I am currently working with Mn doped BST( Barium Strontium Titanate). And investigates it Dielectric and Magnetic properties as a function of frequency from KHz to GHz region. The VSM show narrow hysteresis with small coercieve field. I also find that for a specific concentration the dielectric constant increase with the increasing frequency although it decrease again. A sharp peak is noticed in dielectric loss factor with increasing frequency from stable condition. I am grateful, to let me know which factors plays important role on BST characteristic with frequency.
Dear Robayet,
The magnetic permeability under an oscillatory electromagnetic field is a complex quantity instead a real one. The real part corresponds to the lossless part of the permeability at a given frequency, while the imaginary part corresponds to the losses wasted by the oscillatory field in such magnetic medium. The cocient between the imaginary part respect to the real one gives gives the importance relative of the losses at a given frequncy an it can be thought as a tangent of phase called magnetic loss tangent.
This can be also interpreted as an AC cicuit and the main idea is how the electromagnetic energy distributes on a material assumed to be formed by magnetic dipoles. In the case of the electric permittibity the things are quite similar assuming that there are electric dipoles instead of magnetic ones.
It is not easy to answer because the loss mechanism is came from many thing (electric, magnetic and optics), but mostly from the electric part mechanism.
A Vector Network Analyzer (VNA) will give a complex function of permitivity and permeability as a function of frequency, as well as the absorption. Here you can estimate which one is dominant and what kind of mechanism (relaxation or resonace).
From VSM you can get the Anisotropy Field (Ha) to calculate the FMR frequency. I'm sure the FMR frequency of Mn substituted BST (if has) somewhere in MHz range.
As Dr. Manawan said you need to figure out the frequency dependence of complex magnetic permeability or complex electric permittivity of a specific system using Microwave vector network analyzer (MVNA). Again it is not easy to judge how the magnetic tangent loss parameter varies with frequency i.e. magnetic loss/permeability, however, you need to consider factors such as the temperature and thickness of your sample that also play part in shifting the resonances and thus affecting the results obtained for of both values of magnetic loss and permeability.
Actually I just want to note down one thing that, as the frequency increases the dielectric permittivity of the material will decrease due to the polarization mechanisms within in the material. Then how will be the variation of magnetic permeability with frequency?
For better understanding, you can read the following articles:
1. An experimental insight of the multiferroic properties of magnetoelectrically coupled xLNCZFO+(1−x)BSTDO composites, Journal of Magnetism and Magnetic Materials, Volume 502, 15 May 2020, 166449.
2. Study of impedance and magnetoelectric property of lead-free xLCNZFO+ (1-x)BGTDO multiferroic composites, Materials Chemistry and Physics, Volume 255, 15 November 2020, 123575.
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