Domain wall assisted magnetic recording

Abstract

Using numerical and analytical micromagnetics we calculated the switching fields and energy barriers of the composite (exchange spring) magnetic recording media, which consist of layers with high and low magnetocrystalline anisotropy. We demonstrate that the ultimate potential of the composite media is realized if the interfacial domain wall fits inside the layers. The switching occurs via domain wall nucleation, compression in the applied field, de-pinning and propagation through the hard/soft interface. This domain wall assisted switching results in a significant reduction of the switching field without substantial decrease of the for thermal activation energy barrier. We demonstrate that the Domain Wall Assisted Magnetic Recording (DWAMR) offers up to a three-fold areal density gain over conventional single layer recording.Areal density is one of the most important figures of merits for the information storage technologies. With the increase of the recording density the dimensions of the magnetic media grains have to be reduced to maintain the signal-to-noise ratio. Reducing grains dimensions results in the decrease of the magnetic energy barrier which leads to the thermally activated loss of the stored information. To increase the thermal stability the magnetic anisotropy of the grains can be increased, however the maximum anisotropy is limited by the write head fields. The described "trilemma" [1] constitutes the main physical limit that magnetic recording faces in the attempt to achieve the higher recording densities.As a means to resolve this problem, Victora and Shen proposed the so-called composite media [2], which are made of two layers, one of which ("hard") possesses high magneto-crystalline anisotropy, while the other ("soft") layer has very low anisotropy. It was shown in Refs. [2,3] that for the optimum exchange coupling across the layers interface the switching field of such a structure may be substantially reduced compared to a single layer film. The concept of exchange spring media, utilizing noncoherent magnetization rotation in hard/soft multilayers to reduce the switching field, was independently introduced by Suess et al. [4,5]. Guslienko et al. [6] analyzed the switching field in dual layer media taking into account non-uniform magnetization rotation, and the results were shown [4,7] to differ from the "two-spin" (rigid layers) approximation.In this Letter we will show that the ultimate potential of the composite (exchange spring) media is realized when the interfacial domain wall fits inside soft and hard layers. We will analyze the potential of the Domain Wall Assisted Magnetic Recording (DWAMR) using numerical micromagnetics as well as analytical formulas derived in Refs. [8,9] for exchange spring magnets.In our micromagnetic simulations the hard and soft layers are discretized down to atomic scale (0.2 nm) in the vertical (perpendicular to the film plane) direction. We include the external, anisotropy and vertical exchange fields, however, for simplicity, we do not take into account t...

Exchange-coupled perpendicular media

“…It was shown the required write field decreases by a factor of between two and four in composite media and exchange spring media, respectively 5 , 6 . The effect of different soft layer anisotropies on the switching field was studied in detail by Dobin et al 7 . Garcia-Sanchez et al studied the reversal process of magnetic bilayers using a multiscale approach where the interface between the hard and soft layer is discretized atomistically.…”

Electronic and magnetic properties of bimetallicL10cuboctahedral clusters by means of fully relativistic density-functional-based calculations

“…Because of these diverse applications in nanotechnology [10,11], the development of nanostructured magnetic materials has become a highly active field. Focusing in the field of magnetic recording, a huge amount of experimental and theoretical work has been carried out during the last decade to seek novel approaches to construct advanced materials for ultrahigh density magnetic storage, with the aim of increasing the state-of-the-art beyond 1 Tbit/in 2( [8,[12][13][14][15] ) . Most approaches are focused on thin films or multilayers [16][17][18] and recently on slabs [19].…”

Nucleation and wall motion in graded media

“…Inhomogeneous nanostructures have recently attracted much attention in magnetic recording, because they combine low writing fields with high magnetic anisotropy. [1][2][3] In other words, two-or multiphase hard-soft materials can be used to improve the writability of recording media by reducing the coercivity without negatively affecting the thermal stability. An explicit proposal for continuous media is to exploit that a reduction of the domain-wall energy gradient d␥ / dx makes media easier to write.…”