High-density Magnetic Recording Applications Research Articles

Effect of Yb doping on the structural and magnetic properties of cobalt ferrite nanoparticles

The low coercivity of spinel ferrites is a significant barrier limiting their use in high-density magnetic recording applications. The large magnitude of the magnetocrystalline anisotropy of the rare earth group elements can lead to a high coercivity field by doping the magnetic ferrites with these elements. In this research, using the hydrothermal method, Fe+3 in cobalt ferrite was substituted with Yb+3 to make CoFe2-xYbxO4 with x = 0, 0.025, 0.05, 0.075, and 0.1. By analyzing the X-ray diffraction analysis and confirming the spinel structure, the crystallite sizes were obtained in the range of 31 nm to 45 nm. The lattice parameter was estimated to be in the range of 8.30 nm to 8.36 nm. The FTIR analysis of the nanoparticles showed the ν1 absorption band in the range 584 Cm−1 to 594 Cm−1. The Raman spectroscopy analysis showed that CoFe2-xYbxO4 nanoparticles have a mixed spinel structure. Hysteresis loops at room temperature and 10 K obtained by the vibrating sample magnetometer (VSM) indicate that the coercivity field (HC) increases significantly from 0.55 to 1.05 KOe and 9.48 to 12.00 KOe, respectively, by increasing Yb doping from x = 0 to x = 0.1.

Synthesis and Characterization of Ni-Ti Partially Substituted Hexaferrites for High-Density Magnetic Recording Applications

Synthesis and Characterization of Ni-Ti Partially Substituted Hexaferrites for High-Density Magnetic Recording Applications

Structural and magnetic properties of praseodymium substituted barium-based spinel ferrites

In this research work BaPrxFe2-xO4 (x=0.0, 0.025, 0.05, 0.075, 0.10) spinel ferrites have been synthesized successfully by sol-gel technique. X-ray diffraction analysis confirmed the fcc spinel phase of the synthesized samples. All the samples showed inhomogeneous grain size distribution observed through scanning electron microscopy (SEM).Temperature dependence normalized AC susceptibility and Curie temperature studies revealed that BaFe2O4 exhibited multidomain (MD) structure with high Curie temperature. On the other hand, multidomain to single domain (SD) transitions occurred when the praseodymium is substituted into barium spinel ferrites. Narrow loops showed the soft nature of ferrites and it was confirmed from magnetic properties of the prepared samples. Decreasing trend of saturation magnetization and remanence was observed with the substitution of praseodymium contents. Coercivity and anisotropy constant both enhanced with the praseodymium concentration. The above-mentioned parameters revealed that the synthesized spinel ferrites might be useful for the of high-density magnetic recording applications.

Magneto-optical properties and Mössbauer Investigation of BaxSryPbzFe12O19 Hexaferrites

Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19 and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites were synthesized via sol-gel auto combustion. XRD (X-ray powder diffraction) powder patterns of the products confirmed the formation of M-type hexaferrites without any secındary phase. The crystallite sizes of the products were calculated as 37–41nm by Scherrer equation. SEM (Scanning electron microscopy) analyses revelaed the hexagonal morphology and 200–400nm grain size of the prodcuts. The magnetic hysteresis (σ-H) curves exhibit the ferromagnetic features for all hexaferrites. Especially, Ba0.3Sr0.4Pb0.3Fe12O19 and Ba0.4Sr0.3Pb0.3Fe12O19 samples have suitable magnetic characteristics (saturation magnetizations as 42.58 and 38.55emu/g, coercive fields as 1950 and 2978Oe, larger squareness ratios (SQR) as 0.447 and 0.454, respectively) for high density magnetic recording applications and permanent magnet fabrication. Effective crystalline anisotropy constants (Keff) are between 3.18×105–3.54×105Erg/g. The observed 17000OeHa (anisotropy field) reveal that products are hard magnet. Tauc plots were plotted to determine the Eg (direct optical energy band gap) of the samples. The Eg values are 1.46, 1.51, 1.69eV belonging to Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19, and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites respectively.

Fabrication and Properties of Carbon-Encapsulated Cobalt Nanoparticles over NaCl by CVD.

Carbon-encapsulated cobalt (Co@C) nanoparticles, with a tunable structure, were synthesized by chemical vapor deposition using Co nanoparticles as the catalyst and supported on a water-soluble substrate (sodium chloride), which was easily removed by washing and centrifugation. The influences of growth temperature and time on the structure and magnetic properties of the Co@C nanoparticles were systematically investigated. For different growth temperatures, the magnetic Co nanoparticles were encapsulated by different types of carbon layers, including amorphous carbon layers, graphitic layers, and carbon nanofibers. This inferred a close relationship between the structure of the carbon-encapsulated metal nanoparticles and the growth temperature. At a fixed growth temperature of 400 °C, prolonged growth time caused an increase in thickness of the carbon layers. The magnetic characterization indicated that the magnetic properties of the obtained Co@C nanoparticles depend not only on the graphitization but also on the thickness of the encapsulated carbon layer, which were easily controlled by the growth temperatures and times. Optimization of the synthesis process allowed achieving relatively high coercivity of the synthesized Co@C nanoparticles and enhancement of its ferromagnetic properties, which make this system promising as a magnetic material, particularly for high-density magnetic recording applications.

Cr3+ substituted spinel ferrite nanoparticles with high coercivity

The low coercivity of spinel ferrites is a major barrier that significantly limits their use in high density magnetic recording applications. By controlling the substituting content of Cr3+, in this article we describe how magnetic CoCrxFe2−xO4 (0 < x < 1.2) nanoparticles with coercivity of up to 6.4 kOe were successfully obtained by the hydrothermal process. The high coercivity is attributed to the synergetic effects of magnetocrystalline anisotropy and the nanoscale size effect. X-ray diffraction analysis confirmed the spinel structure of the nanoparticles with transmission electron microscopy (TEM) suggesting regular tetragonal morphology. The TEM indicated an edge length ranging from 15 nm to 150 nm, which increases monotonically with increasing Cr content. Raman analyses supported the proposed model on the formation mechanism of the nanoparticles, i.e. heterogeneous and homogeneous nucleation.

The effect of Argon ion irradiation on the thickness and structure of ultrathin amorphous carbon films

Carbon films synthesized by plasma-enhanced chemical vapor deposition (PECVD) and filtered cathodic vacuum arc (FCVA) exhibit a layered structure consisting of a bottom (interface) and a top (surface) layer rich in sp2 atomic carbon bonding and a middle (bulk) layer of much higher sp3 content. Because of significant differences in the composition, structure, and thickness of these layers, decreasing the film thickness may negatively affect its properties. In this study, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were used to examine the effect of Ar+ ion irradiation on the structure and thickness of ultrathin films of hydrogenated amorphous carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) deposited by PECVD and FCVA, respectively. The TEM and EELS results show that 2-min ion irradiation decreases the film thickness without markedly changing the film structure and composition, whereas 4-min ion irradiation results in significant film thinning and a moderate decrease of the sp3 content of the bulk layer. This study demonstrates that Ar+ ion irradiation is an effective post-deposition process for reducing the thickness and tuning the structure of ultrathin carbon films. This capability has direct implications in the synthesis of ultrathin protective carbon overcoats for extremely high-density magnetic recording applications.

Evaluation of Electrical, Mechanical Properties, and Surface Roughness of DC Sputtering Nickel-Iron Thin Films

The NiFe thin films were prepared at room temperature by DC sputtering technique from a NiFe target onto silicon wafer, NBK7 and STIM35 glass substrates. The optimal deposition condition of NiFe thin films was obtained to be used for high density magnetic recording applications. The film thickness was determined by the SEM measurement. The electrical resistivity of the NiFe thin film with a thickness of 240 nm was 1.17 × 10 -5 Q-cm. The average residual stress and thermo-mechanical parameters were determined by the fast Fourier transform (FFT) method. The average residual stresses on two different substrates are -50 ± 2 MPa. The residual stress versus substrate temperature relation is a linear correlation after heating from room temperature to 100 °C. A double substrate technique was used to determine the thermal expansion coefficients and biaxial modulus of the NiFe thin films. The experimental results show that the thermal expansion coefficient of the NiFe thin films is 6.44 × 10 -6 °C -1 . The biaxial modulus is 779 GPa. The surface roughness was evaluated by using a microscopic interferometer. The root-mean-square roughness of the NiFe thin films were 1.350 nm for NBK7, 1.403 nm for STIM35 and 1.387 nm for silicon wafer.

Anisotropy-graded magnetic media obtained by ion irradiation of L10 FePt

We show that Ar+ irradiation can be used effectively to transform a chemically ordered FePt L10 homogeneous thin film into an anisotropy-graded composite media with tunable magnetic response. This can be exploited to produce magnetic media with high thermal stability and moderate coercivity with potential in high-density magnetic recording applications. The depth distribution of the chemical order parameter, which controls the magnetic switching mechanism of the system, has been determined by high-resolution transmission electron microscopy. The irradiation-induced modifications of the material have been modeled using Monte Carlo simulations for ion transport in solids. The magnetic properties and coupling regimes of the resulting exchange-coupled systems are discussed.

Structural and magnetic properties of conventional and microwave treated Ni–Zr doped barium strontium hexaferrite

M-type hexaferrites of component B 0.5Sr 0.5Fe 12−2 x Ni x Zr x O 19 were investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. Significant increase in line broadening of the XRD patterns was observed indicating a decrease of grain size. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased x = 0.2–0.8 mol%, the grains are agglomerated and the average diameter increased. The H c decreases remarkably with increasing Ni and Zr ions content. It was found that the particle size could be effectively decreased and coercivity H c could easily be controlled by varying the concentration ( x) without significantly decreasing saturation magnetization. In particular, Ba 0.5Sr 0.5Fe 12−2 x Ni x Zr x O 19 with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.

Controlled synthesis and magnetic properties of Co 1− xNi x/MWCNT nanocomposites by microwave irradiation

Co 1− x Ni x alloy nanoparticles ( x = 0.2, 0.5, 0.6, and 0.8) with the diameter 15–28 nm attached on the surface of multi-walled carbon nanotubes (MWCNTs) were prepared to form Co 1− x Ni x /MWCNT nanocomposites by microwave irradiation. Experimental results demonstrated that Co 1− x Ni x alloy nanoparticles with quasi-spherical and face-centered cubic structure had been attached on the MWCNTs, the composition and size of Co 1− x Ni x alloy nanoparticles could be controlled through adjusting the atomic ratios of metal Co to Ni in the mixed acetate solution, the microwave power and microwave irradiation time, respectively. Both the coercivity and the saturation magnetization of Co 1− x Ni x alloy nanoparticles increased with increasing Co concentration from x = 0.8 to 0.5, and decreased when Co concentration was increased from x = 0.5 to 0.2. These confirm that microwave synthesis is promising for fabricating alloy nanoparticles attached on MWCNTs for magnetic storage and ultra high-density magnetic recording applications.

Preparation and magnetic properties of Ni–Zr doped barium strontium hexaferrite

M-type Hexaferrites B0.5Sr0.5Fe12−2xNixZrxO19 were synthesized and investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased from x = 0.2 to 0.8 mol%, the grains are agglomerated and the average diameter increased. This suggests that Ni–Zr substitution increases the grain size, as observed in the FE-SEM micrographs. The results of magnetic measurement revealed that Ms of barium strontium hexaferrite increased when the value of x increased from 0 to 0.4 mol% and then decreased with the increasing Ni–Zr content. The Hc decreases remarkably with increasing Ni and Zr ions content. Hard magnetic material is converted into soft magnetic material when the substitution level is increased from 0.2 to 0.8 mol%. In particular, Ba0.5Sr0.5Fe12−2xNixZrxO19 with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.

Chemical stability of highly (0001) textured Sm(CoCu)5 thin films with a thin Ta capping layer

With the highest magnetocrystalline anisotropy constant (Ku) among practical magnetic materials, SmCo5 could be a very attractive candidate for future high areal density magnetic recording. However, its corrosion resistance is always a concern in recording media applications. In this paper, the chemical stability and microstructures of highly (0001) textured Sm(CoCu)5 thin films with and without a 3 nm Ta capping layer were reported. For Sm(CoCu)5 thin films without a capping layer, the coercivity decreases significantly (from 8kOe to 1kOe) within one month. Sm(CoCu)5 thin films capped with a thin Ta layer (3 nm) behave differently. Even exposed to a laboratory environment (25 °C) over 3 years, the Ta-capped Sm(CoCu)5 thin films are stable in terms of structural and magnetic properties, i.e., there were no changes in X-ray diffraction peaks and vibrating sample magnetometer hysteresis loops. Microstructure of Ta-capped Sm(CoCu)5 thin films showed that Sm(CoCu)5 formed a domelike particle assembly structure on a smooth Ru underlayer and were well covered by partially oxidized Ta capping layer, as shown by TEM cross-section micrographs. Accelerated corrosion treatment (130 °C, 95% relative humidity, 6 h) was performed on Ta-capped Sm(CoCu)5 thin films. X-ray photoelectron spectroscopy (XPS) results showed that no Co was detected on the sample surface before the corrosion treatment, but strong XPS signals of CoOx and Co(OH)x were observed after treatment. Therefore, none of our Sm(CoCu)5 thin films can pass the accelerated corrosion test. Hcp-phased CoPt-alloys are proposed as better capping materials for Sm(CoCu)5 thin films in future high-density magnetic recording applications.

Study on ESD Phenomena of Magnetic Head by 1ns Pulse ESD

Magnetic Recording heads, the most electrostatic discharge (ESD/EOS) sensitive device of all electric devices, are used for high density magnetic recording applications. Recently, as the devices become increasingly smaller, there has arisen a concern for damaging GMR (Giant Magneto Resistive) heads by EMI. Also, CDM or nano second pulse ESD is key issue for Magnetic head manufacturing. In order to study the effect of ESD (Electro Static Discharge) with nano pulse width for GMR heads, transfer curves of GMR heads using high field QST (Quasi Static Tester) were investigated. By applying ESD damage to GMR head, the transfer curves change the waveforms. Also, there are many kinds of waveforms of transfer curves for after ESD damaged heads. It was found that the degradation of pinned layer was caused by nano pulse ESD and the phenomena were detected by high field QST.

Synthesis and magnetic properties of size-controlled FeNi alloy nanoparticles attached on multiwalled carbon nanotubes

FeNi alloy nanoparticles with controllable sizes were attached on the multiwalled carbon nanotubes by adjusting the atomic ratio of metal to carbon in the mixed solution of nitrate with Fe:Ni=1:1 (atomic ratio) via wet chemistry. Transmission electron microscopy (TEM) and high-resolution TEM indicated that quasi-spherical FeNi alloy nanoparticles with sizes in the range 12–25 nm are obtained. FeNi alloy composed of major face center cubic (fcc) and minor body center cubic (bcc) structures, which is proved by the X-ray powder diffraction (XRD). Magnetization measured by vibrating sample magnetometer demonstrated that both the coercive force and saturation magnetizations decrease as the size of the FeNi alloy nanoparticles decreased. The chemical method is promising for fabricating FeNi alloy nanoparticles attached on carbon nanotubes for magnetic storage and ultra high-density magnetic recording applications.

Study on ESD/EMI Phenomena for Magnetic Reproducing Head

GMR heads, the most electrostatic discharge (ESD/EOS) sensitive device of all electric devices, are used for high density magnetic recording applications. A number of problems related to electrostatic discharge phenomena in GMR heads have been reported, including melting and diffusion caused by the Joule heating by ESD currents, pinning rotation and demagnetization resulting from high magnetic field strength, and dielectric breakdown induced by a high voltage. In recent years, there has been a growing concern about damaging GMR heads from Electro-Magnetic Interference (EMI). In this paper, we studied a relatively easy method for comprehending the basic characteristics of EMI using the instruments that are widely used in conventional ESD evaluation for GMR head manufacturing.

(Ni, Zn, Sn) Ru and (Ni, Sn) Sn substituted barium ferrite prepared by mechanical alloying

NiRu, ZnRu, SnRu and SnSn mixtures considerably improved the saturation magnetization, Ms with low substitution values; diminishing quickly at the same times the coercivity, H ci to suitable values for high-density magnetic recording applications. On the other hand, the NiSn mixture also decreased the coercivity rapidly however without enhancing the saturation magnetization. The shown differences on magnetic properties were mainly due both to magnetic nature of divalent ion and to secondary phase apparitions. The mixtures with Sn2 + as partner ion diminished markedly to T c. The tetravalent Ru4 + ion has a special effect on magnetic properties of hexagonal ferrites (increases Ms and diminishes fast H ci with low substitutions).

Magnetization reversal and magnetic anisotropy in patterned Co/Pd multilayer thin films

( Co / Pd ) N multilayers exhibit high vertical magnetic anisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In this work, (Co/Pd)N multilayers are deposited by magnetron sputtering and patterned into large periodic arrays of 200 nm islands to enable controlled domain wall injection for quantitative comparison of magnetic anisotropy energies. Magnetic properties are correlated with x-ray photoelectron spectroscopy data, an approach commonly used to probe the binding energies and valence band positions. Confirming theoretical predictions, it is demonstrated that the degree of d-shell hybridization at Co/Pd interfaces directly correlated with the magnitude of magnetic anisotropy.

Magnetization dynamics: ultra-fast and ultra-small

Ultrafast magnetic processes are of great scientific interest but also form the basis of high density magnetic recording applications. We demonstrate the uniqueness of time resolved, high resolution magnetic X-ray microscopy, and show that the motion of a magnetic vortex core can be imaged. The vortex core direction is hidden to most experimental techniques, but has a decisive influence on the dynamics of the magnetic structure. We imaged the switching of a ferromagnetic nanostructure by a spin polarized current pulse using time resolved X-ray microscopy. As opposed to the common uniform switching process due to Néel and Stoner–Wohlfarth, the magnetization in spin injection devices does not switch uniformly, but involves the motion of a magnetic vortex. To cite this article: Y. Acremann, C. R. Physique 9 (2008).

Composition-controlled synthesis, structure and magnetic properties of ternary FexCoyNi100−x−y alloys attached on carbon nanotubes

Abstract FexCoyNi100−x−y alloy nanoparticles with controllable compositions attached on the surface of carbon nanotubes (CNTs) were synthesized using an easy two-step route including adsorption and reduction processes. The nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The effect of the alloy composition on microstructure and magnetic properties of ternary FeCoNi alloys attached on carbon nanotubes have been studied. During the nominal composition range (x = 21, 24, 33, 37, 46 and y = 60, 46, 48, 48, 35), FexCoyNi100−x−y alloy nanoparticles attached on CNTs are quasi-spherical, fcc–bcc dual phase, and the coercivity (Hc) and saturation magnetization (Ms) vary with the alloy composition. The Hc of FexCoyNi100−x−y alloy nanoparticles attached on CNTs decreases and Ms increases with increasing Fe content. These demonstrate that the two-step route is promising for fabricating alloy nanoparticles attached on CNTs for magnetic storage and ultra high-density magnetic recording applications.