WO2017083994A1

WO2017083994A1 - Alternating magnetic field nanogenerator using a nanowire, which can be used to generate current, and associated method

Info

Publication number: WO2017083994A1
Application number: PCT/CL2016/050061
Authority: WO
Inventors: Alvaro Patricio ESPEJO PIÑA; Nicolás Segundo VIDAL SILVA; Felipe Sebastián TEJO LAZO; Juan Eduardo ESCRIG MURUA
Original assignee: Universidad De Santiago De Chile
Priority date: 2015-11-16
Filing date: 2016-11-11
Publication date: 2017-05-26
Also published as: CL2015003361A1

Abstract

The present invention relates to a time-stable nanometric alternating magnetic field nanogenerator, which can be used in the generation of alternating current at nanoscale level in communication systems, such as wireless communication systems, or telecommunications for mobile telephony. The nanogenerator is formed by a nanowire comprising a portion having a first end and a second end, and a domain wall. According to the invention, a spin-polarised current is applied at the ends of the nanowire, causing the domain wall to move both in translation along the length of the nanowire and simultaneously in rotation in the plane perpendicular to the axis of symmetry of the nanowire, said nanogenerator being formed by the nanowire, the second end of which is located near, or coupled to, an end from which a magnetic field emanates from a magnetic means. The nanogenerator can comprise a single nanowire formed by a first portion having a first end and a second end with a diameter D1 and a second portion having a first end and a second end with a diameter D2, wherein the diameter D1 is less than the diameter D2. Moreover, a diameter variation region is located between said first and second portions, said region having a larger diameter equal to D1 and smaller diameter equal to D2. The invention also relates to a method for generating a time-stable alternating magnetic field on a nanoscale.

Description

ALTERNATE MAGNETIC FIELD NANOGENERATOR USING A NANOHILO THAT ALLOWS TO BE APPLIED IN THE GENERATION OF CURRENT AND ASSOCIATED METHOD DESCRIPTIVE MEMORY

FUNDAMENTALS OF THE INVENTION

The present invention consists of a nanometric alternating magnetic field generator and a method for generating a nanometric alternating magnetic field. Through competition between pulses of polarized spin current and magnetic fields, a transverse or block type domain wall can be located, generating a magnetic region that varies its magnetization direction alternately, thus inducing an alternating magnetic flux. As an example of an alternating magnetic field nanogenerator, a polarized spin current and a demagnetizing field created by the geometric change of a modulated diameter nanowire have been used, by means of which it is possible to set the position of a transverse domain wall, and in this position generate a stable domain wall rotation over time. By generating an alternating magnetic field at a specific position of the nanowire, the variation of the magnetic flux over the area of the loop will produce an induced alternating voltage. In addition, if this conductive loop is part of a circuit, then this induced alternating voltage will generate an alternating current that will feed the components of a nanoscale circuit, which has not been achieved before In addition, the speed of rotation of the domain wall stopped or anchored in a specific place of the nanowire, at speeds of magnitudes of the Giga Hertz (GHz), which allows this generator to have applications in the area of communications such as telecommunications, wire-less and mobile telephony.

SCOPE

At present, an important part of humanity's technological development has focused on reducing electronic circuits to nanometric scales, because in these dimensions it is possible to create devices that greatly outperform their predecessors, such as increasing their information processing speed and / or data writing speed, greater information storage capacity, greater energy efficiency, etc. On the other hand, more and more properties in the behavior of the materials are discovered at these nanometric scales, allowing to open fields for enormous technological developments, as in the past was the discovery of giant magnetoresistance, which allowed to reduce the size of the sensors and magnetic heads and currently found in virtually all our electronic devices, such as cell phones, tablets, etc., or as the case of the recent discovery of graphene, material that has excellent mechanical, electronic and thermal properties, and that promises to cause a technological revolution in the coming years. Considering the operation of the nanoscale electronic components, it is possible to observe a common pattern, and they all work on the basis of pulses of direct current, DC, because it is not yet possible to produce alternating current, AC, in a localized way. These scales. This is why an alternating electrical or magnetic signal could generate a new technological revolution at the nanoscale, changing the paradigm in the way of operating future technological devices.

In order to carry out this invention, a relationship between magnetic fields and spin-polarized currents is required, which must be satisfied to obtain an alternating magnetic field nanogenerator, which consists of a transverse or Bloch-type domain wall, which can generate an alternating magnetic flux, that is, a magnetic field that rotates at a uniform speed in a given position, stable over time and with a controlled angular frequency. The angular frequency will be a function of the demagnetizing field, which depends on the geometric and magnetic parameters of the nanowire, and on the parameters that depend on the polarized spin current, as explained in equation 3, described below. As an example, the propagation induced by a spin-polarized current of a transverse type domain wall in a cylindrical nanowire of modulated diameter has been studied by numerical simulations, where it has been found that it is possible to anchor this magnetic domain wall in a specific region of the system, keeping it fixed in a certain position of the nanowire, and making it "turn" on itself, controlling its angular speed of rotation, which reaches frequencies of the order of 60 GHz. With this system an alternating magnetic field has been created literally from a pulse of direct current. This alternating magnetic field is located (it is generated in a specific region of the magnetic nanowire), whose frequency is stable and can be modified by simply varying the intensity of the applied current pulse. It is important to note that the current pulse must be a current of spin-polarized electrons, that is, they have the same value for their spin. The simplest method for a current to be spin-polarized is to pass it through a ferromagnetic material, so that it filters the electrons evenly.

This phenomenon is completely new and can open a new field of technological development, since it allows to have magnetic sources of variable field in the nanoscale, which does not exist at present.

In addition, when this system approaches a closed conductor of electricity, the alternating magnetic flux will induce an alternating electric current on the conductor, creating a sinusoidal electrical signal nanogenerator. This allows changing the paradigm of only using DC electrical current signals with AC signals.

STATE OF THE TECHNIQUE

The theme of the movement of the domain walls is a fairly current issue with multiple future applications. In the prior art, several related documents are described. For example, the document "Beating the Walker Limit with Massless Domain Walls in Cylindrical Nanowires" of the Authors M. Yan et al., show through micromagnetic theory and simulations the dynamics of the movement of a transverse type domain wall in a homogeneous cylindrical nanowire. This document discloses the movement of the domain wall by applying a polarized spin current, demonstrating that in this magnetic configuration, the domain wall is free to rotate on the cylindrical geometry causing a suppression in the speed limit before the fall of Waiker. The fall of Waiker describes the transition between a stationary movement, conserving its structure, and a precession movement of the domain wall, where it is continually transformed, which will always occur in nanowires of flat geometry. In addition, this document discloses the equations to determine the frequency of rotation of the domain wall as it travels along the wire as a function of the current intensity.

The nanowire (1) with a domain wall (2) in a portion (3) having a first wall (7) and a second wall (8), wherein said domain wall (2) has a rotational movement and translation, is represented in figure 1 of the present application. This document is the closest to the present invention, since both in this document and in the present invention, one works with a transverse domain wall, which is affected by the application of a polarized spin current. However, between said document and the present invention, there are large differences which are explained below. In the document by Yan et al., Only considered in the simulations the effect of the polarized spin current acting on the domain wall, while in the present invention it is incorporated and also the effect of a magnetic field in the opposite direction to the polarized spin direct current, which in one of its modalities correspond to a demagnetizing field with an opposite direction to the flow of electrons, which is created due to the effect of modulation on the nanostructure diameter. This field is responsible for stopping the advance of the domain wall due to the current. In addition, through equations the authors report the oscillation frequency for a domain wall due only to the external magnetic field or only to a polarized spin current, while in the present invention both equations are used simultaneously to be able to stop and locate In a fixed position the domain wall and estimate its oscillation frequency.

In the document "Magnetic power inverter: AC voltage generation from DC magnetic fields" by the authors J. Leda and S. Maekawa, a method for generating an alternating voltage by the movement of a magnetic domain wall, which propagates to along a flat nanowire with modulated geometry. The movement of the domain wall is generated by the application of an external magnetic field with direction perpendicular to the surface of the nanowire. The movement of the wall through the modulations of the system will induce a voltage at the ends of the nanowire. This device differs from that proposed in this invention in many respects. The authors of this document need an external magnetic field to generate the domain wall movement, while a spin-polarized electric current is used in the present invention. In the system disclosed in this document, the longitudinal movement of the domain wall is required to generate voltages at the ends of the nanowire, while in the system of the present invention it is possible to create an alternating magnetic field and simultaneously an alternating voltage with the wall of dominance in a fixed position, which will only rotate on itself. Using the Fadaray Electromagnetic Induction Law, it is established that the voltage induced in a closed circuit is directly proportional to the speed with which the magnetic flux that passes through any surface changes with the circuit as an edge. In this way, if we place this surface near the modulation of the nanowire, we can effectively generate an alternating voltage produced by the variation of magnetic flux (see figure 19). Finally, it is important to note that while the authors of this document convert a DC magnetic field into an AC voltage, in the present invention a DC current is converted into an AC magnetic field, and simultaneously also an AC voltage. Finally, the order of magnitude of the frequency of oscillations that the authors disclose in their document are close to 1000 times less than those proposed in the system of the present invention.

In the document "Stability of spinmotive forced in perpendicularly magnetized nanowires under high magnetic fields" by Y. Yamane, J. Leda and S. Maekawa, it is disclosed that theoretically it is possible to generate a voltage due to the movement of domain walls perpendicular to the surface of a flat nanowire. To this end, this document assumes a nanowire with a high magnetocrystalline anisotropy generated by Co / Ni and Fe / Pt alloys, then induces a movement of the domain walls by applying an external magnetic field perpendicular to the surface of the nanowire . The application of this field will generate a movement of the domain walls, which will induce an electromotive force that can be measured as a voltage at the ends of the nanowire. This document discloses that it is necessary to induce a constant voltage, while in the present invention it is possible to generate an alternating voltage due to the application of a direct electric current and the stable rotation of the magnetic domain wall. In addition, the objective of generating an external magnetic field is not disclosed in said document, but focuses on that for certain materials and magnetic configurations it is possible to increase the voltage induced by the longitudinal movement of a domain wall, while in the present invention, the domain wall stops its longitudinal movement due to the counterposition of the flow of electrons and the magnetic field applied in the opposite direction, thus generating a rotation of the magnetization in a fixed position.

In the document "Domain wall motion on magnetic nanotubes" by the authors P. Landeros and A. Nuñez, the dynamics of a domain wall in a magnetic nanotube driven by an external magnetic field are disclosed. This document shows how the dynamics of the wall generates chirality changes depending on the antiparallel magnetic configuration of its spins, showing that there are two regimes for the movement of the domain wall, one in which it moves at a linear speed depending on the magnetic field strength, and another in which the domain wall generates a precessional movement, generating a fall of Walker. In the present invention a magnetic domain wall of transverse configuration is used, which is simultaneously affected by a polarized spin current flow and by a magnetic field, both in opposite directions. Furthermore, it is demonstrated in the present invention that it is possible to stop the advance of a domain wall, making it rotate on itself in a fixed position, generating an alternating magnetic field product of this rotation.

In the document "Domain wall manipulation in magnetic nanotubes induced by electric current pulses" of the authors JA Otálora et al., The movement of a magnetic domain wall in a homogeneous nanotube by polarized spin current is disclosed. In this document it is pointed out that the dynamics of the movement of this domain wall, which produces a precessional chirality change movement for different current densities, generating a Walker drop, can be predicted using the equations described by the authors. Said document is different from the present invention, since it works with a transverse type magnetic domain wall. On the other hand, the main difference is that with the system disclosed in said document, it is not possible to generate a localized alternating magnetic field, as is the case with the present invention. In US 2013241344 "Fuel Free Nanowire Motors" a system of nanowires immersed in a fluid is disclosed. The wires are electrical diodes that can be displaced within the fluid through electric and magnetic fields. The proposed system is with moving parts submerged in a fluid, where the nanowires are physically displaced. In the present invention, the movement of magnetic domain walls is investigated, but where the nanostructures remain in a fixed position. On the other hand, the application is completely different, and the objective disclosed in this document is to generate the movement of nanowires, while in the present case, it is to generate an alternating magnetic field.

WO 2012/019806 "Method and assembly for exciting spin waves in magnetic solid bodies", by Leibniz-lnstitut für Festkórper und werkstoffforschung Dresden EV, discloses a way to excite domain walls through polarized light to achieve excitation and generation of spin waves using the Kerr effect. This document does not work with magnetic fields or current, nor is it an alternating magnetic field generator, therefore, it is not relevant to our invention.

WO 2010/055333 "Magnetic data storage device with magnetic domain wall motion", by Paul Cowburn Russell, discloses a system of nanowire arrays with magnetocrystalline anisotropy perpendicular to the axis of axial symmetry, which is capable of containing along the magnetic domains thread oriented perpendicular to the main axis. Using a circular external magnetic field surrounding each wire, it is possible to perform a displacement of the domain walls, which will represent binary information stored along the thread. This document has substantial differences with respect to the present invention. First, said document is oriented to the storage of information and its displacement through a circular magnetic field, understood as information to the magnetic domain walls that will represent binary bits. In the present invention, a domain wall is moved using an electric current, to then counteract its displacement with a magnetic field that will stop its movement and rotate it on itself to generate an alternating magnetic field.

SUMMARY OF THE INVENTION

Magnetic domain walls are one of the main sources of study of nanoscale magnetism. These represent the local deformations of the magnetization at the separation limit of two opposite and uniform magnetic domains. They are often present in the processes of reversing ferromagnetic nanostructures, varying their shape, size and behavior depending on the material and geometry of the nanostructure. When an electron flow passes through a ferromagnetic material, they acquire a polarization along the direction of the local magnetization, and a transfer of the angular momentum of the spin of the electrons to the magnetization of the system is generated. This coupling allows to control e! movement of magnetic domain walls through the application of a polarized spin current and has been reported in multiple both theoretical and experimental studies. The movement of domain walls in nanostructures and / or ferro magnetic nanocintas opens a window of opportunities for potential applications in solid state systems and logical devices. To date, the vast majority of these investigations have been developed on planar geometry systems (flat nanowires), and only very few have been carried out in other types of geometries. Among them are cylindrical nanowires, where the movement of the domain walls can reach higher amplitude speeds and a more stable behavior than in planar geometry systems.

On the other hand, when a transverse type domain wall or

Bloch is affected by the presence of a magnetic field or a polarized spin current, the wall will generate two types of movements, one will be of translation, moving in the same direction as the flow of electrons or applied fields; and the other will be a rotational movement in the plane perpendicular to the main axis of the nanostructure, which will periodically vary the magnetization of the nanostructure, creating an alternating magnetic field. Both movements of translation and rotation will occur simultaneously, and will last until the influence of the magnetic fields or currents is removed.

Considering the aforementioned phenomena, this invention relates to an alternating magnetic field nanogenerator, stable over time and maintaining the rotation of the domain wall in a fixed position, thus being able to know in situ the source of field variation. The present invention It establishes the relationship that spin-polarized currents and magnetic fields must meet to obtain the phenomenon described by the alternating magnetic field nanogenerator.

As an example of an alternating magnetic field nanogenerator, a polarized spin current and a demagnetizing field created by the geometric change of a modulated diameter nano-tube have been used, by means of which it is possible to fix the position of a transverse domain wall! , and in this position generate a stable domain wall rotation over time. For this, micromagnetic simulations have been carried out using the free OOM F software, which was extended to also consider the dynamics of magnetization induced by a spin-polarized current.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a nano-thread of the prior art, in which the domain wall advances and rotates at the same time, from when it is generated at the first end until the second end is lost, by applying a continuous current, of polarized spin.

Figure 2 shows a nano-thread of the prior art, where the domain wall advances and rotates at the same time, from being generated at the first end until it is lost at the second end, by applying a spin, continuous current polarized, a magnet having a magnetic field opposite current flow being away from said second end of the nanowire. Figure 3 shows a sequence of nanowires, where the domain wall advances and rotates at the same time, since it is generated at the first end until it stops its advance and is locked before the second end, where said domain wall begins to rotate in the opposite direction and in the same place, since the polarized spin direct current competes with the opposite magnetic field of the magnet that is close to said second end of the nanowire.

Figure 4 shows a nanowire and a magnet where the domain wall is stopped and anchored at the same site of said nanowire and rotates at the same time, because the polarized spin current enters into competition with the magnetic field. opposite of the magnet, which is close to said second end of the nanowire, where this configuration is transformed into a first embodiment of the invention.

Figure 5 shows a perspective view of a second modality of the nanowire formed by two portions of different diameter and having a variable splice zone.

Figure 6 shows a side view of the second mode of the nanowire formed by two portions of different diameter and having a variable splice zone.

Figure 7 shows a graph with the display of the demagnetizing field created by the variation in e! diameter of the nanowire of figures 5 and 8. Figure 8 shows a graph with the average speed of displacement of the domain wall in the two portions of the nanowire, the speed of the wall in thin diameter and the speed of the wall in thick diameter.

Figure 9 shows a schematic perspective view of the second mode of the nanowire, where the domain wall moves from the thinner end, to the thicker end, stopping before the splice area of variable diameter.

Figures 10, 1, 1 and 12 show an enlarged perspective view of the second mode of the nanowire with the domain wall stopped, rotating as a function of time due to the competition between the demagnetizing field and the electric current.

Figure 13 shows a perspective view of a third modality of the nanowire with an abrupt change in diameter between the first and second portion of the nanowire, where the second end of the first portion, splices directly with the first end of the second portion.

Figure 14 shows a schematic perspective view of a third mode of the nanowire, where the domain wall moves from the thinner end, to the thicker end, stopping before the splice zone between the second end of the first portion and the first end of the second portion.

Figures 15, 16 and 17 show an enlarged perspective view of the third mode of the nanowire with the domain wall stopped, rotating in function of time due to competition between a demagnetizing field and electric current

Figure 18 shows the graph of the angular velocity for two current densities, in which the domain wall found an equilibrium position due to competition between the electric current and the demagnetizing field, in the second embodiment of the present invention.

Figure 19 shows a nanogenerator formed by the second mode of the nanowire, where the alternating magnetic field induces an alternating voltage in a coil in the vicinity of the nanogenerator.

Figure 20 shows a graph with the estimation of the angular velocity (squares) and anchor field (circles) of the domain wall for different current densities, and in its internal graph, a zoom is shown for the densities of currents more low.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a nanometric alternating magnetic field generator from the movement of domain walls, by means of direct current pulses. As a result it is obtained that the alternating magnetic field is generated on e! Nano wire and its frequency is stable and can be controlled or modified according to the variation of the intensity of the applied DC pulse.

The present invention consists in generating an alternating magnetic field (AC) of the sinusoidal type on a magnetic nanowire. In general, as described in Figure 1, in relation to the closest art state, in a nano wire (1) having a fixed diameter portion (3) D1, by applying pulses of direct current between a first leg (7) and a second end (8) in a ferromagnetic material, the polarized spin current, causes the domain wall (2) moves moving from the first end (7), and at the same time, during its transit it rotates in the opposite direction to the clockwork. However, since there is nothing to stop it, said domain wall (2) is lost when it reaches the second end (8). The same occurs when, at a distance away from the second end (8) of the nanowire (1), an outlet end (10) of a magnetic field from a magnetic medium (9), such as a magnet (9), is placed, such As can be seen in Figure 2. The magnetic medium (9) can be a natural or artificial magnet, permanent magnet or an electromagnet whose magnetic field can be quickly manipulated over a wide range, controlling the amount of electric current.

However, as seen in Figures 3 to 4, to the extent that the output end (10) of a magnetic field from the magnetic medium (9) approaches its first end (10) from which a magnetic field ( 1 1), it begins to compensate for the polarized spin direct current (12), which travels through the nanowire (1), which translates the domain wall (2), whereby the current and the magnetic field are compensated , the domain wall stops and begins to rotate rapidly in the opposite direction to which it was turning, and begins its rapid rotation clockwise, being able to reach rotation speeds of the order of 100 GHz, whereby said wall anchored at a point and turning, generates a field Alternate magnetic, continuous and stable in e! time, what had not been possible before.

To explain the principles of the present invention, a magnetic particle of elongated geometry in some axis k, which contains a transverse domain wall or of Bloch, whose center can be described in a first approximation by M-M _s r, and In addition, the domain wall will be considered to be under the action of a magnetic field H ₀ , and finally, the domain wall will be considered to be under the action of a polarized spin current. This being so, the dynamics of the domain wall can be estimated using the Landau-Liftshitz-Gilbert equation, with the inclusion of additional spin-torque transfer terms: dM to _→ dM \,, → .. → β → _r _

γΗ ₀ x MM x ----- - ( ^■ V) AÍ + - X fu ^■ V) M. one

dt \ ^J M _s ^{! AJ 1} where M _s is the saturation magnetization, γ is the pyromagnetic rate, a is Gilbert's damping, β is the non-adiabatic spin transfer parameter and Ü (t) = ± u (t ) í, and magnitude i¿ (t)

, here electrons flowing in the direction + k means u> 0, where j (t) is the current density in time, P is the polarization rate of the current, g is the Landé factor, μ _Β the magneton of Bohr ye is the charge of the electron. Solving this equation for the magnetization of the center of the domain wall (θ = π / 2), the following motion equations are obtained, described as a function of Θ and φ for spherical coordinates, where: (1 + β η

θ

1 + a ² 1 + ² \ wc

(2) γΗ ₀ (β ~ α) ιι δθ

φ

1 + α 2 1 + α ² dk.

(3)

36 »

where, - is proportional to the inverse of the width of the domain wall when it is perpendicular to! axis of symmetry of the nanostructure, and wc denotes the center of the domain wall. In addition, Θ is proportional to the speed of wall displacement, ν = θ ^, and φ represents the angular speed of wall rotation and 6 (k) represents the profile of the domain wall along k.

From the above equations it can be deduced that a domain wall can remain rotating in a fixed position, maintaining its angular rotation in the direction ± <p, if the condition of Θ = 0 occurs, which is achieved if the first term of the Equation (2), associated with the magnetic field on the domain wall, was of equal magnitude and in the opposite direction as the second term (associated with the electric current). Then, to stop the propagation movement of the wall, it is required that the magnetic field and the flow of electrons leading to the wall have opposite directions, satisfying the following relationship:

(4) The permanent rotation of the domain wall will create an alternating magnetic field of stable position. In addition, the value of the angular velocity of the wall rotation will be determined by equation (3).

In an alternating magnetic field nanogenerator it is necessary to comply with the conditions indicated above, using a polarized spin current and a magnetic field, which in this particular case owes its origin to a demagnetizing field created by e! geometric change of a modulated diameter nanowire, by means of which it is possible to fix the position of a transverse domain wall, and in this position generate a time-stable domain wall rotation. For this, micromagnetic simulations have been performed using the free OOMMF software, which was extended to also consider the dynamics of magnetization induced by a spin-polarized current.

It is possible to obtain the nanogenerator of the present invention, by means of a nanowire (1) having a first portion (3) of continuous diameter Di, where at its ends (7, 8) a continuous polarized spin current (1) is applied 2) which causes the domain wall (2) to move through the nanowire (1), and the anchoring of said domain wall (2) is achieved, by approaching or splicing the outlet end (1 0) of a magnetic field produced by a magnetic medium (9) from which a magnetic field comes out

(1 1) opposite the direction of advance of the polarized spin direct current

(1 2). This configuration is a first embodiment of the present invention. In a second embodiment, and as shown in Figure 5, said nano-wire (1) is formed by a first portion (3) having a first end (7) and a second end (8), whose diameter is D _; and a second portion (4) having a first end (1 3) and a second end (14), whose diameter is D ₂ . The diameter D is smaller than the diameter D ₂ . Between the first portion (3) and the second portion (4) a region of diameter change (5) is located that has a continuous variable diameter and that forms a truncated cone that splices with the first portion (3) and the second portion ( 4), respectively. In the case of the second embodiment, said diameter change region (5) is a conical type modulation region, which has a smaller diameter equal to D and a larger diameter equal to D ₂ .

Within the first portion (3) a domain wall (2) is located, as shown in Figure 5. As shown in Figure 6, in the case of the simulated nanowire (1), the first portion (3 ) has a diameter Di = 1 0 nm, the region of conical diameter change (5) that splices both portions (3, 4), which has a length L equal to 30 nm, and the second portion (4) has a diameter of D ₂ = 40 nm. As a ferromagnetic study material, Permalloy has been considered, with an exchange constant of A = 1 .3 x 1 0 ^"11 J / m and a saturation magnetization of Ms = 798 kA / m. Since it is considered a polycrystalline sample, the Anisotropy is very small and can be neglected.The volume of the nanostructure is divided into cubic cells of 1.25 x 1 .25 x 2.5 nm ³ , where the largest cell corresponds to the axis of the nanostructure (in this case, in the direction k) Like the simulations they consider the use of current, and the modulated nano-wire produces a variation in the area of its cross-section along the axis of symmetry, it is necessary to modulate in the same way the polarized spin current density along this axis, so that the current entering and leaving the ends of the nanostructure is preserved. Finally, a = 0.01, β = 0.04, and P = 0.4 (parameters defined in the discussion of Equation (1), with values of current density / varying between 1 x 10 ¹² A / m ² and 10 x have been used 10 ¹² A / m ² , and the flow of electrons in the + k direction was defined, moving the domain wall (2) from the end of the first portion (3) to the second portion (4), as observed in the initial magnetic configuration shown in Fig. 1 B, where a cross-sectional domain wall (2) has been used, which minimizes the energy of the system against other types of domain walls.

The advantage of using a nanowire (1) that has a region of change in diameter (5) formed in the first mode by a conical shape that has a smaller diameter D and a larger diameter D ₂ , is to be able to replace the magnetic field source external by the demagnetizing field (7 and 8) created naturally by the nanowire of diameter D ₂ , which ends with a conical section (5), corresponding to the geometric modulation of the nanostructure. As can be seen in Fig. 1 C, the demagnetizing field (7) in the region of the thin nanowire is non-homogeneous, can reach values close to 0.5 T, and is oriented in -k, which could allow braking the domain wall propagation (2) with + k direction, driven by an electric current, generating the stable alternating magnetic field (8).

Due to the non-homogeneity of the demagnetizing field (7 and 8) along the modulated nanowire, for certain current density values it is possible that the domain wall (2) finds an equilibrium position that satisfies equation (4), but that does not suppress its angular rotation.

Using the magnetic configuration in the nano wire as shown in the second mode of Fig. 5, by applying a polarized spin current, whose current densities varied between 1 x 1 0 ¹² A / m ² and 1 0 x 1 0 ¹² A / m ² , a displacement of the domain wall (2) with direction towards a thicker second portion (4) of the nanowire (1) has been generated. From the results obtained, it can be noted that, with respect to the speed of propagation of the domain wall in the region of the diameter Di, a linear relationship is observed between the speed of displacement of the domain wall (2) and the current density , as shown in the graph in Fig. 8.

Once the domain wall (2) approaches and reaches the region of diameter change (5) formed by a conical shape that splices both portions (3, 4), it strongly slows its propagation and two possible results are generated. The first is that if the current is sufficiently high, the domain wall (2) will continue its movement towards the second portion (4) of greater diameter, significantly decreasing its travel speed, this being proportional to the decrease in the current density due to! diameter change from D to D ₂ . These results are shown in the graph in Fig. 18. E! Another possible result is that the domain wall (2) cannot continue its propagation beyond the region of diameter change (5) formed by a conical shape that splices both portions (3, 4), completely stopping its propagation. This will occur for lower current densities, where the negative displacement effect generated by e! demagnetizing field is greater than or equal to that generated by electric current, satisfying in some position the zero displacement condition shown in equation (4). In the simulations for this particular case, the detent of the domain wall in the transition zone was achieved for the current densities of 1 x 10 ¹² A / m ² (curve 15) and 2 x 10 ¹² A / m ² (curve 18} shown in the graph of Figure 18, since the domain wall was not able to reach the second thickest portion (4) of the nanowire (1). This means, that the domain wall stops its advance, it is anchored before the region of diameter change (5) and begins to rotate in the opposite way as it had been moving, achieving frequencies in magnitudes of the GHz, which allows applications in the area of telecommunications.

With respect to the frequency of oscillation of the domain wall (2) it is observed that its rotation speed is much weaker when the wall is driven by electric current than by magnetic field, obtaining that for any current density employed, while the domain wall (2) moves along the first portion (3) more thin of the modulated nanowire (1) and does not feel the effects of the demagnetizing field, it will rotate with a low angular velocity. However, once the domain wall (2) approaches the region of diameter change (5) formed by a conical shape that splices both portions (3, 4), it begins to feel the field stronger and stronger demagnetizing, which will rotate it in the opposite direction as it had been rotating during its movement through the first thin portion (3) of the nanowire (1), and with much greater intensity.

This can be explained due to the factor (? -) found in the second term of equation (3). Once the domain wall reaches the modulation zone, the speed of rotation of the domain wall (2) increases steeply, proportional to the intensity of the demagnetizing field, being able to reach angular speeds that can exceed 80 rad / ns , ~ 10 MHz. The advance of the domain walls (2) through the first portion (3) towards the second portion (4) is shown in Fig. 9. In Figures 1 0, 1 1 and 1 2, a schematic perspective is observed with the change in the direction (rotation) of the magnetization as a function of time before the region of diameter change (5) with a conical shape with diameters between D and D ₂ , where the domain wall (2) stops its displacement and only exhibits a rotational movement. For the cases of current density in which the wall continued its propagation towards the second thickest portion (4) of the nanowire (1), the phenomenon of high rotation speed lasted only as long as the domain wall (2) moved by the region of change in diameter (5) formed by a conical shape that splices both portions (3, 4). However, for lower current densities, where the domain wall (2) finds an equilibrium position, the wall will remain rotating as a function of time, as shown in e! graph in Fig. 18. This graph records e! value of the angular velocity of the domain wall (2) while advancing through the nanowire (1), showing that initially, when the wall advances through the nanowire and does not feel the demagnetizing field, the angular velocity reached is close to 1 rad / ns for both current densities. However, as the domain wall (2) approaches the region of diameter change (5) in a conical shape that splices both portions (3, 4) and is influenced by the demagnetizing field, the rotation accelerates strongly. These results were invariant for more than 300 ns of simulation, with no change in the stability of the rotation of the domain wall (2).

The nanogenerator described does not refer only to the geometric measurements that have been chosen for the simulated nanostructure, but in principle it will work for any nanostructure that satisfies equation 4.

Ta! As shown in Figures 13 and 14, a third mode of the nanogenerator can be carried out through an abrupt change in diameter. Figure 13 shows a nanowire (1) that is formed by a first portion (3) having a diameter D-¡and a second portion (4) having a diameter D ₂ . The diameter D is smaller than the diameter D ₂ . In this case of the region of change of diameter (5) from D to D ₂ , of the first portion (3) and the second portion (4), respectively, is abrupt. Simulations performed in this second mode also consider the use of polarized spin current along this axis. This phenomenon is explained because in the second portion (4) of the nanowire (1) with a diameter D ₂ , a demagnetizing field is generated directed towards the first portion (3) of the nanowire (1) with a diameter Dj, independent of the region diameter change (5). In this way, whether with a modulation zone or not, there is also a competition between the polarized spin current applied and the demagnetizing field generated in the second portion (4) of diameter D ₂ of the nanowire (1), as shown in equation 3. For this reason, as seen in Figures 15, 18 and 17, the domain wall (2) that is advancing through the first portion (3) with diameter D _1; it stops before reaching the second portion (4) with a diameter D ₂ , and continues to rotate at the same point, producing an alternating magnetic field that is stable over time.

In order for said nanogenerator to work, it is necessary to provide a block wall (2) of a bloch or transverse type in a nanowire (1). A polarized spin current must be applied along the axis of the nanowire (1), in order to produce a translation and rotation of the domain wall (2). The current must be intense enough to produce the two movements described above, but not exceeding the limit in which the nanowire loses its magnetization due to thermal effects. In addition, the domain wall (2) must be subjected to a magnetic field in the opposite direction to the propagation of the domain wall (2) until competition occurs between the spin current polarized and the magnetic field in the opposite direction, so ta! that the domain wall stops moving, is anchored at a point of the nanowire (1) and maintains its rotation. In general, the magnetic field in the opposite direction to the propagation of the domain wall (2) can be a demagnetizing field produced in the modulation region of! nano thread This can work with the first modality, that is to say a nanowire (1) formed by a single portion (3) and closely or spliced with a magnetic medium (9), as an example a natural or artificial magnet, permanent magnet or a electromagnet whose magnetic field can be quickly manipulated over a wide range, controlling the amount of electric current. From said magnetic means said magnetic field (1 1) is generated opposite the direction of the polarized spin current. It is also possible that functions with the second modality, that is, with a single nanowire (1) formed by two portions of different diameter, having between both diameters a region of splicing of modulated diameter, or, under the third modality where the Two portions of different diameter, spliced directly without a modulation portion. In all cases, the arrest of the domain wall (2) is obtained by controlling the polarized spin current, applied between the ends of the nanowire (1).

In the simulations carried out with the nanogenerator of the present invention, the magnetization rotation frequencies obtained are of the order of 10 GHz, therefore, the described system could have applications in the microwave range, where it could fulfill different roles, either as an alternating magnetic field nano-generator; It could also be used to induce alternating electric current in metals; or in wire-less applications in nanometric scale devices for telecommunications.

As noted at the beginning of this presentation, the nanoscale electronic components have a common pattern, and they all work based on direct current pulses, DC, because it is not yet possible to produce alternating current, AC, in a localized way at these scales. This is why an alternating electrical or magnetic signal could generate a new technological revolution at the nanoscale, changing the paradigm in the way of operating future technological devices.

For example, as shown in Figure 19, one of the great applications of this invention is the generation of alternating current, to power different elements of a nanoscale electronic circuit. In the case of Figure 19, the alternating magnetic field (1 1) generated in the region of modulation of variable diameter (5), between the first and second portion (3, 4) of the nanowire (1), when approaching a coil (17), causes an alternating voltage, which in turn produces an alternating current between the ends (18, 19), which allows to feed different elements of a nanoscale electronic circuit.

In addition, since the alternating magnetic field can reach GHz scales, this invention can be applied in wire-less communications in nanometer-scale devices for telecommunications. In the field of telecommunications for mobile telephony, the emission / transmission range of the electromagnetic signal of the antennas of these devices occurs between approximately 0.9 GHz to 1 .8 GHz for the 2G / GSM band, between 0.3 GHz to 2.1 GHz for the 3G / WCDMA frequency band and between 0.3 GHz to 2.0 GHz for the 4G / LTE band. In this area, the alternating magnetic field nanogenerator could serve as a base component for the creation of an electromagnetic signal emitting and / or receiving antenna. Although the frequency range of the electromagnetic signal may vary slightly for different countries, in practical terms the nanogenerator technology covers the mentioned frequency spectrum widely. The nanogenerator may modify its frequency of emission of the electromagnetic signal by means of the variation of the applied current density. Figure 20 shows an estimate of the variation of the rotation of the domain wall and the magnetic anchor field for different applied current densities. As can be seen in Figure 20, the frequency of rotation of the domain wall, ω, increases with increasing current density. As we know that ω = 2 ττ ί, where f is the frequency, the frequency is expected to vary proportionally to the speed of rotation of the domain wall. For this case, the frequency range estimated in Figure 20 varies between approximately 0.058 GHz and 58 GHz, completely covering the frequency range used in mobile telephony. Similarly, in the same Figure we can observe the field Magnetic needed to stop wall propagation, which also increases at higher current density.

Claims

one . - A time-stable nanometric alternating magnetic field nanogenerator, which can be applied in the generation of alternating current at the nanoscale level or in communications systems such as wire-less or telecommunications for mobile telephony, which is made up of a nano-wire (1 ) which has a portion (3) with a first end (7) and a second end (8), and a domain wall (2), where at the ends (7, 8) of said nanowire (1) is applied a polarized spin current (12), generating said domino wall (2) to move along said nanowire (1) with a translation movement, and simultaneously, with a rotational movement in the plane perpendicular to the axis of symmetry of said nanowire (1), CHARACTERIZED because said nanogenerator is formed by said nanowire (1) whose second end (8) has a close or coupled end of an outlet (10) of a magnetic field from a magnetic medium (9).

2. - A time-stable nanometric alternating magnetic field nanogenerator according to claim 1, CHARACTERIZED because said magnetic medium (9) is a natural or artificial magnet, permanent magnet or an electromagnet whose magnetic field can be quickly manipulated in a wide range, controlling the amount of electric current.

3. - A time-stable nanometric alternating magnetic field nanogenerator according to claim 1, CHARACTERIZED because said nanogenerator is formed by a single nanowire (1) which is constituted by a first portion (3) having a first end (7) and a second end (8) with a diameter D and a second portion (4) having a first end (13) and a second end (14) with a diameter D ₂ , wherein the diameter D is smaller than the diameter D ₂ , having between said first portion (3) and said second portion (4), a region of diameter change (5), which has an equal smaller diameter to D and a larger diameter equal to D ₂ .

4. - A time-stable alternating magnetic field nanogenerator according to claim 3, CHARACTERIZED because said diameter change region (5) is a conical variable diameter modulation region having a smaller diameter equal to D and a larger diameter equal to D ₂ .

5. - A time-stable alternating magnetic field nanogenerator according to claim 1, CHARACTERIZED in that said nanogenerator is formed by a single nanowire (1) that is constituted by a first portion (3) having a first end (7) and a second end (8) with a diameter D and a second portion (4) having a first end (13) and a second end (14) with a diameter D ₂ , where the diameter D is smaller than the diameter D ₂ , the first portion (3) and the second portion (4) being spliced directly through the second end (8) and the first end (13).

6. - A method to generate a time-stable alternating magnetic field on a nanometric scale, which allows it to be applied in the generation AC power at the nanoscale level or in communications systems such as wire-less or telecommunications for mobile telephony, CHARACTERIZED because it comprises the following steps:

(a) provide a magnetic field nanogenerator;

(b) providing a domain wall (2) in said first portion (3) of the nanowire (1);

(c) apply a polarized spin direct current (12) between the ends of a nanowire (1);

(d) moving said domain wall (2) along said nanowire (1) with a translation and rotation movement:

(e) stop the translational movement of said domain wall (2) by means of the application of a magnetic field (1 1), controlling the intensity of the polarized spin direct current (12).

7. A time-stable alternating magnetic field nanogenerator according to claim 6, CHARACTERIZED because in step (a) said nanogenerator is formed by a nanowire (1) having a ^' portion (3) with a first end ( 7) and a second end (8), which has a close or coupled end of an output (10) of a magnetic field from a magnetic medium (9).

8. A time-stable alternating magnetic field nanogenerator according to claim 7, CHARACTERIZED because in step (a) said magnetic medium (9) is a natural or artificial magnet, permanent magnet or a electromagnet whose magnetic field can be quickly manipulated over a wide range, controlling the amount of electric current.

9. - A time-stable alternating magnetic field nanogenerator according to claim 6, CHARACTERIZED because in step (a) said nanogenerator is formed by a single nanowire (1) that is constituted by a first portion (3) having a first end (7) and a second end (8) with a diameter D and a second portion (4) having a first end (13) and a second end (14) with a diameter D ₂ , where the diameter D it is smaller than the diameter D ₂ , having between said first portion (3) and said second portion (4), a region of diameter change (5), which has a smaller diameter equal to D and a larger diameter equal to D ₂ .

10. A time-stable alternating magnetic field nanogenerator according to claim 9, CHARACTERIZED because in step (a) said diameter change region (5) is a conical-type variable diameter modulation region having a diameter smaller equal to D and a larger diameter equal to D ₂ .

eleven . A time-stable alternating magnetic field nanogenerator according to claim 6, CHARACTERIZED because in step (a) said nanogenerator is formed by a single nanowire (1) that is constituted by a first portion (3) having a first end (7) and a second end (8) with a diameter D and a second portion (4) having a first end (13) and a second end (14) with a diameter D ₂ , in where the diameter D is smaller than the diameter D ₂ , the first portion (3) and the second portion (4) being spliced directly through the second end (8) and the first end (13).

eleven . A method for generating a stable alternating magnetic field, according to claim 8 or 9, CHARACTERIZED because in said step (e) of stopping the translational movement of said domain wall (2) said magnetic field opposite (1 1) in the direction of The polarized spin direct current (12) is a demagnetizing field generated in the second portion (4) to the region of diameter change (5).

12. A method for generating a stable alternating magnetic field according to claim 8 or 9, CHARACTERIZED because in said step (e) of stopping the translational movement of said domain wall (2) said magnetic field opposite (1 1) to the The direction of the polarized spin direct current (12) is a demagnetizing field generated in the second portion (4) to the direct splice region through the second end (8) and the first end (13).