Interplay between magnetocrystalline and configurational anisotropies in Fe(001) square nanostructures

Abstract

We fabricated a set of arrays of single-crystal Fe micron and submicron square elements on MgO using a focused ion beam apparatus. The squares have different size (1-µm and 500-nm side) and orientation with respect to the crystalline axes. The three patterns were magnetically characterized by means of magneto-optical Kerr effect microscopy/magnetometry, and the symmetry and strength of their magnetic anisotropy was determined through transverse susceptibility measurements performed with the modulated field magneto-optical anisometry technique. We observed that the overall anisotropy of the systems is determined by the interplay between the intrinsic magnetocrystalline anisotropy of the material and the anisotropic energy of the magnetic configurations determined by the lateral confinement (the so called configurational anisotropy). Depending on the relative orientation of the patterns with respect to the intrinsic magnetocrystalline anisotropy axes, the interplay can give rise to enhancement or reduction of the configurational contributions compared to the case of identical patterns made of isotropic material. Our results demonstrate that the strength of the latter contribution is comparable to the first one and can be used to create nanoelements with peculiar anisotropy symmetries

Arrays of Metal Nanostructures Produced by Focussed Ion Beam

“…To study the interplay between magnetocrystalline and configurational anisotropies, we fabricated by FIB milling a set of arrays of Fe single crystal square elements on MgO [16,49]. In this system the intrinsic magnetocrystalline anisotropy of the Fe single crystal has a fourfold symmetry, which is the same main symmetry showed by the configurational anisotropy in square nanomagnets [45,47,48].…”

“…The exchange bias effect is larger in the presence of a sharp ferromagnetic/antiferromagnetic interface [44], therefore this partial interfacial broadening is in turn expected to reduce the exchange effect. In addition, the localization of damage at the edges of the nanostructures is expected to affect the magnetostatic dipolar (shape and configurational) contribution [16,45] and the overall anisotropy of the magnetic structure.…”

“…Properties like magnetization switching and magnetic anisotropy have been measured either on the individual nanomagnets, using local magnetic probes [14,15], or collectively, using integral probes that measure average magnetic quantities [16]. Combining perpendicular magnetization media and FIB milling to produce artificial grains in the magnetic film through the cut of trenches or grooves, storage densities as high as 200 Gbit/in 2 have been achieved [17].…”

Macrospin limit and configurational anisotropy in nanoscale permalloy triangles

“…This phenomenon is a direct effect of the rotational symmetry order (n) of a nanostruture on its magnetic anisotropy: triangles (n=3) evidence a six-fold anisotropy, squares (n=4) a four-fold anisotropy, and pentagons (n=5) a ten-fold anisotropy [4,5,6]. Note that the necessity for easy and hard axes to present the same symmetry leads to frequency doubling for odd orders of n [7].…”

“…Different approaches have been proposed to measure higher-order magnetic anisotropies, such as Rotating field MagnetoOptic Kerr Effect (ROTMOKE) [8] in magnetic thin films, or Modulated Field Magneto-Optical Anisometry (MFMA) [9,6] in Supermalloy (Ni 81 Fe 14 Mo 5 ) and Fe nanostructures presenting CA. In both methods, large static fields are used to impose macrospin-like behavior in the structure, in order to interpret the data within a Stoner-Wohlfarth (SW) model and extract a value for the strength of this anisotropy.…”