Magnetic Tape Heads Research Articles

Construction and operation of high-resolution magnetic tape head tweezers for measuring single-protein dynamics under force.

Mechanical forces are critical to protein function across many biological contexts-from bacterial adhesion to muscle mechanics and mechanotransduction processes. Hence, understanding how mechanical forces govern protein activity has developed into a central scientific question. In this context, single-molecule magnetic tweezers has recently emerged as a valuable experimental tool, offering the capability to measure single proteins over physiologically relevant forces and timescales. In this chapter, we present a detailed protocol for the assembly and operation of our magnetic tape head tweezers instrument, specifically tailored to investigate protein dynamics. Our instrument boasts a simplified microscope design and incorporates a magnetic tape head as the force-generating apparatus, facilitating precise force control and enhancing its temporal stability, enabling the study of single protein mechanics over extended timescales spanning several hours or even days. Moreover, its straightforward and cost-effective design ensures its accessibility to the wider scientific community. We anticipate that this technique will attract widespread interest within the growing field of mechanobiology and expect that this chapter will provide facilitated accessibility to this technology.

Talin folding as the tuning fork of cellular mechanotransduction

Cells continually sample their mechanical environment using exquisite force sensors such as talin, whose folding status triggers mechanotransduction pathways by recruiting binding partners. Mechanical signals in biology change quickly over time and are often embedded in noise; however, the mechanics of force-sensing proteins have only been tested using simple force protocols, such as constant or ramped forces. Here, using our magnetic tape head tweezers design, we measure the folding dynamics of single talin proteins in response to external mechanical noise and cyclic force perturbations. Our experiments demonstrate that talin filters out external mechanical noise but detects periodic force signals over a finely tuned frequency range. Hence, talin operates as a mechanical band-pass filter, able to read and interpret frequency-dependent mechanical information through its folding dynamics. We describe our observations in the context of stochastic resonance, which we propose as a mechanism by which mechanosensing proteins could respond accurately to force signals in the naturally noisy biological environment.

Ephemeral states in protein folding under force captured with a magnetic tweezers design

Magnetic tape heads are ubiquitously used to read and record on magnetic tapes in technologies as diverse as old VHS tapes, modern hard-drive disks, or magnetic bands on credit cards. Their design highlights the ability to convert electric signals into fluctuations of the magnetic field at very high frequencies, which is essential for the high-density storage demanded nowadays. Here, we twist this conventional use of tape heads to implement one in a magnetic tweezers design, which offers the unique capability of changing the force with a bandwidth of ∼10 kHz. We calibrate our instrument by developing an analytical expression that predicts the magnetic force acting on a superparamagnetic bead based on the Karlqvist approximation of the magnetic field created by a tape head. This theory is validated by measuring the force dependence of protein L unfolding/folding step sizes and the folding properties of the R3 talin domain. We demonstrate the potential of our instrument by carrying out millisecond-long quenches to capture the formation of the ephemeral molten globule state in protein L, which has never been observed before. Our instrument provides the capability of interrogating individual molecules under fast-changing forces with a control and resolution below a fraction of a piconewton, opening a range of force spectroscopy protocols to study protein dynamics under force.

Vibrating sample magnetometer 2D and 3D magnetization effects associated with different initial magnetization states

Differences in VSM magnetization vector rotation associated with various initial magnetization states were demonstrated. Procedures and criteria were developed to select sample orientation and initial magnetization states to allow for the combination of two different 2D measurements runs (with the same field profiles) to generate a dataset that can be representative of actual 3D magnetization rotation. Nickel, cast iron, and low moment magnetic tape media were used to demonstrate these effects using hysteresis and remanent magnetization test sequences. These results can be used to generate 2D and 3D magnetic properties to better characterize magnetic phenomena which are inherently three dimensional. Example applications are magnetic tape-head orientation sensitivity, reinterpretation of 3D coercivity and other standard magnetic properties, and multi-dimensional shielding effectiveness.

Excellent wear life of silicon nitride/tetrahedral amorphous carbon bilayer overcoat on functional tape heads

Developing ultrathin and highly wear-resistant overcoats for magnetic tape heads is one of the current research areas of interest, because of its potential to delay pole tip recession and increase the operational lifetime of high areal density tape drives. Using optimized process conditions and an appropriate overcoat design, we report on the development of a ∼20 nm thick silicon nitride/tetrahedral amorphous carbon (Si/SiNx/ta-C) bilayer overcoat, where the ta-C film was deposited by a filtered cathodic vacuum arc process. The bilayer overcoat deposited on a functional tape head survived 40–50 × 106 m of testing with commercial tape media under standard industrial testing conditions. The excellent wear resistance of the overcoat was attributed to the generation of high (∼72%) sp3 carbon content and the formation of strong interfacial bonds, such as Si-C, C=N, nitrile, and (Al, Ti)N at the interfaces, as confirmed by various spectroscopic techniques. This study demonstrates the pivotal role of high sp3 carbon bonding combined with enhanced interfacial bonding in developing an ultrathin yet durable protective overcoat for magnetic tape heads.

(Invited) Linear Magnetic Tape Heads and Contact Recording

Linear tape recording heads, introduced in 1984, originally were cylindrical ferrite structures having shunt-biased magnetoresistive sensors. In 2000, heads transitioned to flat-lapped, ceramic wafers and anisotropic magnetoresistive (AMR) sensors fabricated in hard disk drive (HDD) facilities. In 2008, heads transitioned to giant magnetoresistive (GMR) sensors. Engineering tape heads has meant dealing with problems related to the head-media interface. Examples include sub-nanosecond pulses in sensors having metal shields (ca. 1994), signal losses and telegraph noise caused by parasitic electrical connections and spacing due to deposits that form at low relative humidity. Wear management, especially with 'green' media, and stick-slip effects are on-going challenges. A strategy was created for protecting GMR tape heads, leading to the discovery of polycrystalline Al2O3 films.

Magnetic Tape Heads and Contact Recording

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Chromium oxide coatings applied to magnetic tape heads for improved wear resistance

This paper reports on an investigation of the wear of chromium oxide based very thin films. Linear data tape Advanced Digital Recording (ADR™) heads coated with 20- and 40-nm thick chromium oxide films have been tested subject to temperature/humidity matrix of 10 to 40°C/10 to 80% in order to assess the wear behaviour of the coating as a function of environment. The tested heads were analysed at various stages of wear, by use of optical microscopy (OM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The results show that the most severe damage occurs at the highest relative humidity (80% RH) and for a given humidity, at the lowest temperature (10°C). Inversely, stain transferred from the tape to the head surface predominates at the lowest humidity (10% RH). Stain therefore appears to protect the coating against wear with the degree of protection increasing with the temperature. The wear process differs according to the coating thickness. This is attributed to the location of the maximum subsurface stress with respect to the coating/substrate interface. It is shown that this maximum stress occurs below the interface for 20 nm and at the interface for 40 nm thick coatings. This correlates to different observed wear modes.

A model of pole tip recession growth in magnetic heads

Pole tip recession (PTR), which is caused by differences in wear resistance of the various phases in magnetic disk and tape heads, must be reduced because it is probably the main impediment to reduction of spacing. Here, a numerical model of PTR is presented. Experimental results suggest that three-body abrasion, which leads to primarily plastic wear, is the mode responsible for PTR. In the model, the authors assume this wear mode, and assume that wear is a function of load, sliding distance, hardness of the worn surface, and dimensionless wear coefficients. As sliding proceeds, PTR increases continuously, which leads to a continuous change in contact between three-body abrasives and poles; the load carried by the poles decreases as PTR increases. This is modeled by assuming that asperities of the head and medium deform and wear plastically to accommodate passage of particles through the interface. The pole wears less as PTR increases since the opening for sliding particles increases. This accounts for the decreasing rate of change of PTR with sliding distance found for disk and tape heads numerically and experimentally. For tape heads, the model predicts that each of the following leads to higher PTR: increasing the thickness of three-body particles, increasing tape tension, decreasing pole hardness, and increasing the pole wear coefficient.

Numerical modelling of sub-surface stress in magnetic data tape heads due to the dynamic contact with a tape

The stress field at the subsurface of the ceramic used as a tape-bearing surface (TBS) in magnetic head construction is calculated by means of numerical methods taking into account roughness and friction forces at the head to tape interface (HTI). A two-dimensional model confirms the purely elastic character of the contact. However, only a three-dimensional model allows a quantitative interpretation, and thus to estimate the real area to apparent area of contact ratio—in agreement with a previous formal calculation—as well as the depth of the maximum von Mises stress—i.e. the depth at which a crack is more likely to form and extend—near 30 nm, comparable to the pullout depth observed at the surface of the ceramic used in actual heads.

Effect of Particulate Contamination on Pole Tip Recession in a Linear Tape Drive

Three-body abrasion is the cause of differential wear in magnetic tape heads resulting in recession of the magnetic poles with respect to the head substrate; this is called pole tip recession (PTR). The increasing head--tape spacing caused by PTR results in a lower write density, so the recession must be minimized. The three-body particles that may interact with the head--tape interface can originate from the operating environment (contaminant particles) and from the interface itself (debris particles). The effect of airborne particulate contaminants trapped at the head--tape interface (particle concentration, size, and hardness), which results in three-body abrasion, on PTR growth is studied experimentally. PTR increases with increases in any of the following: particle concentration, size, and hardness. Analytical modeling supports the experimental results. Possible mechanisms responsible for the observed behavior are discussed.

Micro/nano-scale differential wear of multiphase materials: pole tip recession in magnetic-tape heads

Wear of multiphase materials at the micro/nano-scale is important in devices such as magnetic tape and disk drives, where the read-write heads are multiphase. Differential wear, which is caused by differences in wear resistance among the heads’ phases, causes the thin-film poles to recede from the bearing surface; this is called pole tip recession (PTR). It is a problem because it increases spacing between the poles and medium, resulting in lower readback amplitude. Here, PTR in tape heads is studied to understand micro/nano-scale differential wear. Test results suggest that three-body abrasion, which leads to primarily plastic wear, is the operative wear mode. Most of the three-body abrasive particles originate from the tape surface; the alumina head-cleaning agents (HCAs) in the tape, which function as load bearing particles at the interface, are believed to be the primary abrasives. Some of the particles originate from the head. These are important if the substrate material is relatively soft. Differential wear can be reduced by choosing a substrate that is harder than the tape’s HCAs, choosing a pole material that is as close as possible to the hardness of the substrate, and lowering the thickness of the head’s thin-film region. Material hardness matching will not reduce differential wear if a substrate is chosen that is less hard than the HCAs. An analytical model that accounts for the observed wear is presented. The model shows that each of the following leads to higher differential wear: increasing the thickness of three-body particles, increasing tension, decreasing thin-film hardness, and increasing the thin-film wear coefficient. An increase in thin-film wear coefficient can be caused by an increase in thin-film thickness or an increase in the number of particles at the interface.

Investigations of nano- and macro-wear of magnetic tape head materials

The nano- and macro-wear characteristics of calcium titanate, single crystal ferrite and polycrystalline ferrite were investigated using nano-scratch testing and wear bar testing. Nano- and micro-indentations were made to determine nano- and micro-hardness, and nano-scratch testing was used to evaluate relative wear rates on the nano-scale. The macro-wear characteristics of the various head materials against metal particle tapes was investigated as a function of tape speed using wear bars mounted in a DLT tape drive. The micro-indentation method was used to investigate wear of the head/tape interface in a linear tape drive. The results from nano- and macro-wear tests were analysed and correlated with the microstructure of the materials.

Naniondentation and scratch resistance testing on magnetic tape heads coated with ultra-thin amorphous carbon layers

We present results on nanoindentation and scratch testing on magnetic recording tape heads coated with sub-20 nm amorphous carbon layers, prepared by filtered cathodic deposition and plasma enhanced chemical vapour deposition. The hardness values of the coated devices are higher than that of the sputtered Al 2O 3 substrate. The coatings do not reduce friction but improve the scratch resistance of the tape heads. Hardness, which shows some correlation with scratch resistance is a contributing factor, especially at high load where it reduces plastic ploughing of the substrate. For low scratching load, the wear seems to be influenced by the adhesive properties of the film/substrate interface. Smoother surfaces and smaller tip radius should improve the accuracy of the results. This could provide better insight into the failure mechanism of these ultra-thin overcoats.

Ultrathin diamond-like carbon coatings used for reduction of pole tip recession in magnetic tape heads

Diamond-like carbon (DLC) coatings were deposited using a commercial direct ion beam deposition technique on thin-film Al2O3–TiC inductive write heads. The coating thicknesses used were 5, 10, and 20 nm. Accelerated wear tests were conducted with metal particle tapes in a linear tape drive. Atomic force microscopy was used to image the thin-film regions to measure pole tip recession (PTR), relative wear of the pole tip with respect to the air bearing surface. It is found that the coating wears off of the head substrate to a significant extent in the first 1000 km of sliding distance. The coating is worn off the substrate long before it wears off of the thin-film region. The existence of the coating on the thin-film region provides close enough wear characteristics between the substrate and thin film that the two wear at similar rates. This results in little growth in pole tip recession. Early in the wear test, the coated substrate wears at a slightly higher rate than the DLC coated thin-film region due to the difference in tape contact pressure between the two materials; decreasing PTR is the result. As the coating on the substrate wears significantly, PTR begins to increase with sliding distance. Failure does not actually occur until the coating has worn off of the thin-film region. Near failure, the coating delaminates locally. Results indicate that coatings of 20 nm thickness may provide protection against PTR in future tape drives.

Wear Mechanisms at the Metal Evaporated Magnetic Tape-Head Interface

The wear mechanisms of Metal-Evaporated magnetic tape-head interfaces have been investigated. A new apparatus was designed for the continuous observation of the tape surface when run in the still frame mode. The mild wear mechanism of the bumps on the ME tapes was proven using SEM and AFM. Four different types of wear debris were observed. Depending on wear debris formation, two types of spalling were emphasized. The effect of humidity in the range of 30–70 percent was also investigated. The wear mechanisms are discussed in terms of contact mechanics theory, coating failure modes, and humidity induced stiction theory.

Generation of magnetic tape debris and head stain in a linear tape drive

The presence of tape debris at the head-tape interface can cause an increase in spacing and consequently an increase in signal loss. In this study, the generation of tape debris in linear tape drives is analysed. Functional drive tests are conducted using thin-film AlO3-TiC and Ni-Zn ferrite heads run against commercial metal particle (MP) tape. Three types of tape debris are found: magnetic particle rich, polymer rich and adherent (stain). Each type is found at a distinct location on the head surface. Optical microscopy and computerized image analysis are used both to quantify the tape debris and to find its distribution on the head. Atomic force microscopy is used to measure the thickness of adherent debris. The Al2O3-TiC sample generates more of all three types than does the Ni-Zn ferrite sample. This is probably a result of the higher hardness of Al2O3-TiC. The differential wear of Al2O3 and TiC probably accounts for the presence of adherent debris on the Al2O3-TiC head. No adherent debris can be found on the Ni-Zn ferrite head. Since the adherent debris collects near the pole tip and is difficult to remove, it potentially poses the greatest head-tape spacing problem, even though its thickness is only of the order of a few nanometres. A relationship is found between the generation of loose debris and the tape speed, tape tension and head wrap. Loose debris generation increases as the tape speed decreases and as the tape tension and head wrap increase. Its generation is found to be approximately proportional to the frictional force. Loose debris, especially the magnetic-particle-rich type, continues to be generated in abundant amounts beyond the burnishing phase for MP tape. The use of an abrasive tape leader is found to reduce the amount of debris at the interface.

Advanced MR read/inductive write heads for high performance, high density tape applications

Multi-track magnetic tape heads for use in high performance, high density storage subsystems are going through a rapid period of change in response to the continuing demand for increased capacity and data transfer rate. The luxuries of wide read and write tracks and low coercivity media have disappeared, increasing the problem posed for tape head design and manufacturing. The multi-track nature of the head is becoming more complex with the move to full thin film write head structures akin to the thin film disk head. The dramatic increases in track density while maintaining interchange requirements are resulting in significant dimensional reductions in the magnetoresistive (MR) read devices. The increasingly complex new heads dictate stringent process control and correspondingly more lenient head designs in order to achieve an acceptable yield. This paper summarizes the technology transition and the factors that drive those head changes from the media type and track density issues to the recording density and recording code advances.

The read/write characteristics of Co-Cr-Ta/Ni-Fe double-layer tape for digital video recording

A digital video recording experiment was conducted by using a Co-Cr-Ta/Ni-Fe double-layer perpendicular magnetic recording tape and ring heads with a track width of 5 μm. The area recording density was 1.1bit/μm2, almost 8 times that of the D-3 VTR. A new equalizing method using FFT analysis was also developed for the experiment, achieving a byte error rate of 1×10-5.

A magnetographic technique for inspection of containment welds through coatings : Liu, S.N. Electric Power Research Institute, Palo Alto, California (United States), NP-6834-D, 92 pp. (May 1990)

The purpose of this project was to develop an inspection technique for typical nuclear plant containment welds that could detect cracks 6 mm (0.25 inch) long or longer through paint thicknesses up to 0.38 mm (0.015 inch). A magnetographic technique was developed for this purpose. This technique incorporates a flexible magnetic medium such as magnetic recording tape which is placed into contact with the component while a magnetic field is applied. The leakage field from a flaw magnetizes the tape, and the signal from the tape can be read by scanning a magnetic tape head over the tape. In this project, both magnetic tape and a commercial product with the brand name Magnafilm were investigated for this purpose. Experimental investigations using cracks produced by a proprietary welding process showed that the magnetic tape had insufficient sensitivity; however, the Magnafilm was to have sufficient sensitivity to satisfy most of the projects goals. The Magnafilm produced permanent visual images on the Magnafilm material itself, and it could also be scanned with a tape head to produce magnetographic signals. Results were obtained from longitudinal cracks in the crown and toe of the welds in flat and 90-degree weld specimen, and from transverse cracksmore » in the crown of the welds in the specimens. Using visual Magnafilm indications, cracks ranging in length from 5 mm (0.2 inch) to 28 mm (1.1 inches) were detectable through simulated paint thicknesses up to 0.38 mm (0.5 inch), with the exception of one 6-mm (0.25-inch) crack which was detectable through thicknesses up to 0.23 mm (0.009 inch). Based on these results, a preliminary inspection procedure for inspecting containment welds through coatings was developed. 7 refs.« less