Large Perpendicular Coercivity Research Articles

Switching of magnetic easy-axis using crystal orientation for large perpendicular coercivity in CoFe2O4 thin film

Perpendicular magnetization and precise control over the magnetic easy axis in magnetic thin film is necessary for a variety of applications, particularly in magnetic recording media. A strong (111) orientation is successfully achieved in the CoFe2O4 (CFO) thin film at relatively low substrate temperature of 100 °C, whereas the (311)-preferred randomly oriented CFO is prepared at room temperature by the DC magnetron sputtering technique. The oxygen-deficient porous CFO film after post-annealing gives rise to compressive strain perpendicular to the film surface, which induces large perpendicular coercivity. We observe the coercivity of 11.3 kOe in the 40-nm CFO thin film, which is the highest perpendicular coercivity ever achieved on an amorphous SiO2/Si substrate. The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime. Importantly, this can be achieved on virtually any type of substrate.

Growth Mechanism of Columnar Grains in FePt–C Granular Films for HAMR Media Processed by Compositionally Graded Sputtering

The optimization of nanogranular FePt–C films for heat-assisted magnetic recording is carried out by varying processing conditions for compositionally graded sputtering. Microstructures and magnetic properties of the films were studied for various thicknesses ranging from 2 to 12 nm to observe the growth steps of the films. An excellent in-plane nanogranular microstructure is obtained for the films of thickness ≥8 nm. Below 6 nm in thickness, the grains are random in shape and the presence of fine grains deteriorates the magnetic properties on account of poor $L1_{0}$ ordering. During the nucleation and grain growth stages, the grain size does not change too much with increasing the film thickness. But, the coarsening of FePt grains occurs and the aspect ratio of the FePt grain changes in the films of thickness ≥8 nm. We achieve a minimum grain size of 6.2 nm having an aspect ratio of 1.9 with a large perpendicular coercivity of 3.9 T for $\sim 12$ nm thick FePt–C films.

Domain wall pinning on strain relaxation defects (stacking faults) in nanoscale FePd (001)/MgO thin films

FePd (001) films, prepared by an electron beam deposition system on MgO(100), exhibit a perpendicular magnetic anisotropy (1.7 × 107 erg/cc) with a high order parameter (0.92). The relation between stacking faults induced by the strain relaxation, which act as strong domain wall pinning sites, and the perpendicular coercivity of (001) oriented L10 FePd films prepared at different temperatures have been investigated. Perpendicular coercivity can be apparently enhanced by raising the stacking fault densities, which can be elevated by climbing dissociation of total dislocation. The increased stacking fault densities (1.22 nm−2) with large perpendicular coercivity (6000 Oe) are obtained for samples prepared at 650 °C. This present work shows through controlling stacking fault density in FePd film, the coercivity can be manipulated, which can be applied in future magnetic devices.

Perpendicular Magnetic Anisotropy in Amorphous Ferromagnetic CoSiB/Pd Thin-Film Layered Structures.

Spin transfer torque (STT) induced switching of magnetization has led to intriguing and practical possibilities for magnetic random access memory (MRAM). This form of memory, called STT-MRAM, is a strong candidate for future memory applications. This application usually requires a large perpendicular magnetic anisotropy (PMA), large coercivity, and low saturation magnetization. Therefore, we propose an amorphous ferromagnetic CoSiB alloy and investigate CoSiB/Pd multilayer thin films, which have a large PMA, large coercivity, and low saturation magnetization. In this research, we propose a remarkable layered structure that could be a candidate for future applications and try to address a few factors that might affect the variation of PMA, coercivity, and saturation magnetization in the CoSiB/Pd multilayers. We investigate the magnetic properties of the CoSiB/Pd multilayers with various thicknesses of the CoSiB layer. The coercivity was obtained with a maximum of 228 Oe and a minimum value of 91 Oe in the [CoSiB 7 Å/Pd 14 Å], and [CoSiB 9 Å/Pd 14 Å], multilayers, respectively. The PMA arises from tCoSiB = 3 Å to tCoSiB = 9 Å and disappears after tCoSiB = 9 Å.

Microstructure and magnetic properties of (0 0 1)-oriented L10 FePt films: Role of Ag underlayer and Fe/Pt ratio

FePt multilayer films were deposited on Si(100) substrate with thermally grown SiO2 film and sputtered Ag underlayer at room temperature by dc magnetron sputtering and subsequently annealing in vacuum. Experimental results suggest that proper thickness of Ag underlayer and slightly rich of Fe content can effectively induce the (001) texture of FePt films. A Fe57.4Pt42.6 thin film on the 8nm Ag underlayer exhibits a large perpendicular coercivity of 7.6kOe with magnetic remanence close to 1.

SmCo$_{5}$ With Perpendicular Anisotropy Induced by a (211) Textured Ni$_{4}$ W Underlayer

In this work, we have successfully induced SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> -(0001) texture using the Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> W-(211) underlayer. A tungsten (W) seed layer of 4 nm resulted in a nanocrystalline (211)-textured Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> W underlayer deposited at room temperature. Highly (0001)-textured SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> was achieved after the sputtering deposition in the temperature range of 500-540°C. The crystallinity of the SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> layer was reduced at higher deposition temperature (¿ 550°C), probably due to W diffusion. The nano-grained SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> thin film deposited at 500°C shows an out-of-plane coercivty of 12.7 kOe with a large perpendicular magnetic anisotropy. The thickness of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> W underlayer can be reduced to 13 nm without a significant change in the large perpendicular magnetic coercivity of the SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> thin film.

Granular $\hbox{Co}_{3}\hbox{Pt}$ Thin Films With Perpendicular Hard Magnetic Properties for Perpendicular Magnetic Recording Media

The granular hcp Co3Pt nano-grains with large perpendicular coercivity (Hcperp) of 3800 Oe and high perpendicular squareness (Sperp) of 0.93 can be achieved by deposited 14 nm thickness of Co3Pt magnetic layer onto the Pt underlayer with thickness of 200 nm and annealing at low temperature of 300degC in a vacuum of 1 mTorr. It is found that the oxygen atoms would diffuse into Co3Pt layer through inter-grains to isolate Co3Pt grains and prevent grain growth that will decrease inter-grains interaction and enhance recording density of the magnetic film. This film revealed its prominent potential to be applied as perpendicular magnetic recording media for ultra high-density recording.

Bias sputtering effect on ultra-thin SmCo 5 films exhibiting large perpendicular coercivity

This paper reports the deposition and characterization of ultra-thin SmCo 5 films exhibiting large perpendicular coercivity under different bias sputtering conditions. The films were deposited onto a Cu (20 nm)/Ti (5 nm) bilayer at 300 °C and 0.5 Pa argon pressure at substrate biases in the range 0 to − 100 V. The effect of a negative substrate bias on the stoichiometric ratio of Sm/Co, surface morphology, structure and magnetic properties of the SmCo 5 films is investigated using inductively coupled plasma atomic emission spectroscopy, atomic force microscopy, X-ray diffractometry and vibrating sample magnetometry. An intrinsic coercivity of 1050 kA/m and unity squareness ratio in the direction perpendicular to the film plane are achieved at a substrate bias voltage of − 60 V. The ideal stoichiometric ratio of Co/Sm, relatively smaller grain sizes, and preferred crystallographic orientation of the easy axis are found to be strong functions of the bias voltage applied. These studies show that the magnetic properties of ultra-thin SmCo 5 films can be significantly improved by using bias sputtering.

Low-temperature ordered CoPtCu/Ag nanocomposite film with (001) texture

CoPtCu/Ag nanocomposite films have been prepared using CoPt/Cu/Ag multilayer precursor by magnetron sputtering and subsequent vacuum thermal annealing. Low-temperature ordered CoPtCu/Ag nanocomposite films with (001) texture have been prepared successfully with the optimized content of Ag and Cu in the films. The CoPtCu/Ag films start ordering at a low annealing temperature of 450℃, which is roughly lower by 150℃ than that needed for most CoPt-based films. Our present study shows that the Ag plays a dominant role in inducing the (001) texture of the film and the Cu additive is very effective to reduce the ordering temperature in CoPtAg system. The Co40Pt36Cu8Ag16 film after annealing at 500℃ exhibits a large perpendicular coercivity of 5.0×105 A/m with a small average grains size of 4—5 nm, implying the potential of the films as future ultrahigh density magnetic recording media.

(0 0 1) textured CoPt-Ag nanocomposite films for high-density perpendicular magnetic recording

CoPt/Ag nanocomposite films were prepared by magnetron sputtering. The dependence of texture and magnetic properties on film thickness, Ag atomic fraction and annealing conditions is investigated. Films with a thickness about 20 nm are easy to form with (0 0 1) orientation. The existence of the Ag in the film plays a dominant role in inducing the (0 0 1) texture of the film and suppressing the growth of the CoPt grains during annealing. The Co 35Pt 38Ag 27 film after annealing at 600 °C exhibits a large perpendicular coercivity of 5.6 kOe and a squareness of 0.90 with a small average grains size of 12.5 nm.

Underlayer-enhanced perpendicular anisotropy of FePt films

(0 0 1)-orientation FePt films were successfully fabricated on hydrogen-terminated Si(1 0 0) substrates by inserting Cu underlayers. By using the Co intermediate layer to suppress the diffusion of Cu and Si, the perpendicular coercivity reaches 6500 Oe after 300 °C postannealing. The dynamic-stress-induced ordering by the formation of Cu 3Si was the main reason for high coercivity. To improve the perpendicular anisotropy, Cu/CoFe/Ag composite underlayer was used. The large lattice constant of Ag provided a sufficient in-plane tensile static stress in FePt films. Both large perpendicular coercivity (8200 Oe) and good perpendicular squareness (∼0.9) were achieved for samples deposited at 300 °C.

CoPt/Ag(Cu) nanocomposite films for ultra-high density perpendicular magnetic recording media

CoPt/Ag nanocomposite films have been prepared by magnetron sputtering and subsequent annealing. The effect of Ag on the structure and magnetic properties of CoPt/Ag nanocomposite films was investigated. It was found that the existence of the Ag plays a dominant role in inducing the (001) texture of the film. (001) textured CoPt/Ag nanocomposite films with a large perpendicular coercivity in the range of 5.6–7.0 kOe have been achieved after annealing at 600 °C. The Cu additive is very effective to reduce the ordering temperature in CoPtAg system. With Cu additive, the CoPtCuAg films start ordering at a lower annealing temperature of 450 °C, which is lower by 150 °C than the pure CoPtAg films.

Effect of Ag on the structure and magnetic properties of CoPt/Ag nanocomposite films

CoPt/Ag nanocomposite films were prepared by magnetron sputtering. The dependenc e of texture and magnetic properties on film thickness, bilayer thickness, Ag at omic fraction and annealing conditions is investigated. Films with thickness bel ow 20 nm are apt to form (001) orientation. The existence of the Ag in the film plays a dominant role in inducing the (001) texture of the film besiles suppress ing the growth of the CoPt grains during annealing. The Co40Pt43 Ag17 film after annealing at 600℃ exhibits a large perpendicul ar coercivity of HC=5.6×105 A/m, a large saturation magne tization of MS=0.65T and a squareness of s=0.95 of the hysteresis loo p.

Ordered Co48Pb52 Nanowire Arrays Electrodeposited in the Porous Anodic Alumina Oxide Template with Enhanced Coercivity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ordered Co48Pb52 Nanowire Arrays Electrodeposited in the Porous Anodic Alumina Oxide Template with Enhanced Coercivity

Co-Pb nanowire arrays with an average diameter of 20 nm and lengths up to several micrometers were grown in ordered anodic alumina templates using AC electrodeposition. The as-deposited samples were annealed at different temperatures. The structure and magnetic properties of Co-Pb nanowires were analyzed by X-ray diffraction and a vibrating sample magnetometer. We found that the sample annealed at 700 °C had large perpendicular coercivity He (as high as 2660 Oe) and high squareness (M R /M s ) (about 0.97), which was much larger than that of pure Co nanowires annealed at 700 °C (2170 Oe, 0.9). The change in coercivity and squareness associated with the microstructure was discussed.

Magnetic properties of carbon nanotubes grown on Fe catalyst layer by microwave plasma enhanced chemical vapor deposition

The magnetic properties of carbon nanotube films grown on an Fe catalyst layer were investigated. The easy magnetization direction of the nanotube films was perpendicular to the film plane when the growth time was more than 2 min. In these films, conical Fe catalyst particles could be found at the tips of the nanotubes. The origin of the perpendicular magnetic anisotropy of these films was considered to be due to the anisotropic shape of the conical Fe catalyst particles at the tips. A large perpendicular coercivity of about 1 kOe was obtained in a nanotube film grown for 10 min.

Terabit Density Cobalt Nanowire Arrays With Tunable Magnetic Properties

AbstractNanoporous templates made from diblock copolymer films are used for electrochemical fabrication of hexagonal arrays of vertical cobalt magnetic nanowires at terabit/in2 density. The nanowire diameter and areal density are determined by the copolymer molecular weight, whereas the nanowire length and internal crystal morphology are controlled through the dc electrodeposition growth process. The array magnetic properties can be modified substantially by electrodeposition pH conditions while keeping wire size and interwire distance constant. Optimum pH control results in preferential growth of c-axis oriented crystallites with large perpendicular coercivity. The appearance of exchange bias behavior, exhibited at low temperatures, is also investigated.

Ｃｏ‐Ｃｒ‐Ｃ／Ａｇ／Ｔｉ膜の磁気特性に与えるＡｇ中間層効果

The magnetic properties of Co-Cr-C/Ag/ Ti films were investigated in relation to Ag interlayer thickness tAg. An Ag interlayer 10A thick enhanced the perpendicular orientation of the c-axis of hcp Co-alloy crystallites, resulting in the highest perpendicular coercivity Hc⊥ and the largest squareness ratio SQR⊥ of the perpendicular hysteresis loop. Atomic force microscope (AFM) observation of Ag/Ti films with various tAg showed that the surface morphology of them became finest and surface roughness became large at tAg = 10A. The morphology of the Co-Cr-C layer corresponds closely to that of the Ag/Ti under layer. The size of the hcp-Co alloy particles, therefore, became finest at tAg = 10A, and the large perpendicular coercivity can be explained by the c-axis orientation of the fine hcp-Co alloy crystallites.

Observation of magnetization reversal processes in Co–Cr and Co–Cr–Ta ultrathin films under the canted magnetic field using anomalous Hall effect

Normalized magnetization vector Me of ultrathin Co–Cr–Ta films under the canted magnetic field were derived from the results of anomalous Hall voltage and the magnetization measured by a vibrating sample magnetometer. The film deposited at high substrate temperature revealed a relatively large amount of an in-plane component because of the faint c-axis orientation in the perpendicular direction of the Co–Cr–Ta crystallites. The in-plane component at the remanent state seems to be larger for the film with worse c-axis orientation. The Pt underlayer was normalized to promote c-axis orientation in Co–Cr–Ta films deposited on it at a high substrate temperature above 200 °C. A 30 nm-thick Co77Cr20Ta3 film deposited on a 20-nm-thick Pt underlayer exhibited large perpendicular coercivity. The locus of normalized magnetization of the Co77Cr20Ta3(30 nm)/Pt(20 nm) implied that the film revealed a large perpendicular magnetization component even though the magnetic field was applied in the direction out of the normal line.

Improvement of Crystallographic and Magnetic Characteristics of ultra-thin Co-Cr Films Deposited on Pt Underlayer

Pt seed layer was effective to improve c-axis orientation of Co77Cr20Ta3 layers deposited on it especially for higher substrate temperature Ts above 200°C. The 50 nm-thick Co77Cr20Ta3 layer deposited at Ts of 250°C on Pt underlayer exhibited relatively large perpendicular coercivity Hc⊥ around 2.5 kOe. Anomalous Hall measurement implied that the Co77Cr20Ta3/Pt bilayered film did not have transition layer, which possessed worse c-axis orientation at the interface. Pt seed layer is effective to deposit the ultra-thin Co-Cr recording layer and improve its crystallographic and magnetic characteristics.