EP2449567A1 - Method for changing the direction of magnetization in ferromagnetic layer - Google Patents

Method for changing the direction of magnetization in ferromagnetic layer

Info

Publication number
EP2449567A1
EP2449567A1 EP10745299A EP10745299A EP2449567A1 EP 2449567 A1 EP2449567 A1 EP 2449567A1 EP 10745299 A EP10745299 A EP 10745299A EP 10745299 A EP10745299 A EP 10745299A EP 2449567 A1 EP2449567 A1 EP 2449567A1
Authority
EP
European Patent Office
Prior art keywords
layer
lower layer
temperature
magnetic field
upper layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP10745299A
Other languages
German (de)
French (fr)
Inventor
Massimiliano Marangolo
Maurizio Sacchi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Centre National de la Recherche Scientifique CNRS
Universite Pierre et Marie Curie Paris 6
Original Assignee
Centre National de la Recherche Scientifique CNRS
Universite Pierre et Marie Curie Paris 6
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Centre National de la Recherche Scientifique CNRS, Universite Pierre et Marie Curie Paris 6 filed Critical Centre National de la Recherche Scientifique CNRS
Publication of EP2449567A1 publication Critical patent/EP2449567A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/32—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying conductive, insulating or magnetic material on a magnetic film, specially adapted for a thin magnetic film
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
    • G11B11/10504—Recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/64—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent
    • G11B5/66—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent the record carriers consisting of several layers
    • G11B5/676—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent the record carriers consisting of several layers having magnetic layers separated by a nonmagnetic layer, e.g. antiferromagnetic layer, Cu layer or coupling layer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/74—Record carriers characterised by the form, e.g. sheet shaped to wrap around a drum
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/74—Record carriers characterised by the form, e.g. sheet shaped to wrap around a drum
    • G11B5/743—Patterned record carriers, wherein the magnetic recording layer is patterned into magnetic isolated data islands, e.g. discrete tracks
    • G11B5/746—Bit Patterned record carriers, wherein each magnetic isolated data island corresponds to a bit
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F10/00—Thin magnetic films, e.g. of one-domain structure
    • H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
    • H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
    • H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
    • H01F10/14—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys containing iron or nickel
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
    • G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G11B2005/0005—Arrangements, methods or circuits
    • G11B2005/0021—Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal

Definitions

  • the present invention relates to a method for modifying the magnetization direction of a layer of a ferromagnetic material.
  • the method makes it possible to locally control the direction of magnetization, in the absence of an external magnetic field.
  • the invention aims to remedy these drawbacks.
  • the invention proposes a method that makes it possible to locally modify the magnetization direction of a layer of ferromagnetic material, in particular to reverse it locally, in the absence of an external magnetic field.
  • the invention thus relates to a method for modifying the magnetization direction of an upper layer comprising a ferromagnetic material.
  • the upper layer is disposed above a lower layer magnetically unmagnetized with the upper layer, the lower layer comprising a material capable of producing or not, according to whether the temperature of said material is greater or less than a threshold value, a radiated magnetic field capable of modifying the magnetization direction of the upper layer, the magnetic field radiated by the material of the lower layer being greater than the coercive field of the material ferromagnetic layer.
  • the method further comprises:
  • the temperature variation steps b) and c) are carried out without applying an external magnetic field.
  • the lower layer and the upper layer are "magnetically unmagnetized" within the meaning of the invention, that is to say that the magnetic coupling between the lower layer and the upper layer is sufficiently weak for the magnetization directions of the upper layer and the lower layer are initially in a first stable relative configuration and that they are at the end of the process in a second stable relative configuration.
  • the material of the lower layer produces a radiated magnetic field capable of "irreversibly” modifying the magnetization direction of the upper layer.
  • the change in the magnetization direction of the upper layer is stably maintained.
  • the method utilizes the ability of the lower layer material to produce a magnetic field radiated above or below a threshold temperature. It is thus possible to modify the magnetization direction of the upper layer by varying the temperature.
  • the material of the lower layer is typically capable of producing a radiated magnetic field capable of modifying the magnetization direction of the upper layer when the temperature of said material is greater than a threshold value.
  • a threshold value if the temperature of the lower layer is below the threshold value, it is possible to stabilize at least two magnetic alignment configurations between the lower layer and the upper layer.
  • the material of the lower layer may have, depending on whether the temperature of the material is lower or higher than a threshold value, a homogeneous entirely ferromagnetic structure or an inhomogeneous structure comprising an alternation of ferromagnetic and non-ferromagnetic zones.
  • the material of the lower layer may in particular have a homogeneous structure when the temperature of the material is less than a threshold temperature, and have an inhomogeneous structure when the temperature of the material is higher than a threshold temperature.
  • the lower layer may be a layer of MnAs formed by epitaxy on a GaAs substrate, in particular of GaAs (OO1) structure.
  • the inhomogeneous structure of the lower structure is obtained by ion implantation in the lower layer, for example by implantation of rare gas ions. Ion implantation allows to modify the Curie temperature of the implanted zone.
  • the Curie temperature is the temperature beyond which a material loses its spontaneous magnetization.
  • the lower layer is characterized by an alternation of ferromagnetic zones having a Curie temperature T1 and T2 respectively.
  • the threshold temperature will be chosen between T1 and T2 to have an alternation of ferromagnetic and non-ferromagnetic zones.
  • the lower layer that can be subjected to such ion implantation may for example be a layer of alloy FePd, FeNi, NiMn, FeGa or FePt.
  • the upper layer may for example be a layer of Fe, Ni or Co, or a ferromagnetic alloy comprising at least one of these elements, such as a permalloy alloy (NiFe).
  • a permalloy alloy NiFe
  • a layer of non-ferromagnetic material may be disposed between the lower layer and the upper layer. It should be noted that when using an epitaxially grown MnAs layer on a GaAs substrate, the formation of a very thin interface alloy layer is observed which makes it possible to limit the coupling between the lower layer and the layer. top, without it being necessary to have an additional layer between the lower layer and the upper layer.
  • the magnetic field radiated by the material of the lower layer is greater than the coercive field of the ferromagnetic material of the upper layer, so as to facilitate the modification of the magnetization direction of the upper layer.
  • FIG. 1 diagrammatically illustrates a device for implementing the method according to the invention
  • FIG. 2 is a detail view from above of the device
  • FIG. 3 is a partial view of the device, during the process,
  • FIGS. 4 to 6 are diagrams useful for understanding the process.
  • FIG. 7 schematically illustrates a particular device for implementing the method according to the invention.
  • the device 1 as illustrated in FIG. 1, comprises an upper layer 2 of ferromagnetic material disposed above a lower layer 3 of ferromagnetic material, itself arranged on a substrate 4.
  • the matrix consisting of the upper layers 2 and 3 as well as the substrate 4 may be disk-shaped.
  • the device 1 also comprises a heating element 5 and a magnetic reading head 6.
  • the heating element 5 locally heats the lower layer 3.
  • the local heating locally modifies the matrix structure, which results in the formation of radiated bipolar magnetic fields, also called leakage flux, at the level of the upper layer 2.
  • the direction of the magnetization of the upper layer 2 is modified locally, by inversion in the case of FIG. 1, at a zone 7 heated by the heating element 5, as illustrated in FIG.
  • the temperature of the matrix is then lowered to its initial value.
  • the new magnetic alignment is stable.
  • the read head 6 controls the local magnetic state at the level of the upper layer 2.
  • FIG. 3 An example of a device is illustrated in more detail in FIG. 3.
  • the device is prepared by molecular beam epitaxy.
  • An upper layer 2 of Fe 5 nm thick is deposited on the upper surface of a lower layer 3 of MnAs 140 nm thick.
  • the lower layer 3 is obtained by epitaxial growth on a substrate 4 of GaAs (OO1).
  • MnAs has good compatibility with semiconductor substrates as well as high spin polarization.
  • MnAs / GaAs has a self-organized structure in bands, alternating ferromagnetic phases ⁇ -MnAs and non-ferromagnetic phases ⁇ -MnAs.
  • the band period i.e., the sum of the width of an ⁇ -MnAs band and a ⁇ -MnAs band, is determined by the thickness of the MnAs layer 3.
  • the period substantially constant as a function of temperature, is approximately equal to five times the thickness of the layer 3 of MnAs.
  • the width of the ⁇ -MnAs bands increases with temperature.
  • the difference in height between the ⁇ -MnAs and ⁇ -MnAs phases is of the order of 2% of the thickness of the layer of MnAs, that is to say only a few nm.
  • the magnetic field radiated by the lower layer 3 orients the magnetization of the upper layer 2 of Fe.
  • the radiated magnetic field (in mT) produced at the level of the upper layer 2 is shown at the top of FIG.
  • the coercive field of the Fe layer 2 can be reduced, for example by using a lower coercivity-field alloy, for example a FeNi alloy or an alloy. FeNiB.
  • the configuration for which the magnetizations of the upper layer 2 of Fe and the lower layer 3 of MnAs have the same direction at low temperature is modified in the presence of the grooves of ⁇ -MnAs, without it being necessary to apply an external magnetic field.
  • Figure 4 is a diagram showing the magnetization of the upper layer and the lower layer as a function of temperature.
  • the magnetic behavior of the sample is observed by resonant magnetic X-ray scattering (X-ray Magnetic Scattering (XRMS) in English), using circularly polarized X-rays.
  • XRMS resonant magnetic X-ray scattering
  • Mn-2p about 640 eV
  • Fe-2p about 707 eV
  • the data are collected in coplanar geometry, the bands being oriented orthogonally to the diffusion plane.
  • the diffusion angle is set at 16 °.
  • the sample holder is integrated in a Peltier device for temperature control, between -1O 0 C and 80 ° C, as well as an electromagnet (up to 1.5 kOe at the sample).
  • the asymmetry rate is proportional to the magnetic moment of the element.
  • the signal magnetic (asymmetry rate) of Fe is represented by the curve starting at the top of Figure 4 and ending at the bottom of Figure 4, while the magnetic signal (asymmetry rate) of MnAs is represented by the curve substantially horizontal located in the middle of Figure 4.
  • FIG. 5 shows the hysteresis cycles of Fe and MnAs at 8 ° C., representing the magnetization of Fe and MnAs as a function of the applied magnetic field.
  • the magnetic pulse prepares the initial state of the thermal cycle with an identical magnetization direction for the Fe layer and the MnAs layer. It is observed that the coupling between the two layers is weak, since the coercive fields of the two layers are very different.
  • the process starts at 8 0 C with the same magnetization direction for the Fe layer and the MnAs layer.
  • the magnetization of the Fe layer remains substantially constant until the ⁇ -MnAs phase appears, around 13 ° C. This is confirmed when the evolution of the ⁇ -MnAs level is observed. in MnAs depending on the temperature, as shown in Figure 6.
  • the magnetization of Fe decreases rapidly, then reverses. Beyond 16 0 C, the zones of ⁇ -MnAs are wide enough to cause irreversible modification of the direction of magnetization.
  • the magnetization of the Fe layer remains opposite to that of the MnAs layer, although the temperature is identical to that of the MnAs layer. from the beginning of the process and that the process proceeds with a zero applied magnetic field.
  • a slight adjustment of the MnAs / GaAs microstructure by a temperature control allows a complete reversal of the magnetization direction of the Fe layer without the application of a magnetic field.
  • the inversion of the magnetization can be obtained locally by using focused laser radiation.
  • a structural variation equivalent to a temperature increase of 5 0 C can be obtained by irradiation with a laser pulse.
  • the structural variation takes place on a time scale of about 10 '11 s.
  • Figure 7 illustrates a particular application of the method according to the invention, called "temperature control”.
  • a plurality of sets A, B, C consisting of an upper layer 2 of Fe and a lower layer 3 of MnAs, as described above, are placed on a substrate 8.
  • a magnetization detector not shown, such as for example a sensor using the Kerr effect, it is detected whether the magnetization of the layers 2,3 is in a parallel configuration (case of the sets A and C) or antiparallel (case of set B). If the configuration is antiparallel, it follows that the local temperature of the substrate 8 exceeds or has exceeded the threshold temperature from which the reversal of magnetization of the upper layer 2 occurs.
  • the method according to the invention thus has many advantages.
  • the modification of the magnetization direction of the upper layer is controlled solely by the temperature. It is not necessary to apply a magnetic field by a coil or an external magnet.
  • the change of the magnetization direction occurs on a small temperature difference, which requires little energy.
  • the local heating is carried out for a very short time, which can be of the order of 10 '11 s with a heating by absorption of radiation laser.
  • the change of magnetization direction can be carried out over a small distance, of the order of 200 nm for the matrix MnAs / GaAs.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Nanotechnology (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mathematical Physics (AREA)
  • Manufacturing Of Magnetic Record Carriers (AREA)
  • Thin Magnetic Films (AREA)
  • Magnetic Record Carriers (AREA)
  • Recording Or Reproducing By Magnetic Means (AREA)

Abstract

The invention relates to a method for changing the direction of magnetization in a top layer (2) including a ferromagnetic material, characterized in that: a) the top layer (2) is placed over a bottom layer (3) that is not magnetically coupled to the top layer (2), the bottom layer (3) including a material capable of producing or not producing, according to whether the temperature of said material is greater than or equal to a threshold value, a radiated magnetic field capable of changing the direction of magnetization of the top layer (2), the magnetic field radiated by the material of the bottom layer (3) being greater than the coercive field strength of the ferromagnetic material of the top layer (2), and in that the method includes: b) a step consisting of passing the temperature of the bottom layer (3) from a first value, for which the directions of magnetization of the top layer (2) and the bottom layer (3) are in a relatively stable configuration and for which the material of the bottom layer (3) does not produce any radiated magnetic field, to a second value, for which the material of the bottom layer (3) produces a radiated magnetic field capable of irreversibly changing the direction of magnetization of the top layer (2), and c) a step consisting of passing the temperature of the bottom layer (3) from the second value to a third value for which the material of the bottom layer (3) does not produce any radiated magnetic field, the temperature variation steps b) and c) being carried out without applying an external magnetic field.

Description

PROCEDE DE MODIFICATION DE LA DIRECTION D'AIMANTATION D'UNE COUCHE FERROMAGNETIQUE  METHOD FOR MODIFYING THE MAGNETIZATION DIRECTION OF A FERROMAGNETIC LAYER
La présente invention a pour objet un procédé de modification de la direction d'aimantation d'une couche d'un matériau ferromagnétique. Le procédé permet de contrôler localement la direction d'aimantation, en l'absence de champ magnétique extérieur. The present invention relates to a method for modifying the magnetization direction of a layer of a ferromagnetic material. The method makes it possible to locally control the direction of magnetization, in the absence of an external magnetic field.
Dans les dispositifs d'enregistrement magnétique, il est particulièrement important de pouvoir contrôler localement la direction d'aimantation d'une bande magnétique.  In magnetic recording devices, it is particularly important to be able to locally control the magnetization direction of a magnetic tape.
Il est connu à cet effet d'appliquer localement un champ magnétique à l'aide d'une bobine magnétique. Ce dispositif présente l'inconvénient d'être lent, car il présente une certaine inertie. En outre, cette procédure demande l'application de champs magnétiques de plus en plus intenses au fur et à mesure que la taille des objets magnétiques diminue, ce qui conduit à l'utilisation d'une bobine de taille importante, peu compatible avec un contrôle précis de la direction d'aimantation sur de petites dimensions de la bande magnétique.  It is known for this purpose to locally apply a magnetic field using a magnetic coil. This device has the disadvantage of being slow because it has a certain inertia. In addition, this procedure requires the application of increasingly intense magnetic fields as the size of the magnetic objects decreases, which leads to the use of a large coil, little compatible with a control precise direction of magnetization on small dimensions of the magnetic tape.
L'invention vise à remédier à ces inconvénients.  The invention aims to remedy these drawbacks.
En particulier, l'invention propose un procédé qui permet de modifier localement la direction d'aimantation d'une couche de matériau ferromagnétique, en particulier de l'inverser localement, en l'absence de champ magnétique extérieur.  In particular, the invention proposes a method that makes it possible to locally modify the magnetization direction of a layer of ferromagnetic material, in particular to reverse it locally, in the absence of an external magnetic field.
L'invention a ainsi pour objet un procédé de modification de la direction d'aimantation d'une couche supérieure comprenant un matériau ferromagnétique.  The invention thus relates to a method for modifying the magnetization direction of an upper layer comprising a ferromagnetic material.
Conformément au procédé selon l'invention :  According to the process according to the invention:
a) La couche supérieure est disposée au-dessus d'une couche inférieure non couplée magnétiquement avec la couche supérieure, la couche inférieure comprenant un matériau apte à produire ou non, suivant que la température dudit matériau est supérieure ou inférieure à une valeur seuil, un champ magnétique rayonné susceptible de modifier la direction d'aimantation de la couche supérieure, le champ magnétique rayonné par le matériau de la couche inférieure étant supérieur au champ coercitif du matériau ferromagnétique de la couche supérieure. a) The upper layer is disposed above a lower layer magnetically unmagnetized with the upper layer, the lower layer comprising a material capable of producing or not, according to whether the temperature of said material is greater or less than a threshold value, a radiated magnetic field capable of modifying the magnetization direction of the upper layer, the magnetic field radiated by the material of the lower layer being greater than the coercive field of the material ferromagnetic layer.
Le procédé comprend en outre :  The method further comprises:
b) une étape consistant à faire passer la température de la couche inférieure d'une première valeur, pour laquelle les directions d'aimantation de la couche supérieure et de la couche inférieure sont dans une configuration relative stable et pour laquelle le matériau de la couche inférieure ne produit pas de champ magnétique rayonné, à une deuxième valeur, pour laquelle le matériau de la couche inférieure produit un champ magnétique rayonné susceptible de modifier de manière irréversible la direction d'aimantation de la couche supérieure, et  b) a step of passing the temperature of the lower layer by a first value, for which the magnetization directions of the upper layer and the lower layer are in a stable relative configuration and for which the material of the layer lower does not produce a radiated magnetic field, at a second value, for which the material of the lower layer produces a radiated magnetic field capable of irreversibly modifying the magnetization direction of the upper layer, and
c) une étape consistant à faire passer la température de la couche inférieure de la deuxième valeur à une troisième valeur pour laquelle le matériau de la couche inférieure ne produit pas de champ magnétique rayonné.  c) a step of changing the temperature of the lower layer of the second value to a third value for which the material of the lower layer does not produce a radiated magnetic field.
Les étapes de variation de température b) et c) sont effectuées sans application de champ magnétique extérieur.  The temperature variation steps b) and c) are carried out without applying an external magnetic field.
La couche inférieure et la couche supérieure sont « non couplées magnétiquement » au sens de l'invention, c'est-à-dire que le couplage magnétique entre la couche inférieure et la couche supérieure est suffisamment faible pour que les directions d'aimantation de la couche supérieure et de la couche inférieure soient initialement dans une première configuration relative stable et pour qu'elle soient à l'issue du procédé dans une deuxième configuration relative stable. A la deuxième valeur de température, le matériau de la couche inférieure produit un champ magnétique rayonné susceptible de modifier de manière « irréversible » la direction d'aimantation de la couche supérieure. On entend par là que lors de la variation de température de l'étape c), la modification de la direction d'aimantation de la couche supérieure est conservée de manière stable. Ainsi, on obtient une nouvelle configuration stable de l'alignement magnétique relatif de la couche inférieure et supérieure. The lower layer and the upper layer are "magnetically unmagnetized" within the meaning of the invention, that is to say that the magnetic coupling between the lower layer and the upper layer is sufficiently weak for the magnetization directions of the upper layer and the lower layer are initially in a first stable relative configuration and that they are at the end of the process in a second stable relative configuration. At the second temperature value, the material of the lower layer produces a radiated magnetic field capable of "irreversibly" modifying the magnetization direction of the upper layer. By this is meant that during the temperature change of step c), the change in the magnetization direction of the upper layer is stably maintained. Thus, a new stable configuration of the relative magnetic alignment of the lower and upper layers is obtained.
Le procédé utilise la faculté du matériau de la couche inférieure à produire un champ magnétique rayonné au-dessus ou en dessous d'une température seuil . Il est ainsi possible de modifier la direction d'aimantation de la couche supérieure en jouant sur la température.  The method utilizes the ability of the lower layer material to produce a magnetic field radiated above or below a threshold temperature. It is thus possible to modify the magnetization direction of the upper layer by varying the temperature.
Le matériau de la couche inférieure est typiquement apte à produire un champ magnétique rayonné susceptible de modifier la direction d'aimantation de la couche supérieure lorsque la température dudit matériau est supérieure à une valeur seuil. Ainsi, si la température de la couche inférieure est inférieure à la valeur seuil, il est possible de stabiliser au moins deux configurations d'alignement magnétique entre la couche inférieure et la couche supérieure.  The material of the lower layer is typically capable of producing a radiated magnetic field capable of modifying the magnetization direction of the upper layer when the temperature of said material is greater than a threshold value. Thus, if the temperature of the lower layer is below the threshold value, it is possible to stabilize at least two magnetic alignment configurations between the lower layer and the upper layer.
Selon un mode de réalisation, le matériau de la couche inférieure peut présenter, suivant que la température du matériau est inférieure ou supérieure à une valeur seuil, une structure homogène entièrement ferromagnétique ou une structure inhomogène comprenant une alternance de zones ferromagnétiques et non ferromagnétiques.  According to one embodiment, the material of the lower layer may have, depending on whether the temperature of the material is lower or higher than a threshold value, a homogeneous entirely ferromagnetic structure or an inhomogeneous structure comprising an alternation of ferromagnetic and non-ferromagnetic zones.
C'est la présence des zones non ferromagnétiques qui entraîne la production, par les zones ferromagnétiques, d'un champ rayonné de la couche inférieure vers la couche supérieure, et qui provoque ainsi la modification de la direction d'aimantation de la couche supérieure.  It is the presence of the non-ferromagnetic zones which causes the ferromagnetic zones to produce a field radiated from the lower layer to the upper layer, and which thus causes the modification of the magnetization direction of the upper layer.
Le matériau de la couche inférieure peut notamment présenter une structure homogène lorsque la température du matériau est inférieure à une température seuil, et présenter une structure inhomogène lorsque la température du matériau est supérieure à une température seuil. The material of the lower layer may in particular have a homogeneous structure when the temperature of the material is less than a threshold temperature, and have an inhomogeneous structure when the temperature of the material is higher than a threshold temperature.
A titre d'exemple, la couche inférieure peut être une couche de MnAs formée par épitaxie sur un substrat de GaAs, notamment de structure GaAs(OOl).  By way of example, the lower layer may be a layer of MnAs formed by epitaxy on a GaAs substrate, in particular of GaAs (OO1) structure.
On peut également envisager que la structure inhomogène de la structure inférieure soit obtenue par implantation ionique dans la couche inférieure, par exemple par implantation d'ions de gaz rares. L'implantation ionique permet de modifier la température de Curie de la zone implantée. La température de Curie est la température au-delà de laquelle un matériau perd son aimantation spontanée. Après implantation, la couche inférieure se caractérise par une alternance de zones ferromagnétiques ayant une température de Curie Tl et T2 respectivement. La température seuil sera choisie entre Tl et T2 pour avoir une alternance de zones ferromagnétiques et non ferromagnétiques.  It is also conceivable that the inhomogeneous structure of the lower structure is obtained by ion implantation in the lower layer, for example by implantation of rare gas ions. Ion implantation allows to modify the Curie temperature of the implanted zone. The Curie temperature is the temperature beyond which a material loses its spontaneous magnetization. After implantation, the lower layer is characterized by an alternation of ferromagnetic zones having a Curie temperature T1 and T2 respectively. The threshold temperature will be chosen between T1 and T2 to have an alternation of ferromagnetic and non-ferromagnetic zones.
La couche inférieure pouvant être soumise à une telle implantation ionique peut par exemple être une couche d'alliage FePd, FeNi, NiMn, FeGa ou FePt.  The lower layer that can be subjected to such ion implantation may for example be a layer of alloy FePd, FeNi, NiMn, FeGa or FePt.
La couche supérieure peut par exemple être une couche de Fe, Ni ou Co, ou d'un alliage ferromagnétique comprenant au moins un de ces éléments, comme par exemple un alliage de permalloy (NiFe).  The upper layer may for example be a layer of Fe, Ni or Co, or a ferromagnetic alloy comprising at least one of these elements, such as a permalloy alloy (NiFe).
Afin de favoriser le non couplage magnétique entre la couche inférieure et de la couche supérieure, une couche de matériau non ferromagnétique peut être disposée entre la couche inférieure et la couche supérieure. Il est à noter que lorsqu'on utilise une couche de MnAs formée par épitaxie sur un substrat de GaAs on observe la formation d'une très fine couche d'alliage d'interface qui permet de limiter le couplage entre la couche inférieure et la couche supérieure, sans qu'il soit nécessaire de disposer une couche supplémentaire entre la couche inférieure et la couche supérieure. In order to promote non-magnetic coupling between the lower layer and the upper layer, a layer of non-ferromagnetic material may be disposed between the lower layer and the upper layer. It should be noted that when using an epitaxially grown MnAs layer on a GaAs substrate, the formation of a very thin interface alloy layer is observed which makes it possible to limit the coupling between the lower layer and the layer. top, without it being necessary to have an additional layer between the lower layer and the upper layer.
Le champ magnétique rayonné par le matériau de la couche inférieure est supérieur au champ coercitif du matériau ferromagnétique de la couche supérieure, de manière à faciliter la modification de la direction d'aimantation de la couche supérieure.  The magnetic field radiated by the material of the lower layer is greater than the coercive field of the ferromagnetic material of the upper layer, so as to facilitate the modification of the magnetization direction of the upper layer.
D'autres caractéristiques et avantages de la présente invention apparaîtront plus clairement à la lecture de la description suivante donnée à titre d'exemple illustratif et non limitatif et faite en référence aux dessins annexés sur lesquels :  Other characteristics and advantages of the present invention will appear more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended drawings in which:
- la figure 1 illustre schématiquement un dispositif de mise en œuvre du procédé selon l'invention,  FIG. 1 diagrammatically illustrates a device for implementing the method according to the invention,
- la figure 2 est une vue de détail de dessus du dispositif,  FIG. 2 is a detail view from above of the device,
- la figure 3 est une vue partielle du dispositif, en cours de procédé,  FIG. 3 is a partial view of the device, during the process,
- les figures 4 à 6 sont des diagrammes utiles à la compréhension du procédé, et  FIGS. 4 to 6 are diagrams useful for understanding the process, and
- la figure 7 illustre schématiquement un dispositif particulier de mise en œuvre du procédé selon l'invention.  - Figure 7 schematically illustrates a particular device for implementing the method according to the invention.
Le dispositif 1, tel qu'illustré à la figure 1, comprend une couche supérieure 2 de matériau ferromagnétique disposée au-dessus d'une couche inférieure 3 de matériau ferromagnétique, elle-même disposée sur un substrat 4. La matrice constituée des couches supérieure 2 et inférieure 3 ainsi que du substrat 4 peut être en forme de disque.  The device 1, as illustrated in FIG. 1, comprises an upper layer 2 of ferromagnetic material disposed above a lower layer 3 of ferromagnetic material, itself arranged on a substrate 4. The matrix consisting of the upper layers 2 and 3 as well as the substrate 4 may be disk-shaped.
Le dispositif 1 comprend également un élément chauffant 5, ainsi qu'une tête de lecture magnétique 6.  The device 1 also comprises a heating element 5 and a magnetic reading head 6.
L'élément chauffant 5 chauffe localement la couche inférieure 3. Le chauffage local modifie localement la structure de la matrice, ce qui entraîne la formation de champs magnétiques bipolaires rayonnes, appelés également flux de fuite, au niveau de la couche supérieure 2. La direction de l'aimantation de la couche supérieure 2 est modifiée localement, par inversion dans le cas de la figure 1, au niveau d'une zone 7 chauffée par l'élément chauffant 5, tel qu'illustré sur la figure 2. La température de la matrice est ensuite abaissée jusqu'à sa valeur initiale. Le nouvel alignement magnétique est stable. La tête de lecture 6 contrôle l'état magnétique local au niveau de la couche supérieure 2. The heating element 5 locally heats the lower layer 3. The local heating locally modifies the matrix structure, which results in the formation of radiated bipolar magnetic fields, also called leakage flux, at the level of the upper layer 2. The direction of the magnetization of the upper layer 2 is modified locally, by inversion in the case of FIG. 1, at a zone 7 heated by the heating element 5, as illustrated in FIG. The temperature of the matrix is then lowered to its initial value. The new magnetic alignment is stable. The read head 6 controls the local magnetic state at the level of the upper layer 2.
Un exemple de dispositif est illustré plus en détail à la figure 3. Le dispositif est préparé par épitaxie par jets moléculaires. Une couche supérieure 2 de Fe d'épaisseur 5 nm est déposée à la surface supérieure d'une couche inférieure 3 de MnAs d'épaisseur 140 nm. La couche inférieure 3 est obtenue par croissance épitaxiale sur un substrat 4 de GaAs(OOl).  An example of a device is illustrated in more detail in FIG. 3. The device is prepared by molecular beam epitaxy. An upper layer 2 of Fe 5 nm thick is deposited on the upper surface of a lower layer 3 of MnAs 140 nm thick. The lower layer 3 is obtained by epitaxial growth on a substrate 4 of GaAs (OO1).
MnAs possède une bonne compatibilité avec les substrats semi- conducteurs ainsi qu'une polarisation de spin élevée. A température ambiante, et plus précisément entre 13 et 4O0C, MnAs/GaAs présente une structure auto-organisée en bandes, alternant des phases ferromagnétiques α-MnAs et des phases non ferromagnétiques β-MnAs. La période des bandes, c'est-à-dire la somme de la largeur d'une bande α-MnAs et d'une bande β-MnAs, est déterminée par l'épaisseur de la couche 3 de MnAs. La période, sensiblement constante en fonction de la température, est environ égale à cinq fois l'épaisseur de la couche 3 de MnAs. MnAs has good compatibility with semiconductor substrates as well as high spin polarization. At room temperature, and more precisely between 13 and 40 ° C., MnAs / GaAs has a self-organized structure in bands, alternating ferromagnetic phases α-MnAs and non-ferromagnetic phases β-MnAs. The band period, i.e., the sum of the width of an α-MnAs band and a β-MnAs band, is determined by the thickness of the MnAs layer 3. The period, substantially constant as a function of temperature, is approximately equal to five times the thickness of the layer 3 of MnAs.
Dans l'intervalle de température compris entre 13 et 4O0C, à l'intérieur duquel coexistent les phases α-MnAs et β-MnAs, la largeur des bandes β-MnAs augmente avec la température. Il existe une différence de hauteur entre les phases α-MnAs, qui se présentent sous forme de crêtes, et les phases β-MnAs, qui se présentent sous forme de rainures ente les phases α-MnAs. La différence de hauteur entre les phases α-MnAs et β-MnAs est de l'ordre de 2% de l'épaisseur de la couche de MnAs, c'est-à-dire de quelques nm seulement. Le champ magnétique rayonné par la couche inférieure 3 oriente l'aimantation de la couche supérieure 2 de Fe. In the temperature range between 13 and 40 ° C., within which the α-MnAs and β-MnAs coexist, the width of the β-MnAs bands increases with temperature. There is a difference in height between the α-MnAs phases, which are in the form of peaks, and the β-MnAs phases, which are in the form of grooves between α-MnAs phases. The difference in height between the α-MnAs and β-MnAs phases is of the order of 2% of the thickness of the layer of MnAs, that is to say only a few nm. The magnetic field radiated by the lower layer 3 orients the magnetization of the upper layer 2 of Fe.
Le champ magnétique rayonné (en mT) produit au niveau de la couche supérieure 2 est représenté en haut de la figure 3.  The radiated magnetic field (in mT) produced at the level of the upper layer 2 is shown at the top of FIG.
Pour favoriser le contrôle de la direction d'aimantation de la couche 2 de Fe, on peut diminuer le champ coercitif de la couche 2 de Fe, par exemple en utilisant un alliage à champ coercitif plus faible comme par exemple un alliage FeNi ou un alliage FeNiB.  To promote the control of the magnetization direction of the Fe layer 2, the coercive field of the Fe layer 2 can be reduced, for example by using a lower coercivity-field alloy, for example a FeNi alloy or an alloy. FeNiB.
Ainsi, la configuration pour laquelle les aimantations de la couche supérieure 2 de Fe et de la couche inférieure 3 de MnAs ont la même direction à basse température est modifiée en présence des rainures de β-MnAs, sans qu'il soit nécessaire d'appliquer un champ magnétique extérieur.  Thus, the configuration for which the magnetizations of the upper layer 2 of Fe and the lower layer 3 of MnAs have the same direction at low temperature is modified in the presence of the grooves of β-MnAs, without it being necessary to apply an external magnetic field.
La figure 4 est un diagramme représentant l'aimantation de la couche supérieure et de la couche inférieure en fonction de la température. Le comportement magnétique de l'échantillon est observé par diffusion magnétique résonante de rayons X (X-ray Résonant Magnetic Scattering (XRMS) en langue anglaise), en utilisant des rayons X polarisés circulairement. En réglant l'énergie photonique aux résonances Mn-2p (environ 640 eV) ou Fe-2p (environ 707 eV), l'intensité réfléchie spéculaire est sensible à l'aimantation de la couche de MnAs ou de la couche de Fe, respectivement. Les données sont collectées en géométrie coplanaire, les bandes étant orientées orthogonalement au plan de diffusion. L'angle de diffusion est fixé à 16°. Le porte échantillon est intégré à un dispositif Peltier pour le contrôle de la température, entre -1O0C et 8O0C, ainsi qu'à un électroaimant (jusqu'à 1.5 kOe au niveau de l'échantillon). Figure 4 is a diagram showing the magnetization of the upper layer and the lower layer as a function of temperature. The magnetic behavior of the sample is observed by resonant magnetic X-ray scattering (X-ray Magnetic Scattering (XRMS) in English), using circularly polarized X-rays. By adjusting the photon energy at resonances Mn-2p (about 640 eV) or Fe-2p (about 707 eV), the specular reflected intensity is sensitive to the magnetization of the MnAs layer or the Fe layer, respectively . The data are collected in coplanar geometry, the bands being oriented orthogonally to the diffusion plane. The diffusion angle is set at 16 °. The sample holder is integrated in a Peltier device for temperature control, between -1O 0 C and 80 ° C, as well as an electromagnet (up to 1.5 kOe at the sample).
Pour une résonance donnée, le taux d'asymétrie est proportionnel au moment magnétique de l'élément. Le signal magnétique (taux d'asymétrie) du Fe est représenté par la courbe commençant en haut de la figure 4 et s'achevant en bas de la figure 4, tandis que le signal magnétique (taux d'asymétrie) de MnAs est représenté par la courbe sensiblement horizontale située au milieu de la figure 4. Après application d'une impulsion magnétique de 1 kOe à 80C, la température de l'échantillon est portée de 80C à 180C (carrés pleins), puis de 180C à 80C (carrés creux), sans application de champ magnétique. For a given resonance, the asymmetry rate is proportional to the magnetic moment of the element. The signal magnetic (asymmetry rate) of Fe is represented by the curve starting at the top of Figure 4 and ending at the bottom of Figure 4, while the magnetic signal (asymmetry rate) of MnAs is represented by the curve substantially horizontal located in the middle of Figure 4. After applying a magnetic pulse of 1 kOe at 8 0 C, the temperature of the sample is increased from 8 0 C to 18 0 C (solid squares), then 18 0 C at 8 0 C (hollow squares), without application of magnetic field.
La figure 5 montre les cycles d'hystérésis de Fe et de MnAs à 80C, représentant l'aimantation de Fe et de MnAs en fonction du champ magnétique appliqué. L'impulsion magnétique prépare l'état initial du cycle thermique avec une direction d'aimantation identique pour la couche de Fe et la couche de MnAs. On observe que le couplage entre les deux couches est faible, puisque les champs coercitifs des deux couches sont très différents. FIG. 5 shows the hysteresis cycles of Fe and MnAs at 8 ° C., representing the magnetization of Fe and MnAs as a function of the applied magnetic field. The magnetic pulse prepares the initial state of the thermal cycle with an identical magnetization direction for the Fe layer and the MnAs layer. It is observed that the coupling between the two layers is weak, since the coercive fields of the two layers are very different.
En se référant à nouveau à la figure 4, le procédé débute à 80C avec une direction d'aimantation identique pour la couche de Fe et la couche de MnAs. Lorsque la température augmente, l'aimantation de la couche de Fe reste sensiblement constante jusqu'à ce qu'apparaisse la phase β-MnAs, vers 130C. Ceci est confirmé lorsqu'on observe l'évolution du taux de β-MnAs dans MnAs en fonction de la température, tel que représenté à la figure 6. Entre 13 et 160C, l'aimantation du Fe diminue rapidement, puis s'inverse. Au-delà de 160C, les zones de β- MnAs sont suffisamment larges pour entraîner une modification irréversible de la direction de l'aimantation. Ainsi, lorsque l'on fait ensuite descendre la température jusqu'à la valeur initiale de 80C, l'aimantation de la couche de Fe reste de direction opposée à celle de la couche de MnAs, bien que la température soit identique à celle du début du procédé et que le procédé se déroule ave un champ magnétique appliqué nul. Ainsi, un léger réglage de la microstructure MnAs/GaAs par un contrôle de la température permet une inversion complète de la direction d'aimantation de la couche de Fe, sans application de champ magnétique. L'inversion de l'aimantation peut être obtenue localement en utilisant un rayonnement laser focalisé. Ainsi, une variation structurale équivalente à une augmentation de température de 50C peut être obtenue par irradiation avec une impulsion laser. On peut par exemple utiliser des impulsions laser (λ=400nm) d'une durée de ICT13 S, chaque impulsion déposant une densité d'énergie d'environ 100 μJ/mm2. La variation structurale a lieu sur une échelle de temps d'environ 10'11 s. Referring again to Figure 4, the process starts at 8 0 C with the same magnetization direction for the Fe layer and the MnAs layer. When the temperature increases, the magnetization of the Fe layer remains substantially constant until the β-MnAs phase appears, around 13 ° C. This is confirmed when the evolution of the β-MnAs level is observed. in MnAs depending on the temperature, as shown in Figure 6. Between 13 and 16 0 C, the magnetization of Fe decreases rapidly, then reverses. Beyond 16 0 C, the zones of β-MnAs are wide enough to cause irreversible modification of the direction of magnetization. Thus, when the temperature is then lowered to the initial value of 8 ° C., the magnetization of the Fe layer remains opposite to that of the MnAs layer, although the temperature is identical to that of the MnAs layer. from the beginning of the process and that the process proceeds with a zero applied magnetic field. Thus, a slight adjustment of the MnAs / GaAs microstructure by a temperature control allows a complete reversal of the magnetization direction of the Fe layer without the application of a magnetic field. The inversion of the magnetization can be obtained locally by using focused laser radiation. Thus, a structural variation equivalent to a temperature increase of 5 0 C can be obtained by irradiation with a laser pulse. For example, it is possible to use laser pulses (λ = 400 nm) with a duration of ICT 13 S, each pulse depositing an energy density of approximately 100 μJ / mm 2 . The structural variation takes place on a time scale of about 10 '11 s.
La figure 7 illustre une application particulière du procédé selon l'invention, dite « témoin de température ». On dispose sur un substrat 8 plusieurs ensembles A,B,C constitués d'une couche supérieure 2 de Fe et d'une couche inférieure 3 de MnAs, tel que décrit ci-dessus. A l'aide d'un détecteur d'aimantation, non représenté, tel que par exemple un capteur utilisant l'effet Kerr, on détecte si l'aimantation des couches 2,3 est en configuration parallèle (cas des ensembles A et C) ou antiparallèle (cas de l'ensemble B). Si la configuration est antiparallèle, on en déduit alors que la température locale du substrat 8 dépasse ou a dépassé la température seuil à partir de laquelle se produit l'inversion d'aimantation de la couche supérieure 2.  Figure 7 illustrates a particular application of the method according to the invention, called "temperature control". A plurality of sets A, B, C consisting of an upper layer 2 of Fe and a lower layer 3 of MnAs, as described above, are placed on a substrate 8. With the aid of a magnetization detector, not shown, such as for example a sensor using the Kerr effect, it is detected whether the magnetization of the layers 2,3 is in a parallel configuration (case of the sets A and C) or antiparallel (case of set B). If the configuration is antiparallel, it follows that the local temperature of the substrate 8 exceeds or has exceeded the threshold temperature from which the reversal of magnetization of the upper layer 2 occurs.
Le procédé selon l'invention présente ainsi de nombreux avantages. La modification de la direction d'aimantation de la couche supérieure est contrôlée uniquement par la température. Il n'est pas nécessaire d'appliquer un champ magnétique par une bobine ou un aimant externe. La modification de la direction d'aimantation se produit sur un faible écart de température, ce qui nécessite peu d'énergie. Le chauffage local s'effectue sur une durée très courte, qui peut être de l'ordre de 10'11 s avec un chauffage par absorption d'un rayonnement laser. En outre, le changement de direction d'aimantation peut s'effectuer sur une petite distance, de l'ordre de 200 nm pour la matrice MnAs/GaAs. The method according to the invention thus has many advantages. The modification of the magnetization direction of the upper layer is controlled solely by the temperature. It is not necessary to apply a magnetic field by a coil or an external magnet. The change of the magnetization direction occurs on a small temperature difference, which requires little energy. The local heating is carried out for a very short time, which can be of the order of 10 '11 s with a heating by absorption of radiation laser. In addition, the change of magnetization direction can be carried out over a small distance, of the order of 200 nm for the matrix MnAs / GaAs.

Claims

REVEN DICATIONS REVEN DICATIONS
1. Procédé de modification de la direction d'aimantation d'une couche supérieure (2) comprenant un matériau ferromagnétique, caractérisé en ce que : a) la couche supérieure (2) est disposée au-dessus d'une couche inférieure (3) non couplée magnétiquement avec la couche supérieure (2), la couche inférieure (3) comprenant un matériau apte à produire ou non, suivant que la température dudit matériau est supérieure ou inférieure à une valeur seuil, un champ magnétique rayonné susceptible de modifier la direction d'aimantation de la couche supérieure (2), le champ magnétique rayonné par le matériau de la couche inférieure (3) étant supérieur au champ coercitif du matériau ferromagnétique de la couche supérieure (2), et en ce que le procédé comprend : b) une étape consistant à faire passer la température de la couche inférieure (3) d'une première valeur, pour laquelle les directions d'aimantation de la couche supérieure (2) et de la couche inférieure (3) sont dans une configuration relative stable et pour laquelle le matériau de la couche inférieure (3) ne produit pas de champ magnétique rayonné, à une deuxième valeur, pour laquelle le matériau de la couche inférieure (3) produit un champ magnétique rayonné susceptible de modifier de manière irréversible la direction d'aimantation de la couche supérieure (2), et c) une étape consistant à faire passer la température de la couche inférieure (3) de la deuxième valeur à une troisième valeur pour laquelle le matériau de la couche inférieure (3) ne produit pas de champ magnétique rayonné, les étapes de variation de température b) et c) étant effectuées sans application de champ magnétique extérieur. A method of modifying the magnetization direction of an upper layer (2) comprising a ferromagnetic material, characterized in that: a) the upper layer (2) is disposed above a lower layer (3) not magnetically coupled with the upper layer (2), the lower layer (3) comprising a material capable of producing or not, depending on whether the temperature of said material is greater or less than a threshold value, a radiated magnetic field capable of modifying the direction magnetizing the upper layer (2), the magnetic field radiated by the material of the lower layer (3) being greater than the coercive field of the ferromagnetic material of the upper layer (2), and in that the method comprises: b ) a step of passing the temperature of the lower layer (3) by a first value, for which the magnetization directions of the upper layer (2) and the lower layer (3) are in a stable relative configuration and for which the material of the lower layer (3) does not produce a radiated magnetic field, at a second value, for which the material of the lower layer (3) produces a radiated magnetic field irreversibly modifying the magnetization direction of the upper layer (2), and c) a step of changing the temperature of the lower layer (3) of the second value to a third value for which the material of the lower layer (3) does not produce a radiated magnetic field, the temperature variation steps b) and c) being carried out without applying an external magnetic field.
2. Procédé selon la revendication 1, caractérisé en ce que le matériau de la couche inférieure (3) est apte à produire un champ magnétique rayonné susceptible de modifier la direction d'aimantation de la couche supérieure (2) lorsque la température dudit matériau est supérieure à une valeur seuil. 2. Method according to claim 1, characterized in that the material of the lower layer (3) is able to produce a radiated magnetic field capable of modifying the magnetization direction of the upper layer (2) when the temperature of said material is greater than a threshold value.
3. Procédé selon la revendication 1, caractérisé en ce que le matériau de la couche inférieure (3) présente, suivant que la température du matériau est inférieure ou supérieure à une valeur seuil, une structure homogène entièrement ferromagnétique ou une structure inhomogène comprenant une alternance de zones ferromagnétiques et non ferromagnétiques. 3. Method according to claim 1, characterized in that the material of the lower layer (3) has, depending on whether the temperature of the material is lower or higher than a threshold value, a homogeneous structure entirely ferromagnetic or an inhomogeneous structure comprising an alternation ferromagnetic and non-ferromagnetic zones.
4. Procédé selon la revendication 3, caractérisé en ce que le matériau de la couche inférieure (3) présente une structure homogène lorsque la température du matériau est inférieure à une température seuil, et en ce qu'il présente une structure inhomogène lorsque la température du matériau est supérieure à une température seuil. 4. Method according to claim 3, characterized in that the material of the lower layer (3) has a homogeneous structure when the temperature of the material is below a threshold temperature, and in that it has an inhomogeneous structure when the temperature material is greater than a threshold temperature.
5. Procédé selon la revendication 4, caractérisé en ce que la couche inférieure (3) est une couche de MnAs formée par épitaxie sur un substrat de GaAs. 5. Method according to claim 4, characterized in that the lower layer (3) is a layer of MnAs epitaxially formed on a GaAs substrate.
6. Procédé selon la revendication 3, caractérisé en ce que la structure inhomogène de la couche inférieure (3) est obtenue par implantation ionique dans la couche inférieure (3). 6. Method according to claim 3, characterized in that the inhomogeneous structure of the lower layer (3) is obtained by ion implantation in the lower layer (3).
7. Procédé selon la revendication 6, caractérisé en ce que la couche inférieure (3) est une couche d'alliage FePd, FeNi, NiMn, FeGa ou FePt. 7. Process according to claim 6, characterized in that the lower layer (3) is a layer of FePd, FeNi, NiMn, FeGa or FePt alloy.
8. Procédé selon l'une des revendications 1 à 7, caractérisé en ce que la couche supérieure (2) est une couche de Fe, Ni, Co, ou d'un alliage ferromagnétique comprenant au moins un de ces éléments. 8. Method according to one of claims 1 to 7, characterized in that the upper layer (2) is a layer of Fe, Ni, Co, or a ferromagnetic alloy comprising at least one of these elements.
9. Procédé selon l'une des revendications 1 à 8, caractérisé en ce qu'une couche de matériau non ferromagnétique est disposée entre la couche inférieure (3) et la couche supérieure (2). 9. Method according to one of claims 1 to 8, characterized in that a layer of non-ferromagnetic material is disposed between the lower layer (3) and the upper layer (2).
EP10745299A 2009-06-29 2010-06-22 Method for changing the direction of magnetization in ferromagnetic layer Withdrawn EP2449567A1 (en)

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FR0954403A FR2947375B1 (en) 2009-06-29 2009-06-29 METHOD FOR MODIFYING THE MAGNETIZATION DIRECTION OF A FERROMAGNETIC LAYER
PCT/FR2010/051274 WO2011001068A1 (en) 2009-06-29 2010-06-22 Method for changing the direction of magnetization in ferromagnetic layer

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WO2011001068A1 (en) 2011-01-06
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FR2947375A1 (en) 2010-12-31
JP2012531691A (en) 2012-12-10
US20120129115A1 (en) 2012-05-24

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