SmCo Films Research Articles

Modification of magnetic properties in SmCo films by controlling crystallization and phase transition

A series of Cr/SmCo/Cr films with high Sm concentration (37.7at%) were prepared by magnetron sputtering. Effects of SmCo thickness, annealing temperature, and annealing time on magnetic properties and crystal structure were carefully studied. Results show that crystallization degree and phase transition in the films can be controlled by the SmCo thickness and optimized by properly increasing the annealing temperature and extending the annealing time. Finally, a SmCo film with high magnetic properties and low MEI was constructed.

A new TiW seed layer for SmCo5 films with perpendicular magnetic anisotropy

A new seed layer TiW is proposed for SmCo5 films with perpendicular magnetic anisotropy. The influence of a TiW seed layer on the microstructure and the surface morphology of Cu underlayer are studied. The grain size and surface roughness dependence of Cu underlayer on the thickness and the annealing of the TiW seed layer are also investigated. The improvement in the perpendicular magnetic properties of SmCo5 film from the TiW seed layer is approved. The results show that a 5nm Ti3W7 seed layer improves the microstructure and surface morphology of Cu underlayer, and significantly improves the perpendicular magnetic properties of SmCo5 film. The diffusion barrier and a high melting point of the TiW seed layer are regarded as the physical mechanism of the improvement for SmCo5 film with perpendicular magnetic anisotropy.

Effect of Cu Substitution on the Magnetic Properties of SmCo5 Film with Perpendicular Magnetic Anisotropy

SmCo5 film with perpendicular magnetic anisotropy is a promising candidate ultrahigh-density magnetic recording medium due to its huge magnetocrystalline anisotropy. This paper investigates the effect of Cu substitution for Co on the magnetic properties and microstructure of SmCo5 film by simulations and experiments. The simulation results based on first-principles theory show that Cu substitution for Co in SmCo5 can reduce the total exchange- correlation constant and increase the coercivity of SmCo5 film. Sm(Co,Cu)5/Cu/TiW film samples with different Cu doping were fabricated on quartz glass substrates by radiofrequency (RF) magnetron sputtering, and the dependence of the coercivity of the Sm(Co,Cu)5 film on the Cu doping and annealing conditions was studied. The experimental results demonstrate that Cu doping can decrease the grain size and increase the coercivity of SmCo5 film. By optimizing the sputtering and annealing conditions, perpendicular coercivity of 3796 Oe was obtained in Sm(Co0.72Cu0.28)5 film.

Effect of film thickness on magnetic properties of Cr/SmCo/Cr films

Cr/SmCo/Cr films with different SmCo thickness were deposited on glass substrates by magnetron sputtering, followed by an annealing process at 550 °C for 20 min. Experimental results showed that the SmCo film of 30 nm exhibited two-phase behavior in the demagnetization process, the obvious kink was observed near zero. For the SmCo film of 50 nm, the kink was invisible, and a single phase like behavior was obtained in the demagnetization process. The reversal behavior became consistent in the thicker films. Moreover, the coercivity reduced and the saturated magnetization increased obviously with the increasing thickness. X-ray diffraction results indicated that the average grain size of SmCo5 in the thicker films were almost 30 nm, but the quantity of SmCo5 grains increased with the increasing thickness, which enhanced the intergrain exchange coupling (IEC) of the SmCo5 hard phases. The increase of IEC improved the magnetic properties of SmCo films with increasing thickness.

Electrodeposition of Thick SmCo Films: Influence of Current Density and Time Deposition

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Buffer Layer Effects on the Structure and Morphology of SmCo/Cu Thin Films

In this paper, we investigated the structure of SmCo films with different thickness and the effects of Cr buffer layer on the structure and morphology of SmCo/Cu thin films. Our data revealed that the magnetic properties of the samples were enhanced by the crystallization of SmCo which was promoted by the optimized Cu underlayers. We also found that the surface roughness can be decreased by Cr layer and the texture can be improved by prolonging the annealing time for thick SmCo film. Thus, we concluded that the magnetic properties of SmCo/Cu films can be further optimized by varying the thickness of Cr buffer layers.

DC Electrodeposition of Thick SmCo Films for MEMS Applications

This paper reports a study of electrodeposition of SmCo in aqueous solution using a Hull cell. Different concentrations of cobalt ion in the electrolyte, addition of supporting electrolyte and different deposition time have been tested. High samarium contents and thicknesses have been obtained: up to 50% of Sm in the deposit and several microns. The oxygen contamination is linked to the samarium content and two elaboration parameters have been found for limiting this contamination: addition of supporting electrolyte and long deposition time.

Sputtering of SmCo Thin Films and Integration Into a Ferrofluidic Microactuator

The fabrication of SmCo films using physical vapor deposition (PVD), patterning by wet-chemical etching, and liftoff techniques as well as annealing processes was investigated. The composition of the film can be adjusted by the applied sputter parameters, i.e., the deposition pressure, the substrate bias voltage, and the power density by using a composite target. An intrinsic coercivity Hci of sputtered SmCo films above 0.8 MA/m and a maximal energy product |B XH|max of above 70 kJ/m3 were achieved after an annealing process, respectively. A concept for the integration of sputtered SmCo permanent magnets in a ferrofluidic microactuator is presented. This microactuator consists of microcoil arrays which manipulate a ferrofluid plug in a microchannel. The permanent magnets provide holding positions for fixing the ferrofluid without power input.

Manipulation of the magnetic exchange interaction in SmCo films with high thermal stability by controlling phase transformation

High thermal stability and tunable magnetic exchange interaction (MEI) in SmCo materials have been the critical problem in applications to magnetic recording media and nanocomposite permanent magnets. We constructed SmCo films with a high thermal stability and tunable MEI by controlling the phase transformation through properly increasing the Sm concentration (20.5–37.7 at.%) and controlling the annealing process. Microstructure studies show that the SmCo5 phases ensure that the film has a high thermal stability. Moreover, we manipulated the MEI in the film with non-magnetic precipitated SmCo2 particles in the vicinity of SmCo5 particles. These results provide a novel way to tune the MEI in SmCo materials while maintaining a high thermal stability.

Investigating the correlation between crystalline and magnetic nanostructures in Co-Sm films by means of electron microscopy

We visualize nanocrystalline and magnetic structures in thin films of Co-Sm (fabricated by means of ion resputtering) using transmission electron microscopy and Lorentz microscopy. Filters based upon Gauss wavelets were used to decompose images of nanostructures with spatial periods ranging from 0.5 nm to 390 nm. It was found by wavelet filtration of images of the magnetic structure that nanostructures with the above periods determine the boundaries of the magnetic structure in thin films of Sm-Co.

Using deep eutectic solvents to electrodeposit CoSm films and nanowires

A Deep Eutectic Solvent of 1 chlorine chloride: 2 urea eutectic mixture at 70 °C has been tested as useful to electrodeposit both magnetic SmCo films and nanowires. Galvanostatic deposition allows obtaining homogeneous deposits over metallic substrate with variable composition as a function of the current density applied. The deposits obtained at 0.5–1.5 mA cm − 2 were uniform and they correspond to a cobalt hexagonal crystalline phase with magnetic anisotropy and coercivity of 250 Oe. It has been possible to deposit SmCo nanowires from the DES solvent using alumina templates. Uniform CoSm nanowires of 50 nm of diameter have been obtained; they correspond also to hexagonal phase, but they present higher coercivity.

Electroplating hard magnetic SmCo for magnetic microactuator applications

Patterned SmCo thin films were electroplated from an aqueous solute containing glycine by using dc and pulse dc current on the beaker level. Micromolds prepared by photolithography allow an accurate pattern transfer for patterned deposition of the material. A flux guide of a magnetic microactuator was chosen as a pattern, and Al2O3 was used as the substrate. Au and Cr were investigated as seed layer materials. The content of Sm in the SmCo films is strongly dependent on the applied cathodic current density. A relative Sm content of up to 13.8 at. % could be determined by energy dispersive x-ray (EDX) spectroscopy. The SmCo thin films were annealed at 560 °C in a vacuum oven. Vibrating sample magnetometer (VSM) measurements were applied to characterize the magnetic properties. This film features hard magnetic properties with an intrinsic coercivity Hci of up to 44 kA/m. Electron probe microanalysis (EPMA) measurements showed that up to 40 at. % of O may be integrated in these films. The phases in the deposited films were determined by applying X-ray diffraction (XRD) measurements. These films consist of a mixture of SmCo alloy, Sm oxide, and Co.

Nanostructured SmCo<SUB>5</SUB> Thin Films with Perpendicular Anisotropy Formed in a Wide Range of Sm–Co Compositions

In this work, we prepared SmCo5 thin films with (0001) texture exhibiting perpendicular anisotropy in a wide range of Sm(x)Co(100-x) compositions (x = 13.2 approximately 37.0) on Cu/Ta underlayers. At a composition of Sm16.7Co83.3 (SmCo5), the SmCo5 film exhibits a maximum perpendicular coercivity of 18.2 kOe, which is attributed to a good crystallinity and an excellent (000l) texture. The SmCo5 (000l) peaks are shifted to smaller angles compared to the standard powder sample which indicates the formation of a SmCoCu alloy through Cu diffusion. The EDX result for this sample gives a composition of SmCo3Cu2.1 which confirms Cu diffusion into the SmCo5 layer. TEM image shows that SmCo5 film is well crystallized with a grain size of 50 nm.

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.

Effects of the Applied Magnetic Field and Magnetic Interaction on the Magnetic Switching Volume in CoSm Films

Effects of the Applied Magnetic Field and Magnetic Interaction on the Magnetic Switching Volume in CoSm Films

Textured growth and microstructure of pulsed laser deposited Nb/Cr/SmCo5 hybrid structures

AbstractHybrid structures based on superconducting Nb and highly coercive ferromagnetic SmCo5 films grown on MgO(100) substrates were fabricated by pulsed laser deposition under UHV conditions. Thin film architectures of SmCo5 on Nb and the reversed system both with and without Cr spacer layer between superconductor and ferromagnet were examined by transmission electron microscopy and X‐ray diffraction concerning their microstructure and epitaxial relationship, respectively. For SmCo5 on Nb with thick intermediate Cr spacer the epitaxial relationship MgO(001)[100]//Cr(001)[110]//Nb(001)[110]//Cr(001)[110]//SmCo5(11 − 20)[0001]//Cr(001)[110] was found. With decreasing thickness of the Cr spacer layer the strength of the texture decreases and finally crystallinity of SmCo5 is lost. In the reversed layer system, Nb on Cr on SmCo5, with decreasing thickness of the Cr spacer layer the epitaxial relationships change from SmCo5(11 − 20)[0001]//Nb(001)[110] to local SmCo5(11 − 20) [0001]//Nb(110)[1 − 11] and the Nb texture changes from the (001)[110] component to a 〈110〉 fibre. The orientation relationships observed are discussed with regard to elastic strain energy minimization.

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.

Thickness determination of SmCo films on silicon substrates utilizing X-ray diffraction

This paper presents a nondestructive measurement technique for the determination of the film thicknesses of Co and SmCo based magnetic films deposited by sputtering on single-crystal silicon (100) substrates. X-ray diffraction of Cu Kα radiation has been used to measure the intensity of the (400) reflection from bare silicon substrates and as attenuated by sputter coated Co and SmCo based films on Si substrates. A four-axis research diffractometer allowed the substrate orientation to be fine adjusted to maximize the (400) diffraction intensity. The thickness of SmCo based films was in a range from 0.05 to 5 μm. Co film thicknesses on Si could be measured to a few tens of nanometers. The accuracy of the thickness measurements depends on the effective mass attenuation coefficient of the film material. For the materials considered, the thicknesses determined by the X-ray attenuation method agree within at least several percent to values determined by other methods.

Modeling of Intergrain Exchange Coupling for Quantitative Predictions of $\delta m$ Plots

The study of irreversible switching processes via δm-plots is a common experimental technique to assess intergrain interactions in nanoscaled magnetic materials. Theoretical predictions, on the other hand, of the influence of grain size, texture and field direction on the shape and absolute values of δm-plots are missing. In this paper direct intergrain exchange coupling is evaluated in a combined numerical/analytical approach for a model system of two coupled, hard magnetic grains. The influence of grain size and easy axis orientation on the outcome of a δm-analysis is determined quantitatively. As expected from the short range characteristic of direct exchange coupling, the field-integrated δm-signal decreases with increasing grain size. However, whereas directly coupled grains with parallel easy axis orientation possess large positive δm -values, for increasing misorientation angle the integrated δm-signal reduces and reaches even negative values. Such an effect of negative δm is so far only associated with indirect magnetostatic interactions. In a statistical extension of the model, grain ensembles with Gaussian distribution of their texture axis along one well defined sample direction are examined. The shape, width and height of the calculated δm-plots bear characteristic features known from experimental studies on nanocrystalline, well textured SmCo5 films.

Temperature dependence of magnetization reversal processes in exchange-spring magnets

We investigated the temperature dependence of magnetization reversal processes of exchange-spring magnet, hard/soft ferromagnetic heterostructures. In most previous works, the thicknesses of the soft and hard layers were used as the main control parameters to investigate the reversal mechanism of the exchange-spring magnet. In our work, the anisotropy energy of the hard layer changes as a function of temperature, while the change in the magnetic properties of the soft layer is negligible in the temperature regime in which we are interested (between 10 and 300 K). The magnetic hysteresis loops of SmFe/Py(=Ni80Fe20) and SmCo/Py exchange-spring magnets were measured at various temperatures. Magnetic reversal behaviors of SmFe/Py and SmCo/Py were explained using the parameters extracted from the single layer measurements, SmFe or SmCo films, and the existing theory, where the reversal mechanism is controlled by the thicknesses. With a proper conversion of the temperature dependent anisotropy energy to the scaled thickness scheme, the reversal mechanisms of SmFe/Py and SmCo/Py could be explained with a simple model theory for a wide range of temperatures.