Contribution antiferromagnetic

Both extended Hiickel and DFT calculation have been carried out in order to rationalize the observed trends. According to the magnetochemical theories,2120,2121 the antiferromagnetic contribution to the exchange coupling JAF is proportional to the squared energy difference (ci - e2), where (ei-e2) represents each of the gaps created between the symmetric and antisymmetric... 

There are several types of magnetic behaviour that affect the specific heat of a material paramagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. Diamagnetism, being independent of temperature, causes no specific heat contribution and is not considered. 

An example of magnetic contributions to the specific heat is reported in Fig. 3.9 that shows the specific heat of FeCl24H20, drawn from data of ref. [35,36]. Here the Schottky anomaly, having its maximum at 3K, could be clearly resolved from the lattice specific heat as well as from the sharp peak at 1K, which is due to a transition to antiferromagnetic order (lambda peak). 

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. 

Figure 6. Illustration of exchange interactions in homovalent system consisting of two metal sites A and B. The system contains two electrons. The six distinct microstates are indicated on Ae left. The antiferromagnetic contribution results from mixing an excited state ionic configuration wiA Ae ground state singlet.

Curium metal is antiferromagnetic and its resistivity has been measured as well as that of isostructural non magnetic americium metal The resistivity difference is taken as the magnetic contribution and is shown in Fig. 13. It passes through a maximum for... 

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