WO2012019806A1 - Method and assembly for exciting spin waves in magnetic solid bodies - Google Patents

Abstract

The invention relates to a method and assembly for spin wave excitement in ferro- or ferrimagnetic solid bodies, such as in a magnetic conductor path or in a magnetic nanowire. The invention is in particular applicable for signal and information transport on the basis of propagating spin waves in electrical switch circuits and components and in the field of the implementation of logical circuits. The aim of the invention is to provide a method for spin wave excitation by means of which spin wave types of the same type can be reproducibly excited in simply structured solid bodies without using electrical currents, magnetic fields and heat effects. Included in said aim is the creation of an advantageously usable assembly for carrying out the novel method. The method according to the invention is characterized in that a domain wall, spatially fixed in a magnetic solid body, is illuminated by polarized, pulsed laser light using the inverse magneto-optical gradient effect, wherein the illumination of the domain wall takes place in vertical incidence in the case of magnetized domains in the plane of the solid body and in angled incidence in the case of magnetized domains perpendicular to the solid body plane, especially avoiding heat input into the solid body.

Description

 Method and arrangement for exciting spin waves in magnetic solids

Technical area

The invention relates to a method and an arrangement for spin wave excitation in ferromagnetic or ferrimagnetic solids, for example in a magnetic conductor or in a magnetic nanowire. The invention is particularly applicable to signal and information transport based on propagating spin waves in electrical circuits and devices as well as in the field of logic circuit implementation.

State of the art

 In addition to an electrical charge, electrons have an intrinsic angular momentum, the so-called spin. The spin system in this way in a magnetic solid can be excited by an external pulsating energy supply such that a collective movement of the spins in the form of a wave in the

Solid forms and propagates example as a spin wave packet. This is possible both in electrically conductive magnetic solids and in electrically insulating magnetic solids. By spreading

Spin wave packets, which can also be interpreted as spin wave current, can transport signals and information in the solid state, which conventionally can only be realized by electrical currents or light in optical fibers (for example glass fibers).

It is already known to excite spin waves by means of alternating magnetic fields. For example, to the two ends of a strip from the

magnetic material Ni ₈ iFeig (permalloy) sinusoidal alternating magnetic fields applied in the GHz range. The energy pumped by the permalloy stripe leads to the excitation of the spin waves (SJ Hermsdörfer, Investigations to the Interaction of Spin Waves and Domain Walls in Thin Magnetic Structures, Dissertation December 2009, pp. 70-75, Technical University

Kaiserslautern). Also known is the excitation of spin waves by the action of microwaves on magnetic solids (M. Rohmer, investigations on microwave-excited spin waves, diploma thesis April 1998, University of Kaiserslautern).

Furthermore, the generation of spin waves by the magnetic field excitation of magnetic vortices and counter-vortices in circular magnetic layer elements is known. The excited vortices generate spin waves in a coupled nanowire (US 2008/0231392 A1, WO 2007/037625 A1).

Furthermore, it is known to transfer spin waves by the method of spin pumping into the solid state. In this case, a spin torque, which results from a magnetic field-induced precession movement of the magnetization, is transmitted to the spin of the conduction electrons of the magnetic solid. The use of metal / insulator boundary layers makes it possible to produce spin waves in electrically insulating magnetic solids as well (Y. Kajiwara et al., Transmission of electrical signals by spin-wave interconversion in a magnetic insulator, Nature 464, 2010).

In all these known methods, an electric current is converted into a magnetic field, which finally generates the spin signal. These methods have the disadvantage that

 (i) the necessary electrical currents often cause considerable heating of the component,

 (ii) by the indirect generation of the spin waves via electric currents

Time delay occurs, which limits the speed of electrical circuits and

(iii) the non-local character of the exciting magnetic fields and a required minimum size of the interconnects in which an electric current generates a stimulating magnetic field preclude a very high spatial integration density of the spin-wave generating elements. A method for exciting spin waves by a pulsed laser beam in exchange coupled layers has also been known (Keoki A. Seu, Hailong Huang, and Anne C. Reilly: Ultrafast laser excitation of spin waves by permanent modification of the exchange bias interaction in IRMn / Co, cond-mat.mtrl-sci, 04 Nov. 2005, p. 1-5). The exchange-coupled layers form a composite of a ferromagnetic layer and an antiferromagnetic layer, wherein the laser light interacts in particular with the boundary layer of the layer system.

In this case, the heat input caused by the laser light is utilized in the

Layer system. The heat input changes the exchange coupling between the layers, thereby exciting spin waves. Since the heat input to a permanent, non-reversible change of the material and thus the

Exchange coupling can, with this method only once, i. non-reproducible, a particular type of spin wave can be stimulated.

Presentation of the invention

The invention has for its object to provide a method for spin wave excitation, can be stimulated with the spin wave types of the same type reproducible in simply constructed solids without the use of electrical currents, magnetic fields and heat effects. Included in this task is the creation of an advantageously usable for carrying out the new method arrangement.

This object is achieved with the features contained in the patent claims, wherein the invention also includes combinations of the individual dependent claims in terms of an AND operation.

The inventive method is characterized in that a locally fixed in a magnetic solid domain wall is illuminated using the inverse magneto-optical gradient effect with polarized pulsed laser light, the illumination in vertical incidence in magnetized in the plane of the solid domains and in oblique incidence in Trap is made perpendicular to the solid state level of magnetized domains. In order to excite the spin waves, the inverse magneto-optical gradient effect is used according to the invention. This is a reversal of the direct

Gradient effect, a magneto-optical birefringence effect, which is caused by local changes in the magnetization. The direct

Gradient effect manifests itself as a line contrast at the location of a domain wall in a ferromagnetic or ferrimagnetic material, if the wall is suitably illuminated in a polarizing optical microscope with linearly polarized light, according to the symmetry of the effect (R. Schäfer and A. Hubert, A new magnetooptical Physic Stat. Sol. (a) 118, 271 -288 (1990) and R. Schaefer, C. Hamann, J. McCord, L. Schultz and V. The invention relates to non-uniform magnetization on the surface of a ferromagnet. Kambersky, Magnetooptical gradient effect in exchange-biased thin film:

experimental evidence for classical diffusion theory. Submitted to New Journal of Phys. (2010)). The reflected light at the site of the domain wall is often elliptically polarized.

The present invention is based on the idea of inverting the gradient effect. According to the invention, a planar-magnetized domain structure is illuminated perpendicularly with linearly polarized light, or a perpendicularly magnetized one

Domain structure obliquely illuminated with linearly polarized light, which may be (but not necessarily) previously polarized by means of a phase shifter elliptical or circular. The occurring inverse gradient effect causes a suitable direction of rotation of the incident light and with a suitable orientation of the domain wall according to the dielectric law of

Gradient effect a change of existing magnetization gradients, which in particular affects existing domain walls. At the site of a domain wall, a gradient change is caused by the magnetization slightly rotating in the immediate vicinity of the wall. As a result, spin waves are triggered on both sides of the wall, which then propagate away from the wall in the ferro- or ferrimagnetic solid.

An essential feature for the use of the inverse magneto-optical

Gradient effect and thus for the function of the method according to the invention is that illuminated with the polarized pulsed laser light Domain wall is fixed locally in the magnetic solid. As a rule, domain walls are known not fixed, but relatively easy to move. The present invention includes useful technical measures for fixing the domain wall in the solid state.

Another essential feature of the invention is that the locally fixed domain wall is illuminated with the polarized pulsed laser light while avoiding heat input into the solid. The condition of

Avoiding a heat input into the solid can be realized in an expedient manner by means of the choice of the wavelength, the pulse duration and / or the fluence of the pulsed laser light.

According to the invention, linearly polarized, elliptically polarized or circularly polarized pulsed laser light is used to illuminate the solid.

The laser light may be a pulsed laser beam with a pulse duration in the picosecond or femtosecond range.

The polarization direction or the direction of polarization of the laser beam can be changed during illumination.

As a magnetic solid, a ferromagnetic or ferrimagnetic material is used, in which the laser-light-illuminated domain wall by a material processing by means of embossing or bending of the solid or by a local change of the magnetic properties by

Ion implantation or by tempering the domain wall by means of a

Heat treatment is fixed locally.

According to the invention takes place to produce spin waves with different

Characteristic lighting on domain walls with accordingly

different character, namely a locally fixed domain wall with Neelcharakter or with spiked wall character or with Bloch character or with asymmetric Bloch character or vortex character. The inventive arrangement for exciting spin waves in a magnetic solid contains a pulsed laser source for illuminating a locally fixed in a solid domain wall with a polarized laser beam, wherein the pulse laser source is a femtosecond or picosecond laser.

According to the invention, a device for changing the polarization of the laser beam is arranged in the laser beam. This device can be a phase shifter with which a linear or elliptical or circular polarization of the laser light can be set.

According to the invention, a device for changing the focus of the laser beam is also arranged in the laser beam.

A further feature of the arrangement according to the invention is that the laser beam can be directed onto the surface of the solid by means of a pivotable pulse laser source or by means of a mirror arrangement in a vertical or oblique incidence.

The inventive method has several advantages over the prior art.

 A significant advantage is that spin waves are excited optically by illumination with a pulsed laser. As a result, no electric currents for magnetic field generation are required and it eliminates the known solutions adhering adverse heating due to the current flow. Another advantage is that the direct nature of the excitation eliminates the time delays inherent in the prior art. A further advantage is that no electrical conductors for spin wave generation are required. The electrical switching and logic circuits can thus be made less complex and it is a higher integration density possible.

Compared to the known method for spin wave excitation, in which by a pulsed laser beam exchange coupling at the boundary layer of

Modified heat exchange layer-coupled layer systems, the present invention also has advantages. A significant advantage is that Layer systems are not required, since according to the invention the spin waves in

Simple layers are generated. In addition, the present invention does not rely on heat effects for spin wave generation, which also lead to permanent changes in the material. According to the invention

Spin waves purely optically, thus generated completely athermisch. Due to the fact that in the present invention, no permanent change of the material occurs, the method is not fixed to the single excitation only a certain spin wave type.

 embodiments

The invention will be explained in more detail using an exemplary embodiment. In the accompanying drawing show

Fig. 1: the schematic diagram of an arrangement for exciting spin waves

 magnetic spin waveguide,

Figure 2: three examples of further suitable for spin wave excitation

 magnetic spin waveguide tracks.

The arrangement shown in Fig. 1 is used to excite spin waves in a consisting of a ferromagnetic material solid, the one

Spin waveguide 1 is. The ferromagnetic material is NisiFei9 (permalloy).

The spin waveguide 1 and has a locally fixed domain wall 2, which separates two perpendicularly magnetized domains. The local fixation of the domain wall has been done by ion implantation.

The pulsed laser source 3 generates a pulsed laser beam with a pulse duration in the picosecond range, with which the locally fixed domain wall 2 is illuminated.

The pulse laser source 3 is by means of a not shown in the drawing

mechanical or optical device via an angle 4 pivotally

executed. Thus, the laser beam in vertical incidence in the case of the present in the example parallel to the spin waveguide track plane magnetized domains or in oblique incidence with domains magnetized perpendicular to the plane of the spin waveguide path aligned with the domain wall.

In the laser beam, the arrangement comprises a first means 5 for changing the polarization of the laser beam, which is a phase shifter with which an elliptical or a circular polarization of the laser light can be adjusted.

In addition, the arrangement in the laser beam on a second means 6, with which the focus of the laser beam can be changed.

With the polarized pulsed laser light takes place at the spatially fixed in the Spinwellenleiterbahn 1 domain wall 2 a metered energy input, which triggers a collective movement of existing at the location of the domain wall in the track spins in the form of a wave, but which is metered so that he no heat input caused. In fact, there is a reversal of the known magneto-optical gradient effect.

The condition of avoiding heat input into the solid body is by means of the choice of the wavelength, the pulse duration and / or the fluence of the pulsed one

Laser light realized.

The generated spin wave is advantageously used for signal and information transport in the spin waveguide 1. The spin waveguide tracks shown in FIG. 2 consist of ferromagnetic or ferrimagnetic material and each have a locally fixed domain wall 2. In the upper spin waveguide, the local fixation of the

Domain wall 2 realized by means of an embossing. In the Spinwellenleiterbahn shown below, the local fixation of the domain wall 2 is realized in a simple manner by means of a turn. In the lower spin waveguide path is the

Domains wall 2 fixed in a circular disk-shaped end of the conductor.

Claims

 claims Method for exciting spin waves in magnetic solids, characterized in that a locally fixed in a magnetic solid domain wall using the inverse magneto-optical Gradient effect is illuminated with polarized pulsed laser light, wherein the illumination is made in vertical incidence in the plane of the solid magnetized domains and in oblique incidence in the case of perpendicular to the solid state level magnetized domains. A method according to claim 1, characterized in that the locally fixed domain wall is illuminated while avoiding a heat input into the solid body with the polarized pulsed laser light. A method according to claim 2, characterized in that the condition of avoiding a heat input into the solid body by means of the choice of the wavelength, the pulse duration and / or the fluence of the pulsed laser light is realized. Method according to one or more of claims 1 to 3, characterized in that for illuminating the solid linearly polarized, elliptically polarized or circularly polarized pulsed laser light is used. 5. The method according to one or more of claims 1 to 4, characterized  in that a pulsed laser beam with a pulse duration in the picosecond or femtosecond range is used for illumination. 6. The method according to one or more of claims 1 to 5, characterized  characterized in that the polarization direction or the polarization direction of rotation of the laser beam is changed during the lighting. 7. The method according to one or more of claims 1 to 6, characterized  characterized in that as a magnetic solid a ferro- or  ferrimagnetic material is used. 8. The method according to one or more of claims 1 to 7, characterized  in that a solid body is used in which the domain wall illuminated by the laser light is processed by material processing by means of embossing or bending of the solid or by a local process  Changing the magnetic properties by means of ion implantation or by means of annealing the domain wall by means of a heat treatment is fixed locally. 9. The method according to one or more of claims 1 to 8, characterized  characterized in that to generate spin waves with different characteristics, the illumination takes place on domain walls  accordingly different character, namely a locally fixed domain wall with Neelcharakter or with spiked wall character or with Blochcharakter or with asymmetrical Bloch character or with  Vortex character. 10. Arrangement for exciting spin waves in a magnetic  Solid body (1), characterized by a pulsed laser source (3) for Illumination of a fixed in a solid body (1) locally fixed domain wall (2) with a polarized laser beam, wherein the pulse laser source is a femtosecond or picosecond laser. 1 1 .Anordnung according to claim 10, characterized in that in the laser beam means (5) for changing the polarization of the laser beam is arranged. 12. Arrangement according to claim 10 or 1 1, characterized in that the means (5) for adjusting the change in the polarization of  Laser beam is a phase shifter for adjusting a linear or elliptical or circular polarization of the laser light. 13. Arrangement according to one of claims 10 to 12, characterized in that in the laser beam, a device (6) for changing the focus of the laser beam is arranged. 14. Arrangement according to one of claims 10 to 13, characterized in that the laser beam can be directed by means of a pivotable pulse laser source or by means of a mirror arrangement in vertical or oblique incidence on the surface of the solid body (1).