SmCo Layer Research Articles

SmCo/Fe and SmCo/Co magnetic heterostructures: Micromagnetic simulation using the MuMax3 package

The magnetic SmCo/Fe and SmCo/Co heterostructures were numerically investigated in an external magnetic field using the micromagnetic simulation package MuMax3. The magnetization reversal curves and magnetic phase diagrams for these structures were plotted for different thicknesses of the magnetic layers and directions of the external magnetic field. The SmCo(20 nm)/Fe(20 nm) heterostructure reached saturation along the hard magnetization axis at an external magnetic field of 18 T, while a single SmCo(20 nm) layer achieved saturation at 18.2 T. The highest values of (BH)max were found to be 29.2MG∙Oe for the SmCo(20 nm)/Fe(10 nm) and 35.5MG∙Oe for the SmCo(20 nm)/Co(20 nm) heterostructures.

The fundamental role of Ta diffusion on the high coercivity of Ta/SmCo5/Ta and Ta/Sm2Co17/Ta films

The fundamental contribution of the Ta layer to the highly coercive Ta/SmCo / Ta films was investigated. A room temperature coercivity value of 4.5 T was achieved in film with 60% SmCo5 and 40% Sm2Co17. In films, in which only the Sm2Co17 phase was observed in XRD (X-ray diffraction), a high coercivity of 2 T was also obtained. All films were obtained by codeposition at temperature environment of Sm and Co atoms on a Ta layer, followed by annealing to promote the crystallization of the Sm-Co film. The following results were observed: (i) the presence of voids in the Sm-Co layer, observed in the cross- section STEM (Scanning Transmission Electron Microscope) images, (ii) the presence of stable Taα phase, observed in the XRD analysis, (iii) Ta diffusion in the Sm-Co layer, identified in the XPS (X-ray Photoelectron Spectroscopy) deep profile and, (iv) the initial magnetization curve, typical of a magnetization reversal controlled by pinning that led us to conclude that the voids produced during annealing by the diffusion of Ta in the Sm-Co layer, and they act as a pinning for the magnetization inversion, resulting in highly coercive films. Ta diffusion promoted the transition from the metastable Taβ phase to the stable Taα phase, at temperatures below 800 ◦C. Another important result was the strong exchange interaction between the grains reflected in the square hysteresis with Mr/Ms≈1.

Microstructure and Magnetic Anisotropy of SmCo‐Based Films Prepared via External Magnetic Field Assisted Magnetron Sputtering

SmCo‐based thin films have excellent permanent magnetic properties for application in magnetic functional devices. The conventional methods to control the magnetic anisotropy are inserting the suitable buffer layer or applying magnetic field heat treatment. However, the selection of the buffer layer and the thickness of the SmCo layer are limited. Additionally, the magnetic field heat treatment is detrimental to suppressing the grain growth. Herein, the SmCo‐based thin films by magnetic field assisted magnetron sputtering followed by a rapid thermal annealing (RTA) is prepared. The characteristic diffraction peak of SmCo5 (200) with in‐plane orientation disappears, indicating that the in‐plane magnetic anisotropy could be further decreased. Meanwhile, the out‐of‐plane coercivity highly increases when applying an external magnetic field, which is contributed partly by the refined SmCo grains under the external magnetic field due to the reduction of critical free energy of Sm–Co cluster nucleation. Furthermore, micromagnetic simulations indicates that the out‐of‐plane magnetic moments of Sm2Co17 phase are more difficult to reverse because the ratio of in‐plane and out‐of‐plane oriented moments changed from 1:1 to 1:1.4, and proves that the proportion of magnetic moment direction is significant to control magnetic anisotropy and coercivity which is consistent with the experiment results.

Effects of temperature gradients on magnetic anisotropy of SmCo based films

The magnetic anisotropy of SmCo-based permanent magnetic thin films are generally controlled by introducing buffer layer or heating substrate. However, the design for the multi-layer thin film system is complicated and the thickness of SmCo is limited due to a short range of interfacial stress/strain between the buffer layer and SmCo layer. In this work, the effects of temperature gradients, generated by RTP (rapid thermal process), on the magnetic anisotropy of the SmCo-based films were systematically investigated. The results show that the as-deposited films exhibit amorphous state. The out-of-plane coercivity of RTP-treated films is strongly correlated with the heating rate, and its optimum value (2810 Oe) is larger than that of the CTA (conventional thermal annealing) treated films (1670 Oe). For the RTP-treated films, the intensity of characteristic diffraction peaks for in-plane oriented SmCo5 (200) and Sm2Co17 (300) decreases, together with reducing the roughness. Besides, the grain size is finer and the contrast of magnetic domains becomes stronger for the RTP-treated films due to that the easy axis of SmCo5/Sm2Co17 phase gradually changes from in-plane to out-of-plane direction. It is suggested that the RTP treatment with a shorter annealing time has beneficial effects on obtaining finer microstructure and improving the out-of-plane magnetic anisotropy of the SmCo-based films. This work provides a novel way to control the magnetic anisotropy via annealing temperature gradients for permanent magnetic thin films, compared with conventional methods, to induce the magnetic anisotropy.

Effect of CoSi2 interfacial layer on the magnetic properties of Si|CoSi2|Sm-Co thin films

Abstract Magnetic thin films with a layer sequence of Si|CoSi2|Sm-Co were grown by direct sputter deposition at elevated temperatures, through interfacial diffusion between Si (1 0 0) substrate and the overlying Sm-Co layer. HR-TEM analysis revealed the occurrence of CoSi2-interfacial layer close to the Si-substrate surface, with controllable thicknesses of ~20 and 35 nm at deposition temperatures: 450 and 500 °C, respectively. XRD studies confirmed the crystallization of Sm2Co17 and SmCo5 magnetic phases accompanied by the other phases such as CoSi2 and SmCoSi2 due to the intermixing of Co and Si -atoms at higher deposition temperatures. The measured coercivity values are found to be increased from 8.7 to 11.6 kOe at higher CoSi2-layer thickness. The angular-dependent hysteresis measurements demonstrated a distinct isotropic and uniaxial magnetic anisotropy characteristics for the Sm-Co films consisting of 35 and 20-nm thick CoSi2 interfacial layers, respectively and the associated magnetization reversal mechanisms are discussed using the Stoner-Wohlfarth model. The temperature coefficients of remanence (α) and coercivity (β) were determined from the temperature-dependent hysteresis curves. The Sm-Co films consisting of 35-nm thick CoSi2-layer exhibited a better thermal stability with ‘α’ and ‘β’ values of 0.35 ± 0.05%/°C and −0.13 ± 0.02%/°C, respectively. The results of present study provide splendid opportunities for exploiting the potential of CoSi2 as an under layer, for growing the Sm-Co films towards high-temperature applications.

Interfacial layer formation during high-temperature deposition of Sm-Co magnetic thin films on Si (100) substrates

The interfacial layer that has formed during the deposition of ∼240-nm thick Sm-Co films on the bare Si (100) substrate was investigated at different deposition temperatures, Td,Sm-Co: 400, 450 and 500 °C with respect to structural and magnetic properties of Sm-Co films. X-ray diffraction analysis showed the crystallization of both Sm2Co17(R) and SmCo5(H) magnetic phases. Rutherford back scattering studies demonstrated that the surface-diffusion reactions between the Sm-Co layer and Si-surface not only accompanied by the quasi-layered growth of CoSi2-phase; but also led to the formation of SmCoSi2-phase. Cross-sectional transmission electron microscopy analysis revealed uneven boundary with deeply grown CoSi2-layer and Moiré fringes at limited regions of Co/Si interface. Magnetic measurements showed a square hysteresis loop with maximum values of coercivity (11.6 kOe) and remanence ratio (0.99) for the films grown at 500 °C. Magnetic force microscopy images depicted patch-like domains with increasing phase contrast against Td,Sm-Co. In addition, the changes that has occurred in the magnetization reversal processes accompanied by coercivity enhancement due to higher Td,Sm-Co is discussed in the context of domain morphology and first-order reversal curves.

Atomic diffusion and microstructure of SmCo5 multilayers with high coercivity

Sm-Co multilayer films are deposited by plasma sputtering with a Cr underlayer and a Cu buffer layer, followed by annealing at different temperatures. The as-deposited films show low hard magnetic properties due to the existing amorphous Sm-Co phase. After annealing, for the films without Cu buffer layer, there is only Sm2Co17 phase in the films even at high annealing temperature and the coercivity is less than 12kOe. When inserting a Cu buffer layer, the well-crystalline SmCo5 single phase is obtained at relatively lower annealing temperature (500 °C and 550 °C) and extremely high in-plane coercivity (38kOe) is achieved. An analysis of Transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) reveals that Cu atoms started to diffuse during the annealing process induced by thermal dynamics, concentration gradient and microstructure variations, and eventually uniformly distribute in SmCo layer and form Sm(Co,Cu)5 phase. The exchange interaction energy calculation indicates that small fraction of Cu atoms preferentially substitute the Co(2c) site in SmCo5 lattice, which reduces the exchange coupling effects of Sm-Co and gives rise to the coercivity. The results provide a guidance to fabrication of single-phase Sm(Co,Cu)5 multilayer films with superior performance that have applications in advanced electromagnetic and electronic devices.

Investigations of SmCo Thin Films Grown on Kapton Substrate

In this study, SmCo-based films with different thicknesses were grown on a Kapton substrate by ultra-high vacuum (UHV) evaporation process. Two effects on magnetic properties of SmCo films have been investigated: the effect of the variation of the magnetic layer thickness and the effect of the substrate temperature. The morphology and the structure were explored by atomic force microscopy and X-ray diffraction. It has been shown that the film morphology and its crystallographic orientation changed significantly with increasing thickness. Magnetic measurements reveal a strong correlation between magnetic and structural properties. The highest magnetic squareness ratio M r/ M s (0.8) and a maximum coercive field at room temperature, of about 2 kOe, are obtained when the SmCo layer thickness is 15 nm.

Transmission electron microscopy study on Co/Fe interdiffusion in SmCo5/Fe and Sm2Co7/Fe/Sm2Co7 thin films

We demonstrate a sharp composition transition at the interface of an as-deposited SmCo5/Fe bilayer, while annealing results in measurable Co/Fe interdiffusion near the boundary. For the annealed SmCo5/Fe bilayer, phase separation occurs within the bcc-layer, forming regions with 3 different Fe:Co ratios. Depositing Fe between Sm-Co layers provides a realistic model for bulk systems. Co/Fe interdiffusion was observed by TEM in an annealed Sm2Co7/Fe/Sm2Co7 “sandwich” thin film, confirming Co/Fe interdiffusion as the main mechanism controlling phase chemistry in Sm-Co/Fe bulk nanocomposites. The degree of Co/Fe interdiffusion is primarily chemically driven, and the approximate 20% Fe substitution for Co is thermodynamically stable.

Magnetic structure in Fe/Sm-Co exchange spring bilayers with intermixed interfaces

The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer fabricated under nearly optimal spring-magnet conditions was determined by complementary studies of polarized neutron reflectometry and micromagnetic simulations. We found that at the Fe/Sm-Co interface the magnetic properties change gradually at the length scale of 8 nm. In this intermixed interfacial region, the saturation magnetization and magnetic anisotropy are lower and the exchange stiffness is higher than values estimated from the model based on a mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields superior exchange coupling between the Fe and Sm-Co layers, but at the cost of average magnetization.

Effect of Palladium Nuclei Insertion by Electroless Deposition on Magnetic Intergranular Isolation and Read/Write Characteristics in SmCo5 Perpendicular Magnetic Recording Media

In order to improve the magnetic intergranular isolation between the magnetic grains in the SmCo5 perpendicular magnetic recording media, the palladium nuclei deposited by an electrochemical process were introduced into a sputter deposition process of the SmCo5 film. A few nanometer size Pd nuclei were electrochemically deposited on the sputtered Cu underlayer by a displacement deposition (chemical plating). The sizes of Pd nuclei were controlled by adjusting the Pd ion concentration in electrolyte solutions. The magnetic domain size in Sm-Co layer deposited on Pd nuclei / Cu / Ti underlayer became smaller and the magnetization reversal process was changed from the wall motion to the coherent rotation. Moreover, the read/write characteristics were improved at higher linear recording densities.

Fabrication of SmCo$_{5}$-CrTa Granular Films

A Sm-Co-CrTa granular layer between a Sm-Co continuous layer and a Cu underlayer was prepared in order to improve magnetic properties and magnetic reversal process of Sm-Co perpendicular film. A phase of CrTa alloy in Sm-Co-CrTa layer has a role in control of Cu partial interlayer diffusion between the Sm-Co continuous layer and the Cu underlayer. The Cu diffusion provides the partial crystallization of SmCo5 in the continuous layer. Although the perpendicular coercivity of films decreased slightly by introducing the CrTa alloy into Sm-Co layer, the magnetic intergranular exchange interaction in the films was drastically improved. Size of average magnetic cluster became smaller and magnetization reversal process was changed from a wall-motion to a coherent rotation for increasing the thickness ratio of Sm-Co-CrTa/Sm-Co layers. We confirmed that an addition of Sm-Co-CrTa layer is effective to reduce the intergranular exchange interaction in Sm-Co perpendicular films without deterioration of perpendicular magnetic anisotropy.

Effect of Mo interlayer on magnetic properties of exchange coupled Sm-Co/Fe bilayers

Sm-Co/Fe, hard/soft magnetic bilayers have been fabricated on 70 nm Cr buffered Si (100) substrate by dc and rf magnetron sputtering and annealed at 525O C for 30min. Very thin Mo layers (0-0.7 nm) were introduced between Sm-Co and Fe layers. The samples were analyzed by X-Ray Diffraction (XRD) and Alternating Gradient Magnetometer (AGM). All of the samples showed strong exchange coupling between hard and soft magnetic phases. Magnetization, coercivity and energy product (BH)max suggest a sinusoidal behavior. The energy product was found increased to 45% for 0.3 nm Mo interlayer as compared to sample without Mo layer.

Magnetic property and microstructure of SmCo magnetic recording films

Cr/SmCo/Cr thin films with Sm concentration of 37.7 at.% were deposited on glass substrates by magnetron sputtering. Measurement of magnetic properties showed that the SmCo film possessed good magnetic anisotropy, a high coercivity of 3019 kA/m and low magnetic exchange coupling. Microstructure analysis showed that crystallized SmCo 5 magnetic phase, non-magnetic SmCo 2 phase and Sm 2Co 7 phase co-existed in the film. The non-magnetic SmCo 2 phase might function as isolator of SmCo grains, leading to a decrease of magnetic exchange coupling. Moreover, a Cr 2O 3 oxide layer which could protect the SmCo layer from oxidation formed at the surface of the Cr cap layer.

Effects of Co/Sm Composition on the Ordered Phase Formation in Sm-Co Thin Films Grown on Cu(111) Single-Crystal Underlayers

Sm-Co thin films were prepared on Cu(111) single-crystal underlayers by changing the Sm composition from 12 to 35 at.% and the effects of Co/Sm composition on the ordered phase formation were investigated. The epitaxial SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> thin films were obtained for all samples. The SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> epitaxial layer grown on Cu underlayer has two different types of domains whose orientations are rotated around film normal by 30 degrees to each other. Cu atoms substitute a part of the Co sites in the SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> structure, and an alloy compound of Sm(Co,Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> phase was formed for all samples. The Sm(Co,Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> phase was more Cu enriched with increasing the Sm composition. The Cu atom diffusion into Sm-Co layer plays an important role in assisting the formation of Sm(Co,Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ordered phase.

Effect of chromium interlayer on magnetic exchange coupling of SmCo/Cr/TbFeCo multilayer thin films

A series of SmCo/Cr/TbFeCo multilayer thin films with perpendicular anisotropy were prepared by RF-magnetron sputtering system, and the effects of Cr interlayer thickness on magnetic properties and interlayer exchange coupling were investigated. It was found that the magnetic properties varied with the thickness of Cr interlayer, especially the values of saturation magnetization M s and the coercivity H c fluctuated periodically with the thickness of Cr interlayer. STM images revealed that the variation of coercivity H c was attributed to the microstructure change of SmCo layer influenced by Cr interlayer, and the variation of M s was related to interlayer exchange coupling.

Tunable negative and positive coercivity forSmCo∕(Co∕Gd)exchange springs investigated with SQUID magnetometry

Temperature dependent static magnetic properties of $\mathrm{Co}∕\mathrm{Gd}$ multilayers, grown on SmCo, are experimentally investigated by means of SQUID magnetometry. The $\mathrm{Sm}\mathrm{Co}∕(\mathrm{Co}∕\mathrm{Gd})$ system shows an exchange spring behavior above the compensation temperature $({T}_{\mathrm{comp}})$ at which the magnetization of the antiferromagnetically coupled multilayer is zero. Below ${T}_{\mathrm{comp}}$, a tunable negative coercivity state (inverse hysteresis) appears, due to the coupling between the hard SmCo and soft $\mathrm{Co}∕\mathrm{Gd}$ multilayers, irrespective of whether Co or Gd is proximate to the SmCo. However, for the strongly ferromagnetically coupled Co interface layer, negative coercivity persists over a larger temperature interval. The negative coercivity state vanishes if the coercivity of the SmCo layer is increased by controlling the Cu underlayer thickness.

The property of multilayered SmCo5 film with perpendicular magnetic anisotropy

AbstractIn order to fabricate thick SmCo5 film, the dependences of the magnetic properties of SmCo/Ru/Cu/Ru films and its multilayer films on the SmCo layer thickness were studied. The SmCo/Ru/Cu/Ru film with the SmCo layer thickness up to 200 nm showed the perpendicular magnetic anisotropy while the multilayer film with the total SmCo layer thickness of 1000 nm indicated the magnetic easy axis was in the perpendicular direction. It was found that the multilayered structure is preferable for the increase in total thickness of the SmCo layer with the perpendicular anisotropy. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Fabrication of SmCo$_{5}$ Double-Layered Perpendicular Magnetic Recording Media

We fabricated SmCo5 double-layered perpendicular magnetic recording media with high perpendicular magnetic anisotropy for realizing ultra high density recording. A double-layered medium with a Ru buffer layer introduced between a Cu/Ti intermediate layer and a Co-Zr-Nb soft magnetic underlayer exhibited high perpendicular magnetic anisotropy, whereas that without the Ru buffer layer did not. Auger electron spectroscopy revealed that the Ru buffer layer inhibited interdiffusion between the Cu/Ti intermediate layer and the Co-Zr-Nb soft magnetic underlayer. We report here for the first time the read-write characteristics of SmCo5 double-layered perpendicular magnetic recording media. The medium noise was small in the medium with a Sm-Co layer deposited under high Ar gas pressure owing to small magnetic clusters

Thin film SmCo magnets for use in electromagnetic microactuators

Efficient magnetic microactuators require a deposition and patterning of a permanent magnetic material. A material that can be deposited in the range of up to a couple of 10μm is sputtered SmCo. For the fabrication of magnetic microactuators, alternative substrate materials besides silicon are of great interest. Therefore, alumina-ceramic as well as B270-glass substrates were included in the investigation. A maximum energy product of 90kJ∕m3 was achieved for rather thick layers of 30μm deposited on glass or ceramic substrates. The latter substrates were found to be suitable for the deposition of SmCo layers up to a thickness of 50μm. Furthermore, the SmCo exhibits isotropic magnetic properties, thus a magnetization of the permanent magnetic layer can be performed in plane as well as perpendicular to the film plane. For the patterning of these thick SmCo layers ion beam etching and wet chemical etching were examined. For both methods, the suitability of patterning thick SmCo layers could be demonstrated. For the integration of a SmCo permanent magnet in a magnetic microactuator, the two technologies for deposition and patterning of the SmCo layer had to be combined. Two linear microactuators are presented utilizing different integration methods of the SmCo component as well as direction of magnetization.