ES2566429A1 - Method and magnetic material to determine manipulation or fraud produced by the application of fields (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Method and magnetic material to determine manipulation or fraud produced by the application of magnetic fields. The invention consists of TbxFe100-x-yGay composition materials that have magnetic anisotropy properties that make it possible to use them as a sensor for tamper detection in systems sensitive to magnetic fields. The materials present a thin film, which facilitates both their camouflage and their insertion in small-sized devices. It is applied to control the manipulation or deletion of magnetically recorded documentation, or modifications in other sensitive systems such as water meters. It does not need to be continuously connected to the electrical network, which facilitates its placement in different areas and reduces maintenance costs.

Description

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Method and magnetic material to determine manipulation or fraud produced by applying fields.

Technical Sector

The present invention fits in the field the manufacture of magnetic materials. More specifically, the invention describes magnetic materials for use in document security systems and other systems sensitive to magnetic fields.

State of the art

Access to sensitive documentation by unauthorized persons is a problem still unsolved. This unauthorized access to confidential documents occurs both in public institutions (ministries, courts, hospitals, schools, ...) and in private companies. In many cases, after making a copy of the sensitive information, it is manipulated or erased with the consequent damages that it entails.

In many devices, information is stored magnetically as on hard drives. By applying magnetic fields, both manipulation and deletion of information can occur. It is important, then, to be able to develop mechanisms that allow to detect if there has been alteration of said information through the application of a magnetic field.

On the other hand, there are other systems such as water meters in which it has been seen that there are alterations in their measurements by applying a sufficiently intense magnetic field.

Systems are known that detect the presence of a magnetic field, whether produced by an electric current or by a magnet, through the deformation of a magnetic material or other techniques, as shown by

documents W02008078108 and W02003065055. Document CN201489630 describes a magnetic field detection system by magnetic labels. There are also documents describing methods of detecting magnetic fields, such as WO2014186128 and CN103914993, in which 5-coil systems or axial magnetic field sensors are used in combination with relatively complicated electronic circuits. In general, the disadvantage of these known systems is their cost, the use of electrical systems for the system to function properly and their size. In particular, the large size makes it difficult to camouflage the security device, which prevents its use to detect fraud.

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US2014133284 describes magnetic structures detected by magneto-optical systems. In this system it is verified how the change in the magnetic structure induces changes that are detected in a transducer. However, the system is used as a recording system without allowing its use as a magnetic sensor.

Therefore, there is a need for systems to determine the manipulation of information in devices sensitive to magnetic fields that have a small size that allows their insertion into small devices and, therefore, be easily transportable to be able to check if there has been manipulation or fraud in situ.

To solve this need, the present invention proposes the use of magnetic materials in the form of thin film and based on ternary alloys of Tb, Fe and 25 Ga that have two magnetic properties: moderate magnetic anisotropy perpendicular to the plane of the film and rotating magnetic anisotropy . In addition, the method described here does not require a continuous connection to the power grid, which facilitates its placement in different devices and areas to be controlled, while reducing its maintenance cost.

Although there is literature on the magnetic materials used here, ternary alloys based on Tb, Fe, and Ga [L. Jiang, J. Yang, H. Flao, G. Zhang, S.

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Wu, Y. Chen, O. Obi, T. Fitchorov, V.G. Harris, Appl. Phys. Lett. 102 (2013) 222409; T. I. Fitchorov, S. Bennet, L. Jiang, G. Zhang, Z. Zhao, Y. Chen, and V. G. Harris, Acta MAterialia 73 (2014); R. Ranchal and V. Gutiérrez-Díez, Thin Solid Films 534 (2013) 557; R. Ranchal, S. Fin, D. Bisero, and C. Aroca, J. Alloys Compd. 582 (2014) 839], the existence of rotating magnetic anisotropy (rotatable magnetic anisotropy) has not been described so far for any of the possible compositions of ternary alloys based on Tb, Fe, and Ga.

Description

Method and magnetic material to determine manipulation or fraud produced by applying magnetic fields.

The materials object of the present invention are designed and prepared in the form of a thin film and have moderate magnetic anisotropy perpendicular to the plane of the film and rotating magnetic anisotropy {rotatable magnetic anisotropy) in the surface domains. These two joint behaviors give rise to stripe-like domains whose orientation can be set by applying a magnetic field in the sample plane high enough to be able to magnetically saturate the sample. That is, the minimum detectable field will be marked by the magnetic field necessary to saturate a hysteresis cycle with the field applied in the sample plane. There is no restriction in the direction of this field unless it is contained in the sample plane.

These magnetic materials can be used to detect if there has been manipulation or erasure of magnetically recorded information by applying a magnetic field.

They can also be used to know if a sufficiently intense magnetic field has been applied in the vicinity of a sensitive area that can be altered by applying a magnetic field such as, for example, a water meter.

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The magnetic materials considered in this invention are in the form of a thin film, have a thickness of hundreds of nanometers (between 250 and 400 nm) and are based on ternary alloys of TbxFeioo-x-yGay. Due to their size, they can be inserted in a multitude of electronic devices in which the available size is usually reduced. In turn, this small size facilitates camouflage. On the other hand, the need to use nanotechnology to obtain the materials, hinders or prevents the falsification and duplication of the security system. Finally, the method described here does not require a continuous connection to the power grid. This allows both its installation in areas where there is no electrical connection (such as in the vicinity of a water meter) and the reduction in its maintenance cost.

Detailed description of the invention

The ternary alloys on which the magnetic material of the invention is based (TbxFeioo-x-yGay) are obtained by sputtering by firing two Feioo-zGaz and TbwFeioo-w targets simultaneously. For the thin film to form it is necessary that there is an angle of inclination between the targets and the substrate. The composition of the sample is controlled by varying the power of each of the targets. The process is carried out under an inert atmosphere of Ar.

The magnetic structure of these thin films is controlled by the balance between anisotropy energy and magnetostatic energy. To quantify the relationship between these two energies, parameter Q is usually defined, also known as a quality factor or reduced anisotropy. This parameter Q is given by the relationship between the anisotropy constant (Ku) and the magnetostatic energy constant (Kd). Moderate anisotropy means that material system with a factor of Q <1.

For certain compositions and growth conditions, the material obtained has a moderate magnetic anisotropy perpendicular to the plane of the sample (Q <1) with stripe-like magnetic domains on its surface, and which also results in the existence of rotating magnetic anisotropy (rotatable magnetic anisotropy).

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In the authentication process, the orientation of the domains is fixed by applying a field in a certain direction within the sample plane. Subsequently, to know if the material has been manipulated by applying another magnetic field, it is observed if the magnetic domains are oriented in a different direction than the preset.

It can also be known if there has been manipulation by applying a magnetic field by placing the material in a sensitive area, with the domains placed at random. In the event that a field greater than is necessary to saturate the sample is applied, the magnetic domains will be oriented in the direction of that field and may then know that there has been a manipulation since the domains were initially randomly oriented.

The two previous procedures can be used both to check if there has been manipulation of magnetically stored information such as fraud in counters sensitive to magnetic fields.

Description of the figures

Figure 1. Image obtained by magnetic force magnetometry of the surface magnetic domains of a sample with a composition of TbioFe7óGai4 before applying a magnetic field, with the randomly oriented domains.

Figure 2. Image obtained by magnetic force magnetometry of the surface magnetic domains of a sample with a composition of TbioFe7óGai4 after applying a magnetic field of 800 mT in the plane of the sample saturating the magnetic magnetization of the same.

Figure 3. Image obtained by magnetic force magnetometry of the surface magnetic domains of a sample with a composition of TbioFe7óGai4 with the stripe domains alienated in the direction in which the

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magnetic field in the plane of the sample that allowed to saturate the magnetization of the sample, after zeroing the magnetic field of the sample after saturation.

Embodiment of the invention

The present invention is illustrated by the following examples, which are not limiting of its scope.

Example 1:

This example refers to the obtaining of thin films of ternary alloy TbxFeioo-x-yGay by means of the sputtering technique.

Two targets of composition Fe72Ga28 and Tb33Fe67 are lit simultaneously. The material is grown on substrates covered with a layer of Mo with a thickness around 20 or 40 nm. To obtain the thin alloy film, the angle of inclination between the targets and the substrate is maintained at 25 ° and the distance between the targets and the substrate is maintained at 15 cm. The atmosphere in the growth hood is Ar and a pressure of 2x10'3 mbar is maintained. The composition of the sample is controlled by varying the power in each of the targets. Specifically, for a continuous power of 100 W in the Fe72Ga28 target and a pulsed power of 100 W of amplitude and frequency of 25 kHz in the target of Tb33Fe67, a thin film of 250 nm thickness and of TbioFe7óGai4 composition is obtained which has a Moderate magnetic anisotropy perpendicular to the sample plane with stripe domains on its surface (Figure 1).

Example 2:

This example describes the authentication of the material obtained according to example 1.

The orientation of the surface stripe domains is fixed by applying a magnetic field of 800 mT in the sample plane (Figure 2). The value of this applied magnetic field allows saturation of the magnetization of the sample. This minimum field necessary to saturate the sample is also the minimum field that can

detected by this technique, in the case that a material with a TbioFe7óGai4 composition is used.

By reducing the field to 0 T, the orientation of the stripe domains is fixed in the direction in which the previous field was applied (Figure 3).

Example 3:

This example describes the application of the magnetic material obtained and authenticated as shown in examples 1 and 2 to detect manipulation or erasure of computer material.

In order to know if there has been manipulation of information stored magnetically on a hard disk by means of the application of a magnetic field, it is verified that the orientation of the stripe domains has changed with respect to that generated during authentication. For this, it has been necessary to create a certain orientation before placing the thin film in a region near the hard disk.

Example 4:

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The application of the material obtained as described in example 1 to detect fraud in a water meter is described.

The unauthenticated material is introduced, with stripe-like domains on its surface 25 randomly oriented. If, subsequently, the domains are placed in a certain direction, there has been a manipulation by application of a magnetic field greater than necessary to saturate the sample since in the case of no manipulation they would remain randomly oriented.

30 This same example would be used to control whether there has been manipulation of information on a hard disk.

Claims (4)

1. Method of detection of manipulation or fraud of systems produced by application of a magnetic field using the claimed material comprising: - Fix the orientation of the magnetic domains on the surface of a material by applying a magnetic field, which allows saturating the magnetization of the material, in a certain direction within the plane of the sample of said material. Check if the default orientation of the domains has changed, in which case, there has been system manipulation where the magnetic material is in the form of a thin film and has moderate anisotropy perpendicular to the plane of the film and rotating magnetic anisotropy. 2. Method of detection of manipulation of systems by application of a magnetic field using the claimed material comprising: Leave the magnetic domains on the surface of a randomly oriented magnetic material. Check if the domains have been oriented, in which case, there has been manipulation of the system by applying a magnetic field. where the magnetic material is in the form of a thin film and has moderate anisotropy perpendicular to the plane of the film and rotating magnetic anisotropy. 3 3. Magnetic material in the form of a thin film of composition TbxFeioo-x-yGay for detection of manipulation or fraud of systems produced by application of a magnetic field, characterized in that it presents moderate magnetic anisotropy perpendicular to the plane and rotating anisotropy for its surface magnetic domains . 4. Magnetic material in the form of a thin film, according to claim 3, wherein x = 10 and y = 14. 5 5. Procedure for obtaining thin film magnetic material claimed, by means of sputtering technique by lighting two targets of Fe72Ga28 and Tb33Fe67 simultaneously with an inclination angle between the targets and the 25 ° substrate, where the material is grown on substrates covered with a layer of Mo with a thickness between 20- 40 nm, the 10 atmosphere being in the Ar growth hood and maintaining the pressure at 2x10'3 mbar during growth.