Can anyone help me to do a simulation and interpretation of ESR spectra of Fe3+ in different environment? When does the g value come about 6? What will be the effect of spin cycloidal on ESR spectra of perovskite (BiFeO3)? How can I interpret the anisotropy in g value for powder samples?
Please send the book "Electron Paramagnetic Resonance: Techniques and Applications" by Raymond S. Alger to "[email protected]".
Usually one would expect g-factors in the range of roughly 1.5-3.5 for the stated ions in your question. A good start for reading about this is the Abragam & Bleaney "Electron Paramagnetic Resonance of Transition Ions".
A g-factor of 6 is quiet high and you probably measured inside an ordered phase. I don't exactly remember the critical temperatures of BiFeO3, but they are quiet high (>500K). So if you are in an ordered state you have to take the internal fields, anisotropy energies and in some cases also demagnetizing fields into account.
What do you exactly mean by anisotropy of the powder samples? One usually records a signal shape that depends on the crystal structure, the symmetry of the ESR active ions environment and the linewidth. The fit function should also take the angle distribution of the powder grains into account. If the linewidht is small compared to the anisotropy it might work to use a fit with 2-3 Lorentzians. But analysing the anisotropy from powder is only a compromise, one should prefer single crystals for that. Also if you are in an ordered state one has to be realy careful, because the mentioned anisotropy energies and demagnetizing effects can dominate angle dependencies.
Thanks for your consistent explaination.Your guess was correct that the anstropy was about the crystal structure only.
BiFeO3 is having rhombohedral crsytal structure and have G-type antiferromagnetic magnetic structure alongwith the presence of incommensurate spin cycloidal structure. The Neel temperature is about 630 K which is well above the room temperature.
This is Prof. S.L.reddy
I will suggest the following reference please go through it.P.S.Rao and S.Subramanian,” E.P.R. studies of some first-row transition ions in hexaimidazole zinc(II)dichloride tetrahydrate”, Mol.Phys. 54 (1985) 415
"BiFeO3 is having rhombohedral crsytal structure and have G-type antiferromagnetic magnetic structure alongwith the presence of incommensurate spin cycloidal structure."
It will be difficult to extract the asymmetry of the g-tensor for that one. You need to measure angle dependence on single crystals above the Neel temperature.
1. Firstly, Fe2+ and Mn3+ are non-Kramers' ions and observation of their EPR signals would be quite difficult unless you go to very low temperatures; and it may not always be possible at low local symmetries.
2. A lot of data exists on the EPR of Fe3+ in various materials including Pevoskites BaTiO3, SrTiO3 and many biological substances. In the ccase zero field splitting is small, you will observe five fine structure lines - all of them can be described by a single g-value close to 2.00 (also you will observe sets of five lines for each symmetry related site). When the zero field splitting is large, and with lowest plus-minus 1/2 state you can observe a highly anisotropic line with g parallel 6.0 and g perpendicular=2.0. In a number of glasses you can obseve an isotropic line at g=4.2 due to admixture of states. (see Abragam and Bleaney).
3. In magnetically ordered systems you may not observe the ESR signal as it would get broadened.
4. Observation of anisotropic features in powder spectrum can easily be identified from the line shape. A parallel line will have a bell like feature and a perpendicular line - a typical but asymmetric derivative.
You may go through the masterly work of Alex Muller ( Discoverer of High Tc super conductivity) on the EPR of Fe-V0centre in Sr TiO3. It gives an excellent exposition on the EPR of Fe3+ in large zero field splitting and also on the potential of EPR for structural pahse transitions.
Thanks Prof. M D Sastry for your relevant answer. I have gone through the papers and books and now i am able to explain my experimental results.
Thanks a lot for your kind support.
Thank you. You also may please see this paper. We dealt with the ESR of Fe in some interesting situations.
IOPPUBLISHING JOURNALOF PHYSICS: CONDENSED MATTER
J.Phys.:Condens.Matter 20(2008)025224(9pp) doi:10.1088/0953-8984/20/02/025224
Anunusual radiation dose dependent EPR
g = 2.54infeldspars:possible
line at
eff
3+ 2 2+
O Fe O and
evidenceofFe
3+ 2+
–Fe –nO
exchangecoupledFe
1 1 2 3 4
MDSastry ,YCNagar ,BBhushan ,KPMishra ,VBalaram
1,5
andAKSinghvi
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Material Characterization