Applications In Magnetic Recording Media Research Articles

Effect of Annealing Temperature on the Characterizations of Cobalt Ferrite Nanoparticles Synthesized via Co-precipitation

This study investigates the effect of annealing temperature on the structural and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles synthesized via the co-precipitation method. The results indicate that the annealing temperature significantly enhances the crystal size and quality, yielding well-defined, impurity-free CoFe2O4 crystals. Magnetic measurements reveal that both saturation magnetization (Ms) and coercivity (Hc) are improved with annealing. The nanoparticles exhibit a soft-magnetic, single-domain state up to an annealing temperature of 1200°C. They reach a critical size of 39.7 nm and begin transitioning to a multi-domain state. These findings highlight the crucial role of annealing temperature in optimizing the properties of CoFe2O4 nanoparticles for potential applications in magnetic recording media, magnetic resonance imaging, magnetic fluid hyperthermia, biosensors, drug delivery, and cell separation.

Effect of Cr substitution on nickel spinel ferrite’s surface morphology, structure, antibacterial activity and magnetic properties

This study reports the sol–gel auto-combustion (SGACT) synthesis of Cr-substituted NiFe2O4 nanoferrites with a composition, of CrxNi(1−x)Fe2O4 (where x = 0.000, 0.025, 0.050, 0.100, 0.150, 0.200), and it examines the effects of chromium on spinel ferrite’s structure and properties. The doping of Cr at the nickel site is first reported in the present study. The computed crystallite size “t” from the XRD results was found in the range of 34.2–40.4 nm, whereas, FESEM plots show larger-sized grains due to the aggregation of a large number of crystallites for the produced nanoferrites. Maximum saturation magnetization of 42.44 emu/g was attained by the Cr0.050Ni0.950Fe2O4 (x = 0.050) specimen, whereas, the Cr0.200Ni0.800Fe2O4 (x = 0.200) specimen attains the maximum coercivity in the current study. All these excellent values of magnetic parameters make our SGACT-produced nanoferrites useful for magnetic recording media applications. In S. aureus, Cr0.200Ni0.800Fe2O4 nanoparticles showed the highest zone of inhibition (ZOI) whereas, Cr0.050Ni0.950Fe2O4 nanoparticles showed the least ZOI. On the other hand, in E. coli, Cr0.850Ni0.150Fe2O4, Cr0.200Ni0.800Fe2O4 and Cr0.050Ni0.950Fe2O4 nanoparticles showed good ZOI. This makes our developed nanoferrites beneficial for biological applications as antibacterial agents.

Rietveld refinement, magnetic and dielectric properties of Sr2+-Co2+-doped Zn2Y-type hexaferrites

In this experimental study, Sr2+-Co2+ was doped in Zn2Y-type hexaferrite to improve its magnetic and dielectric properties. Sol-gel auto combustion was used to synthesize Ba2-xSrxZn2-yCoyFe12O22 (x ​= ​0.0, 0.4, 0.8 and y ​= ​0.0, 0.5, 1.0), and the Retrieved refinement of XRD data confirmed the single-phase Y-type. Lattice constants a and c decreased from 5.867 to 5.854 Å and 43.566 to 43.470 Å, respectively. FTIR identified the absorption bands of hexaferrite at 405 cm-1 and 546 ​cm−1. An average grain size from FESEM decreased from 350 to 250 ​nm. Saturation magnetization and coercivity from M-H hysteresis loop for x ​= ​0.0, y ​= ​0.0, x ​= ​0.4, y ​= ​0.5, and x ​= ​0.8, y ​= ​1.0 are 40.04 emu/g, 42.77emu/g, 52.91emu/g, and 381.24 ​Oe, 261.44 ​Oe, 236.14 ​Oe respectively. The decrease in grain size, coercivity, and an increase in saturation magnetization make the prepared sample suitable for application in magnetic recording media. The material also deemed ideal for microwave devices due to its decreased dielectric constant values

Compositional Dependence of Magnetocrystalline Anisotropy, Magnetic Moments, and Energetic and Electronic Properties on Fe-Pt Alloys.

This work reported the first-principles calculations for the compositional dependence of the energetic, electronic, and magnetic properties of the bimetallic Fe-Pt alloys at ambient conditions. These hybrid alloys have gained substantial attention for their potential industrial applications, due to their outstanding magnetic and structural properties. They possess high magnetocrystalline anisotropy, density, and coercivity. Four Fe-Pt alloys, distinguished by compositions and space groups, were considered in this study, namely P4/mmm-FePt, I4/mmm-Fe3Pt, Pm-3m-Fe3Pt, and Pm-3m-FePt3. The calculated heats of formation energies were negative for all Fe-Pt alloys, demonstrating their stability and experimentally higher formation probability. The P4/mmm-FePt alloy had the lowest magnetic moment, leading to durable magnetic hardness, which made this alloy the most suitable for permanent efficient magnets, and magnetic recording media applications. Moreover, it possessed a relatively large magnetocrystalline anisotropy energy value of 2.966 meV between the in-plane [100] and easy axis [001], suggesting an inside the plane isotropy.

Correlation between Composition and Magnetic Properties of SrFe<sub>12</sub>O<sub>19</sub>/Co Nanocomposite Synthesized by the High Energy Ball-Milling Process

Nanocomposites (NCs) (100-x) SrFe12O19/x Co (x = 10, 20, and 30 wt. %) were produced using the high energy ball-milling (HEBM) process. The effects of hard/semi-hard ratio and annealing temperature (800, 900, and 1000 °C) on the exchange-spring in magnetic NCs were discussed. X-ray diffraction examination showed the coexistence of M-type hexaferrite SrFe12O19 (SFO) as the hard phase and CoFe2O4 spinel ferrite (CFO) as the semi-hard phase. Using a scanning electron microscope (SEM), the morphology and elemental analysis of the NCs were analyzed. The magnetic performances were investigated via a vibrating sample magnetometer at room temperature. With increasing the CFO content and annealing temperature, the hysteresis loop became narrower and possessed semi-hard magnetic properties. The 10 wt. % Co NCs annealed at 800 °C had the highest coercivity of Hc = 4.2 kOe. These results are correlated with switching field distribution plots that have indicated the efficient exchange-spring between SFO and CFO phases NCs annealed at 800 °C. The studied samples can be a promising candidate in permanent magnets and magnetic recording media applications.

Néel Skyrmionic States and Chiral Stripes in the Magnetic Bilayer with Transverse Easy Axis

Chiral spin structures, such as skyrmions, are topologically nontrivial magnetization configurations, which have potential applications in magnetic recording media. In particular, an antiferromagnetically coupled system that hosts skyrmions is of great interest because of high-speed skyrmion motion and reduced skyrmion Hall effect. Here, we consider TbCo/GdFe-based amorphous ferrimagnetic system showing chiral stripe domains and Neel-type skyrmions. It is observed that skyrmionic configurations are stabilized with the help of dipolar interactions that exist in the system. Optimized thicknesses of TbCo (30 nm) and GdFe (6 nm) show isolated skyrmions in both the layers with average skyrmion diameter of 40 ± 5 nm. We have also investigated a phase diagram in a wide range of layer thickness, which represents the presence of the mixture of either vortex, chiral stripes, or/and Neel-type skyrmions. To understand the underlying phenomena which help chiral ferrimagnetism in this kind of amorphous system, we perform layer-resolved micromagnetic modeling. We found variety of chiral textures in a wide thickness range of ferrimagnetic bilayer systems, which may be useful for fundamental understanding of formation of skyrmion and their application in spintronic devices.

Synthesis and tuning the electro-magnetic properties of Co-Cr substituted Sr-hexaferrite towards diverse usages

Strontium hexaferrite is one of the powerful commercial magnets due to its unique characteristic combination of physical, magnetic, and dielectric properties. According to the necessity, their magnetism may be altered as either hard or soft by substitutional effectiveness of the transition elements and optimization of processing parameters. Here, SrFe12-(x+y)CoxCryO19 (x,y = 0,0; 0,1; 0.25,0.75; 0.50,0.50; 0.75,0.25; 1,0) nano ferrites have been successfully synthesized by the sol–gel self-propagation process and the impacts of Co-Cr on the microstructure, densification, magnetic, dielectric, and electrical properties have been analyzed. The XRD data discloses the crystalline ferrite phase with a hexagonal structure (P63/mmc). It is found that the magnetic properties can be tuned up effectively by the substitutions. The samples show a range (0.02–0.48) of the squareness (Mr/Ms) ratio suitable for diverse industrial applications. SrFe11CrO19 composition reveals magnetic improvement in Ms (60 emu/g) and Hc (6.3 kOe) along with decent energy product, i.e., 27.17 MGOe, optimized to approach for a permanent magnet. SrFe11Co0.75Cr0.25O19 & SrFe11CoO19 compositions show a great dilution in hard magnetism having Ms of 71 emu/g along with Hc of 36.21 Oe and 3.23 Oe, respectively. It has opened up the opportunity of possible emersion of the hard magnet in the magnetic recording media application. The proposed work is expected to offer a good notion to modify strontium hexaferrite in order to expand its application areas.

Effect of Cr3+ Doped on Structural, Magnetic and Electrical Properties of Sol-Gel Synthesized SrFe12O19 Hexaferrite Nanoparticles

Nanocrystalline SrFe12-xCrxO19 hexaferrite particles were successfully synthesized via Sol-gel route from Sr3+ and Fe3+ nitrates at molar ratio of 1:9 (Fe/Sr). The XRD results revealed single hexagonal magnetoplumbite SrFe10Cr2O19 phase formation in the presence of non-magnetic (α-Fe2O3) phases in the heated samples. The dielectric properties as a function of frequency under normal conditions were also measured in the frequency range of 500 Hz to 1 MHz. The variations of dielectric constant are discus on the basis of Maxwell–Wagner and Koops models. In VSM graph, coercivity and saturation magnetization confirms that the synthesized materials are suitable for applications in magnetic recording media.

Relationship between microstructural and magnetic properties of PrCo-based films prepared by the vacuum evaporation method

In this work, Ce2Ni7 type structural PrCo-based films were deposited on Si(100) substrate by ultra-high (UHV) vacuum evaporation process. The structural and magnetic properties of these films have been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometer (VSM) and magnetic force microscopy (MFM) techniques. Two effects on structural and magnetic properties of PrCo films have been investigated: the effect of the annealing temperature (Ta) and the effect of the variation of the magnetic X-layer thickness. The as deposited PrCo films have a magnetic coercivity (Hc) of about 40–100 Oe. But after annealing at 600 °C, Hc has increased hight about 9.5 kOe for PrCo(X = 20 nm) and 10.2 kOe for PrCo(X = 50 nm) were observed. The magnetic properties were affected by the thickness due to the morphology, also the relationship between the intergrain exchange coupling (IEC), the size and quantity of the PrCo grains. The hight extrinsic properties of Hc = 10.2 kOe, maximum energy product (BH)max of 5.12 MGOe and remanence ratio Mr/Ms = 0.53 are reported for the PrCo(X = 50 nm) films. These properties are highly desirable for extremely high-density magnetic recording media applications.

Magnetic and electrical properties of M-type nano-strontium hexaferrite prepared by sol-gel combustion method

Herein, we report the synthesis of M−type nano-strontium hexaferrites co-doped with hetrovalent cations (Dy-Ni) having composition Sr(1−x)DyxFe12−yNiyO19 (x=0.00–0.20, y=0.00–0.80). The synthesized compounds were analyzed by XRD, FE-SEM, VSM, along with electrical resistivity and dielectric property analyses. XRD peak patterns revealed the magnetoplumbite-type hexagonal crystal structure of the synthesized materials. The SEM micrographs reflected the spherical and hexagonal shaped particles with an average size 40–50nm. The magnetic squareness ratio (Mr/Ms) of the synthesized nano-ferrites particles lies in the range of 0.60–0.68 assuring their single magnetic domain nature. The rise in the values of saturation magnetization, remanence and coercivity reflect that the fabricated compounds can be beneficial for the perpendicular magnetic recording media. Both the electrical resistivity increment and decrease in dielectric energy loss with increasing Dy-Ni substitution level authenticates that such materials can find applications in magnetic recording media and microwave device fabrication.

Suppressing FePt order-disorder structural phase transition temperature by Ag doping: First principles investigation for enhancing magnetic recording density

ABSTRACTIn this work, we used density functional theory to study the structures, formation energy and order–disorder structural transition temperature (To) of L10 FePt with Ag additive. The results show that an Ag atom substituting for a Fe site is more energetically preferable than that of substituting for a Pt, thus Ag atom should replace Fe site. We found that To is significantly suppressed by Ag impurity because of the increasing in configurational entropy, whereas the magnetism tends to decrease due to the absence of some Fe atom in doping processes. The decrease in To could open the opportunity to prepare FePt with lower temperature and small grain size for the high density magnetic recording media application.

CoPt Antidot Arrays Fabricated With Dry-Etching Using AAO Templates

We demonstrate a technique to fabricate large-area, highly ordered CoPt antidot arrays with perpendicular orientation. Using ultrathin anodic aluminum oxide (AAO) templates as a dry etching mask, the pattern of the pore array was transferred to the film without deteriorating the magnetic properties, in particular coercivity and preferential perpendicular orientation. The size, spacing, and density of the nonmagnetic nano-columns within the CoPt antidot arrays can be adjusted by changing the fabrication parameters of the AAO templates. The nano-columns can serve as pinning sites, impeding the magnetic domain wall motion, which can influence the magnetic properties of the film. The magnetic properties of the antidot arrays depend sensitively on the antidot morphology. The coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of the CoPt antidot array with a pore density of 2.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> fabricated using the AAO template anodized at 20 V is increased from 9.2 to 12.5 kOe due to the existence of such pinning sites.

Equiatomic CoPt thin films with extremely high coercivity

In this paper, magnetic and structural properties of near-equiatomic CoPt thin films, which exhibited a high coercivity in the film-normal direction—suitable for perpendicular magnetic recording media applications—are reported. The films exhibited a larger coercivity of about 6.5 kOe at 8 nm. The coercivity showed a monotonous decrease as the film thickness was increased. The transmission electron microscopy images indicated that the as fabricated CoPt film generally consists of a stack of magnetically hard hexagonal-close-packed phase, followed by stacking faults and face-centred-cubic phase. The thickness dependent magnetic properties are explained on the basis of exchange-coupled composite media. Epitaxial growth on Ru layers is a possible factor leading to the unusual observation of magnetically hard hcp-phase at high concentrations of Pt.

The effect of high deposition energy of carbon overcoats on perpendicular magnetic recording media

High-energy carbon deposition techniques provide thin overcoats with high corrosion and wear protection for magnetic recording media applications. The effect of high-energy (0–300 V substrate bias) deposition on the implantation induced changes in magnetic and structural properties of granular perpendicular magnetic recording media is studied. To observe subtle changes in a thin region of recording media, antiferromagnetically coupled layer structure was used. Clear changes in the magnetic properties, observed as a function of the carbon deposition energy, correlate with other measurements such as X-ray photoelectron spectroscopy, indicating the need to consider such effects when designing media and overcoat.

Synthesis and characterization of barium ferrite–silica nanocomposites

In this work, we prepared barium ferrite-silica (BaM-SiO2) nanocomposites of different molar ratios by high-energy ball milling, followed by heat-treatment at different temperatures. The microstructure, morphology and magnetic properties were characterized for different synthesis conditions by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results indicate that 15h of milling was enough to avoid the generation of hematite phase and to get a good dispersion of barium ferrite particles in the ceramic matrix. For milling periods beyond 15h and heat treatment above 900°C, the XRD patterns showed the presence of hematite phase caused by the decomposition of BaM. The agglomerate size observed through SEM analysis was around 150nm with a good BaM dispersion into the SiO2 matrix. The highest saturation magnetization (Ms) value obtained was 43emu/g and the corresponding coercivity (Hc) value of 3.4kOe for the composition 60BaM-40SiO2 milled for 15h and heat treated at 900°C. This coercivity value is acceptable for the application in magnetic recording media.

Grain Isolation Control of FePt Thin Film by Using Ag Nucleation Layer

The multilayer films with structure of Glass/CrRu/MgO/Ag (0 or 3 nm)/FePt were prepared. It was found that the introduction of an ultrathin Ag nucleation layer could induce the grain isolation of the FePt films. The microstructure of the SEM and TEM images clearly demonstrated the FePt grains were well-isolated for film with Ag nucleation layer. The magnetic properties of the films were consistent with the microstructure of the films. The work demonstrated a different approach to isolate the FePt grains, the combination of this approach with the self-assembly has the potential to be used for magnetic recording media application.

Conversion of Worm-Shaped Antiferromagnetic Hematite to Ferrimagnetic Spherical Barium-Ferrite Nanoparticles for Particulate Recording Media

We used a modified, two-step hydrothermal process to produce worm-shaped antiferromagnetic hematite-barium iron oxide particles and converted them to 25-45 nm spherical ferrimagnetic barium-ferrite (S-BaFe) nanoparticles for high-density magnetic recording media application. Saturation magnetization and coercivity of the S-BaFe nanoparticles were 50.7 emu/g and 4311 Oe, respectively. The thermal stability of KuV/k B T ≈ 81 was estimated for the S-BaFe nanoparticles from time-dependent remanent coercivity measurements.

Nano-grain Al 2O 3 crystals grown by sputtering of aluminium on CoCrPt thin films for potential application in ultra-high-density recording media

Designing supraceramic assemblies based on Al 2O 3 has remained a challenge due to the problems associated with the suitable dispersion in neat compounds and ability to control the preferred orientation in a unique fashion. Herein, granular HCP-(CoCrPt) 100− X (Al 2O 3) X ( X represents the percent weight) thin films with Si(1 0 0) substrates have been fabricated using sputtering technique followed by annealing treatment. Structural and magnetic properties of thin film have been investigated for potential application in magnetic recording media. It was shown that coercivity increased from 0.5 to 2.5 kOe by increasing the nano-grain Al 2O 3 content in the CoCrPt magnetic layers. In CoCrPt-Al 2O 3 thin films coercivity of 2.5 kOe has been obtained with increasing the Al 2O 3 content from 3 to 13 wt.% in the annealed thin films. The structural properties of the samples were studied using X-ray diffraction (XRD) and transmission electron microscope (TEM) equipped with selected area electron diffraction (SAED). The magnetic properties of the samples were measured with a vibrating sample magnetometer (VSM). The VSM results showed that the HCP-CoCrPt-Al 2O 3 granular films are a promising candidate for ultra-high-density recording media because of its low Al 2O 3 content and simple manufacturing process.

DOUBLE-LAYER THIN FILMS MAGNETIC PROPERTIES DEPENDENCE ON ANISOTROPIC HEISENBERG MODEL PARAMETERS

The study of thin ferromagnetic films has become a field of great interest due to their importance for applications in magnetic-recording media, in order to create ultrahigh density magnetic data storage. Such an interest is also due to numerous specific phenomena related to the low dimension of these systems. In this paper we investigate the magnetic properties of bilayer thin film. The specific behavior of the mentioned system type is simulated using the Monte Carlo technique, in the extended anisotropic Heisenberg model. The magnetization, out-of-plane and in-plane magnetic susceptibilities behaviors according to temperature are investigated in order to find out the contingent magnetic ordering phase and the critical temperature, for two easy-axis anisotropy set parameter assignments. We have also presented the specific heat as a function of temperature for different direct exchange parameter values and we have found out a single-peak shape of the graphs, the critical point traveling to lower temperatures as the direct exchange parameter decreases, the similarity of the two presented cases being evident.

Magnetic properties of TbFeCo film with Ag under-layer

Tb 19.05Fe 22.01Co 58.94 (500 Å)/Ag (0–1000 Å) double films were deposited on nature oxidized Si(1 0 0) substrates at room temperature by DC magnetron sputtering. The TbFeCo /Ag films were sandwiched between two 300 Å SiN x protective layers which were prepared by RF magnetron sputtering to prevent the films from oxidation. The effects of Ag under-layer on the magnetic properties of the TbFeCo film were investigated. It was found that increasing the thickness of Ag under-layer would rise the perpendicular coercivity of the TbFeCo film. The perpendicular coercivity value of the TbFeCo (500 Å)/Ag (500 Å) films was 3176 Oe. This film is a promising candidate for heat-assisted magnetic recording media applications.