Hello all,
I am trying to analyze the differences of stiffness of magnetic moments in the bulk of a thick permalloy disk against the moments on the surface, when they are excited with an ac external field. Same study on thinner disks. I have exported from mumax different parameters, such as exchange constant, anisotropy field... but which magnitude would you analyze in both cases in order to support the idea that moments are not that prone to precess when they are pinned by the surface, in contrast to those in the bulk?
I tried with anisotropy field, but the matrix is empty... and with the effective field, but I don't know how to procced with the reasoning... When talking about "stiffness" of magnetic moments, is the exchange field what matters, is it?
Thank you so much in advance.
You seem to be tied with iron chains to muMax, did not you try to calculate the same for oommf? It's not very clear, are you just doing a calculation or are you still doing an experiment? It is known that there is a Brown paradox, and the experimentally obtained magnetic fields will be less than calculated ones. Tell us more about your task, then you will be answered on the merits
Dear Lev, thank you for your answer. It is all a numerical results task to show some evidence on the mentioned idea. At the moment we are not planning an experiment on the matter. The task is to show some intuitively reasoning, that may explain whether magnetic moments are more free to precess in the bulk and more pinned close to the surfaces of the disk , but I lack the physics connection between that pinning and which parameter is affected by that, so it could shed some information and ideally, work as an "estimator" or a "pinning factor".
I am trying to reduce the problem down to dipolar and exchange interactions, so it could provide a more intuitive answer. All I am asking is which physical property do you think it could work the best to that purpose.
For example, we have checked dipolar field varies a lot from the top layer to the bulk, when close to the core. If the dipolar field could work as an estimator of the pinning, which is the equation or physical relation that would explain that? In other words, does a larger dipolar field fixes more magnetic moments, in general? Are they independent things and it is just a coincidence or is there really a connection?
Again, thanks.
Within the framework of micromagnetism and neglect of anisotropy, I see no reason for pinning of magnetic moments on the surface. Let us consider, for example, a uniformly magnetized sphere. At any of its points including the surface, the dipole field is the same. The exchange field have a jump on the surface, but the exchange field is isotropic in directions, there is no dedicated direction, and hence no pinning
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