Ferromagnetic susceptibility

Ferromagnetism may occur as the result of strong spin-spin interactions. This requires unpaired spins and high order. The ferromagnetic susceptibility t can be given as ... 

Ni(2-CH, C,H40N)3Cl2 300- 80 3.87 + 35 at room temperature ferromagnetic susceptibility strongly Tield-dependent 69D18... 

Figure 539 A ferromagnetic susceptibility / in external magnetic field H.

NmI point The temperature at which magnetic susceptibility becomes normal. See anti-ferromagnetism and ferromagnetism. 

Equation (A2.5.20) is the Curie-Weiss law, and the temperature at which the magnetic susceptibility becomes infinite, is the Curie temperature. Below this temperature the substance shows spontaneous magnetization and is ferromagnetic. Nonnally the Curie temperature lies between 1 and 10 K. However, typical ferromagnetic materials like iron have very much larger values for quantum-mechanical reasons that will not be pursued here. 

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. 

The limited magnetic measurements of very mixed -metal clusters are summarized in Table XIII. The magnetic behavior of some anti-ferromagnetic very mixed -metal carbonyl clusters (Fig. 82) has been studied by Pasynskii and eo-workers. Temperature dependences of the magnetic susceptibilities of Cr2Co(/t3-S)3(/i-SBu )(CO)2() -C3H4R)2l (R = H. Me) have been determined us-... 

Above a critical temperature Tc, the Curie temperature, a ferromagnetic material becomes paramagnetic, since thermal motion inhibits the parallel orientation of the magnetic moments. The susceptibility then follows the Curie-Weiss law with a positive value of the Weiss constant, 0 > 0 (Fig. 19.6). 

The magnetic susceptibility of p-[Fe(Cp )2][Pt(mnt)2] follow a Curie-Weiss behavior with 6 - 9.8 K. The dominant ferromagnetic interactions are assigned to the magnetic intrachain D+A interactions from the type I chains, as the contribution from the D+ [ A2]2 D+ unit chains is expected to respect only to the cations due to the strong dimerization of the anions, S - 0 for [A2]2. ... 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

Magnetic susceptibility measures the strength of interaction of a sample with a magnetic field. Information obtained includes identification of spin state and spin coupling—ferromagnetic or antiferromagnetic. An example would be identification of the Fe(III)-0-Fe(III) p-oxo dimer moiety. 

---