Longitudinal Recording Media Research Articles

Enhancing the magnetization, dielectric parameters and elastic parameters while simultaneously minimizing coercivity and dielectric loss in nickel-manganese-cobalt ferrite nanoparticles through Ce3+ doping assistance

This study focuses on examining how the rare-earth cerium incorporation affects the magnetic, dielectric, and mechanical characteristics of Ni0.5Mn0.25Co0.25CexFe2-xO4 spinel ferrite nanoparticles. (NMCCF). The nanoferrite Ni0.5Mn0.25Co0.25Ce0.04Fe1.96O4 acquires the lowest coercivity of 567 Oe and the highest saturation magnetization of 52.23 emu/g. All the NMCCFx nanoferrites exhibit a microwave frequency range of 9.47–11.55 GHz, suggesting potential applications in longitudinal recording media and microwave absorbance. Moreover, the nanoferrite Ni0.5Mn0.25Co0.25Ce0.1Fe1.9O4 demonstrates the highest dielectric value of 1871, with an enhancing ratio of 754 %, excellent conductivity at 3.12 μ(Ω.m)−1 along with a remarkably enhanced percentage of 369 %. Additionally, it shows a loss factor of 2.17, with a notable improvement percentage of 26 % compared to the pure NMCCF0 sample at 50 Hz and room temperature. The elastic moduli (longitudinal, shear, Young, and bulk) of the Ni0.5Mn0.25Co0.25Ce0.1Fe1.9O4 nanoferrite increased from 1.21 to 2.77 GPa, 0.25–0.76 GPa, 0.68–1.99 GPa, and 0.87–1.75 GPa, respectively. This study introduces a novel approach to Ni–Mn–Co–Ce spinel nanoferrites, highlighting their magnetic, electrical, and mechanical characteristics, which hold promise for electronic and high-frequency device applications.

Effect of Cd on Structural, Spectral, Morphological and Dielectric Properties of Sr1-xCdxZn2Fe4O11 R-type Hexaferrites Synthesized via Sol-gel Technique

Sol–gel method was used to prepare Sr1-xCdxZn2Fe4O11 (x = 0.00, 0.02, 0.06, 0.1) R-type hexaferrite. The synthesized materials were sintered at 850oC and desired phase was obtained. X-ray diffraction analysis confirms that R-type hexaferrite exists only as a single phase. Using the Scherer formula, crystallite size for all of the prepared samples was found to be in the range of 10.39–12.62 nm. Crystallite size (D), the lattice parameters (a, c), and the cell volume (Vcell), d-spacing, bulk density, X-ray density, porosity, dislocation density and micro strain were determined in structural analysis. Fourier transform infrared spectroscopy method was used to identify the metal-oxygen vibrations at different locations. FT-IR verifies the presence of the Fe–O stretching vibration band at 743 and 867 cm−1. The typical grain size in surface morphology investigation ranges from 0.56 to 0.82 μm. Dielectric response of ferrite ceramic samples replaced with Cd2+ was investigated in the frequency range of 1 MHz–3 GHz. The AC conductivity rises with an increase in frequency because they are proportional to one another. This increasing tendency is effectively described by the theory of Maxwell-Wagner and Koop. Q-values remain constant as frequency rises and behaves independently of frequency as long as frequency reaches 1.7 GHz. These types of materials are utilized in high-frequency applications including frequency filters and resonant circuits. All of the magnetic properties determined by analyzing the M − H loops, including saturation magnetization (Ms), retentivity (Mr), and coercivity (Hc), exhibit an increasing trend as the substitution of Cd2+ rises. Ms (49.76–56.38 emu/g), Mr (15.82–18.30 emu/g) and Hc range from 203.20 Oe to 215.80 Oe. Grain size decreases cause arise in coercivity, which is caused by an enhancement in magneto-crystalline anisotropy. Overall results suggest that Cd2+ replaced R-type hexagonal ferrites are a great resource for longitudinal recording media; they have the potential to be used in a wide variety of electronic applications, including resonant circuits and high-frequency filters, security, detecting and switching.

Structural, optical, electrical, dielectric, molecular vibrational and magnetic properties of La3+ doped Mg–Cd–Cu ferrites prepared by Co-precipitation technique

Ferrites are among the most frequently investigated materials mainly due to interesting and practically different properties. Therefore, easily and cost-effective lanthanum doped Mg0.5Cd0.25Cu0.25Fe2-xLaxO4 (x = 0.0, 0.0125, 0.025, 0.0375 and 0.05) ferrites were synthesized by a co-precipitation route, a comprehensive characterisation of their structural, optical, electric, dielectric, molecular vibrational, and magnetic properties were carried out. X-ray diffraction analysis confirmed the formation of a cubic spinel structure. Variations in frequency bands were also observed with amplification in optical band gap energy (2.95 – 3.38 eV) due to La3+ ions insertion. The electric resistivity had opposite trends at low and high temperatures with increasing La3+ content. The Curie temperature, activation energy, and drift mobility were also determined to have values consistent with the semiconducting behavior of the soft ferrites. The saturation magnetization (MS) has a maximum value 49.385 emu/g with remanent magnetization (Mr) was 34.928 emu/g and coercivity 661.4 Oe for La3+ concentration x = 0.05. The minimum dielectric loss was observed for La3+ concentration x = 0.025. Moreover, the resistivity (ρ) has a maximum value of 7.95 × 104 Ω cm for La3+ concentration x = 0.025. The calculated frequency range of La3+ doped Mg–Cd–Cu ferrites was detected in the microwave range (3.36 – 10.80 GHz), suggesting the potential application of the materials in longitudinal recording media and microwave absorbance.

Structural, spectral, dielectric and magnetic properties of Sr2CuxNi2-xFe28-xCrxO46 (0 ≤ x ≥ 0.5) ferrites synthesized via micro-emulsion route

In the present study, Sr2CuxNi2-xCrxFe28-xO46 where (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) X-type ferrites were fabricated by micro-emulsion procedure. X-ray diffraction technique assured the phase of fabricated ferrites to be that of pure X-type ferrites. The reduction in lattice constants (a & c) seemed with the incorporation of Cr3+-Cu2+ metals. The crystalline size of the synthesized materials was obtained in 19–23 nm range, using the Scherer's formula. The iron-oxygen bands of X-type hexagonal ferrites at tetrahedral and octahedral sites were confirmed from FTIR spectra. The FTIR spectra also showed the strong influence of Cr3+-Cu2+ substitution, which confirmed that the dopants have a meaningful role in these ferrites. The dielectric parameters were explored in a large frequency range (i.e. from 1 MHz to 3 GHz) and these parameters showed significant variations with Cr3+-Cu2+ doping contents. Moderate values of dielectric constant, low tangent loss, high Q values, and significant response to the high frequency of these X-type ferrites ensured their applicability for the high (GHz) frequency applications. Vibrating sample magnetometry technique (VSM) was applied to unfold the magnetic parameters. The Coercivity (Hc), saturation magnetization (Ms) as well as remanence magnetization (Mr) revealed considerable variations with doping Cr3+-Cu2+cations. The enhancement in magnetic parameter i.e. coercivity Hc with the doping of Cr3+-Cu2+ reflects the uses of these materials in longitudinal recording media.

Impact of yttrium on the physical, electro-magnetic and dielectric properties of auto-combustion synthesized nanocrystalline strontium hexaferrite

Yttrium substituted strontium hexaferrite, SrAl4YxFe8−xO19 with x = 0.0, 0.05, 0.10, 0.20, and 0.30, are prepared by the auto combustion method. The ferrites have been examined using XRD, SEM, FTIR, and VSM. The structural study confirms that the Y3+ ions reorganize themselves without troubling the parent lattice. In FTIR, the low wavenumber absorption bands confirm the hexagonal ferrites. Saturation (Ms) and remanence (Mr) magnetization is observed to decrease whereas, coercivity (Hc) and Curie temperature (Tc) is improved with Y3+ content. The variation in the dielectric constant $$( \in )$$ and dielectric loss factor (tanδ) is discussed in the frequency range of 20Hz–20 MHz. The value of dielectric constant $$( \in )$$ and dielectric loss factor (tanδ) is decreased with Y3+ content. The optimized magnetic properties are obtained from x = 0.20 compositions having Ms ~ 4.45 emu/g, Mr ~ 1.91 emu/g, Hc ~ 36 kOe, (BH)max ~ 36.64 MGOe and Tc ~ 614 °C. This material is very suitable for longitudinal recording media.

Study of structural transformation and hysteresis behavior of Mg-Sr substituted X-type hexaferrites

Effect of Mg-Sr substitution on thermal, structural, spectral, dielectric and magnetic properties were explored in the X-type hexagonal ferrites having composition of Ba2-xMgxCo2-ySry Fe28O46 (x = y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized via a sol-gel auto-combustion process. The sintered material was characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), dielectric measurement and vibrating sample magnetometer (VSM) techniques. The sintering temperature necessary for the entire degradation of nitrates and the hexagonal phase development was found 1250 °C which was determined from thermo-gravimetric analysis. The formation of the single phase hexagonal was confirmed from XRD patterns. The lattice constants and cell volume were found to be decreased. This decreased was attributed to the lower ionic size of the substituted metal ions. The porosity of the synthesized material was found to be decreased from 0.463 to 0.417 with the increase in the substitution. FTIR spectroscopy of Mg-Sr doped material revealed the characteristics absorption bands of hexa-ferrites and it was investigated in the frequency range of 400–1000 cm−1. The dielectric measurement has been explored as the function of frequency and composition. Ac conductivity was found to be increased from 1.46 to 2.029 Ω cm−1. The Cole-Cole graphs of prepared materials revealed the promising role of grain boundaries in the conduction mechanism. The improvement in the coercivity was observed with the increase in the Mg-Sr cations, while the saturation magnetization was decreased with the increase in the substitution. The higher value of the coercivity of these synthesized material proposed their use in longitudinal recording media.

Magnetic and dielectric characteristics of Nd and Nd-Mg substituted strontium hexaferrite

A systematic investigation on the phase formation, magnetic, dielectric and impedance properties of strontium hexaferrites doped with Nd and Nd-Mg was performed. All ferrite samples were prepared by the citrate-precursor method and characterized with a combination ofX-ray diffraction, Vibrating sample magnetometer and impedance analyser. XRD analysis confirms the magnetoplumbite structure with space groupp63/mmcwithout any secondary phase. The lattice parameter ratioc/alies in the range of 3.92 to 3.94 and shows that the prepared material exhibits M-type hexagonal structure. An increase in coercivity and a decrease in magnetization were observed for all the samples. Large value of coercivity suggests that these materials are useful in longitudinal recording media. Further, it was found that the value of magnetocrystalline anisotropy constantK1decreases with the substitution of Nd and Nd-Mg. Measurement of dielectric loss and dielectric constant were performed as a function of temperature and frequency. Dielectric constant and ac conductivity of Sr0.95Nd0.05Mg0.05Fe11.95O19is more as compared to Sr0.95Nd0.05Fe12O19and SrFe12O19for all frequencies. The value of grain boundary resistance (Rgb) of Sr0.95Nd0.05Fe12O19is less as compared to SrFe12O19and Sr0.95Nd0.05Mg0.05Fe11.95O19and vice versa trend is observed in the value of capacitance of the grain boundary (Cgb) and in the values of relaxation time (τgb).

Structural, spectral, electrical, dielectric and magnetic properties of Yb doped SrNiCo-X hexagonal nano-structured ferrites

Abstract Ytterbium (Yb) doped X-type hexagonal nano-sized ferrites (Sr2NiCoFe28O46) were fabricated by micro-emulsion method. The development of hexagonal structure of ferrite materials was confirmed by XRD analysis. The size of crystallites as determined by Scherrer's formula was found in the range 29–41 nm. The lattice strain of these ferrites was increased from 3.62 × 10−2 to 3.73 × 10−2 with the increased Yb-contents. The tetrahedral absorption bands shifted slightly towards higher frequency whereas octahedral bands shifted towards lower frequency side. The incorporation of Yb enhanced dc electrical resistivity significantly from 2.05 × 108 to 3.35 × 109 Ω-cm. The AC conductivity was increased with frequency whereas it decreased with the inclusion of Yb3+ ions. This distinctive behavior of these hexagonal ferrites may be suitable for microwave devices and electromagnetic attenuation applications. The doping of Yb3+ optimized coercivity whereas remanence and saturation magnetization were decreased. These ferrite materials can be used in longitudinal recording media due to more thermally stable and higher coercivity (577–671 Oe).

Structural elucidation and magnetic behavior evaluation of rare earth (La, Nd, Gd, Tb, Dy) doped BaCoNi-X hexagonal nano-sized ferrites

Rare-earth (RE=La3+, Nd3+, Gd3+, Tb3+, Dy3+) doped Ba2NiCoRExFe28−xO46 (x=0.25) hexagonal ferrites were synthesized for the first time via micro-emulsion route, which is a fast chemistry route for obtaining nano-sized ferrite powders. These nanomaterials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as vibrating sample magnetometer (VSM). The XRD analysis exhibited that all the samples crystallized into single X-type hexagonal phase. The crystalline size calculated by Scherrer's formula was found in the range 7–19nm. The variations in lattice parameters elucidated the incorporation of rare-earth cations in these nanomaterials. FTIR absorption spectra of these X-type ferrites were investigated in the wave number range 500–2400cm−1. Each spectrum exhibited absorption bands in the low wave number range, thereby confirming the X-type hexagonal structure. The enhancement in the coercivity was observed with the doping of rare-earth cations. The saturation magnetization was lowered owing to the redistribution of rare-earth cations on the octahedral site (3bVI). The higher values of coercivity (664–926Oe) of these nanomaterials suggest their use in longitudinal recording media.

Tunable microwave absorbing nano-material for X-band applications

The effect of rare earth elements substitution in Sr1.96RE0.04Co2Fe27.80Mn0.2O46 (RE=Ce, Gd, Nd, La and Sm) X-type hexagonal ferrites prepared by using sol gel autocombustion method was studied. The XRD and FTIR analysis show the single phase of the prepared material. The lattice constants a (Å) and c (Å) varies with the additives. The particle size measured by Scherer formula for all the samples varies in the range of 54–100nm and confirmed by the TEM analysis. The average grain size measured by SEM analysis lies in the range of 0.672–1.01µm for all the samples. The Gd-substituted ferrite has higher value of coercivity (526.06G) among all the samples which could be a good material for longitudinal recording media. The results also indicate that the Gd-substituted sample has maximum reflection loss of −25.2dB at 11.878GHz, can exhibit the best microwave absorption properties among all the substituted samples. Furthermore, the minimum value of reflection loss shifts towards the lower and higher frequencies with the substitution of rare earth elements which confirms that the microwave absorption properties can be tuned with the substitution of rare earth elements in pure ferrites. The peak value of attenuation constant at higher frequency agrees well the reflection loss data.

Synthesis and Characterization of Rare Earth Elements Substituted X-type Hexagonal Ferrites

A series of Sr1.96 RE0.04 Co2Fe27.80Mn0.2O46 (RE= Ce, Gd, Nd, La, Sm) X-type hexagonal ferrites was prepared by Sol gel method. The lattice constants a (Å) and c (Å) varies with the doping concentrations. The magnetic properties vary with the substitution of different rare earth elements. The Gd-substituted ferrite has higher value of coercivity (526.06 G) among the all samples which could be a good ma-terial for longitudinal recording media. The results indicate that the Gd-substituted sample with maximum reflection loss of -25.2dB at 11.878GHz can exhibits the best microwave absorption properties among all the samples. Furthermore, the minimum value of reflection loss shifts towards the lower and higher frequencies with the substitution of rare earth elements which confirms that the microwave absorption properties can be tuned with the substitution of rare earth elements in pure ferrites.

Quantifying Corrosion Growths on Perpendicular Magnetic Recording Media

High media roughness associated with perpendicular recording introduces the phenomenon of widely separated single needle-like corrosion growths after temperature-humidity stress. Previous generation longitudinal recording media demonstrated clusters of corrosion growths around a central media defect, which were detectable by reflected light. However, because of the isolated nature of this new type of corrosion, traditional ellipsometry is no longer effective. As a result, we have developed a method for quantifying scattered isolated corrosion growths on perpendicular recording media disk surfaces, using existing optical surface technology. Our method can detect corrosion densities down to 5000 corrosion sites/mm2, given corrosion size at least 0.3 mum in length and 7 nm in height. The amount of corrosion reveals itself as an increase in laser light scatter across a disk surface referenced to its original prestress scatter. Scanning electron microscopy and atomic force microscopy analysis of the corrosion growths verified that the scatter measurements correlate to physical properties such as density and size of corrosion needles.

Investigation on the magnetic anisotropy of particulate and thin film recording media

Some aspects of the magnetic anisotropy of fine particles and thin films, employed in longitudinal recording media, are studied. The analysis is carried out through the measurement of perpendicular magnetization and the calculation of the second derivative, which allows to obtain the distribution of anisotropy fields. In assemblies of α-Fe metal particles, where shape anisotropy prevails, the evolution of the anisotropy field distribution with packing is studied. In Ba ferrite particles, where both magnetocrystalline and shape anisotropy are present and comparable, the effect of the ionic substitutions is analyzed. In thin film media, a comparison between magnetic layers with different composition (ternary and quaternary Co-based alloy) is carried out. In all materials, the relevance of the analysis of the whole distribution is underlined. From the anisotropy results, information on the magnetization switching is drawn.

Correlation of fluctuation field and temperature coefficient of coercivity in a CoCrPtB thin film

The effect of the ratio of fluctuation field ( H f) to coercivity ( H c) on the temperature coefficient of coercivity [ α( H c)] was investigated for Co 55Cr 15.5Pt 28B 1.5/Co 63Cr 37/Cr, Co 69Cr 19Pt 9Ta 3/Cr, and Co 86Cr 10Ta 4/Cr thin films (longitudinal recording media) with very small average grain volume ( V phy). α( H c) increases markedly with increase in temperature between near 250 and 350 K for Co 55Cr 15.5Pt 28B 1.5/Co 63Cr 37/Cr thin films. α( H c) is approximately proportional to the ratio H f/ H c for all thin films, as in the case of advanced data backup tapes prepared from ultrafine particles. α( H c) and the ratio H f/ H c increase as V phy decreases. Smaller H f/ H c values are necessary for small α( H c) values, which is very important for the thermal stability of high-density recording media with very small V phy.

Calibration of Coercive and Stray Fields of Commercial Magnetic Force Microscope Probes

Variable-field magnetic force microscope (MFM) is introduced to characterize the magnetic behavior of commercially available MFM probes that is relevant to interpret MFM imaging. A Nanotec Electronica S.L. microscope has been conveniently modified to apply magnetic fields in axial direction (up to 1.5 kOe) and in-plane direction (up to 2.0 kOe). Axial and transeverse hysteresis loops of the probes have been generated by measuring the changes in the MFM contrast observed when the magnetic field is applied. The variation of the MFM signal is ascribed to the modification of the magnetic state of the tips. This is enabled by the large coercitivity (~1.7 kOe) of the checked longitudinal recording media. The properties of the probes depend on the coating material, the macroscopic tip shape, and tip radius. In only a few cases, the magnetization of the probe can be oriented along in-plane orientation. In addition, the stray field of the tips has been deduced by measuring the influence of the probe in the magnetic state of the checked samples.

Magnetic interactions in Co-based alloy thin films

The interactions in ternary and quaternary Co-based alloy thin films for longitudinal recording media, with different thickness, are studied. The analysis is performed through the measurement of the initial magnetization and ordinary hysteresis curves. The interactions result stronger in quaternary than in ternary alloy films and when the film thickness is smaller. These findings are discussed in relationship with the evolution of the magnetization switching, characterized by a tendency towards a more coherent rotation of the magnetization in single-domain grains of thinnest and quaternary films, owing to the complex structure of these films. The impact of this evolution on the thermal stability of the magnetic properties is also discussed.

Microstructure and Exchange Coupling of Segregated Oxide Perpendicular Recording Media

The magnetic properties and corresponding microstructure of (Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (metal oxide) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> perpendicular recording media have been studied as a function of the volume percentage (vol%) of metal oxide sputtering into the magnetic film. The exchange coupling field (Hex) estimated from the coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and nucleation field (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> ) decreases rapidly between 0-20 vol% of metal oxide. The analytical transmission electron microscope composition analysis of (Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x </sub> media confirms that the microstructure includes crystalline grain cores in an apparently amorphous oxide matrix. The grain cores comprise only Co and Pt in a nearly constant ratio independent of the vol% of oxide addition. The amorphous matrix contains Co, Ti, and O, but no Pt. The Co concentration is nearly constant in grain boundary and core regions, unlike high-temperature longitudinal recording media wherein Co segregates to form a concentration gradient in the grain core. Perpendicular media thus maintain fairly high anisotropy of the grain core phase, even for very high-oxide concentrations that significantly decrease remanant magnetization (Mrt), Hc, and thermal stability (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> V/kT)

State-of-the-Art Magnetic Hard Disk Drives

AbstractMagnetic recording has progressed dramatically over the last 50 years, with an increase of almost eight orders of magnitude in the amount of information stored per unit area of disk space.Two key enablers of this progress have been the recording medium and the read-back head.This article reviews the current state of the art in multilayer thin-film longitudinal recording media and giant magnetoresistive (GMR) read heads, with particular emphasis on the nanostructured magnetic materials that are key to today's high-performance hard disk drives.

Relation between interface stress in the seed layer and the orientation ratio of longitudinal media

The orientation ratio (OR) is a key issue to achieve high density in longitudinal recording media. Recent recording media have seed layers which exclusively promote small grain growth of the recording layer. In this paper, the effect of seed layers on OR was investigated by the use of various seed materials deposited twice. OR tends to decrease as the thickness of the seed layer is increased; however, the degree of decrease is quite different with seed material. A seed material with small Young’s modulus is preferable for a large OR. These results suggest that OR depends on the interface stress which is relieved as seed layer thickness is increased. Moreover, the relation between the stress in the seed layer and OR was also considered with a multilayer model.

Micromagnetic simulation of small-angle neutron scattering from magnetic recording media

A micromagnetic simulation of the magnetic morphology of CoCrPtB based longitudinal recording media is used to model small-angle neutron scattering data and provide a quantitative description of the local flux density in these nanostructured magnetic materials. The model addresses several aspects of the experimental measurements and, in particular, explains an unusual increase in scattering along the applied field direction for certain values of the scattering vector q. The increased scattering along the field direction results in a change of the phase of the angular variation of the scattering by 90∘. This 90∘ change in scattering phase arises naturally from the influence of stray fields when modeling the media as a heterogeneous alloy consisting of grains with a high saturation magnetization core and a permeable shell.