldred (1974) report on this system. Apparently, the sample qualities were not very convincing. The samples remain ferromagnetic up to 50% ThS. The Curie temperatures decrease, and the effective paramagnetic moments increase towards the free-ion value. Varma (1976) suggests that uranium turns into the tetravalent state. No single crystals have been investigated, so that the anisotropic exchange forces cannot be studied. 

The values for the paramagnetic moment of GdSe indicate that one extra electron of the Gd ion remains in the 5d state. The threefold degenerate t2g branch of the 5d band can overlap sufficiently with the 12 next-nearest Gd ions to provide a metallic bond. Thus the excess electron in (Gd3 Se3 + e") may be regarded as a conduction electron in the 5d(t2g) level [19, 20]. A model of a simple rigid conduction band is proposed in which the number of free carriers is determined by the stoichiometry [3]. Apparently, there is an energy gap between the bottom of the 5d conduction band and the top of the p valence band. Deviations from... 

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