Since other orbitals partially filled and also for from nuclues ..like 2p1 3p1 4p2 .but it is not showing magnetic behavior ..
Only d and f orbitals are enough localized and narrow to give a high value to the exchange integrals between the spins. The five d orbitals (2 eg and 3t2g) allow very interesting configurations with stable magnetic configurations in Fe, Ni or Co which are at the same time metallic.
Tnq sir,
But when am calculating magnetic moment partially filled p orbital am getting magnetic moment.
For example: in p orbital 2 electrons occupied so
Magnetic moment is 2 magnetic moment right ?
If it is so all orbitals should show magnetism .
Very interesting question. I think that the reason is that they are outter most orbitals.
Hello Reddy Vara,
as you restrict yourself to a consideration of atoms, you are partially right with your own answer. Any orbital which is partially filled (thus excluding s2, p6, d10 and f14 orbitals) obtains a certain magnetic moment, as there is an inequality between occupied spin-up and spin-down electrons. Thus the spin-polarization P = (nspin-up - nspin-down)/(nspin-up + nspin-down) is not zero.
Kai,
That is not true. Magnetic order in a solid is never got fo s or p electrons independently of the orbital filling. The reason is that is necessary to have a certain value of the Weiss field or the coupling constant J among the spins. This is only obtained if you have the orbials or bands narrow engough, which happens for d and f electrons. It is true that we need also certain filling allowed by Hund's rules.
Hello Daniel,
there is a reason why I restricted my answer to atoms. There the explanation holds. For solids or molecular compounds more effects have to be considered, like the ones you already mentioned.
Daniel is right in pointing out that the consideration of Hund's rule concepts is not applicable to solids unless there is very strong localization such as in the 4f shell of the rare earth elements.
Also, when really considering atomic physics, there is no such thing as numbers of "up" and "down" electrons, because the electronic shell is to be described as a single many body state, usually more complex than a (single) Slater determinant. Atomic (and molecular) physics is not the realm ofthe physics of independent particles.
For magnetic(ally ordered) states in solids, the discussion needs to be refined. If we think about metals in an elementary manner, two ingredients are important. One is exchange interaction as Daniel mentioned. This btw. is not exceptionally strong in the 3d transition metal series - some alcaline metals have larger values although we are dealing with s & p electrons there. The second ingredient is the density of states near the Fermi level which needs to be sufficiently high in order to obtain a total energy gain (total energy = exchange + kinetic energies) by forming the magneticlly polarized state.
These considerations, in elementary manner, are the basis of the so-called Stoner model of metallic ferromagnetism. To understand it, pick a good solid state text book treating this and use it to do the calculation yourself.
Magnetism reality is more complex, though, and only partially covered by the simple Stoner model. For a more extensive study, consult the Magnetism book by Stöhr and Siegmann. It's currently my best recommendation (but I haven't read all books on magnetism... :-) .
In magnetic insulators, the formation of local magnetic moments can often reasonably well be understood by applying concepts of atomic physics to the magnetic (usually ionic) sites. Modifications are brought upon by the so-called crystal field, which lifts the degeneracy between states that would be degenerate in a free ion. Care must again be taken when discussing the magnetic states in terms of single electron orbitals -- this can go wrong. The next step then is to ponder the mechanisms by which the local moments "feel each other" (interact) to produce a configuration with magnetic order. Again, consult appropriate introductory magnetism textbooks for more information.
As a very gross and rough argument as to why 3d and 4f elements are most prone to the formation of permanent magnets consider the idea mentioned by Ramanathan Krishnan above. When forming a solid, the valence electrons interact, forming bands (as a precursor, you have bonding, nonb. and antibonding states in molecules).. Consider 2 electrons having the choice of ocupying the lowest energy (single electron) states (and hence, opposite spin) or another pair of states with their spins aligned. In terms of single electron orbital (band) energy, the former is preferable. In terms of exchange energy, the latter is preferable. There thus is a competition of two terms and whoever is larger wins. For s- and p- valence electrons the bonding-antibonding splitting is large (translating to a large band width due to strong orbital overlap in the solid). Formation of magnetic states is then unfavorable. (Large band width is equivalent to small density of states). In contrast, the spatial extent of 3d and 4f states is much smaller, resulting band widths therefore are, and densities of states near the Fermi level may become elevated as a result (details depending on the specific band structure [whatever that means for 4f shells - but that is a separate topic... :-])
Dear Roman,
I am not certain to fully understand your comment. But certainly there is little to no classical part in it: (i) angular momentum physics and number of available states in angular momentum shells is quantum physics (ii) even worse: there is no possibility for a magnetically ordered state in a classical ensemble (Bohr-van Leeuwen theorem, a most fascinating piece of physical insight & not utterly difficult to understand [when you know what the Hamiltonian of an ensemble is]).
And then, as to the physics of several electrons on a single shell -- this is, where it may get complicated and we say that one often needs to consider electronic correlations to not get it wrong. This is the more true the more atomic-like the configuration is.
And in one sense you're absolutely right: the maximum moment which can be obtained with a single open (partially filled) shell scales with its angular momentum quantum number.
When it comes to magnetic order, the dominant interaction driving that order is virtually always some form of "exchange interaction". Again, this is intrinsically a quantum mechanical thing with no analog in classical physics.