Paramagnetism and Ferromagnetism

The susceptibility of paramagnetic substances is mostly determined by permanent magnetic moments p which are aligned by the magnetic field. The field induced magnetizatimi is determined by the total projection of molecular magnetic moments in a unit volume onto the field axis 

What is a nature of p in a molecular system The molecular paramagnetism is mostly originated from the unpaired electron spins. The magnetic moment for a/ree electron spin is 

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The little atomic magnets are of course quantum mechanical, but Weiss s original theory of paramagnetism and ferromagnetism (1907) [7] predated even the Boln atom. He assumed that in addition to the external magnetic field Bq, there was an additional internal molecular field B. proportional to the overall magnetization M of the sample. 

Other magnetic measurements of catalysts include electron paramagnetic resonance and magnetic susceptibility. Although those are not as common as NMR, they can be used to look at the properties of paramagnetic and ferromagnetic samples. Examples of these applications can be found in the literature [87. 

For such materials it is desirable for there to be a miscibility gap due to magnetism (Fig. 10.70(a,b)) as described in Chapter 8. In these circumstances, spinodal decomposition can occur by the formation of paramagnetic and ferromagnetic phases. The best magnetic properties can be produced if annealing is performed just below the temperature where instability begins. 

The relations between paramagnetic and ferromagnetic properties and structure are less simple than in the case of diamagnetic substances, and will not be dealt with here the reader is referred to the review by Lonsdale (1937 a). 

Several investigations of y-FeNi Invar type alloys (20-34 at. % Ni) have reported the coexistence of paramagnetic and ferromagnetic contributions in the spectra [49-54]. 

Chemists discuss magnetism in terms of three basic categories diamagnetism, paramagnetism, and ferromagnetism. 

Suryanarayanan and Brun (1976) have observed in the X-band paramagnetic and ferromagnetic resonances in EuS. The Curie temperature is 16.6 K, indicating a good stoichiometry for the film. 

For most paramagnetic and ferromagnetic materials, the isothermal magnetic entropy change per unit of magnetic induction usually ranges from 1 to 4 J.kg .K .T . 

The variation in the relative areas of the paramagnetic and ferromagnetic components (Table 21.4) suggests the formation of a minor solid solution phase initially. This Al-rich metastable phase begins to disappear after 60 min of milling. 

Relative Permeability, ft,., of Some Diamagnetic, Paramagnetic, and Ferromagnetic Materials... 

Frohlich electron-phonon interaction, see, for example, Guntherodt [30], Tsang et al. [21], Safran et al. [31], A detailed review of the theoretical background for the observations in the paramagnetic and ferromagnetic phase has been given in the Section on EuS in Rare Earth Elements C 7, 1983, pp. 479/80. 

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