Is this possible for ferrites at low temperature? If so, what is the magnetic ordering?
I am not sure about a particular case of ferrites (could be another mechanism, perhaps related to some kind of orientation misalignment in applied magnetic field), but in any case the difference between FC and ZFC magnetizations M_ir=M_FC-M_ZFC always measures the irreversible properties of the sample. The situation when M_ir0. Usually, MS contribution is a result of structural martensitic transformation, which can significantly modify the initial FM phase (like, e.g., in manganites, see the attached paper).
I think of one more possibility. Sometimes we do see curve. It is understood to arise due difference in heating and cooling rates. It is better to rule out. Correct me if I am wrong
But I feel, some thing should be there which can cause this, we need to find out the reason.
Since there is a difference based on the history, can you do isotherm measurements during ZFC and FC . Make sure to wipe out by taking the sample above Tc
You may even see negative FC magnetization. The sample has two sub-latices. In FC mode, the sublatice that has larger anisotropy will align with the magnetic field. In the case where the other sublatice, which has smaller anisotropy, but the magnetization develops faster on cooling, you may see a decrease of magnetization on cooling. Below a compensation point, the total FC magnetization may even become negative.
Thank you D N H Nam, can you provide some references where this perticular negative behaviour is observed, especially I am looking for some references related to FERRITES where such type of negative behaviour of ZFC & FC observed.
Once again thank you for your interest on my topic.
An argument only; will not mind if it goes wrong:
Relation between ZFC, FC and coercivity (Hc) at any temperature T is:
Mzfc (T) = Mfc (T).HA/2Hc.
If Ha is less than 2Hc, Mzfc is less thanMfc.If Ha is equal to 2Hc, then Mfc=Mzfc.When Ha is more than 2Hc, then Mzfc is more than Mfc. At TN=TB; ZFC=FC.In between TB and TN, Ha is more than Hc to make ZFC more than FC; implying a ferrimagnetic behaviour.
Thanks for ur reply, I want to understand physically what is actually happening, I want to clearly read about the mathematical expression that you have provided. could you please tell me where I can find the explanation for above formula that you have mentioned.
In order to understand the ZFC/FC, one needs to know about Coercivity [HC], SPM phenomenon, Neel relaxation time [TN] and blocking temperature (TB).
Both Mzfc and Mfc are temperature dependent for which we should know the behavoiur of the magnetic moments of ZFC andFC processes as follows.
When a substance is cooled to nonzero temperature (FC), the angles between spin moments and applied field lie within pi/2. So the sample shows a nonzero magnetization even if magnetic field reduces to zero. Now, when the sample is cooled to zero degree, the spin domains are totally disordered and the sample shows zero magnetization when the field is zero.
If the field Ha is applied at low temperatures, the spin moments rotates towards the direction of the applied field and the substance shows a net magnetization. The larger the value of Ha, the larger will be Mfc and Mzfc.So Mzfc (T) at any temperature is proportional to Mfc (T) and Ha. The relation becomes Mzfc proportional to Mfc (T).HA. In order change any proportionality into equality, we need a constant which in this case, is 1/Hc. In fact, it is 1/2Hc.
Now, how comes this fraction (1/2) is an experimental fact as in most of the SPM materials, Mzfc was observed to the half of Mfc. So the relation becomes:
Mzfc=Mfc.Ta.1/2Hc.
If you need to know further as to how the terms mentioned in beginning help in ZFC/FC, I will love to do my humble bit.Again, it is the way, I have tried to understand this tedious phenomenon which involved a lot many of mathematical relations and will not mind my limitation as I, being old, belong to an old school of thought.
Good luck, my young friend.
Dear sir (Manohar Sehgal),
Thank you very much for your patience to explain. Its Useful to me.
I am searching for the same. If some literature with this regard, can you plz share with me
NOT YET Nilesh still I am searching for valid reason.
What is your system?
the explanation can be found in our published work attached below.
(Applied Physics Letters, 105, 052412 (2014): doi: 10.1063/1.4892476
Article Anomalous magnetic behavior in nanocomposite materials of re...
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