JP2004523928A - Method for determining reference magnetization in layered systems - Google Patents

Abstract

The invention relates to a method for determining a reference magnetization, which relates to the area of material technology and can be used, for example, for elements in magnetic sensor technology. It is an object of the present invention to provide a method for determining a reference magnetization in a layer system, in which the reference direction can be chosen arbitrarily in terms of number and spatial direction. The object is to provide a method for determining a reference magnetization in a layer system in which a hard magnetic layer and / or a soft magnetic layer are geometrically structured and a hard magnetic layer is formed before, during or after one or more stages of heat treatment. Producing at least one layer system by depositing a layer and / or a soft magnetic layer on at least one antiferromagnetic layer, wherein the temperature increase is performed at least above the coupling temperature and subsequently the layer system It is solved by making it cool.

Description

【Technical field】
[0001]
The present invention relates to the field of materials technology and is advantageously used, for example, for elements in magnet-sensotronic (magnetic sensor technology) or spin-electronics, for example GMR sensors or MRAM memory cells, The present invention relates to a method for determining a reference magnetization.
[0002]
Utilizing exchange coupling between ferromagnetic magnets and antiferromagnetic magnets (Antiferromagnet = AFM) or artificial antiferromagnetic magnets (Artical Anti Ferromagnet = AAF) to fix the magnetization in magnetic layer systems It is known to
[0003]
Devices in magnet sensotronic or spin electronic often require a spatially fixed reference magnetization direction. For this purpose, a magnetic coupling to the so-called "anchor layer" is often used. This anchor layer may consist of a hard magnet and a natural or artificial antiferromagnetic magnet. The exchange direction between the ferromagnetic magnet and the anchor layer spatially fixes the magnetization direction of the ferromagnetic layer.
[0004]
This anchor layer itself must likewise be magnetically oriented. To this end, the following methods have hitherto been used, depending on the material properties of the anchor layer;
Layer deposition in external magnetic field Thermal post-treatment in external magnetic field Magnetic field cooling after local laser irradiation.
[0005]
These in all three cases be implemented effective magnetic field cooling (field Cooling), i.e. systems: conditions that are above the ferromagnetic magnet / anchor layer have a magnetic field is applied critical bonding temperature (blocking temperature T _B) To the combined state. Thereby, the homogeneous magnetization of the ferromagnetic layer, forced by the magnetic field, is imprinted in the spin configuration of the antiferromagnetic layer by direct exchange coupling. When the external magnetic field strength is equal to or less than the coupling magnetic field strength, the adjusted and uniform magnetization of the ferromagnetic layer is maintained and is therefore used as the reference magnetization.
[0006]
Only the last of the methods listed above can locally change the reference magnetization in the region of focus of the laser beam.
[0007]
A disadvantage of this known method is that, apart from the laser method, multiple reference directions cannot be realized simultaneously with one another in any direction. This is necessary for the operation of complex magneto-electric elements such as, for example, angle sensors.
[0008]
Finally, a process after the orientation of the AFM is required, and there is a limit to miniaturization of the micro size.
[0009]
It is furthermore known that in soft magnetic layer elements, the magnetization is oriented along the element edges so that stray magnetic fields are avoided. This results in a closed arrangement of the magnetic flux. As discovered by van den Berg, magnetization remains parallel to adjacent element edges even inside the element. Different magnetic regions collide at having the same distance to the two element edges. This results in a state having homogeneous magnetic domains separated by magnetic domain walls.
[0010]
It is well known that mutually distinct elements interact when their distance is small enough via their stray magnetic fields. In order to reach an energetically favorable state, the neighboring elements adopt a magnetization arrangement which is close to the closed magnetic flux and causes only a small stray magnetic field.
[0011]
DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a method for determining a reference magnetization in a layer system, in which the reference direction can be chosen arbitrarily in terms of number and spatial direction.
[0012]
This problem is solved by the invention described in each claim. Embodiments are the subject of the dependent claims.
[0013]
In the method for determining the reference magnetization in the layer system according to the invention, the hard magnetic layer and / or the soft magnetic layer is geometrically structured and the hard magnetic layer is formed before, during or after one or more stages of heat treatment. At least one hard magnetic layer and / or soft magnetic layer is manufactured by bringing the soft magnetic layer into direct contact with the at least one antiferromagnetic layer. In this case, the heat treatment is carried out with a heat rise at least above the bonding temperature. Subsequently, the layer system is cooled.
[0014]
The layer system is preferably cooled without the application of a magnetic field, so that the demagnetized state or the remanent magnetic state is recorded without disturbance as reference magnetization.
[0015]
More preferably, after the heat treatment, the layer system is cooled in an external magnetic field and the demagnetized or remanent state changed by the magnetic field is remembered as the reference magnetization.
[0016]
Advantageously, layers are produced whose lateral extent is in the micro and nano range and the layer thickness is in the nanometer range.
[0017]
It is also advantageous to heat several layers of the same or different composition above the bonding temperature and subsequently cool them without a magnetic field.
[0018]
According to the invention, the method for determining the reference magnetization is a magnetoresistive sensor element or a magnetoresistive switching based on anisotropic or giant magnetoresistance or tunnel or spin injection resistance. Applied to devices or active magneto-electric devices based on giant magnetoresistance, tunnel magnetoresistance or spin injection resistance.
[0019]
In the method according to the invention, first the hard magnetic and / or soft magnetic layer is geometrically structured. This can be done by methods known from microelectronics, for example lithographic methods. This geometric structuring determines the shape, number and arrangement of these geometric elements. This step has a decisive effect on the magnetization direction of the hard magnetic and / or soft magnetic layer. This is because the direction of magnetization is determined in each shape by choosing a geometric shape in accordance with Van den Berg's discovered principle. Magnetic domains are formed in the shape, the magnetization of which is oriented parallel to adjacent edges. Alternatively, stray field interactions of adjacent elements can be used to form the desired magnetic domain pattern.
[0020]
In this way, any number of reference directions and optionally different reference directions can be produced in a layer system, depending on the number, shape and / or arrangement.
[0021]
According to the geometrical structuring, the magnetization configuration of the hard magnetic and / or soft magnetic layers, which is freed by the increase in temperature by heating above the coupling temperature, can be set in accordance with the magnetic domain element. become. Upon subsequent cooling without applying a magnetic field, the antiferromagnetic layer assumes the magnetization configuration of the hard and / or soft magnetic layers. Thus, the layer system has a uniform magnetization form.
[0022]
According to the method of the invention, it is also possible that the heat treatment is carried out only on the hard and / or soft magnetic layer and is only applied to the antiferromagnetic layer during or after cooling. Again, the antiferromagnetic layer assumes the magnetization configuration of the hard and / or soft magnetic layers.
[0023]
If hard- and / or soft-magnetic layers are applied or can be applied only after the production of the antiferromagnetic layer, their structuring may be effected, for example, by ion exchange controlled by mask exchange or lithography. Can be done by
[0024]
If the antiferromagnetic layer is present during the heat treatment, the magnetization of the antiferromagnetic magnet is not determined by the applied magnetic field, but by the magnetization of the exchange-coupled ferromagnetic layer.
[0025]
According to the present invention, it is also possible to apply a magnetic field during the heat treatment. The use of a decaying alternating magnetic field at this time makes the pattern adjustment settings described by Van den Berg more effective. If a sufficiently large DC magnetic field is used, a residual magnetization state can be intentionally induced.
[0026]
Another advantage of the method of the present invention is that the magnetic domain pattern of the hard and / or soft magnetic layers is maintained even at relatively high temperatures, so that the method is, for example, as with PtMn and similar materials It is also compatible with temperature processing for generating an antiferromagnetic state.
[0027]
Furthermore, it is advantageous that the reference magnetization determined by the method of the invention is reproducible (self-healing). This can only be achieved by newly heating the layer assembly above the bonding temperature. Thereby, the magnetization destroyed above the coupling temperature is adjusted and set again, and can be used again as the reference magnetization after cooling.
[0028]
If the magnetoelectric element is miniaturized, the method of the present invention can be used satisfactorily. Because it can be used over a wide range of scales. In the submicrometer range, in particular, a reliable determination of the reference magnetization can be realized.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail based on several embodiments.
[0030]
At that time it shows:
Figure 1 is an exemplary magnetization alignment of the ferromagnetic layer and antiferromagnetic layer, namely a) if the previous b) T> T _B of the heat treatment, but the T _B is a bond temperature c) after the heat treatment (layers clarity Shown separately for
2 and FIG. 2 show Kerr microscopy images of a similarly structured element with four ellipses, with the black element showing downward magnetization and the white element showing upward magnetization.
[0031]
Example 1
A mutually perpendicular reference magnetization is required for a 360 ° GMR angle sensor. For this purpose, a 10 nm thick FeMn layer is first deposited on silicon as an anchor layer and a 100 nm thick ferromagnetic Ni ₈₁ Fe ₁₉ layer is deposited thereon. Using a lithography technique, a square with a side length of 24 μm is structured. The ferromagnetic layer must be completely removed outside this structure. Then, heat treatment is performed at 200 ° C. When a temperature of 200 ° C. is reached, the sample is demagnetized in a decaying magnetic field with a maximum amplitude of 1 kA / cm and subsequently cooled to room temperature without magnetic field action. The layer system now shows a stable magnetization configuration as shown in FIG.
[0032]
Example 2
The magnetoresistive field sensor is preferably implemented in a Wheatstone bridge circuit. In order to realize mutually opposite signals of the individual elements of the Wheatstone bridge, mutually antiparallel reference magnetizations are required. Double layer consisting of FeMn and 100 nm _Ni 81 _{Fe 19} layer of 10nm is sputtered on a silicon substrate. During layer deposition, a homogeneous magnetic field with an intensity of 240 A / cm is applied. In a subsequent lithography step, four elliptical shaped elements having a lateral dimension of 100 μm × 20 μm are structured. These elements are parallel to one another and are oriented in the direction of the magnetic field during the deposition of the layers and are arranged adjacent to one another with a spacing of 30 μm. Next, heat treatment is performed at 200 ° C. Upon reaching 200 ° C., the sample is demagnetized in a decaying magnetic field with a maximum amplitude of 1 kA / cm, oriented diagonally to the element axis and subsequently cooled to room temperature without magnetic field action. The layer system now shows a stable magnetization configuration as shown in FIG.
[Brief description of the drawings]
[0033]
FIG. 1 is a schematic diagram illustrating a typical magnetization arrangement of a ferromagnetic layer and an antiferromagnetic layer.
[0034]
FIG. 2 is a schematic diagram showing a Kerr micrograph of an element structured like four ellipses.

Claims (11)

A method for determining a reference magnetization in a layer system, comprising:
Geometrically structuring the hard magnetic layer and / or the soft magnetic layer and placing the hard magnetic layer and / or the soft magnetic layer on at least one antiferromagnetic layer before or during or after one or more heat treatment steps; Producing the at least one layer system by depositing the at least one layer system, wherein the temperature increase is carried out at least above the bonding temperature and the layer system is subsequently cooled to determine the reference magnetization in the layer system. 2. The method according to claim 1, wherein the layer system is cooled without the application of a magnetic field. 2. The layer system according to claim 1, wherein the layer system is cooled while a magnetic field is being applied, wherein the magnetization arrangement of the hard magnetic and / or soft magnetic layer and / or the antiferromagnetic layer is changed depending on a desired reference magnetization. Method. The method of claim 1 wherein the layer is made to remember a magnetic field. 2. The method according to claim 1, wherein the layer has a lateral dimension in the micro and nano range and a layer thickness in the nanometer range. The method according to claim 1, wherein the layers having the same or different composition are heated above the bonding temperature and subsequently cooled without applying a magnetic field. 2. The method of claim 1, wherein the method generates a square, square, triangle, circular structuring or a shape derived therefrom. The method according to claim 1, wherein the heat treatment is performed until completely penetrated. The method according to claim 1, wherein the geometric structuring is performed two-dimensionally or three-dimensionally. 2. The method according to claim 1, wherein the hard magnetic layer and / or the soft magnetic layer are geometrically structured and deposited on the antiferromagnetic layer, followed by a one-step heat treatment with cooling. Magnetoresistance effect sensor element or magnetoresistance switching element or giant magnetoresistance effect based on anisotropic magnetoresistance effect or giant magnetoresistance effect or tunnel magnetoresistance effect or spin injection resistance of the method for determining the reference magnetization Or use for active magneto-electric devices based on tunnel magneto-resistance effect or spin injection resistance.

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