DyFeCo Films Research Articles

Improvement of stress-induced magnetization reversal process of DyFeCo thin films

DyFeCo films sputter deposited at relatively low Ar gas pressure condition exhibited the change of easy axis of magnetization by applying relatively low mechanical stress. In order to attain magnetization reversal at lower magnetic field and low applied mechanical stress, a critical mechanical stress, which means the minimum mechanical stress to cause the change of magnetic anisotropy from perpendicular to in plane, should be as low as possible. The saturation field of the magnetization characteristics of the film at the critical field should be as low as possible.

Micromagnetic study of magnetization reversal in patterned DyFeCo thin films

AbstractMagnetization reversal in patterned perpendicular anisotropic DyFeCo films was investigated using micromagnetic simulations. The model consists of a square film of dimension 1 μm × 1 μm × 50 nm and a circular hole of diameter 500 nm on the top surface, with depth varying from 0‐30 nm. The results show that for shallower holes the coercivity decreases rapidly with the hole depth, but for the deeper holes, the coercivity in the hole region is much larger than in the land region. Further analysis indicates the variation in coercivity is due to the narrow transition region formed near the hole boundary where the magnetization has a tilted distribution determined mainly by the competition between anisotropy and exchange interactions. The simulation results are qualitatively consistent with our previous experimental outcome. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetization Reversal Technique of DyTbFeCo Films at Magnetic Field as Low as 1/6 of Coercivity Using a Stress-Induced Magnetic Anisotropy

A method to cause magnetization reversal in rare earth-transition metal (RE-TM) films at low magnetic field for perpendicular magnetic random access memory (MRAM) was demonstrated. The magnetic anisotropy was changed from perpendicular to in-plane in DyFeCo and TbDyFeCo films while the mechanical tensile stress is applied to the films. It is succeeded to cause magnetization reversal at low magnetic field as low as 1/6 of original coercivity of the film

Magnetization reversal process of DyFeCo films under an addition of mechanical stress for application of MRAM

Magnetization reversal process of DyFeCo films with stress was evaluated by the anomalous Hall effect. Anomalous Hall effect measurement is suitable to observe the change of perpendicular magnetic anisotropy of DyFeCo films when the mechanical tensile stress is applied to them. Stress applied to the RE-transition metal (TM) thin films significantly reduced the perpendicular coercivity of the film in comparison with that of the film in stress-free condition.

Stress Induced Enhancement of Magnetization Reversal Process of DyFeCo Films With Perpendicular Magnetization

A method to control magnetization reversal in magnetic films with perpendicular magnetic anisotropy was demonstrated in this study. Alloys of rare earth-transition metals (RE-TM) with their extremely large anomalous Hall coefficient and relatively large magnetostriction constants were suitable to observe the stress induced anisotropy using anomalous Hall effect. Stress applied to the RE-TM thin films significantly reduced the perpendicular coercivity and nucleation field of the film in comparison with that of the film in stress-free condition. Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> thin films revealed large Hall voltage and remarkable change in the coercivity under the mechanical tensile stress

Thickness dependence of magnetic properties in DyFeCo films

Films of amorphous DyFeCo were deposited on glass substrates using RF sputtering deposition system. The thickness dependence of the coercivity of DyFeCo films prepared under the same sputtering conditions was investigated. It is found that the composition is nearly thickness independent, while the coercivity is shown to increase with the film thickness increasing at the beginning, then above a certain thickness decrease with the thickness increasing. The thickness dependence of the coercivity is believed to be due to microstructure-induced variations in the short-range order during the film growth.

Magnetoresistance anomaly in DyFeCo thin films

Microstructured rare-earth–transition-metal DyFeCo films have been investigated using magnetoresistance and extraordinary Hall-effect measurements. The Hall loops reveal variation of coercive fields depending on the linewidth and the composition of the films. The magnetoresistance curves, with changes up to as high as 1.3%, show positive/negative magnetoresistance peaks centered on the coercive fields depending on the linewidth of the films only. The variation of the coercivity can be attributed to the magnetic moment canting between the Dy and FeCo subcomponents and the existence of the diverged magnetization on the edges, and the anomalous magnetoresistance peaks observed are discussed with the existing theories.

Magnetization reorientation in ferrimagneticGd27.5Fe59Co13.5/Dy28Fe60Co12double layers

We present experimental results on magnetization reversal for double-layer (GdFeCo/DyFeCo) magneto-optical films. The structure of interest consists of a 40 nm DyFeCo layer with perpendicular magnetization and a 50 nm layer of GdFeCo with in-plane magnetization. A transition from in-plane to perpendicular orientation of the magnetization in GdFeCo film caused by the effect of exchange interaction with DyFeCo has been observed in just a small temperature range. For higher temperatures, the exchange effect becomes smaller and GdFeCo magnetization returns back to in-plane orientation. On the basis of a micromagnetic model, we predict a change in orientation of GdFeCo magnetization from in-plane to perpendicular when it is coupled to DyFeCo film in a certain temperature range. This transition is sensitive to the magnetic properties of each layer that are dependent on temperature and on the values of compensation and Curie temperatures of both GdFeCo and DyFeCo films.

Compositionally modulated films for magneto-optic recording

Compositionally modulated DyFeCo films, prepared in a co-sputtering system incorporating a variable speed, rotating, substrate table, have structures that change from homogeneous mixtures of the different components to discrete layers of the different target materials. Films are characterised by measurement of magnetic, thermo-magnetic, and magneto-optic properties. Optimum thermo-magnetic recording characteristics are found in the films with the Dy, rare earth, layer approximately one atom thick.

TEMPERATURE INDUCED FERRO-ANTIFERROMAGNETIC TRANSITIONS IN EXCHANGE-COUPLED DOUBLE LAYERS WITH MIXED ANISOTROPIES

The temperature dependence of the magnetization processes in mixed exchange-coupled double layers ECDL with a planar GdFeCo film 1 and a perpendicular anisotropy DyFeCo film 2 is analyzed from Faraday rotation measurements. During heating the magnetic state of the ECDL presents strong modifications depending not only on the external field applied along the normal to the layers, but mainly on the ECDL type which can change from a type 1 with an interlayer macroscopic antiferromagnetic (AF) coupling -A12M1.M2 to a type 2 with a ferromagnetic (F) coupling. From appropriate choice of the deposition parameters the films compositions were adjusted for either Tcp1<RT<Tcp2 or RT<Tcp2<Tcp1 where Tcp1,2 are the compensation temperatures of the layer 1 and 2 which gives the possibility to obtain at RT ECDL of type 1/AF or type 2/F respectively. Depending on the respective values of Tcp1 and Tcp2, it is observed by increasing the temperature, F→AF or AF→F type transitions at Tcp1 and Tcp2. The evolutions with the temperature of the magnetooptical (MO) hysteresis loops of the ECDL are explained at the first order from the parallel change of the individual loops of the layers 1 and 2. However very close to Tcp2 more complex MO loops are observed and can be explained from the rise of the hysteresis Hc1 in the planar layer 1 induced by a strong increase of the coercitivity Hc2 of the perpendicular layer 2 near its compensation temperature.

The magnetic properties of DyFeCo thin films

A dc magnetron co-sputtering system incorporating a rotating substrate table has been used to produce Dy-FeCo films with a multilayered structure. For this study a series of films were produced in which the periodicity was varied whilst the overall composition and film thickness were kept constant. The magnetic, thermo-magnetic and magneto-optic properties of the films have been measured in an attempt to establish the best layer structure and periodicity for good thermo-magnetic recording characteristics. For the two compositions studied, Dy22Fe68.5Co9.5 and Dy28Fe52Co20, the optimum characteristics were found for films in which the rare earth Dy layer is approximately one atomic layer thick.

Sputtering of DyFeCo layers with an unbalanced magnetron

DyFeCo films were d.c. sputtered from a magnetically unbalanced magnetron cathode. Their density, composition and magnetic properties were investigated systematically as a function of the sputter parameters pressure and power, and were compared with evaporated films. They exhibit a lower anisotropy constant and behave in terms of the ferrimagnetic properties like evaporated films with 5 at.% less transition metal content. Corresponding magneto-optical discs show a low recording performance. These effects are attributed to the bombardment of the growing layer with energetic particles during deposition, which probably leads to a precipitation of transition metal clusters in the amorphous matrix, possibly nanoscale superparamagnetic transition metal crystallites.

Ferro- and antiferromagnetic exchange coupling in magnetooptical bilayers with planar and perpendicular anisotropy

Macroscopic ferro- (F) and antiferromagnetic (AF) exchange couplings -A/sub 12/M/sub 1/.M/sub 2/ between a planar GdFeCo film 1 and a perpendicular anisotropy DyFeCo film 2 have been investigated from the magnetization processes of the bilayer as observed from Faraday rotation measurements. Whatever the F or AF coupling, the microscopic exchange interaction between the rare-earths and the transition metals at the interface induces mutual effects with a reduction of the coercivity H/sub C2/ and the squareness M/sub r2//M/sub s2/ of the "perpendicular" layer and a reduction of the saturation field H/sub s1/, but an increase of the coercivity H/sub C1/ of the planar layer. Experiments performed in single planar and perpendicular layers and in both pseudo F and AF bilayers are in agreement with our theoretical model which enables deduction of the macroscopic exchange constant A/sub 12/.

Thermomagnetically written domains in compositionally modulated DyFeCo thin films

Magnetic properties of critical importance to the thermo-magnetic recording process are shown to be structure dependent. The use of structure as an additional tool in the control of these properties is illustrated by experiments that compare the size of domains written thermo-magnetically into different structured DyFeCo films. Samples with a common average composition and all 40 nm thick and with form that varies from the conventional homogeneous amorphous alloy to a material consisting of discrete Dy and FeCo layers, have been investigated. It is found that, whilst the Curie temperature, compensation temperature and saturation magnetization reflect the consistency of the average composition and remain constant across the range, the perpendicular anisotropy and coercivity are structure dependent and increase as the films become more layered, reaching a maximum when the rare earth (RE) layers are nominally one monolayer thick. In the writing experiments this behaviour is observed as the creation of different sized stable domains under constant write conditions.

Magneto-Optical Storage Media Using DyFeCo Film for Magnetic Field Modulation Direct Overwriting

Amorphous DyFeCo films have been studied for use as magneto-optical (MO) storage media for magnetic field modulation direct overwriting. The Dy-rich DyFeCo film has been found to be suitable for magnetic field modulation recordings by applying small-modulation magnetic field. The magnitude of the external recording magnetic field required for direct overwriting has been considerably reduced through adjusting the Dy content in DyFeCo film. In addition, the read-write characteristics have been improved by controlling the content of Co in the film. The DyFeCo disk prepared for this study shows the carrier to noise ratio (CNR) up to 49.5 dB when the modulation magnetic field is about 80 Oe and the recording mark length is 0.83 µ m. Furthermore its reliability performance has been examined by the accelerated test in humid environment at an elevated temperature for long periods of time.

Structure and stability of magneto-optical recording bits in rf-magnetron-sputtered DyFeCo Films

We characterized relationships between argon gas pressure, microstructures, and the magnetic properties of rf-magnetron-sputtered DyFeCo films. In addition, we studied the stability of magneto-optical recording bits. Increasing argon gas pressure promotes the growth of columnar structures perpendicular to the film, thereby forming microvoids. Even in films of the same composition, the saturation magnetization and perpendicular magnetic anisotropy decreased when the argon gas pressure increased while the coercive force increased. In addition, the magneto-optical recording bits of films having microvoids were more stable when exposed to the heat from a high-power-readout-laser beam.

Magnetooptical Recording with Optical Modulation and Magnetic Field Modulation

The magnetooptic recording characteristics of three types of DyFeCo films with a quadrilayer structure were measured using three recording methods: optical modulation, magnetic field modulation and the laser-off method. In the laser-off method, the laser power was lowered only while the magnetic field was changing. The transition metal (TM)-rich medium had the best carrier-to-noise (C/N) ratio when using the optical modulation method. When using magnetic field modulation, the C/N was lower than for optical modulation recording. The three media had similar characteristics when using magnetic field modulation. Adoption of the laser-off method improved the C/N and the magnetic field dependence of the C/N. In particular, the TM-rich medium exhibited the same C/N as when using optical modulation.

DyFeCo magnetooptical memory with reflective film structure

The magnetic properties and magnetooptic effects of amorphous DyFeCo thin films with various compositions and thicknesses were investigated. The product of magnetization times coercive force of 15-30-nm-thick DyFeCo film gave a high value of 2.5-3 erg/cm/sup 3/, comparable to that of Tb-enriched rare earth (RE) transition metal (TM) films. The dynamic characteristics of a quadrilayered magnetooptical disk having a reflective layer, i.e., carrier-to-noise ratio (C/N), optimum recording power and jitter were also evaluated. A high reproducing 60-dB C/N performance, comparable to that of Tb-enriched RE-TM films, was obtained by the 15-30-nm-thick DyFeCo films having a room temperature compensation composition. It is concluded that the use of this film is as efficient as the use of Tb films, while at the same time being much more inexpensive.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

光変調・磁界変調での光磁気記録特性

The magneto-optical recording characteristics of three types of DyFeCo films with a quadri-layers structure were measured using three recording methods: the optical modulation method, magnetic field modulation method and the laser off method. In the laser off method, the laser power was lowered only while the magnetic field was changing.As for carrier to noise ratio (C/N), the transitionmetal (TM) rich type medium was best with the optical modulation method. C/N with the magnetic field modulation was lower than that with optical modulation method. The three media were similar to the magnetic field modulation method.The laser off method improved the C/N and the magnetic field dependence of the C/N. Especially TM rich type medium exhibited the same C/N value as in the optical modulation.

Magneto-optical recording on amorphous rare earth-transition metal thin films with an artificially layered structure

Amorphous rare earth (Cd, Tb and Dy)-transition metal (Fe, Co and FeCo alloy) thin films with an artificially layered structure have been investigated. The films were deposited in an alternating multi-layer structure by the multi-source DC-sputtering method. Films with a repeat unit composed of a monatomic layer of RE and a few atomic layers of TM show excellent magnetic properties when considered as magnetooptical recording media, such as a large magnetization and perpendicular magnetic anisotropy. RE-FeCo and RE-CoFe films used in magnetooptical recording showed carrier-to-noise ratios higher than 52 db, and Dy-FeCo films showed a high carrier-to-noise ratio over a wide frequency range that extended from 57 dB at 1 MHz to 38 db at 10 MHz.