Hi all,
I am trying to measure the Ferromagnetic resonance of different arrays of holes with a few microns diameter (from 4 to 10). The samples are made by laser writing techniques on a photoresist and the holes are filled with magnetic material through electrodeposition.
The setup I have got is as usual, I place the sample, face down on a coplanar waveguide and connect it to a VNA. I have managed to measure the curve for a nanostructure, but I am having troubles with my arrays of microns size. No matter if I turn the CPW 90 degrees to test the easy axis, the plot Frequency vs B field doesn't show any clear curve for any array...
Please, any ideas on what I may be doing wrong?
Explain, "what is the meaning of clear curve?"
Are you able to pick up the FMR signal from your arrays or not?
Or may be the FMR signal wings are not clear .
So first explain somewhat more so that we can discuss it clearly?
Yes. From other samples, arrays of squares but in the size of nanometers, I can see a square root shape curve in the plot Freq vs B field, where intensity is the S12 magnitude. Thin enough to distinguish from the background. When measuring my arrays, in the order of microns, we don't see that thin curve going up. Rather, we see like broad stains on the intensity plot. We don't know if that is our FMR line, now way much wider, or we are just not measuring the FMR and that is some kind of background.
What we were expecting was a thin curve, as it is seen in thin films or in these nanostructures, so we were wondering how we could improve our readings. Could be due to the fact that the samples are fabricated through electrodeposition and the deposition is not that good, so there are polycrystals and these broaden too much the curve?
Hope I've been clear enough. Many thanks.
Polycrystalline nature definitely broadens the FMR signal linewidth but at the same time as you are depositing micron size so magnetic volume increases which shows the strong FMR signal intensity as compared to thin films.
First of all tell me that in nanostructures sample what was the intensity of FMR signal?also tell me the same for microstructure arrays?
One thing i understand that you are measuring FMR signal in frequency sweep mode so in that case strength and SNR is low?
I recommend that try to measure the FMR in field sweep mode which will definitely enhance your signal strength?
In what frequency range you are measuring, i mean that CPW is showing flat response in this frequency range or not?
I was electrodepositing CoNiP before, and now I am electrodepositing Co, can I still get polycrystals in my structure using Co or it is no related?
The intensity in the nanostructure, which is permalloy, is in the order of 0.002 dB and the same for the microarray. The thing is that in this last case,
I am measuring the FMR in a frequency and B field sweep, sweeping in frequency for each value of B, from 1 MHz to 20 GHz. Response of the CPW is not that good up to 20 GHz, it has a absortion peak around 10 GHz and it is not flat enough. Even do, I can see the FMR for nanostructures, although there is some noise in the background. By the way, I subtract for each measure, a certain measure (say, at B= 90 mT) to try to minimize the background effect.
Do you mean something else by saying "to measure FMR in field sweep mode"?
Field sweep means that frequency is fixed and you are sweeping the B field from zero to maximum value you have. In this case the SNR is high and also you will get rid of the problem of CPW mismatch.
Intensity(0.002dB) is not so high in freq sweep mode so try to measure in field sweep mode.
Also i suppose that you have calibrated all the working cables and your CPW.Isn't it?
Yes, in essence is the typical VNA-FMR setup. I sweep in frequency for each value of B field. I calibrate everything, with the CPW connected without the sample, I update the thru calibration and then I start stepping up the field.
In my search of magnetic materials in the setup, I have found that the ends of the SMA cables connecting the CPW to the VNA, are magnetic, so I have thought of using a high mu non magnetic material around them to redirect the magnetic field....
I am trying as well to redesign the CPW so I have a better transmission parameter up to 20 GHz. Do you know any webpage or book that I could have a look?
Thank you so much in advance
In any FMR type experiment the excitation field must be applied perpendicular to the applied field. If they are parallel you will not pump the spins correctly and hence you cannot measure the dynamic response. It is a question of geometry.
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