Obviously both kinds of behaviour are simultaneously present. It is the kind of result I would expect to get for a thin ferromagnetic film on a diamagnetic substrate.

Many people would now determine the slope at large fields and subtract a straight line through the origin with the same slope - and voilà - they have gotten rid of the disturbing diamagnet. So they believe.

More often than one might suspect, this procedure is likely to produce erroneous results, though, because it takes for granted that the magnetization curve of the ferromagnet is truly saturated in the high field limit of the measurement range. That's a dangerous assumption unless you know the sample/material very well. Usually, this belongs to the things you actually want to find out about your sample.

What to do? Carefully measure empty substrates and carefully weigh them. from the diamagnetic response you can then determine the diamagnetic susceptibility. Cross check with literature values. If that doesn't fit well (enough) measure the empty sample compartment, the sample holder or holding capsule or whatever to know precisely how everything contributes. Later, do the same with film samples and do subtract the diamagnetic background according to the substrate weight and susceptibility.

Other scenarios are possible: you didn't expect to have a ferromagnet? Maybe you (or someone else) unadvertedly used wrong (e.g.. iron) tweezers to manipulate your sample and contaminated it. It may then be no longer usable for magnetometry. Even worse: the magnetometer is contaminated by ferromagnetic debris. (As they say: shit happens... and not so seldom, unfortunately, with magnetometers.)

Some oxide substrates may exhibit impurity phases with ferromagnetic response, others with paramagnetic response and that may be subject to change when you buy them next time or from another supplier. Do yourself the favor and pain to thoroughly check the quality of all equipment you use. Be assured: lousy measurements are much more painful -- and it need not at all be your own fault.

Good luck with your research!

Dear Jeya Saravanan,

If may I know, what kind of your sample. So We can a reference to identify the type of material.

Regards,

Indra Pardede

Possible problems occurred during VSM measurement. If I am not wrong, then you have shown the MH curve for thin film sample and diamagnetic behaviour is coming due to your substrate which is possibly non magnetic so to make this graph sensible you have to do any of the following:-

1. Do the VSM of your substrate also and subtract it from your graph.

2. Either use the slope deduction method to remove the diamagnetic effect of your substrate.

Goodd Luck............

If it is a powder sample or substrate the MH curve is diamagnetic. But if you grow thin film on the substrate then it may contain both diamagnetic + ferro orother magnetic curves

You did not mention the type of sample (powder or thin film). If you want to know correct answer for your MH curve, then in the beginning of the discussions, always it is better to give complete samples details.

Thanks to Kai, you have recommendations for operating quite better. But the main question here is what do you measure???

Your magnetization signal is so weak that it looks well a thin film (polluted or not) deposited on a dia substrate... but your question looks as" finding a needle in a haystack".. should the needle made of steel or copper, what is the nature of the haystack.

So what type of sample do you measure, what is the composition of the material....as said earlier by Dr Raghavender?

For people working in rock magnetism this graph is not so strange. Kai Fauth make an interesting observation about saturation and "corrected" -it is pure ferromagneic curves, without the para or diamagneic contribution. But you must tokeep in mind that the ferromagnetic signal has a very low intensity, so it seem as a minor concentration material, perhaps, as D. Fruchart suggest, it may be impurities.

Thank you Mr. Kai Fauth, D.Fruchart and Carlos. My sample is a thin film coated on a glass substrate. Specifically it is a Copper doped ZnO thin film. I have obtained this M-H curve for the lowest concentration and when the dopant concentration increases I have obtained a complete ferromagnetic with hysteresis loop. I have collected the journals and in one case they have mentioned the similar graph as that of mine as diamagnetic . And in another journal it was mentioned as ferromagnetic . In a reprint the reason they have written as "for low magnetic field it behaves as ferromagnetic and for high magnetic field it behaves as diamagnetic" . My question is whether the above mentioned reason is correct. 

Vinay sharma can you please suggest the slope deduction method to remove the diamagnetic effect of the  substrate.But I have already given the data which has been corrected from the diamagnetic contribution from the substrate.

Dear Jeya Saravanan,

the "slope deduction method" is described in my (first) post. And no, the diamagnetic contribution is not fully removed from the curve you posted along with your question. Independent of dopant concentration, your sample should display the same diamagnetic contribution (per substrate volume; this assumes the films to only represent a very small fraction of the total sample volume).

Dear Jeya

Please have a look on :

https://www.google.fr/?gws_rd=ssl#q=hysteresis+loop+of+diamagnetic+materials

Please look at images...

and consider

the ref http://www.mdpi.com/1996-1944/6/11/5247/htm

could be a very similar system as yours, combining doped Co film on ZnO.

Best regards

Daniel

In Lisa Tause book about rock magnetism (is free on line, you con search it9 you encountered examples of rocks with ferromagnetic and diamagnetic minerals that added show that graph. On the other hand, to substract the diamagnetic contribution you could take the line defined by the higher H field and from this line you obtain the slope; multiple the slope by the H field and substracte it from de M signal,  and you will see the ferromagnetic hysteresis graph alone. The slope is the magnetic susceptibility of the diamagnetic sustance, so, in principle you can to single out it. You will be very carefull with the units used. 

... and, as noted before, the recipe mentioned by Carlos (and myself above) is only correct when one can be sure that the M(H) slope at high fields is uniquely given by the diamagnetic response. This is nontrivial in general.

Even in colloids with diamagnetic cap and ferromagnetic core such effect may occur.As stated by Fauth one to ensure the slope at very high magnetic field folloed diamagnetic behaviour.

All the above are correct......but close examination of your figure suggests odd things

1. The hysteresis loop is not symmetric

2 the ferro bits(s) are clearly magnetically very soft eg like transformer steels unlike mineral ferromagnets eg  lodestone

Other things you could do if warranted

Try applying a big field preferably with the sample heated as much you can . then let sample cool back to RT  IN THAT FIELD. now do the MH curve ... is it even more asymmetric about  H=0 . Does the middle bit change in shape  .

If this "sample is moderately large cf the pickup coils in the VSM and you can alter the sample position , a sweep through different sample positions will tell you whether the mixture is fine grained eg uniformly  distributed or discrete lumps of two or more different "species" . That needs a bit more analysis eg  you need to know ythe output t profile of a truly uniform sample (a sphere of SC lead is great or a sphere of  say gold ( best not to use Fe or another  ferromagnet... unless saturated there will e domains = spatially nonuniform M

Actually what is your sample ?  

Jeya provided specimen information a couple posts up!

Since you have such a weak signal ,  you must :

-consider the contribution of the sample holder(you must make measures in the same conditions of the sample holder only without any sample!)

- take into account  the demagnetizing field correction Heff = Hext - Nd  M

Nd : demagnetization coefficient in the considered direction

M: magnetization

Hext = applied field

and you replot M vs Heff

The M-H curve you have described indicates that your sample is likely a ferromagnetic material. The presence of the hysteresis loop in the center suggests that the material experiences a very small amount of magnetic field, which is characteristic of ferromagnetic materials.

Dear Dr. Saravanan,

If you are looking for better proof or evidence of your magnetic samples, I suggest that you take first-order reversal curve (FORC) analysis. We perform this analysis for researchers affordably. Please contact me if you need more information. Email: [email protected]

Regards