ES2343099B1 - USEFUL TEMPERATE IN THE MANUFACTURE OF A SYSTEM OF INFORMATION STORAGE AND PROCEDURE OF OBTAINING. - Google Patents

Abstract

Tempered useful in the manufacture of a system of computer storage and procurement procedure.

The invention describes a tempering, useful as nanomold for obtaining a system comprising said Tempered and magnetic dots. This system is useful for computer data storage magnetically, allowing the development, for example, of a hard disk. The invention describes also a procedure for its preparation.

Said procedure comprises obtaining a tempered by superficial reconstruction of a substrate of Au (111) and the deposition of an element of the group of rare earth by molecular beam epitaxy technique on the Au (111) substrate previously rebuilt. Then on the temperate thus obtained, a coating is grown that it consists of a periodic network of islands of a ferromagnetic metal, for example Co.

Description

Tempered useful in the manufacture of a system of computer storage and procurement procedure.

Field of the Invention

The present invention fits within the field of nanoscience and nanotechnology, more specifically in the surface physics. In particular the present invention is relates to useful systems for computer storage of data magnetically, using a metal island network ferromagnetic as a means of magnetic recording, and allowing the development, for example, of a hard disk with high capacities to store information with densities approaching 40 Teradot / in2.

Background of the invention

The magnetic recording was introduced something ago more than fifty years in the computer systems of the time through hard drives that at the beginning were very expensive and of great dimensions, but that supposed a revolution in the Information storage field. Over time the disks hard were improving reducing the size and costs of production until in the eighties they were introduced in Personal computers Currently hard drives produced have reached dimensions and storage capacities unimaginable in the beginning, joining different electronic devices such as laptops, MP3 players, video cameras, consoles, etc ... that have been assimilated by the society of consumption becoming fundamental elements for life daily The capacity of the current disks exceeds 700 GB with a bit density per unit area of about 130 GB / in2 which contrasts with the 2 KB / in2 of the first disk hard [R. Sbiaa, S. N. Piramanayagam. Recent Patents on Nanotechnology 1, 29-40 (2007).].

In the first hard drives were used magnetic iron oxides, but as it increased information density became necessary to change to others materials with more possibilities and add additional layers that Help improve magnetic stability. However the technology base behind data storage is still the same as in its beginnings; the presence of a magnetic medium where to record the information and a head reader / writer of this information. The magnetic medium consists on a substrate coated by a permanent magnetic material that allows to store the information magnetically, and the head reader / writer consists of an electromagnet that is located very close to the magnetic medium, working differently if is in read or write mode [J. Phys. D: Appl. Phys. 32 (1999) R147-R168.]. The huge technological advances who have experienced each of the components associated with the writing and reading process have made possible a reduction huge in the size of the hard drive components. In particular the large decrease in grain size has made it possible to increase the storage capacity of hard drives, and greatly reduce measured the noise signal that is associated with the granularity of the magnetic medium [R. L. White JMMM 209 (2000) 1-5.]. However, the drastic reduction in grain size seems to go accompanied by a thermal instability of the information stored, which can begin to be critical from volumes small grain [R. Sbiaa, S. N. Piramanayagam. Recent Patents on Nanotechnology 1, 29-40 (2007)]. In this point Magnetic anisotropy becomes important, since a reduction very steep grain volume could only be compensated with an increase in the anisotropy of the system. The product K_ {u} \ cdotV (where K_ {u} is the anisotropy constant and V is the volume of grain) represents the energy barrier that the particle should exceed to modify its magnetization in the opposite direction. The limit of reduction of this barrier is the thermal energy k_ {B} \ cdotT (k_ {B} represents the constant of Boltzman and T is the temperature, T> 300 K on most discs hard). At this critical point it would be close to the limit that known as superparamagnetic, which could limit the evolution in The recording capacity of magnetic media. Undoubtedly It is known that the use of materials with high anisotropy implies high coercive fields that should be reached technically in order to be able to write and erase the information magnetic

An alternative not to curb this evolution and overcoming the inconveniences of the superparamagnetic limit was proposed by the already disappeared "IBM storage division" in 1990, and consisted of the use of two separate ferromagnetic layers by a thin non-magnetic layer of ruthenium in order to couple them antiferromagnetically [S. S. P. Parkin, N. More, K. P. Roche. Phys. Rev. Lett. 64, 2304-2307 (1990)]. This way the magnetization of the bits was stabilized allowing further reduce the grain size of the magnetic layers that at the present time it is around 7 nm [R. Sbiaa, S. N. Piramanayagam Recent Patents on Nanotechnology 1, 29-40 (2007)].

Another new strategy proposed and that constitutes a new path of development towards higher densities of the environment magnetic supposes the replacement of parallel magnetic recording used so far by perpendicular recording, joining and this type of reading to the latest hard drives. With the perpendicular recording confers greater bit stability reducing the demagnetization factor between adjacent bits with opposite magnetizations. In this way the transition zone (no magnetic) between bits can be reduced, and consequently the Bit density per area can be increased. Additionally the new architecture associated with perpendicular writing is capable of generate magnetic fields twice as high, which is fundamental if increasingly higher materials are used magnetic anisotropies that confer greater bit stability stored but that require larger coercive fields to be able to Be treated. In this context, it is possible to achieve bit densities per area in the Terabits / in2 range and of designing magnetic media that cover these needs.

In order to successfully overcome this border, raises the design of new media much more optimized. Currently each bit contains hundreds of grains of the magnetic medium, and high granularity can affect the boundaries that They define each bit producing a noise signal. That is why it has raised the design of magnetic media formed by a network of perfectly ordered and homogeneous magnetic units where each unit or island is able to store an individual bit.

These means are currently prepared by various methods that are fundamentally based on techniques lithographic [R. Sbiaa, S. N. Piramanayagam. Recent Patents on Nanotechnology 1, 29-40 (2007)].

However, these methods involve the use of expensive and complicated techniques for its implementation, which makes the means obtained more expensive. Furthermore, these do not satisfactorily meet expectations regarding
effectiveness.

Therefore the need still exists in the state of the art of developing new media with high capacity of storage that are flexible, and economical, as well as new simpler procedures to obtain it.

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Brief description of the figures

Fig. 1: Image of STM (V_ {bias} = -1.5 V) of a tempering of the invention showing the superred structure formed by the surface alloy of Gd and Au with atomic resolution: (a) Image of the surface of an area of
50 nm x 50 nm; (b) 3-dimensional image in an area of 15 nm x 15 nm, showing the surface undulations that serve as nucleation centers for the growth of the islands of Co.

Fig. 2: Image of STM (V_ {bias} = -1.0 V) of the islands of Co evaporated on the superred structure of the tempered of the invention shown in Figure 1. The density of the Islands in the picture is 38 Teradots / inch2.

Fig. 3: Hysteresis cycles measured at 300 K using the vibrating sample magnetometer technique, in a PPMS Quantum Design 9T with the magnetic field applied perpendicular to the sample plane, and parallel to the sample plane. The cycle of Hysteresis is detected only in perpendicular geometry.

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Description of the invention

In a first aspect, the invention relates to with a useful tempering to prepare a system capable of being used for magnetic data recording and storage. He tempered, hereinafter tempered of the invention, is obtained by evaporate on an Au substrate an element of the family of rare earths (RE) comprising the following elements: lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, tulio, ytterbium, lutetium, scandium and ytrium. As a result a surface alloy is formed RE-Au with 1-3 layer thicknesses atomic on the evaporated surface of the Au. The difference of the network parameter between the alloy of RE-Au formed on the surface of the Au and the own Au substrate on which it grows produces a structure of superred that is characterized by an additional periodicity to which they already have the atoms of the alloy surface RE-Au. It is this periodicity that characterizes the tempered of the invention and makes it useful as a nanomold for subsequent growth of nanostructures.

Therefore the tempering of the invention comprises a substrate of Au (111) on which a element selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, tulio, ytterbium, lutetium, scandium and ytrium, which has a surface alloy of Au and said element, whose thickness is between 1 and 3 atomic layers and has superred structure.

The periodicity of the superred structure, hereinafter superred, that characterizes the tempering of the invention varies depending on the element selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium , tulio, iterbio, lutetium, scandium and ytrium, hereinafter element
RE.

In a preferred embodiment of the tempering of the invention, it comprises an Au substrate on which Gd has evaporated, and has a super alloy of an Au and Gd alloy with a periodicity of 38 ± 2 Å, which is associated with a superficial undulation shown in the STM images. In addition, X-ray photoelectron spectroscopy measurements (XPS) show that in a particular embodiment the stoichiometry is GdAu 2. The XPS measurements were carried out with a photon energy of 135 eV, thus obtaining surface information (layers of GdAu 2) and just information on the Au volume ( bulk ) of the substrate. The measurements were made in a synchrotron, where it is possible to reach the photon energy used, since the conventional XPS devices of the laboratories work in other photon energy ranges. Figure 1 shows the STM images of a temper that has an Au and Gd supernet, in particular a) shows the surface image, and b) a three-dimensional image in which the undulations of the surface that serve as a surface can be clearly observed. Nucleation centers for the growth of islands or magnetic dots.

The tempering of the invention can be used. therefore for the preparation of a network of dots or magnetic islands with high island densities per unit area, which can be used for the design of a magnetic data recording system and Your storage This system, which constitutes an additional aspect of The present invention comprises:

(i) the tempering of the invention as has been defined above, and

(ii) a coating on the supernet of alloy of said tempering consisting of a periodic network of Islands of a ferromagnetic metal.

The ferromagnetic metal of the islands of the The present invention may in principle be any material with Ferromagnetic properties, both metals and alloys. In a particular embodiment the material is selected from Co, Ni, Fe and its alloys.

In accordance with the present invention the coating (ii), has a variable thickness. These islands or dots Magnets that grow in the nucleation centers of the temperate maintain the periodicity determined by tempering, and present a distribution of very homogeneous sizes.

In a preferred embodiment the dots Magnetic are from Co and the tempered presents a superred of GdAu 2; the density of the periodic network of Co islands is is between 36 and 38 Teradot / in2 depending on the amount of Co evaporated to form the coating; the islands of Co have diameters between 3.8 nm and 4.0 nm, and the islands have thicknesses between 3.6 \ ring {A} and 4.6 Å measured by tunnel effect microscopy (STM). In this sense, in a particular embodiment of the system of the invention the tempering (i) has a supernet of GdAu_ {2}, such as defined above, and the coating (ii) consists of islands of Co with 3.6 \ A {high} and with a density of 38 Teradot / in2, and the Co islands present 3.8 nm diameters (see Figure 1). In another particular embodiment of the system of the invention the tempering (i) has a supernet of GdAu_ {2}, such as the one defined above, and the Coating (ii) consists of Co Islands with 4.6 Å with a density of 36 Teradot / in2, and the Co islands have 4.0 nm diameters.

In a particular embodiment the system of the invention further comprises a support on which the tempered of the invention. Said support can be any material that allows the growth of a layer of Au (111) above he. In a particular embodiment said support is a substrate of mica of variable thickness, and with a thickness of 0.15 mm according to a particular realization

In another aspect the invention relates to a process for the preparation of the tempering of the invention which It comprises the following stages:

a) superficial reconstruction of a substrate of Au (111);

b) evaporation of an element selected from group formed by lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, tulio, ytterbium, lutetium, scandium and ytrium by epitaxy technique of molecular beam.

The starting Au (111) substrate is you can select between a single crystal of Au (111) and a substrate comprising a layer of Au (111) evaporated on a mica support with a thickness of 0.15 mm over which evaporated a layer of Au (111) with 150 nm thickness. Both of them Substrates can be purchased commercially.

The superficial reconstruction of a substrate of Au (111) is a well known procedure in the state of technique and aims to eliminate impurities located in the Au surface

Surface reconstruction is performed typically in an ultra-high vacuum hood, to pressures of the order of 1x10-10 mbar. It consists of a series of Combined cycles of ion bombardment and surface annealing. In this way the first layers of Au's film are removed and with it all kinds of rust or impurities that could be in the surface. After four cycles you usually get a surface perfectly reconstructed and free of impurities, on the which evaporation of one of the elements above is carried out defined.

The evaporation stage b) is carried out in the same ultra-high vacuum hood at pressures from order of 1x10 -9 mbar and with a substrate temperature of Au (111) around 500-550 K. The bell of ultra-high vacuum prevents contamination of surfaces and the oxidation of the species to evaporate. Speed Deposition of the selected item depends on the conditions to which is carried out the molecular ray epitaxy technique. These conditions such as voltage applied to the crucible it contains the selected element, current of the filament that emits electrons, evaporator-substrate distance can be easily determined by an expert in the field. In function of these conditions obtain different deposition rates and evaporation times

In a particular embodiment of the invention the evaporated element is gadolinium.

In another particular embodiment they evaporate between 10 and 16 \ ring {A} of Gd with a deposition rate of 2 \ ring {A} / min and an evaporation time of 5 minutes. The temperate of the invention obtained consists of a substrate of Au (111) which features a surface alloy of Gd and Au that covers all the Au surface (111) and form a superred periodically of 38 ± 2 \ ring {A} as shown in Figure 1.

In another aspect the invention relates to a procedure for the preparation of the system of the invention which understands:

(i)

the preparation of the tempering of the invention according to described above, and

(ii)

the growth of a ferromagnetic metal over said tempered by lightning epitaxy technique molecular.

For the preparation of the system of the invention, once the RE element has evaporated at the temperature already indicated, the tempering obtained is allowed to cool to room temperature, and then the growth of the tempering by STM is analyzed " in-situ " in the same hood. The ferromagnetic metal growth is then carried out. This growth stage is generally carried out at room temperature, and also in an ultra-high vacuum hood in which the pressure is also maintained at values around 3x10-10 mbar. The growth involves the deposition of a metal with coatings of the order of 1 monolayer (ML) of said metal, where 1 monolayer is considered as a complete layer of that metal with a thickness equivalent to the height of an atom of that species. The result is islands or magnetic dots with a distribution of very homogeneous sizes and well defined positions determined by tempering. The conditions at which growth is carried out by the molecular beam epitaxy technique, such as current filament voltage, evaporator-substrate distance can easily be determined by one skilled in the art. Depending on these conditions, different deposition rates and evaporation times are obtained.

In general as already mentioned above, the density of the islands of a metal and the size distribution of they can be controlled through the amount of metal evaporated. The sizes are highly homogeneous in the case of that the islands have a height greater than 2 \ ring {A}. The densities of ferromagnetic islands by area reached in the The present invention is around 40 Terabits / in2, and the islands or magnetic dots have a magnetic anisotropy perpendicular that is interesting due to the enormous interest that it is currently in perpendicular magnetic recording.

In a particular embodiment Co is grown, using a tempered Au-Gd, and islands are obtained with average heights between 3.6 \ ring {A} and 4.6 \ ring {A}, and with diameters that vary between 3.8 to 4.0 nm respectively depending on the amount of evaporated Co. Your order keeps the periodicity determined by the supernet, as they grow in the lower topographic zones of the temperate that act as centers of nucleation As a result, a hexagonal network of islands or metal dots with ferromagnetic properties and a distribution of very homogeneous sizes when the islands exceed a height of 2 \ ring {A}.

The inventors have observed in a way experimental that by increasing the diameter of the dots from 3.8 to 4.0 nm a slight decrease in the density of dots of 38 is detected Teradot / in2 towards values of 38-36 Teradot / in2 depending on the amount of evaporated Co. It it would be due to a possible local coalescence that reduces the density.

The inventors have also made measurements magnetic system of the invention carried out to various temperatures in a quantum PPMS vibrating sample magnetometer Design 9T, which reveal a ferromagnetic behavior of the islands of Co with a coercive field of about 100 Oersted measured at 300 K of temperature, when the magnetic field is applied perpendicularly to the sample. Magnetic moment measurements made with the field applied parallel to the surface of the sample reveal a totally different behavior, without a hysteresis cycle visible. The absence of hysteresis cycle in a direction parallel to sample plane and the presence of a hysteresis in the direction perpendicular indicates the presence of a magnetic anisotropy in the direction perpendicular to the plane. These results are shown in the Figure 3. This figure compares the hysteresis cycles measured in the two geometries (parallel and perpendicular). The little girl interior image represents an increase in the central part of both magnetization curves

The systems of the invention are therefore useful for computer data storage so magnetic, using the network of ferromagnetic metal islands as magnetic recording medium, and allowing the elaboration, by example of a hard drive with high storage capacities information with densities approaching 40 Teradot / in2. High metal island densities by area achieved in the present invention are interesting, since exceeds the border of 1 Tera / in2 that is so much sought after currently in high density magnetic media.

The procedure for obtaining these systems has numerous advantages derived from the use of the phenomena of self-organization of metal evaporated, which make it a highly flexible procedure and simplicity compared to other existing techniques.

Below is an example illustrative of the invention set forth for a better understanding of the invention and in no case should be considered a limitation of the scope of it.

Examples Example 1

A substrate of Au (111) was introduced, which it could be either an Au crystal (111) or a layer of Au (111) about 150 nm thick over mica in a Handler in a vacuum bell. Once located in the manipulator degassed from 10 to 12 hours, heating it slightly at temperatures above room temperature (approximately 350 K). In this way the possible water film which covers the entire substrate due to the ambient humidity that was outside the hood evaporates more easily, allowing that good pressure ranges can be obtained during Sample preparation

Then 4 cycles of ion bombardment with an ion cannon installed in the hood of empty. The bombardment was done with Ar + ions with pressures of 3x10-6 mbar. The ion acceleration voltage was 1000 V, and the currents measured in the samples of 4.0. Every bombing cycle lasted about 10 minutes and it alternated with substrate annealing processes with a duration each of 15 minutes, reaching temperatures of approximately 600 K with pressures of 1x10 -9 mbar. The purpose of each annealing was to crystallize and rebuild the surface of Au (111).

Once a clean Au surface was obtained, Gd was evaporated by means of molecular beam epitaxy applying a voltage of +1000 V to the crucible containing the Gd and a current of 1 A to the filament of W (\: 0.15 mm), which produced an electron emission of the 30 mA filament. Under these conditions and considering the evaporator-substrate distance of 10 cm, a deposition rate of 2 Å / min was obtained. The evaporation time was 5 minutes, and what finally formed were between 1 and 2 GdAu2 alloy monolayers on the Au substrate, as detected in situ by tunnel effect microscopy analysis. in an Omicron VT-STM and low energy electron diffraction in a Spemic LEED Omicron. During the evaporation of Gd the substrate is heated to about 500-550 K to favor the reaction of the Gd with the Au and the formation of the GdAu 2 supernet which will be the temperate. The sample was then allowed to cool to room temperature (300 K).

At this point the deposition of Co, always keeping the substrate at room temperature. For the evaporation of Co also used an epitaxy evaporator of molecular beam, applying a voltage of 970 V and a current of 1.95 A filament, which generated an emission of 9.6 mA. The evaporator-substrate distance was also 10 cm and in these conditions the deposition rate could be estimated as 0.4 \ ring {A} / min. The optimal deposition times are they found about 9 minutes, obtaining island sizes of 3.8 nm in diameter and area densities of 36 Terabit / in2.

Claims (15)

1. Tempering comprising a substrate of Au (111) over which a selected item has evaporated of the group formed by lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, tulio, iterbio, lutetium, scandium and ytrium, which presents a Au surface alloy and said element, whose thickness is between 1 and 3 atomic layers and has a structure of superred. 2. Tempering according to claim 1, which presents a supernet with a periodicity of 38 ± 2 \ ring {A} of an alloy of Gd and Au. 3. Tempering according to claim 2, which presents a stoichiometry of GdAu2 measured with spectroscopy of photoelectrons using X-rays. 4. Useful system for magnetic recording of data and its storage comprising: (i) a tempering as defined in a any of claims 1 to 3, and (ii) a coating on the supernet of alloy of said tempering consisting of a periodic network of Islands of a ferromagnetic metal.

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5. System according to claim 4 wherein The ferromagnetic metal of the islands is selected from Co, Ni, Faith and its alloys. 6. System according to claim 5, wherein The metal of the islands is Co. 7. System according to claim 6, wherein the tempered features an Au-Gd supernet and the Co islands have diameters of 3.8 nm, with heights of 3.6 \ ring {A} measured by STM and a density of 38 Teradot / in2. 8. System according to claim 6, wherein the tempered features an Au-Gd supernet and the Co islands have diameters of 4.0 nm, with heights of 4.6 \ ring {A} measured by STM and a density of 36 Teradot / in2. 9. System according to any one of claims 4 to 8, further comprising a support characterized in that it allows the growth of an Au layer (111). 10. System according to claim 9, wherein The support is a mica substrate. 11. Procedure for the preparation of a tempered according to any one of claims 1 to 3, which understands: a) superficial reconstruction of a substrate of Au (111); b) evaporation on the substrate obtained in the step a) of an element selected from the group formed by lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, tulio, ytterbium, lutetium, scandium and ytrium by the molecular beam epitaxy technique.

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12. Method according to claim 11 in which step b) is performed at pressures of the order of 1x10 -9 mbar and with a substrate temperature between 500-550 K. 13. Method according to claim 11, in which the starting Au (111) substrate is selected from a single crystal of Au (111) and a substrate comprising a Au layer (111) evaporated on a support, preferably a mica substrate. 14. Procedure according to any one of the claims 11 to 13, wherein they evaporate between 10 and 16 \ ring {A} of Gd with a deposition rate of 2 \ ring {A} / min. 15. Procedure for the preparation of a system comprising:

(i)

the preparation of a temper according to any one of claims 11 to 14, and

(ii)

the growth of a coating consisting of a periodic network of islands of a ferromagnetic metal on said tempered by lightning epitaxy technique molecular.