Image from the paper

Magnetic reversal process: The pictures show the magnetic flux lines. The color denotes the magnetization direction (red: magnetization up, blue magnetization down).
The gap between the soft magnetic spheres (d incl = 8 nm) is 1 nm in the first two columns and 4 nm in the third column. The external field is applied in z-direction and its value is written next to each picture.
In the first column the soft magnetic inclusions are aligned perpendicular to the applied external field. The interaction with the outside inclusions is weakening the central sphere and forces it to switch first.
In the second and third column the soft magnetic spheres are aligned in a parallel manner to the applied external field. The two outside spheres reinforce the central one and therefore nucleation should not start in the center. But for gaps smaller than 4 nm a strong demagnetizing field in the location of the central sphere caused by the shell diminishes the strengthening effect due to dipolar interaction.

Our paper titled “Enhanced Nucleation Fields due to Dipolar Interactions in Nanocomposite Magnets” was presented by first author, Johann Fischbacher, at the JEMS 2012 conference and subsequently published in the The European Physical Journal B.

We are now making a PDF preprint of the resulting paper available here. The paper can be found on the journal webpage here.

Abstract:

One approach to construct powerful permanent magnets while using less rare-earth elements is to combine a hard magnetic material having a high coercive field with a soft magnetic material having a high saturation magnetization at the nanometer scale and create so-called nanocomposite magnets. If both materials are strongly coupled, exchange forces will form a stable magnet. We use finite element micromagnetics simulations to investigate the changing hysteresis properties for varying arrays of soft magnetic spherical inclusions in a hard magnetic body. We show that the anisotropy arising from dipolar interactions between soft magnetic particles in a hard magnetic matrix can enhance the nucleation field by more than 10% and strongly depends on the arrangement of the inclusions.Fischbacher et al., “Enhanced Nucleation Fields due to Dipolar Interactions in Nanocomposite Magnets”, Eur. Phys. J. B (2013) 86: 100
DOI: 10.1140/epjb/e2013-30938-1