Self consistent measurement and removal of the dipolar interaction field in magnetic particle assemblies and the determination of their intrinsic switching field distribution

Abstract

Using low density arrays of bistable magnetic nanowires as a model dipolar system, it is shown that the dipolar interaction field coefficient can be measured from the remanence curves as well as from other functions of the isothermal remanent magnetization and the DC demagnetization remanence obtained as an affine transformation of the Wohlfarth relation. Based on mean field arguments, these measurements are used to subtract and remove the contribution of the configuration dependent dipolar interaction field from the major loop and remanence curves. The corrected remanence curves are first used to obtain the

Modelling of isothermal remanence magnetisation curves for an assembly of macrospins

“…Because the IRM curve reflects the irreversible switching of nanomagnets, it seems convenient and physically meaningful to define the irreversible susceptibility χ irr as χ irr ¼ dIRM=dH [4,7,9,10,12,15,17,[24][25][26]. From the expressions established before, we can write…”

“…Among the various magnetic measurements used to characterise a nanomagnet assembly (or a granular system), Isothermal Remanent Magnetisation (IRM) is a long-established protocol which is however rarely quantitatively exploited [1][2][3][4][5]. Originally, is was used to evaluate the switching field distribution (SFD) or, combined with Direct Current Demagnetisation (DCD) measurements, to detect the nature of interactions via the parameter Δm or via a Henkel plot [6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Configuration dependent demagnetizing field in assemblies of interacting magnetic particles

“…(2) and the IRM and DCD remanence curves are done solely along the wire axis, this is, the measurement is related to the component of the interaction field along this direction, as pointed out in Ref. 23. From Eq.…”

“…As discussed in Ref. 23, assuming an interaction field of the form αm, the shearing can be corrected once the value of the coefficient is known, which;…”

“…(28), (29) and (30) provide different expressions for the interaction field which have different physical meaning. Moreover, depending on the measuring technique, each of these three quantities can be measured independently, 18,23,29 so it is important to distinguish between them.…”