Sensor component incorporating nanomagnets

FIELD: metallurgy.

SUBSTANCE: proposed sensor component that uses axial symmetry to impart magnetic properties to materials has magnetic material in the form of nanomagnets whose sides measure 40 - 500 nm and thickness is 3 - 10 nm; they function as zero-hysteresis superparamagnetic components.

EFFECT: use of configurational anisotropy through component symmetry to set magnetic properties and to ensure zero hysteresis.

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The technical field

The present invention relates to magnetic materials, in particular to the use of axial symmetry to set the magnetic properties of materials.

Prior art

The amount of information that can be stored on the hard drive of the computer has increased 10⁷times over the last 40 years and, apparently, will continue to increase exponentially over the coming decades. Traditionally used in modern magnetic materials will be unable in the future to meet the requirements of the industry performance requirements for storing data on magnetic media. One of the currently considered variants of solving this problem is joint use of nanotechnology and quantum mechanics for the manufacture of magnetic particles of nanometer scale, called nanomagnetism. The latter, due to their very small size, have magnetic properties that differ from the original three-dimensional (solid) material. Each nanomagnet similar giant atom artificial element that allows the formation of new magnetic materials (nanomagnetite) by forming one giant atom after another giant atom. Rapidly developing area of nanomag is Eisma can provide, in addition, advanced alternative media for hard disk drives and a new generation of high-speed non-volatile computer memory chips with low power consumption.

The most important property of natural magnetic element or alloy is its anisotropy. It is the presence of preferred directions of magnetization in such material and, ultimately, it is responsible for the behavior of magnetic material, and determines the suitable technological applications. In traditional magnetic material anisotropy due to the shape and symmetry of the electronic Fermi surface and therefore is characteristic of a specific element or alloy and may not be a simple image set (changed). In nanomagnetic, however, the anisotropy depends not only on the band structure of the source material, but also on the shape of nanomagnet. One of the most attractive characteristics of artificial magnetic materials is that their magnetic properties can be specified in the select form components of their nanomagnets.

Disclosure of inventions

In accordance with the present invention proposed a sensor element containing nanomagnetic with the size of the parties 40-500 nm and a thickness of 3-10 nm, with a geometric axial symmetry rotations is of 3 or 5 of the order and which superparamagnetic particles with zero hysteresis.

The device of the present invention is an artificial magnetic materials formed on a substrate such as a substrate of silicon using electron beam lithography. Such devices may have dimensions in the range of 40-500 nm and a thickness in the range of 3-10 nm and can have a triangular or pentagonal geometry, which corresponds to the axial symmetry of the 3-rd and 5-th order. The procedure may, however, large. Source material may be supermalloy (Ni₈₀Fe₁₄Mo₅), which was selected for two reasons. First, this alloy is, by its nature, is almost isotropic, and therefore, any anisotropy in nanomagnets must come from their form. Secondly, supermalloy and like him not containing molybdenum permalloy are two soft-magnetic alloys, widely used in industry and in scientific research, and as such are effectively new and changed properties, which can be attributed to simple material by nanometer structuring. As will be shown below, the authors of the present invention can give an artificial magnetic materials magnetic properties in a very wide range simply by changing the symmetry of the components of their nanomagnets.

Brief description of drawings

Below describe the Xia related to the present invention of examples with reference to the accompanying figures of the drawings, including:

Figure 1 depicts a micrograph obtained in the scanning electron microscope, some artificial magnetic materials;

Figure 2 depicts the hysteresis loop for nanomagnets various sizes, thickness and geometric shapes;

Figure 3 depicts the hysteresis loop of superparamagnetic particles triangular nanomagnet;

Figure 4 depicts the experimentally measured coercivity depending on the size of nanomagnet;

Figure 5 depicts the experimentally measured anisotropy field inside various nanomagnets;

6 depicts a core member of the anisotropy figure 5, expressed as a field (A) anisotropy and the energy (In) anisotropy on one nanomagnet for different nanomagnets;

Fig.7 depicts the magnetic susceptibility depending on the size and symmetry of nanomagnets; and

Fig depicts a schematic design of superparamagnetic particles of nanomagnet when used as a magnetic field sensor or logic element.

Preferred embodiments of the inventions

Standard inverse process of electron-beam lithography may be used to form devices in accordance with the present invention. The substrate sample was selected oriented monocrystalline silicon. The distance between the home is the nits was always at least equal to the diameter of nanomagnet, and for the smallest structures it was up to 3 diameters. The surface roughness of nanomagnets was less than 0.5 nm, and the microstructure showed the presence of randomly oriented 5-nanometer grains. The upper surface of each nanomagnet was covered with a layer of gold with a thickness of 5 nm to prevent oxidation. It was found that the integrity of the geometric shape was preserved in structures with sizes up to 50 nm. Figure 1 shows pictures of some of the structures obtained in the scanning electron microscope.

In order to determine the magnetic properties of these various synthetic materials the authors of the present invention have measured their hysteresis loops (loops M-N) using well-known high-sensitivity magneto-optical method. The silicon surface can be viewed through the optical microscope, while the laser spot (size ≈5 μm) is moved over the surface until, until you focus on the upper part of one of the sections of synthetic material. The reflected laser beam is subjected to polarization analysis to achieve the meridional Kerr effect, which serves as an indicator to detect the component of the magnetization, which lies in the optical plane of incidence. This magnetization in the future reg the exhibits under the application of an alternating magnetic field frequency of 27 Hz with intensity up to 1000 e in the sample plane. All measurements were performed at room temperature.

Figure 2 and 3 shows some hysteresis loops measured at nanomagnets with different size, thickness and geometry. It seems obvious that the loops are very different from each other and from those obtained from conventional unstructured material. Noteworthy is the variety of technological applications covered by the samples shown on this drawing. Known small rectangles shown in Figv may be suitable for the manufacture of artificial substitute media for hard disk drives used in this case, nanomagnet in principle can achieve densities of data storage of more than 100 Gbit/square inch, that is 10 times greater than that traditionally used today media known from the prior art. Known large rectangles on Fig.2D well suited for magnetic memory with random access (MH) is a close alternative to semiconductor memories: memory chip using magnetic elements of this size may have a capacity of 1 GB non-volatile high-speed memory. Unexpected is the fact that a wide range of magnetic properties is found in the triangular and pentagonal nanomagnets. Triangular nanomagnet on f is he, which have a high residual magnetic induction and low coercive force, can be used as a memory element (memory element), while the pentagonal nanomagnets on Fig.2F and superparamagnetic particles triangular elements figure 3 can be made of high-quality magnetic field sensors with high sensitivity or read heads for hard disk drives, having an effective relative magnetic permeability of 3000 and zero hysteresis. These diverse applications are a direct result of changes in the size, thickness, and, most importantly, the symmetry of nanomagnets, which form artificial material.

In order to quantify this important effect by the authors of the present invention was measured coercive force, on the basis of the hysteresis loops depending on the size, thickness and order of symmetry of nanomagnets. Coercivity is a measure of the applied field required to reduce the magnetization to zero (i.e. hysteresis loop has a Central width equal to twice the coercive force), and is essentially a measure of how easily an external field can reverse the direction of magnetization of nanomagnets. The coercive force is a key parameter when assessing the suitability Yes the aqueous magnetic material for technological applications. Figure 4 presents the results, which, in order to be able to compare different geometry, size nanomagnets was expressed by the authors through the square root of their area (measures of length). The authors confirmed the repeatability of some of these experimental results on the second set of samples.

The first sign, the obvious way as follows from the figure 4 data, is that double and fourfold symmetry demonstrate the behavior of the same type, while the three-fold and five-fold symmetry demonstrate the behavior of another type: nanomagnet with double/quadruple symmetry have a high coercive force, which first increases with decreasing measures of length; nanomagnet with three/five-fold symmetry have a low coercive force, which goes to zero with decreasing measures of length. The second conclusion that can be made regarding Figure 4, is that in all cases, the increase in thickness leads to a strong increase in the coercive force, which is not in unstructured magnetic films.

The behavior of nanomagnets with twofold symmetry is very predictable and due to the well-known phenomenon, called shape anisotropy. The magnetization prefers to "sort" the longest axis of nanomagnet for minimizer is of square surfaces of the poles. Field that creates this effect, is the demagnetizing field which passes between the surfaces of the poles inside the magnet. Demagnetizing field is scaled approximately with the ratio t/a, where t is the thickness of nanomagnet, and his size, and Figa it is seen that the coercive force increases with decreasing size.

The effects observed in the case of three -, four-and five-fold symmetry, in contrast, to understand is not so simple. This is because the demagnetizing field of any structure describes a Cartesian tensor of the second rank, and so may be only uniaxial (double) symmetry. Therefore, there is no shape anisotropy, at least in the usual sense, in the plane of these structures with the symmetry of a higher order. However, square nanomagnet undoubtedly have some moderately strong opposition to changing the direction of magnetization, and thus some anisotropy should still attend. The fact that this anisotropy is undoubtedly weaker in the triangular magnets, proves that, although it is not the classic shape anisotropy, it is still linked with the form of nanomagnet.

Square nanomagnets inherent recently a public property named configuration anisotropy. It is associated with a very small off what changes from uniform magnetization, which is almost all nanomagnetic. Up to the present time has not been clarified to what extent this new anisotropy important in determining the magnetic properties of nanomagnets. To test the hypothesis that the different behaviour, which can be seen in Fig. 2-4, due to the configuration of the anisotropy, the authors performed a direct measurement of the anisotropy in nanomagnets using the method, which the authors call the magneto-optical anisometry with modulated field. In this method, in the plane of nanomagnets put in a strong static magnetic field H (=350 OE), while the weaker vibrating (oscillating) the field H_t(with an amplitude of 14 e) is applied in the plane of nanomagnets, but perpendicular to N. The amplitude of the resulting oscillations of the magnetization recorded the same magneto-optical method used to obtain the hysteresis loops in figure 2 and 3, and is directly related to the amplitude and symmetry of any anisotropy in nanomagnets. The authors have experimentally measured anisotropy in the case of triangular, square and pentagonal nanomagnets in the size range 50-500 nm at a thickness of 5 nm, and the obtained results are presented in figure 5. The presented polar diagrams angle determines the in-plane direction φ nanomagnet, the radius op is delaet radius nanomagnet in this direction, and the tone determines the experimentally measured valuefor nanomagnet with the same size, where M_Sthe saturation magnetization (800 edgs cm^-3), and E(φ) - the average density of the magnetic energy of nanomagnet when the magnetization direction φ. Although H₂is not the generally accepted definition of the field of anisotropy, it is possible to show that any fluctuations in N₂have the same symmetry as the underlying anisotropy and amplitude equal to the magnitude of the anisotropy field. Figure 5 shows the experimental data for 22 different samples of the artificial magnetic material (8 sizes of triangles, 8 sizes of squares and 6 sizes pentagons), and each was measured either 19 or 37 different directions φ (0-180° steps 10° for triangles and squares, 0-180° steps 5° for pentagons), and the total number of measurements amounted to 526.

From Figure 5 clearly implies that there are strong anisotropy field in all the investigated nanomagnetic. Triangular nanomagnet exhibit anisotropy with sixfold symmetry, square nanomagnet exhibit anisotropy with fourfold symmetry, and pentagonal nanomagnet have a noticeable anisotropy with tenfold symmetry. Doubling symmetry occurs in t is ugolnik and pentagonal structures, because energy is always quadratic in the magnetization, and therefore the odd orders of symmetry may not be supported.

The authors used the diagrams in Figure 5 Fourier analysis in order to obtain the amplitude of the anisotropy fields depending on the size of nanomagnets and symmetry, and the results obtained are shown in two different types of figure 6. On Figa, the authors have built a dependency graph directly anisotropy field, while Figv authors depicted a graph of the dependence of anisotropy energies one nanomagnet (in units of kt, where K is the Boltzmann constant, and T is equal to 298K) using theoretical dependencies. In this equation, U_a- energy anisotropy one nanomagnet (in ergs), N_and- anisotropy field (in oersteds), n is the order of symmetry of anisotropy (4 - squares, 6 - triangles, 10 - pentagons) and V is the volume (in cm³) nanomagnet. According to the authors ' understanding important element of influence of symmetry order on the magnetic properties is in this equation, a member of the n². This means that, although all geometry demonstrate approximately similar field anisotropy on Figa, they demonstrate the very different energy anisotropy on Figv.

Energy anisotropy is of particular interest because of the phenomenon called what superparamagnetism, which is the process in which energy anisotropy barriers can be overcome due to the fluctuations of thermal energy kt in nanometer-scale magnets. As a rough guide to action, the barrier can be overcome in the time scale under consideration by the authors of the measurements, if its height is less than 10 kt. This means that, if the energy of anisotropy is less than 10 kt, one can expect that the coercive force of will quickly drop to zero. According Figv in the case when the element size is less than about 150 nm, and squares this fall with decreasing size is very weak. Conversely, if the energy of anisotropy is more than 10 kt, the coercive force is about to repeat field anisotropy. This explains the difference in behavior that can be observed in figure 4 between the squares on one side and triangles and pentagons on the other. Field anisotropy of squares (Figa) has a peak (maximum) during the reduction of the size of the elements, and this peak is directly reflected in the data on the coercive force of squares (Figs). Field anisotropy pentagons does not show any peak, and it also directly affects data on the coercive force (Fig), while falling to zero occurs when several who are larger in the case of data on coercive force, than in the case of a field anisotropy, due to thermal activation (thermal excitation). Finally, field anisotropy triangles really is peak, just as in the case of the square, but because the anisotropy energies of the triangle is smaller, thermal activation occurs when a larger size and prevents the appearance of a peak in the data for the coercive force (Pigv). Thus, the authors of the present invention is able to explain the experimentally defined data coercive force as resulting from the combination of the configuration of anisotropy and thermal activation.

Materials with high residual magnetic induction with limited coercive force (and therefore memory function), are not only technologically important magnetic materials. Equally important are the materials with zero residual magnetic induction and zero coercive force, which are used in magnetic sensors and logic elements, and in this case, it is the magnetic susceptibility χ is a key parameter. Susceptibility χ is defined as 4π∂M/∂H, where M is the magnetization of nanomagnets, and H is the applied magnetic field. Susceptibility χ is directly proportional to the slope of the hysteresis loop zero field, such as is shown in Fig.2F. The authors have measured the susceptibility χ using the above-mentioned magneto-optical experiment (at a frequency of 27 Hz) depending on the size of nanomagnet and symmetry at a constant thickness of 3.7±0.5 nm, and the obtained results are shown in Fig.7. Susceptibility χ has a value only when the coercive force is equal to zero, and the authors have limited themselves of this opportunity. For comparison, the diagram also plot theoretical magnetic susceptibility, derived from the Langevin function. It is a statistical thermodynamic representation, which is applied to one giant back in free space. When considering Fig.7 we can come to three conclusions. First, all experimentally defined magnetic susceptibility least nanomagnets close to the Langevin model in free space, despite the failure of the approximation parameters, which proves that good control of the experimental system. Second, deviations from the Langevin model are greatest for nanomagnets with square symmetry. This is consistent with the fact that they have the largest energy configuration anisotropy, and this means that the giant spin, available square nanomagnets, in the least degree like a Gian the WMD back in free space. It configurational anisotropy ultimately causes the deviation from the model Langevin for all types of symmetry with increasing size. Thirdly, as measured here, the magnetic susceptibility is two orders higher than the values that would be obtained from the magnetic particles with the same shape and aspect ratio, but is made in a larger scale of a nanometer (i.e. micrometers and above who use the most conventional magnetic field sensors). In this latter case, the magnetic susceptibility due to the motion of domain walls against internal demagnetizing field, which can be very strong. Thus clearly demonstrated the unique role of structuring in the nanometer scale.

4 and 5 illustrate well the manner in which nanometer structuring truly emulates the creation of new magnetic materials. Supermalloy grown with a face-centered cubic (FCC) crystal lattice, which usually leads to anisotropy with a twofold or fourfold symmetry. However, Figa shows a sixfold symmetry, which usually belongs to the materials with hexagonal close-Packed crystallographic lattice. In this case, the symmetry of the shape nanomagnet (triangular) can the be used to simulate changes in crystallographic phase. Similarly, a relatively high coercive force square and rectangular nanomagnets (Figa and Figs) generally found in magnetic materials with high anisotropy and weak microstructure. In this case, the careful choice of the symmetry of nanomagnet emulates the change in the item and the change in the microstructure. Finally, elementary crystallography dictates that the lattice cannot have a ten-fold symmetry, and therefore we should not expect the discovery of natural crystalline element or alloy with a tenfold symmetry of the magnetic anisotropy. Figs, however, shows that the authors have successfully created one such element artificially using nanostructuring. In this case it was used nanometer molding to give a crystalline material properties, which is usually found in quasicrystals.

On Fig schematically shows a possible model of the device that uses the superparamagnetic particles nanomagnet as part of the sensor or logic element. Three-layer spin valve 12 is connected on both sides with connecting lines 14. The valve 12 includes a lower magnetic layer 16, the nonmagnetic spacer layer 18 and one or more nanomagnets 20 in super-paramagnetic state as the top of the layer. Arrow 22 indicates the current passing through the valve 12, and the arrow 24 indicates the magnetization in the magnetic lower layer 16.

In conclusion, it should be noted that the authors had determined the effect of symmetry forms nanomagnets on their magnetic properties, and this effect was used in practically important applications. The authors found that symmetry plays an important role, allowing you to control the magnetic properties within a wide range. It was shown that a key effect of linking the symmetry of the magnetic properties is the configurational anisotropy. This allows you to create new artificial magnetic material in which magnetic properties can be adjusted (set) for a particular application with a very high degree of precision.

The first new idea is the use of the configuration anisotropy through the symmetry of the element to set the magnetic properties. To date, the experts in this field of technology considered only rectangular, square or circular elements. The authors of the present invention have determined that the configurational anisotropy caused by other forms, such as triangles, pentagons and hexagons can be used to control the magnetic properties of the element. The second new idea is that IP is the use of superparamagnetism in nanostructures to eliminate hysteresis. In ordinary materials superparamagnetism leads to very strong fields saturation and as such is not used in magnetic sensors. However, the authors of the present invention have shown here that in nanostructures superparamagnetism can lead to very weak fields saturation (several OE - see Fig.2F). By itself, this fact can be very useful for sensor and logic element. But even more interesting is the fact that superparamagnetism ensures almost zero hysteresis, which is a necessary requirement for a good sensor (see figure 3). The biggest problem faced when using currently nanostructures as sensors, is the fact that usually the hysteresis becomes larger with decreasing transverse dimensions of the device.

These two ideas can be combined by adding the configuration of the low anisotropy values by choosing an appropriate shape (triangular, pentagonal or circular), which allows the nanostructure become superparamagnetic particles and, therefore, function as a good sensor or logic element.

1. The sensor element containing a magnetic material, wherein the magnetic material is made in the form of nanomagnets with the size of the parties 40-500 nm and a thickness of 3-10 nm, having the geometrical what kind of axial symmetry of rotation 3 or 5 of the order and which superparamagnetic particles with zero hysteresis.

2. The sensor element according to claim 1, characterized in that nanomagnet formed from artificial magnetic material on the surface of the substrate, with their axis of rotation perpendicular to said surface.

3. The sensor element according to claim 1 or 2, characterized in that the magnetic material is made of superalloy Ni₈₀Fe₁₄Mo₅.