Simulation Of Magnetic Recording Research Articles

Component Design Considerations for High Areal Density in Heat-Assisted Magnetic Recording

To provide useful component design guidance, micromagnetic simulations of heat-assisted magnetic recording (HAMR) must include estimates of the areal density (AD) of the recording system. In this work, we investigate the influence of both near field transducer (NFT) and medium design on AD. Exploring a range of medium and NFT designs we demonstrate that once the thermal gradient of the head and medium system is sufficient, the achievable jitter (and hence linear density) is governed by the magnetic properties of the medium. Including readback parameters, we outline requirements for HAMR recording systems capable of achieving >2 Tbpsi in hard disk drives with product margins.

The superior role of the Gilbert damping on the signal-to-noise ratio in heat-assisted magnetic recording

In magnetic recording the signal-to-noise ratio (SNR) is a good indicator for the quality of written bits. However, a priori it is not clear which parameters have the strongest influence on the SNR. In this work, we investigate the role of the Gilbert damping on the SNR. Grains consisting of FePt like hard magnetic material with two different grain sizes d=5 nm and d=7 nm are considered and simulations of heat-assisted magnetic recording (HAMR) are performed with the atomistic simulation program VAMPIRE. The simulations display that the SNR saturates for damping constants larger or equal than 0.1. Additionally, we can show that the Gilbert damping together with the bit length have a major effect on the SNR whereas other write head and material parameters only have a minor relevance on the SNR.

Statistical analysis of read-back signals in magnetic recording on granular media

The comprehensive simulation of magnetic recording, including the write and read-back process, on granular media becomes computationally expensive if the magnetization dynamics of each grain are explicitly computed. In addition, in heat-assisted magnetic recording, the writing of a single track becomes a random process since the temperature must be considered and thermal noise is involved. Further, varying grain structures of various granular media must also be taken into account to obtain correct statistics for the final read-back signal. Hence, it requires many repetitions of the write process to investigate the mean signal as well as the noise. This work presents a method that improves the statistical evaluation of the whole recording process. The idea is to avoid writing the magnetization to one of its binary states. Instead, we assign each grain its probability of occupying one of its stable states, which can be calculated in advance in terms of a switching probability phase diagram. In the read-back process, we combine the probabilities to calculate a mean signal and its variance. Afterwards, repetitions on different media lead to the final read-back signal. Using a recording example, we show that the statistical behavior of the evaluated signal-to-noise ratio can be significantly improved by applying this probability mapping method, while the computational effort remains low.

Micromagnetic simulator for complex granular systems based on Voronoi tessellation

Abstract A micromagnetic code based on Voronoi tessellation and the non-uniform fast Fourier transform (NUFFT) method is presented. The code is capable of efficiently and accurately simulating magnetization dynamics in large and structurally complex granular systems, such as multilayer granular media used for perpendicular magnetic recording, bit patterned media, granular nanowires, and read heads. In these systems the granular microstructure and distributions in grain and interface properties play an important role in device performance. The presented Voronoi simulator allows comprehensive studies to be performed as it accounts for the detailed granular microstructure and distributions that characterize true systems. Simulation time is greatly reduced by a non-uniform fast Fourier transform algorithm and implementation on graphics processing units (GPUs). Simulations of conventional magnetic recording, heat-assisted magnetization reversal, domain wall dynamics in granular nanowires, and particulate tape recording are presented.

Martingale weak solutions of the stochastic Landau–Lifshitz–Bloch equation

The present paper studies the stochastic Landau–Lifshitz–Bloch equation which is recommended as the only valid model at temperature around the Curie temperature and is especially important for the simulation of heat-assisted magnetic recording. We study the stochastic Landau–Lifshitz–Bloch equation in the case that the temperature is raised higher than the Curie temperature. The global existence of martingale weak solutions is proved by using a new argument and regularity properties of the weak solutions are discussed.

面記録密度1Tb/in^2-2.5Tb/in^2を達成するための熱アシスト磁気記録計算機シミュレーション(媒体,一般)

面記録密度1Tb/in^2-2.5Tb/in^2を達成するための熱アシスト磁気記録計算機シミュレーション(媒体,一般)

Transition Jitter in Heat-Assisted Magnetic Recording by Micromagnetic Simulation

In this paper we apply an extended Landau-Lifschitz equation, as introduced by Ba\v{n}as et al. for the simulation of heat-assisted magnetic recording. This equation has similarities with the Landau-Lifshitz-Bloch equation. The Ba\v{n}as equation is supposed to be used in a continuum setting with sub-grain discretization by the finite-element method. Thus, local geometric features and nonuniform magnetic states during switching are taken into account. We implement the Ba\v{n}as model and test its capability for predicting the recording performance in a realistic recording scenario. By performing recording simulations on 100 media slabs with randomized granular structure and consecutive read back calculation, the write position shift and transition jitter for bit lengths of 10nm, 12nm, and 20nm are calculated.

Exchange interaction energy in magnetic recording simulation

Based on a phenomenological theory, micromagnetic simulations and experiments are used to evaluate an improved function for the exchange interaction between magnetic particles in perpendicular recording media. Assuming diluted spin layers in the particle boundary and a gradual rather than abrupt rotation of magnetization between grain cores, the exchange energy is better described by an even power series of θ, rather than a cosine function. The conventional cosine function does not have a restoring torque near θ = π and adjacent grains tend to align strictly antiparallel. In contrast, using a power series of θ, adjacent grains tend to align at a small angle away from θ = π. This gives rise to a small in-plane magnetization component and therefore a distinct peak in in-plane susceptibility is observed around H = 0. From magnetization measurements of a real medium, a peak is observed around H = 0, which matches with an assumption of 2 or 3 spin layers. In some situations, the exchange interaction between discretized cells for numerical calculation is better described by a power series rather than a cosine function.

Micromagnetic model analysis of high frequency heat-assisted magnetic recording

FEM-boundary integral method micromagnetic software was used to analyze the recording field response of an indented magnetic head to high frequency recording currents (1–4 GHz). Next, micromagnetic simulations of heat-assisted magnetic recording were performed and the signal-to-noise ratio (SNR) calculated at high frequencies. With a soft magnetic underlayer, the head field was large enough and gave higher SNRs. The large head field strength at low frequency did not cause any deterioration of the SNR.

Off-Track Capability Simulation of Shingled Magnetic Recording Under Mechanical Track Misregistration

Shingled magnetic recording (SMR) is suitable for higher density recording due to its writing ability. We calculate the SMR's offset error rate with a probabilistic approach by using a linear geometric model. The results show the SMR's offset error rate as being a little better than conventional recording. We also quantify the error rate degradation of multiple adjacent track erasures in conventional recording, which is the largest merit of shingled recording.

Simulation of Heat-Assisted Magnetic Recording Using Renormalized Media Cells

A new scheme for the simulation of heat-assisted magnetic recording (HAMR) that systematically includes fluctuating material properties above a predefined length scale, while retaining magnetostatic interactions, is introduced. Renormalized media parameters Ms, Ku, Aex, and αdamp, suitable for useful length scales, are found numerically. These renormalized parameters are then used to model the Voronoi-cell-composed medium in the HAMR simulation. Transition jitters are obtained under various conditions. The results show that moderate maximum temperature of the heat spot, intergranular exchange coupling, media thickness of at least 10 nm, nonzero canting angle of the head field, relatively low head velocity, and large head-field strength are helpful for a successful recording.

Microwave-assisted magnetic recording simulation on exchange-coupled composite medium

The potential of microwave-assisted magnetic recording on exchange-coupled composite (ECC) media is investigated by numerically simulating read/write processes with respect to the physical and magnetic properties of the soft section of ECC media. To obtain desirable recording performance, the thickness of the soft section must be comparable to the exchange length. Under such condition, the optimal microwave frequency decreases owing to the non-uniformity of the reversal mode. A relatively high anisotropy field in the soft section produces high signal-to-noise ratios. Moreover, large saturation magnetization of the soft section enhances the magnetization reversal of ECC grains but excessive enhancement is likely to induce wide writing, which decreases the high track density.

High speed magnetisation reversal in heat-assisted magnetic recording

Calculations of switching times as a function of temperature and damping constant are discussed. Near to the Curie temperature, the switching time can be much shorter than at room temperature and independent of Ku. Simulations of heat-assisted magnetic recording were used to study the effect of heat and magnetic field pulse durations on the size and sharpness of bits written on various media. In media with small damping constants, the transition width was hardly influenced by the heat pulse duration, whereas, in media with higher damping constants, the transition width increased with the heat pulse duration.

Simulations of recording media for [formula omitted

Simulations of magnetic recording onto perpendicular media were carried out to determine parameters suitable for supporting an areal density of 1 Tb / in 2 . Composite media showed sufficient thermal stability and SNR to meet this goal, provided that dispersions of magnetic and microstructural parameters are sufficiently well controlled.

Magnetic Recording Simulation of Thermally Stabilized Recording Media with a thin Film Head

The decay of the recorded magnetization due to the thermal fluctuation has become one of the most important problems to be overcome in the technology of high density magnetic recording. In this paper, a self-consistent 2D read/write simulation based on the Poisson equation by a finite element method(FEM) is performed on a system of an AFC medium and a thin film head by using an extended Stoner-Wohlfarth(SW) model for the recording layers, where the switching rate of each SW particle at finite temperatures is taken into account by using the Neel-Arrhenius law and the master equation.

Hardware-in-the-loop simulation and analysis of magnetic recording of nerve activity

The focus of the reported research was on examination of properties of a special toroidal arrangement for magnetic recording of nerve activity. Toroidal high permeability coil placed around a nerve trunk can be used to record voltage induced by magnetic field generated by ionic nerve currents associated with propagating action potentials. The properties were examined in hardware-in-the-loop simulations that were used to identify the input–output relationship of the recording arrangement in case of different simulated intra-axonal current amplitudes and conduction velocities. Based on the recorded data, a nonlinear dynamical model (Wiener model) of the recording arrangement was identified, and subsequently used for predicting the voltage waveform expected in actual magnetic recording. This waveform was also used to estimate the potential of the method with the respect to obtainable signal quality (signal-to-noise ( S/ N) ratios). The manuscript also contains new theoretical results for sensitivity of toroidal and electroneurographic recording arrangements to different disturbances like, for example, EMG pickup. It can be concluded that high S/ N ratios, short length, and superior disturbance rejection of the toroidal magnetic recording arrangement can make magnetic recording an attractive alternative to acute and chronic electroneurographic recording techniques.

Efficient techniques for the computer simulation of magnetic recording in complex layered materials

Recent advances in magnetic recording technology are increasing the relevance of simulation to magnetic media design. In particular, the difficulties inherent in developing perpendicular recording technology require the write process to be modeled at an integrated level via the simulation of a nanoscale machine consisting of the media, the soft underlayer, and the moving head. These simulations need to be very efficient in order to permit extensive testing of both materials and drive specification. Thus, significant methodological improvements that increase the accuracy and speed of the micromagnetic modeling are required. In this article, a method for calculating the magnetic fields in a complex layered material with grained morphologies whose computational cost scales linearly with system size is presented. The speed, accuracy, and parallel efficiency of the method is demonstrated on both supercomputers and PC clusters using our Almaden-Yorktown micromagnetic simulator (AYM). The method and AYM software are then used to perform an example simulation of perpendicular magnetic recording, writing a “tribit” in a grained data layer.

Novel efficient techniques for computer simulation of magnetic recording

Perpendicular recording--a new paradigm for high-density magnetic recording currently under intensive development--presents complex engineering challenges which require that design be assisted by computer simulation. However, simulating perpendicular recording is itself a challenge for several reasons; it requires a large simulation box that includes both write head and hard disk and must be treated at high spatial resolution, and the simulations must run for long periods of time and for numerous data inputs. To accomplish this complex modeling, we have developed novel techniques which involve a mixed real-space/Fourier-space representation and which compute time scales linearly with system size, enabling large simulations to be performed efficiently. We show tests of our methodology and provide an example of a simulation that involves writing three bits (a tribit) to disk.

Simulation of magnetic recording of periodic antidot array

Micromagnetic simulation is performed to study the recording quality of a permalloy (Py) antidot array. A Karlqvist head field is applied to a single bit region to reverse its magnetization. The signal quality is quantified by the reciprocal of noise N −1 and contrast ratio C r, The results showed that N −1 and C r increase significantly with the increasing of the bit aspect ratio. The value of C r can also be improved by applying a bias field H y throughout the film, for films with high aspect ratio. For those with low ratio, H y causes undesirable switching of the neighbouring bits instead.

Simulations of magnetic recording in coupled granular/continuous perpendicular media with random pinning sites

Magnetic recording in coupled granular/continuous (CGC) media is simulated using a three-dimensional (3-D) micromagnetic model. Pinning sites are introduced via a random anisotropy constant K/sub u/, which follows a log-normal distribution with a mean value of 1 /spl times/ 10/sup 6/ (ergs/cc) and a standard deviation /spl sigma//sub Ku/ (ergs/cc). For a range /spl sigma//sub Ku/, we vary the thickness of the continuous layer c and the thickness of the granular layer g, while maintaining a constant media thickness. We analyze simulated tracks to produce SNR data for a range of c and /spl sigma//sub Ku/. We find that increasing /spl sigma//sub Ku/ reduces signal and increases bit transition irregularity and noise, which is then reduced via a mechanism driven by domain wall (DW) energy minimization by increasing c. Thus, we find that previous results hold in a more realistic CGC media model that contains random irregularity. In order to explain the observed effects, we identify three regimes of behavior that depend on the energy of domain wall relative to the pinning energy barriers provided by the granular layer.