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Papers by Gerardo Bertero

Magnetic recording has been the technology of choice of massive storage of information. The hard-... more Magnetic recording has been the technology of choice of massive storage of information. The hard-disk drive industry has recently undergone a major technological transition from longitudinal magnetic recording (LMR) to perpendicular magnetic recording (PMR). However, convention perpendicular recording can only support a few new product generations before facing insurmountable physical limits. In order to support sustained recording areal density growth, new technological paradigms, such as energy-assisted recording and bit-patterined media recording are being contemplated and planned. In this talk, we will briefly discuss the LMR-to-PMR transition, the extendibility of current PMR recording, and the nature and merits of new enabling technologies. We will also discuss a technology roadmap toward recording densities approaching 10 Tv/in2, approximately 40 times higher than in current disk drives.

IEEE Transactions on Magnetics, 2017

The areal density capability (ADC) of a magnetic recording disk drive is highly dependent on the ... more The areal density capability (ADC) of a magnetic recording disk drive is highly dependent on the application or market segment. In this paper, we define a new areal density metric, which represents what areal density is possible under ideal recording conditions. This proposed areal density metric enables the industry to standardize and compare the ADC of magnetic recording disk drives across various recording technologies independent of market segment. We demonstrate the performance of experimental 2-D magnetic recording and heat assisted magnetic recording technology components measured using the proposed areal density metric.

IEEE Transactions on Magnetics, 2016

By averaging multiple writes of opposite polarity waveforms captured synchronously from heat-assi... more By averaging multiple writes of opposite polarity waveforms captured synchronously from heat-assisted magnetic recording (HAMR) media, we distinguish random noise of the HAMR writing process from the spatially anti-correlated repeatable noise due to media microstructure variations. We show both analytically and experimentally how the normalized cross correlation coefficient, R, of two opposite polarity waveforms quantifies the random and repeatable dc-noise fractions, showing where dc-noise reduction efforts should be concentrated. The value of R also reflects the degree of media saturation. At optimal recording conditions for the head and media studied here, the total dc-noise comprises appreciable fractions of both random and repeatable noise. The experimental results are supplemented with micromagnetic modeling and analytic calculations.

Metall Mater Trans a, 1991

Metallic multilayer thin films have found widespread use in technological applications. A number ... more Metallic multilayer thin films have found widespread use in technological applications. A number of multilayer films are being studied as perpendicular magnetic media for both magnetic and magneto-optic recording. The most promising of all are Pt/Co periodic multilayers because of their large magnetic anisotropy and magneto-optic Kerr rotations. A key property of these multilayer structures is the presence of a strong perpendicular magnetic anisotropy, K_{bot}, when the thickness of the Co layers is of just one or two atomic monolayers. The origin of the uniaxial magnetic anisotropy has been historically attributed to a symmetry breaking effect at the Pt/Co interfaces which favors an out-of-plane magnetic easy axis large enough to overcome the demagnetizing effect favoring in-plane magnetization in thin films. It is found, however, that the magnitude of K_ {bot} is strongly process dependent. We have undertaken a structure-property study in Pt/Co multilayers in an effort to identify...

IEEE Transactions on Magnetics, 1998

The microstructure and time-dependent magnetic properties of 2.8-60-nm-thick films of CoCrTa sput... more The microstructure and time-dependent magnetic properties of 2.8-60-nm-thick films of CoCrTa sputtered onto a Cr underlayer were measured. The thinnest films have a discontinuous microstructure with several CoCrTa nuclei forming on each Cr grain, with small angular misalignments from the exact epitaxial crystal orientation. For films of 10-nm thickness and above, the grains coalesce. There is evidence for stacking faults

Recording areal density in current drives is approaching 200 Gb/in^2. While compositions of indiv... more Recording areal density in current drives is approaching 200 Gb/in^2. While compositions of individual layers do generally vary, the structure of the PMR media in today's drives is remarkably similar with synthetic antiferromagnetically coupled soft underlayer (SAF SUL) structures, Ru based nucleation layers and oxide segregated recording (storage) layers [e.g., 1,2]. As areal density increases and track width is correspondingly

Systems and methods for controlling the damping of magnetic media for heat assisted magnetic reco... more Systems and methods for controlling the damping of magnetic media for heat assisted magnetic recording are provided. One such system includes a heat sink layer, a growth layer on the heat sink layer, a magnetic recording layer on the growth layer, where the growth layer is configured to facilitate a growth of a preselected crystalline structure of the magnetic recording layer, and a capping magnetic recording layer on the magnetic recording layer, the capping recording layer including a first material configured to increase a damping constant of the capping recording layer to a first preselected level.

MRS Proceedings, 2000

ABSTRACTThis article presents a transmission electron microscopic (TEM) investigation of the rela... more ABSTRACTThis article presents a transmission electron microscopic (TEM) investigation of the relationship between the magnetic and underlayer grain sizes in CoCrPtTa/CrMo longitudinal magnetic recording media. A great deal of effort has been expended on decreasing the underlayer grain size in order to decrease that of the magnetic layer. However, our results show that the two grain sizes may not always correlate. When the underlayer (CrMo) grains are sufficiently small, the magnetic layer (CoCrPtTa) grain size does not necessarily decrease with further underlayer grain size reduction. By carefully controlling the processing conditions, CrMo grain sizes were made to vary from 16nm down to 10nm. However, the corresponding CoCrPtTa grain sizes remained nearly the same. As the underlayer grain size decreased, the ratio of magnetic to underlayer grain size increased from 0.9 to 1.4.

Journal of Applied Physics, 2003

The effects of the stabilizing layer thickness and its temperature dependence on the magnetic pro... more The effects of the stabilizing layer thickness and its temperature dependence on the magnetic properties were investigated experimentally. These results were used to analyze the magnetic structure of the thin stabilizing layer and its effect on the coupling strength, which is valuable for improving the design of synthetic antiferromagnetically coupled media.

Journal of Applied Physics, 2009

Adding Pt into CoCr-oxide alloy for controlling magnetic softness in a soft layer on hard/soft (H... more Adding Pt into CoCr-oxide alloy for controlling magnetic softness in a soft layer on hard/soft (H/S) stacked composite media significantly affects magnetic properties and microstructure. Hc values for capping layer (CL) media with a relatively high-Hk soft layer initially increase with increasing tcap. However, Hc values are relatively constant for H/S media with Pt 3% and 10% soft layers and reduced for the media with a CoTaZr–SiO2 soft layer having in-plane Hk. The simulation results explain these experimental Hc trends by the compensation effect between the decrease in average Ku due to the use of less-Ku soft layer and the increases in volume with increasing tsoft. Reduction in Hc with increasing tsoft is anticipated when Ku in a soft layer reduces by >27%. As the Pt content in a soft layer increases from 3% to 18%, higher Hc and Hn but lower Hs are observed. Plan-view transmission electron microscopy images for the medium with Pt 18% soft layer show no subgrains and thinner ...

Journal of Applied Physics, 2010

We have studied the time-scale and temperature dependence of the magnetization reversal in perpen... more We have studied the time-scale and temperature dependence of the magnetization reversal in perpendicular magnetic recording media. One of the under-reported phenomena associated with this reversal is the thermal dependence of the squareness of the magnetic hysteresis loop. Understanding this phenomenon is important because the coercive squareness parameter S∗ is often used to evaluate the strength of the magnetic exchange-coupling interactions between the grains. In this work, we demonstrate that S∗ is a dynamic quantity which depends on the thermal agitation of the magnetization, and it is imperative to take this dependence into account in interpreting magnetic and microstructural effects. Based on the Sharrock model for the dynamic coercivity, we built an expression for the time-scale and temperature dependence of S∗ in highly oriented perpendicular magnetic recording media. Fits of experimental data to the resulting expression were then used to extract the intrinsic squareness pa...

Journal of Applied Physics, 2011

L10 FePt film exhibits a very large magnetocrystalline anisotropy (7×107 ergs/cc). It therefore b... more L10 FePt film exhibits a very large magnetocrystalline anisotropy (7×107 ergs/cc). It therefore becomes a promising material candidate for ultrahigh areal density heat assisted magnetic recording media. This paper discusses the effect of pressure on the microstructure and magnetic properties of L10 FePt:X thin films. It has been found that Ar pressure plays an important role in controlling the properties of the composite polycrystalline thin films. As the pressure increases, FePt:X films show much better segregation in the microstructure of the amorphous materials within the grain boundary, and the FePt grain size decreases accordingly. It was also found that media coercivity increases as the film microstructure changes from a maze type to a granular type, along with the pressure increase. This is likely due to the enhanced exchange decoupling of the FePt grains in the magnetic layer. The microstructure’s evolution with pressure is in agreement with a structural zone model of the co...

IEEE Transactions on Magnetics, 2002

IEEE Transactions on Magnetics, 2003

Areal density growth in longitudinal magnetic recording requires physical scaling of component fe... more Areal density growth in longitudinal magnetic recording requires physical scaling of component features and properties that cannot continue indefinitely. The authors discuss in this paper the limitations and extendibility of longitudinal recording media focusing on its microstructural features and historical rate of change. Based on these trends, they estimate that an areal density of 200 Gb/in 2 is achievable. In order to make such media thermally stable, synthetic antiferromagnetic structures will likely be used. The crystallographic grain size will be between 5 and 6 nm and the coercivity of the media will likely not exceed 5000 Oe. Additionally, a significant decrease from current values in the width of the grain size distribution will need to occur to satisfy SNR requirements in the drive.