Unless there is some systematic error on the instrumentation used, I have observed an inverted peak when measuring the FMR absorption derivative for a YIG/NM/m-FM thin-film sample. The YIG layer was deposited via magnetron sputtering on GGG(111) substrate and is not monocrystalline but exhibits only a few crystalline phases. The observed anomalous peak is normal at lower frequencies, goes through a change at 2.5 GHz and becomes inverted at the higher range. Another peak observed for the same sample (probably corresponding to a different crystalline phase) is not inverted but at least four times more intense, both at lower and at higher frequencies. Both peaks occur on the same FMR dispersion curve.
Dear Eric,
could you give us the spectra so that someone can more definitely express their assumptions on this matter?
Dear Professor Morchenko, thank you for your interest. I am posting some images.
This may happen due to homogeneity and strain in the sample, see
http://iopscience.iop.org/0957-0233/25/7/075502 .
According to my experiments, this also depends on frequency. I found at some frequencies normal signal while at other (such as at 7 GHz and 8GHz) an inverted derivative signal for the same sample.
I agree with Sadeq H. Lafta that the lack of homogeneity in the sample may be the main reason for the inverted peak but, depending on the sample thickness, you should also take a look at the interplay the sample thickness and the skin depth. See, for example, Article Low‐field microwave magnetoabsorption in manganites
andArticle Surface resistance of thin Perovskite films - High-temperatu...
Dear professors Sadeq H. Lafta and Manuel Dominguez , thank you for participating in this debate.
The article "Thin film’s magnetostriction investigated by strain modulated ferromagnetic resonance at low temperature", suggested above, shows inverted peaks obtained with strain modulation, which seems to be a different case.
Professor Sadeq H. Lafta , which technique did you use when you obtained inverted peaks? How do you interpret the inverted FMR absorption peaks in terms of the energy balance in the system (RF source/sample absorption)?
The absorption dip shown in the article "Low-field microwave magnetoabsorption in manganites" corresponds to a feature known as ferromagnetic anti-resonance (FMAR), as mentioned in the article, and it is different from the inverted peak mentioned in my question, especially in that it never reaches a negative value for the absorption, while the inverted peak of the absorption derivative that I report, when integrated, leads to negative absorption.
So the question remains: Is it possible to have this inverted peak?
I used broadband multi-frequency stripline technique when I obtained inverted peaks. I interpreted them according to homogeneity of the sample and the standing wave due to reflection within the sample and sample thickness.
I hope these information is useful and let us know if there is an other explanation.
Regards
Thank you, professor Sadeq H. Lafta for your answer. By the way, I came across an article, Ferromagnetic relaxation in yttrium iron garnet and the relation to applications (1962!), by E.G. Spencer and R.C. LeCraw, that shows an inverted peak caused by parametric excitation. We have not used parametric excitation in the experiment. The article is illustrative of the interplay of magnetic energy between oscillation modes of spin waves and the uniform mode.
Professor Sadeq H. Lafta is there any publication where you include these inverted peaks that you have observed?
Dear Eric-Hermanny, we just discussed that in our lab and not published in details in our publishing. Here the links
Article Broadband ferromagnetic resonance of non-stoichiometric nano...
Article Impact of Ni²⁺ Content on Broadband Ferromagnetic Resonance ...
I hope they are useful.
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