Ferromagnetism and Antiferromagnetism

The effective magnetic moment for a transition metal complex containing unpaired electrons has contributions from both orbital [L] as well as angular momentum [S], which can be represented 

Meff = y (T-Fl)-F4S(S+l) B.M. The spin-only magnetic moment Ps can be calculated by the following formulae = y/4S S + 1) or y/n n + 2), which is iUustrated below. The formula p = y/4S S + 1) can be used to calculate the spin only magnetic moment for a term symbol for a d ion F using a general formula of a term symbol as 

---

Describe the differences between diamagnetism, paramagnetism, ferromagnetism, and antiferromagnetism. 

Fig. 6.7 Temperature dependence of the magnetic properties of hematite. Tc = Curie temperature,Tm = Morin temperature, pm = paramagnetic region, wfm = weakly ferromagnetic region afm = antiferromagnetic region. The insets show simulated Mossbauer spectra of hematite in the paramagnetic, weakly ferromagnetic and antiferromagnetic states (Murad, 1988, with permission).

Matte HSSR, Subrahmanyam KS, Rao CNR (2009) Novel magnetic properties of graphene presence of both ferromagnetic and antiferromagnetic features and other aspects. J Phys ChemC 113 9982-9985... 

Fig. 8.13 The regions of stability of the ferromagnetic and antiferromagnetic states as a function of the normalized exchange integral l/W and d band filling Nd. The crosses mark plausible values of I/W across the 3d series. (From Pettifor (1980).)...

Fig. 11.58 Schematic representations of magnetic dipole arrangements in (a) paramagnetic, (b) ferromagnetic, and (antiferromagnetic materials.

Fig. 11.59 Variation of magnetic susceptibility with temperature for diamagnetic, paramagnetic, ferromagnetic, and antiferromagnetic substances. Transitions to paramagnetic behavior for ferromagnetic and antiferromagnetic substances occur at the Curie (Tc) and Neel (TN) temperatures, respectively.

ESR is subject to some serious limitations. For reasons which need not concern us, resonance may be difficult or impossible to observe if the paramagnetic centre has an even number of unpaired electrons. This means, for example, that ESR can make little contribution to the extensive chemistry of nickel(II). Another problem arises from interactions between paramagnetic centres in magnetically non-dilute samples the resonance may be very broad and uninformative. ESR is best performed on magnetically-dilute samples, which means that we cannot obtain the kind of information furnished by bulk susceptibility measurements about ferromagnetic and antiferromagnetic interactions. 

If several exchange pathways exist in polynuclear coordination complexes, ferromagnetic and antiferromagnetic pathways can compete for a given spin dimer, usually resulting in a dominant antiferromagnetic exchange. 

---