Perpendicular Magnetic Recording Media Research Articles

Structural, Electrical, Dielectric, Magnetic, and Microwave Absorption Properties of Cr Substituted BaSrCo2Fe12O22 Hexaferrites for High-Frequency Applications

In the recent decade, advancements in technology and the excessive use of electronic devices in everyday life have harmed human health and produced electromagnetic pollution. To overcome these problems, hexagonal ferrites are used as excellent microwave-absorbing materials to clean the environment and protect human health. In this study, chromium (Cr3+) substituted Y-type BaSrCo2CrxFe12-xO22 hexaferrites (x=0.0, 0.5, 1.0, 1.5, and 2.0) have been synthesized through self-ignited sol-gel method and sintered at 1150 °C for 5.5 hours. The single phase of the synthesized nanomagnetic materials was confirmed by X-ray diffraction analysis. FTIR analysis unfold the Fe-O vibrational bands at tetrahedral and octahedral sites due to iron oxide base material. The incorporation of Cr3+ limits the transfer of electrons. As a result, DC electrical resistivity significantly increases from 7.59×109-4.85×1010 (Ω cm). The dielectric behavior and impedance analysis was carried out in the 1 MHz - 6 GHz range. By replacing Cr3+, the dielectric constant and loss exhibit a decreasing behavior. For all compositions, the values of reflection loss are calculated in the range of -39.37 to -32.95 to make them excellent microwave-absorbing materials due to their lower cost, small size, and lightweight properties. The substitution of Cr3+ increases the saturation magnetization (61.35-96.10 emu/g), coercivity (62.31-897.99 Oe), and remanence (12.30-46.52 emu/g). An increase in the coercivity value indicated that samples are thermally stable and suitable for perpendicular magnetic recording media.

High-resolution alternating magnetic force microscopy using an amorphous FeB-based tip driven by an inverse magnetostrictive effect: Imaging of the high-density magnetic recording media

The improved spatial resolution of the alternating magnetic force microscopy (A-MFM) technique developed in this work is demonstrated using a tip coated with a very thin magnetostrictive Fe-B-based amorphous film. Its magnetization can be periodically reversed using an applied alternating current magnetic field, which leads to alternating mechanical stress at the tip end, thus affecting localized magnetization reversal via an inverse magnetostrictive effect. Spatial resolution improvement is achieved via effective reversible magnetization volume at the sharpened tip end, which promotes a decrease in the total magnetic volume and maintains sufficient sensitivity at a lower coating thickness. A-MFM uses frequency modulation induced by an off-resonant alternating magnetic force between the tip and the sample. Therefore, a magnetic force can be selectively detected near the sample surface, independent of non-magnetic interactions. Due to their smooth surfaces without crystalline grain boundaries, large magnetization, and large magnetostriction compared with those of other magnetic materials, Fe-based amorphous films are suitable for tip coating applications. A 500-kfci perpendicular magnetic recording medium (PMR) was imaged using a 6-nm thick amorphous Fe-B coated tip to produce highly resolved images with minimal detection of the wavelength of the magnetic field of less than 10 nm. Also, 1600-kfci PMR imaging was successfully achieved, with the images showing individual ∼ 15-nm bits.

Recovering magnetic domains of nanoscale-mechanically damaged ferromagnetic thin film of information data storage

Combined effects of stress and temperature on magnetic domains and scratch morphology of the ferromagnetic film of a perpendicular magnetic recording media are investigated using nanoscratch, atomic force microscope, and magnetic force microscope. The stored magnetic signals in the non-scratched area become weak with increasing temperature due to the thermal agitation of magnetic spins. The high local stress permanently damages the magnetic signals at the scratch center. However, the weakened magnetic signals at lightly stressed regimes recover significantly with increasing temperature up to 300 °C due to the partial recovery of ferromagnetism. Regarding the nanoscratch morphology, when the temperature increases up to 300 °C, the scratch is healed noticeably due to metal oxides (CoO, Cr2O3, and PtO2) built-up on the scratched surface. Surprisingly, the scratch deepens at 400 - 600 °C. This is attributed to PtO2 evaporation and the phase transition of magnetic grains from HCP to FCC.

Effects of SiO2 content on the nanomechanical properties of CoCrPt-SiO2 granular films

CoCrPt material is used for perpendicular magnetic recording media due to its high magneto-crystalline anisotropy that brings good thermal stability on the media. The addition of SiO2 between the CoCrPt grains offers benefits including lower noise and better thermal stability. It has been reported that the SiO2 content has strong effects on the media’s recording performance such as coercivity, anisotropy and noise. In this work, we focus on studying the effects of the SiO2 content on the nanomechanical properties of the media which are critical for the head-disk interface reliability. Variations of these properties with SiO2 content provide guidelines for optimum designs considering both recording and mechanical interface performance.

Electric-Field-Enhanced Bulk Perpendicular Magnetic Anisotropy in GdFe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Multiferroic Heterostructure.

Perpendicular magnetic anisotropy is important for increasing the information storage density in the perpendicular magnetic recording media, and for rare-earth-transition-metal alloys with bulk perpendicular magnetic anisotropy that generate great research interest due to their abundant interesting phenomena, such as fast domain wall motion and skyrmion. Here, we deposit amorphous GdFe ferrimagnetic films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate and investigate the effect of electric-field-induced piezostrain on its bulk perpendicular magnetic anisotropy. The anomalous Hall effect and polar Kerr image measurements suggest an enhanced bulk perpendicular magnetic anisotropy by electric field, which originates from a positive magnetoelastic anisotropy due to the positive magnetostriction coefficient of the GdFe film and the electric-field-induced tensile strain along the z axis in Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate. Our results enrich the electrical control of perpendicular magnetic anisotropy and are useful for designing spintronic devices based on perpendicular magnetic anisotropy.

Structural, Dielectric, and Magneto‐Optical Properties of Al‐Cr Substituted M‐Type Barium Hexaferrite

M‐type barium hexaferrite, BaFe12‐2xAlxCrxO19 (x = 0.0, 0.2, 0.4), is prepared using sol–gel auto‐combustion method and calcined at 1000 °C for 7 h. The effects of Al‐Cr substitution on the properties of the barium hexaferrite are investigated through XRD, FTIR, FESEM, UV‐vis‐NIR, VSM, and impedance analyzer. XRD analysis reveals the formation of hexaferrites with single phase and no impurity phase is detected. FTIR spectra show bands at 437 and 590 cm−1 which indicate the possible of hexaferrites. The micrographs of FESEM shows agglomerated grains with hexagonal plate‐like shape while the EDX spectra confirm the composition of the synthesized samples. Dielectric constant decreases abruptly at lower frequencies and an increment in dielectric constant at much higher frequency region is observed. Grain boundaries dominate the AC conductivity at lower frequencies while the grains could be responsible for the observed dispersion at higher frequencies. The values of coercivity for all the samples are found to be greater than 1200 Oe; this makes the prepared samples useful for high‐density perpendicular magnetic recording media.

Temperature dependence of the microscopic magnetization process of Tb12Co88 using magnetic Compton scattering

Abstract Tb-Co perpendicular magnetization films are mother materials for perpendicular magnetic recording media. Since the magnetic recording technique is based on magnetic switching of a material, investigating a magnetic the response of the material to a magnetic field is important. The magnetic response of the entire system is the net of each microscopic response of the spin magnetic moment and orbital magnetic moment of the elements. Herein we study the magnetization processes of the spin, orbital, and the element-specific magnetic moments by measuring the magnetic field dependence of the magnetic Compton profile of a Tb12Co88 film. The spin and orbital magnetic moments have opposite orientations. Similarly, Tb and Co magnetic moments have opposite directions. When the total magnetic moment reverses, the orientation of spin and orbital magnetization as well as Tb and Co reverse. Decreasing the temperature, the fluctuation of the magnetic moment of Tb in the perpendicular direction decreases. So the cancelation between the Tb and Co moments reduces total magnetic moment.

Investigation of FePt-SiO2-C granular film in columnar structure

We worked on a FePt granular film with a columnar structure, for the purpose of ultrahigh density perpendicular magnetic recording media. In experiments, a Fe53Pt47-SiO230%-C25% (10 nm) film was deposited on a silicon substrate with a MgO (12 nm) interlayer at 510 °C. The perpendicular coercivity of the film is 29 kOe, with a squareness of 1. Bright-field TEM images show that the FePt granular film has small and uniform grains of 8.3 ± 1.9 nm with a columnar structure. More work of high-resolution TEM imaging shows excellent L10 ordering inside the FePt grains. The measurement of remnant coercivity proves that it has an energy barrier of 290kBT at room temperature, meaning excellent thermal stability. We demonstrate FePt granular film to be a qualified candidate for high-density perpendicular magnetic recording media, and both SiO2 and C addition helps form columnar structure.

Microstructure and Magnetic Properties of Exchange-Coupled Co72Pt28/Pt/Co81Ir19 Composite Media for Perpendicular Magnetic Recording

In this work, we report the investigation of microstructure and magnetic properties of the Co72Pt28/Pt/Co81Ir19 exchange-coupled composite (ECC) media using soft-layer (SL) of Co81Ir19 with negative magnetocrystalline anisotropy (MA). Our TEM images show that the hard-layer (HL) exhibits a columnar type microstructure with well-isolated grains and the exchange-coupled SL with hcp-structure show the same texture. Strong coupling of the two layers have been evidenced by the magnetic characterization for all the studied films with Pt inter-layer thickness ranging from 0 to 2 nm. Importantly, these ECC media films have much lower coercivities and much higher thermal stabilities in the favor of high-density magnetic recording.

Reduction of Intergranular Exchange Coupling for CoPt–B2O3 Granular Media by Employing a RuCoCr-Oxide Buffer Layer With Oxide of Various Melting Points

CoPt-oxide granular films have been widely used for perpendicular magnetic recording media. To further increase recording density of the media, enhancement of magnetocrystalline anisotropy $(K_{u})$ to overcome the thermal stability issue and reduction of media noise to increase signal-to-noise-ratio are essential. The requirements can be realized through the promotion of columnar growth of magnetic grains which are phase separated with oxide boundary material and intergranular exchange decoupling 1), respectively. Generally, for the grain boundary materials of the granular media, oxides with amorphous phase which do not dissolve into CoPt metal have been utilized. The oxide is expected to segregate into the trench of Ru underlayer so that CoPt grains can grow heteroepitaxially on the bump of Ru underlayer. Many authors have proposed various kinds of oxide materials to be segregated into the grain boundaries, like SiO 2 2), TiO 2 3), Ta 2 $\mathrm {O}_{5}^{3)}$, Nb 2 $\mathrm {O}_{5}^{4)}$, WO 3 4), MgO 5), Cr 2 $\mathrm {O}_{3}^{5)}$, and $\mathrm {Y}_{2} \mathrm {O}_{3}^{5)}$. Previously, we had found that a granular medium with high magnetocrystalline anisotropy $(K_{u})$ was successfully realized when B 2 O 3 was applied for the grain boundary material 6). However, the separation between magnetic grains at the initial growth region in the Ru trench by low melting point oxide such as B 2 O 3 is not sufficient 7). Therefore, we have carried out an investigation on the deposition of a buffer layer (BL) with non-ferromagnetic metal and oxides of various melting points $(T_{m})$ on the Ru underlayer to grow the non-ferromagnetic metal and oxide on the Ru bump and trench, respectively, aiming to intergranular exchange decouple the magnetic grains. In this paper, we will discuss about the effect of utilizing BL with oxide of various $T_{m}$ on the intergranular exchange decoupling of CoPt$- \mathrm {B}_{2} \mathrm {O}_{3}$ granular media in relation with magnetic properties.

Alternating Magnetic Force Microscopy: Effect of Si doping on the temporal performance degradation of amorphous FeCoB magnetic tips

In order to increase the resolution of traditional MFM and extend its applications in the past, we created an Alternating Magnetic Force Microscopy (A-MFM) with a magnetic force modulation by applying an off-resonance AC magnetic field. A new magnetic tip has been developed for A-MFM in this work. Perpendicular magnetic recording medium with 500 kfci recording density is successfully imaged and analyzed by using the new tips coated by 6–15 nm amorphous FeCoSiB-based soft magnetic film. The effect of Si doping to the magnetic film on the A-MFM imaging was studied. It was found that Si additive had no effect on the imaging properties, such as signal-to-noise ratio and spatial resolution (kept at ∼5 nm level). But on other side, Si additive significantly degraded the chemical stability of FeCoSiB film due to oxidation in ambient atmosphere. Surface passivation by metal and boron oxides is considered to have a main effect on improvement of chemical stability of Si-free magnetic coating. The results have shown that Si-free FeCoB-based magnetic tips are appropriate candidates for A-MFM imaging in ambient conditions.

Gap-mode-assisted light-induced switching of sub-wavelength magnetic domains

Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrical restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a λ=785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25–50 nm for efficient heating of FePt recording media with a gap of 5 nm.

Coercivity enhancement of FePd thin films prepared by the post-annealing of off-stoichiometric magnetron-sputtered multilayers

Attainment of perpendicular coercivity higher than 900 Oe and accurate calculation of the degree of long-range order in an FePd alloy thin film is essential in the realization of the perpendicular magnetic recording media. Here, we prepared the off-stoichiometric FePd films through the multilayer growth of [Fe(2 nm)/Pd(2 nm)] × 30 deposited on MgO(001) substrates by magnetron sputtering. The effects of post-annealing these films at 700 °C for 1 and 10 h on their surface morphologies, and crystallographic and magnetic characteristics were investigated. The results show that, with increasing annealing time, the FePd thin films are predominantly (001)-oriented with a progressive increase of the grain size and surface roughness, as well as the improved crystallinity and reduced micro-strain. Accordingly, the perpendicular coercivity is significantly increased to the value of 1.5 kOe, and Pd loses its 4d electrons upon alloying. Furthermore, analysis of X-ray absorption data elucidates some structural details of the Fe scattering phase in addition to the dominant tetragonal FePd phase. We also present a way of determining the long-range order parameter for the FePd alloy thin film, using the combined information of the tetragonality ratio extracted from extended x-ray absorption fine-structure spectroscopy and the stoichiometric deviation of the thin film.

Hexagonal Closed Packed CoPtRu Alloy as a Buffer Layer Material for Promoting Heteroepitaxial Growth for Perpendicular Magnetic Recording Media

Crystal structure and magnetic properties for Co–Pt–Ru alloy films and Co–Pt–Ru–oxide granular films were investigated for material to reduce the lattice mismatch between the magnetic layer and the nuclei control layer of the perpendicular magnetic recording media. The laminate stacking structure of the sample was sub/NiFeCr (20 nm)/Ru (20 nm)/Co–Pt–Ru (20 nm). The amount of stacking faults in the films was evaluated as a probability of occurrence of fcc stacking, Pfcc measured by an in-plane X-ray diffractometry profile. As a result, it was found that: 1) hcp atomic stacking structures of the Co100– x Ru x alloy films were stable compared with that of Co100– x Pt x alloy films for almost all of the additional content x; 2) lattice constant a and c for Co–Pt–Ru ternary alloy film could be controlled between 2.51 to 2.59 A, and 4.07 to 4.41 A, as changing the Pt and Ru content with a total amount of 0 to 50 at.%, respectively. And the lattice constant ratio c/a decreased from 1.62 to 1.59 with increasing Ru content more than 20 at.%; 3) Pfcc in the Co–Pt–Ru ternary alloy films was less than 0.5% for the samples with Ru content were more than 20 at.%; 4) uniaxial magnetocrystalline anisotropy K u could be controlled from 12.6 to 0 106 erg/cm3 by adding Pt and Ru with a total amount of 30 at.% to a Co75Pt25 film; and 5) Co–Pt–Ru–(SiO2) film with the columnar structure was realized for Ar gas pressure of 4 Pa during sputtering.

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.

Co-Cr-Ta/Pt bilayered films for perpendicular magnetic recording media

Co-Cr-Ta/Pt bilayered films for perpendicular magnetic recording media

Transition noise analysis for double-layered perpendicular magnetic recording media

Transition noise analysis for double-layered perpendicular magnetic recording media

Grazing-incidence optical magnetic recording with super-resolution.

Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ0H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface – six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features – thus suggesting full compatibility with NFT-HAMR.

Cluster Cutting: A Better Understanding of Media Noise in Perpendicular Magnetic Recording

For perpendicular magnetic recording media, integrated media noise power plotted versus linear density typically shows a linear rise at low densities, then plateaus over the mid density range, and sharply rises in a supralinear fashion at very high densities. Various proposed explanations of this behavior have been less than simple and direct. Here we give evidence and theoretical analyses to support the simple idea that granular clusters existing at low densities can be cut into smaller average cluster lengths by write heads having sufficiently high field gradients, thus accounting for the plateau behavior. Not only is the plateau noise behavior explained, along with nonlinear partial erasure, but also a new insight into the nature of noise and granular cluster results.

Review Article: FePt heat assisted magnetic recording media

Heat-assisted magnetic recording (HAMR) media status, requirements, and challenges to extend the areal density (AD) of magnetic hard disk drives beyond current records of around 1.4 Tb/in.2 are updated. The structural properties of granular high anisotropy chemically ordered L10 FePtX-Y HAMR media by now are similar to perpendicular CoCrPt-based magnetic recording media. Reasonable average grain diameter ⟨D⟩ = 8–10 nm and distributions σD/D ∼ 18% are possible despite elevated growth temperatures TG = 650–670 °C. A 2× reduction of ⟨D⟩ down to 4–5 nm and lowering σD/D < 10%–15% are ongoing efforts to increase AD to ∼4 Tb/in.2. X = Cu ∼ 10 at. % reduces the Curie temperature TC by ∼100 K below TC,bulk = 750 K, thereby lowering the write head heat energy requirement. Multiple FePtX-Y granular layers with Y = 30–35 vol. % grain-to-grain segregants like carbides, oxides, and/or nitrides are used to fully exchange decouple the grains and achieve cylindrical shape. FePt is typically grown on fcc MgO (100) seedlayers to form well oriented FePt (002). A FePt lattice parameter ratio c/a ∼0.96 and high chemical order S > 0.90 result in magnetic anisotropy KU ∼ 4.5 × 107 erg/cm3, and only 25% below the FePt single crystal value KU = 6.6 × 107 erg/cm3 has been achieved in 7–8 nm diameter grains. Switching field distributions depend on anisotropy field (HK) distributions, which are currently of the order of ΔHK/HK ∼ 10% (ΔHK ∼ 10–12 kOe, HK ∼ 10–11 T) at room temperature. High thermal conductivity heat sink layers, including Ag, Au, Cu, and Cr, are used to optimize the cooling rate and maximize the down- and cross-track thermal gradient, which determines the achievable track density.