Hi, Sir/Madam,
I am currently enrolled in PhD physics. i have first hand knowledge of Origin. Now i want to find the MCE in Rare - Earth Doped Ferrites but i don't know how to get started. As i am so much confused in the characterization Phase. After preparation of sample what type of characterization is needed for MCE? Simply VSM data is enough or some other calorimetric data is required?
and if i have hysteresis loop data with me. how can i calculate the entropy change.
I followed different questions here but i am so much confused.
Can you guide me in this respect please.
I am a starter. I need someone to guide me thoroughly. your cooperation will be highly appreciated.
your's
Waheed Alam
Kashmir Pakistan
The magnetic entropy change can be calculated either from heat capacity measurements or indirectly from magnetization curves. Using indirect method, the temperature dependent magnetization or isothermal magnetization plots can be used for obtaining magnetic entropy change. However, the recommended method involves a set of magnetic field dependent magnetization curves around the Curie temperature at constant temperatures. Once you get the magnetic entropy curves, you can estimate the relative cooling power (RCP) of the material. For details, you can check the attached papers.
You can calculate MCE I mean magnetic entropy change delta_Sm using M vs. H curve collecting at different temperatures. It is relatively simple method. You can review my papers which are on Researchgate.
Greetings
Piotr
Yes, it is possible to calculate the change in magnetic entropy using only the VSM data. However, it is easier to determine it directly from heat capacity data, CP. With heat capacity, you only need to take two measurements: one in high field, H2, and another in zero field, H1. The total entropy is given by ΔST = ∫ (CP/T)dT. The change in magnetic entropy is found using ΔSm = ΔST(H2)−ΔST(H1).
But, if you only have access to VSM data, you will need to take several measurements of M(T) using different (constant) field strengths. If you have hysteresis, you may need to be mindful about how you apply the field. The change in magnetic entropy can be determined through the Maxwell relation
ΔSm = ∫ ( ∂ M/ ∂ T)dH.
I.E. take several measurements of M vs T, each under a different applied field strength, then use Origin to take the partial derivatives and integrate over field. (Ideally, the low field would be zero, but that is not possible with VSM). Despite being two different methods, the magnetic entropy from VSM and heat capacity measurements agree rather well.
You can further characterize the MCE by calculating the change in temperature given an applied magnetic field. If you have performed the two measurements above, you can use the equation: ΔT = – ∫ (T/CP)( ∂ M/ ∂ T) dH. Note that the integrand should contain data sets for each field value you chose for magnetization data, meaning you may also need to take additional Cp(T) measurements at those same fields. Another useful quantity is the Relative Cooling Power, given by RCE = – ∫ ΔSmdT.
You may find the following papers useful in regards to the MCE.
Best of luck!