Asymmetric magnetic dots: A way to control magnetic properties

Abstract

Artículo de publicación ISIWe have used Monte Carlo simulations to investigate the magnetic properties of asymmetric dots as a function of their geometry. The asymmetry of round dots is produced by cutting off a fraction of the dot and is characterized by an asymmetry parameter . This shape asymmetry has interesting effects on the coercivity (Hc), remanence (Mr), and barrier for vortex and C- state formation. The dependences of Hc and Mr are non monotonic as a function of with a well defined minima in these parameters. The vortex enters the most asymmetric part and exits through the symmetric portion of the dot. With increasing the vortex formation starts with a C-state which persists for longer fields and the barrier for vortex exit diminishes with increasing asymmetry, thus providing control over the magnetic chirality. This implies interesting, naively-unexpected, magnetic behavior as a function of geometry and magnetic field

Magnetization reversal in asymmetric trilayer dots: effect of the interlayer magnetostatic coupling

“…For example, the M r / M s value decreases from 0.98 to a minimum of 0.71 and subsequently ascends to 0.93 at the semicircle dot. This behavior is also found by NM Vargas and co-workers [ 5 , 8 ] and is explained as a consequence of the competition between exchange, local dipolar interactions, and geometry effect. The cutting surface facilitates the emergence of a C-state due to the elimination of the magnetic poles on it, which decreases the remanence.…”

“…Furthermore, the flux-closed configuration leads to negligible stray fields and thus can reduce the interelement interactions in densely packed arrays. Because magnetic vortices have potential applications in ultrahigh-density recording media [ 1 ], magnetic random access memories [ 2 , 3 ], and spintronic logic devices [ 4 ], many methods are proposed to control them efficiently exploiting, such as element shape deviating from symmetry [ 5 - 8 ], nonuniform external magnetic field [ 9 - 11 ], magnetostatic and exchange coupling between element layers [ 12 - 14 ], and electric field [ 15 ].…”

Controlling vortex chirality and polarity by geometry in magnetic nanodots

“…This reversal process can be due to non-resonant single field/current pulse 5 or by means of applied magnetic bursts 6 or spin-polarized currents 7 inducing an oscillatory mode in the vortex core around its equilibrium position (gyrotropic mode 8 ), or else to spin waves 9 inducing some excitation in the azimuthal modes. 10 On the other hand, some works show how to control the chirality of the vortex by introducing some asymmetries in the shape of dot, [11][12][13][14] in its magnetic properties, 15 or in the applied field distribution. [16][17][18] Some of them also control the vortex polarity by adding an out-of-plane magnetic field 13 or by using non practical complex geometry.…”

Breaking the configurational anisotropy in Fe single crystal nanomagnets

“…As an example, the nucleation and annihilation sites can be selected and their corresponding nucleation and annihilation fields can be tuned by choosing the geometry of the dots in combination with the orientation of the applied field. [19][20][21][22][23][24][25] Most studies have emphasized the relevance of the dipolar fields in controlling the hysteresis of dots. So far we know, the role of the magnetocrystalline anisotropy energy (MAE) has not been usually considered since most of the experimental studies in the literature deal with dots patterned on Permalloy 14,15,18,23 (low MAE) or on isotropic polycrystalline films 16,22,25 (no preferential crystalline orientation).…”

“…They traverse the dot when the applied field is reversed and they are finally expelled when the annihilation field H ann is reached. [18][19][20] Vortex dynamics can be controlled using different strategies. As an example, the nucleation and annihilation sites can be selected and their corresponding nucleation and annihilation fields can be tuned by choosing the geometry of the dots in combination with the orientation of the applied field.…”