Dear Irfan,

Let me try to summarize some magnetic properties related with the size of the nanoparticles.

The size is very important in magnetism because the anisotropy energy depends of it. On the other hand the magnetic domains have a finite size and the monodomain nanoparticles presents superparamagnetism, i,e, hysteresis cycles without area and therefore without losses (i.e. without heat within a DC field the AC allows to produce it in very subtle form). This means that the spins rotate coherently as if you had an only superspin for the whole nanoparticle. On the other hand, this produces a Neel relaxation time exponentially dependent of the size of the nanoparticles. That is to say, the size directly tells you how the magnetizacion of the samples can relax from a kind of "macroscopic ferromagnetism" to a "paramagnetism".

Dear Irfan,

You might find some useful information from the work below of Sheng et al (2017) in which they presented a systematic study of the size-dependent of heat generation by MNPs (6-40nm) under AMF.

Article Size-Dependent Heating of Magnetic Iron Oxide Nanoparticles

And the similar work of Jeotikanta et al (2018) examined the size-dependent magnetic and heat generation of MNPs (3-32nm).

Article Size-dependent magnetic and inductive heating properties of ...

Heat generation also depends upon the magnetic phase of nano particles. If particles have FM phase then the domains and the dynamics of domain wall motion will leads to large hysteresis loop area that results in more heat. Additionally, Neel losses and Brownian losses also contribute to heat generation.

Dear Prof Daniel Baldomir , Dr Loi Tonthat and Muhammad Nauman,

Can you please summarize idea about the Neel's relaxation (internal rotation of the magnetic moment) and Brownian relaxation (physical rotation of the magnetic Np).

If mag Np's are doped in polymer material and Alternating Mag field is applied to the material, so the easily rotation of Np according to above mentioned Neel's & Brownian will cause more heat energy release or if the particles do no rotation in presence of AMF than more heat energy release.

I need to understand that in which we get more energy NP's rotation or

no-rotation ?

Thanks