I carried out RT VSM measurements of iron oxide nanoparticles using 7400 series Lakeshore VSM system. I noticed the curve splits at saturation magnetization (see the attached pic). Could anyone please tell me the reason of this and how to solve it?
First idea is that the temperature (RT) drifted during the measurement cycle and the sample is temperature-sensitive around ~300K. The drift may be caused by local weather but if the sample is conducting then it may be an effect created by eddy currents heating the sample. This seems likely, as the sample is a soft magnetic material, thus probably more or less metallic. Heating is more effective at higher fields what is consistent with presented result. It may be also an effect of non-isotropic sample reorientation during measurements (unlikely).
In my opinion it's exactly what you described last. If the sample is not perfectly attached to the vibrating rod, it can slightly move from its starting position therefore causing the splitting in M in the end. You see it starts to deviate already for 0.2 T.
Repeat your measurement, but make sure your sample is perfectly mounted to the vibrating rod. Mostlikely, you won't see this splitting again.
The sample is not attach the VSM holder, I faced the same problem for thin film. Regards
Dear Mark, thank you very much. Yes, I guessed this could be the technical problem. I will try with the standard sample once.
Literally, yes. We need to mount and fix the sample properly. Better to grind the sample to fine powder and use it. Also, you can check the curve by changing the rate of magnetic field.
Yes, the last sentence points into correct direction. The change of magnetization after external field is changed does not occur momentarily, it takes some time. This is sometimes called magnetic viscosity and is most easily observed in hard magnetic materials (i.e. those having wide hysteresis loop). Magnetic material adapts itself to sudden change of external field in a matter of microseconds (soft materials like transformer steels, permalloy, some amorphous alloys) up to hundreds of years (permanent magnets).
Dear Marek,
How do you have only splitting for the positive saturation magnetization and not of the negative one?
Please what about the split for the negative saturation magnetization?
Pl. mount the sample properly and repeat the measurement, hope you will get a perfect loop
Dear Baldomir,
You'll see the split at negative field when you start recording the complete loop from minus saturation. Magnetic viscosity may be made better visible by using various field sweep speeds ( |dH/dt| , fixed during given test): higher values of |dH/dt| should correspond to bigger splitting. Still another result might be obtained when there is some waiting time between recordings of upper and lower branch of hysteresis loop - up to two disconnected branches (within experimental accuracy, naturally).
I carried out RT MH measurements of cadmium oxide nanoparticles. There is small hump at low magnetic field in both sides of MH curve. Can anyone give the reason of this. and how to solve it.
Very interesting, indeed. The sample looks roughly like a paramagnet, but its crystal structure may be the key to understand observed small humps. We are most likely dealing not with individual spins, but rather with their pairs (or other small clusters).
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