WO2008032274A2

WO2008032274A2 - Magneto-mechanical markers for use in article surveilance system

Info

Publication number: WO2008032274A2
Application number: PCT/IB2007/053674
Authority: WO
Inventors: Yuri Tarakanov; Vladimir Manov
Original assignee: Megasec Ltd.
Priority date: 2006-09-13
Filing date: 2007-09-12
Publication date: 2008-03-20
Also published as: WO2008032274A3

Abstract

For use in a magnetic theft detection system a magneto- mechanical marker containing semihard ferromagnetic strip and amorphous magnetostrictive element made from alloy having composition in atomic % corresponding to the formula: NiaFebCocM' kM' 'mBdSie; wherein M' is at least one element from the group consisting of Cr, Mo, and Mn, and M' ' is at least one element from the group consisting of surface active elements like Sn, Pb and Bi, and 'a' ranges 15 to 32, 'b' ranges 22 to 29, 'c' ranges 24 to 29.5, 'd' ranges 15 to 25, 'e' ranges O to 3, 'k' is the sum of amount of elements of group M' and ranges from 5.1 to 10, 'm' ranges from 0.001 to 0.04 and sum of 'a-m' is 100, consisting of at least one or more amorphous magnetostrictive strip pieces disposed in a stack, each having a length and width and the respective widths of said at least two or more magnetostrictive strip pieces being substantially different or equal and not exceeding 10 mm, and the respective lengths of said at least two or more magnetostrictive strip pieces being substantially equal, and semihard ferromagnetic strip disposed so to bias said magnetostrictive element with dc magnetic field ranging from 3.0 to 10.0 Oe.

Description

MAGNETO-MECHANICAL MARKERS FOR USE IN ARTICLE SURVEILANCE SYSTEM

Field of the Invention

The invention relates to magneto-mechanical markers for use in electronic article surveillance systems and the method for their production.

Background of the invention

Magneto-mechanical markers for electronic article surveillance (EAS) typically include elongated strip pieces of a magnetostrictive amorphous alloy, which are magnetically biased, by an adjacent strip of a magnetically semi-hard metal strip.

Production of magneto-mechanical markers comprises several steps. These steps consist of selecting alloy composition; casting amorphous alloy in the form of a ribbon having a certain width and thickness; thermal treatment of the ribbon in presence of magnetic field adjusted to the alloy composition; cutting the ribbons into pieces of a predetermined length to provide them with resonant properties when exposed to an AC electromagnetic field of certain frequency; and packing them into a housing together with pieces of semi-hard materials which provide magnetic bias for the amorphous strips, to form a magneto-mechanical marker.

For example, U.S. Pat. No. 4,510,489, issued to Anderson et al . , discloses a marker formed of a ribbon-shaped length of a magnetostrictive amorphous material contained in an elongated housing in proximity to a biasing magnetic element. Biasing ferromagnetic element comprises one or a plurality of pieces of high magnetic coercivity material, such as SAE 1095 steel, Vicalloy, Remalloy or Arnokrome. As magnetostrictive strip pieces the following amorphous alloys are suggested to use: Fe₇₈Si₉Bi₃O, Fe₇₉Si₅Bi₆ , Fe₈IBi_3-5Si₃.₅C₂, Fe₆₇Cθi₈Bi₄Sii, Fe₄₀Ni₃₈Mo₄Bi₈ . The magnetostrictive element is made of above mentioned amorphous strip pieces annealed in a saturating magnetic field applied in a direction perpendicular to the strip pieces length at the temperature ranging from about 300°C to 450°C for an annealing time ranging from about 7 to 120 min .

In accordance with the US patents 6,181,245 and 5,729,200, issued to Copeland, a relatively low coercivity material such as the alloy designated as "MagnaDur 20-4" (which has a coercivity of about 20 Oe) is used as a biasing element for the acoustomagnetic marker. MagnaDur 20-4 essentially has the composition Fe₇₇.₅₄Niig.₂₈Cr₀.1₉Mn₀.₃iMo₂.₃₈Si₀.₃o (atomic percent) . The magnetostrictive element is formed from a ribbon of amorphous metal alloy Metglas 2628CoA, having a composition of Fe₃₂COi₈Ni₃₂Bi₃Si₅ or alloy Metglas. 2826 MB having a composition of Fe₄₀Ni₃₈Mo₄Bi₈.

The magnetoacoustic marker is fabricated in a such manner that it resonates at a predetermined frequency when the biasing element has been magnetized to a certain level and a suitable oscillator provides an AC magnetic field at the predetermined frequency. When a magnetostrictive material such as an amorphous metal ribbon is in a magnetic field (H), the ribbon's magnetic domains are caused to grow and/or rotate. This domain movement allows magnetic energy to be stored. When the field is removed, the domains return to their original orientation releasing the stored magnetic energy. Amorphous metals have high efficiency in this mode of energy storage. Since amorphous metals have no grain boundaries, their energy losses are extraordinarily low.

When the ferromagnetic ribbon is magnetostrictive, additional energy storage is also possible. In the presence of a magnetic field, a magnetostrictive amorphous metal ribbon will have energy stored magnetically as described above but will also have energy stored mechanically via magnetostriction. This mechanical energy per unit volume stored can be quantified as Ue = (1/2) TS where T is the stress and S is the strain on the ribbon, respectively. This additional energy storage may be viewed as an increase in the effective magnetic permeability of the ribbon. When an AC magnetic field and a DC field are imposed on the magnetostrictive ribbon, energy is alternately stored and released with the frequency of the AC field. The magnetostrictive energy storage and release are maximal at the material ' s mechanical resonance frequency and minimal at its anti- resonance. The transfer of magnetic and mechanical energy described above is called magneto-mechanical coupling (MMC), and can be seen in all magnetostrictive materials. The efficiency of this energy transfer is proportional to the square of the magneto-mechanical coupling factor (k) . It is defined as the ratio of mechanical to magnetic energy. This factor strongly depends on the ribbon surface defects. The presence of different cavities and pins on the ribbon surface, results in additional stresses around defects and in losses of mechanical and magnetic energy. Therefore, these surface defects reduce magneto-mechanical factor and detecting ability of the marker, so one can reduce the losses if the quality of the ribbon surface improves due to improvement of the ribbon production technology.

In view of the small thickness of the ribbon, its properties are also affected by the solid inclusions of foreign materials such as, e.g., ceramic particles or other inclusions, which are insoluble at the temperatures of the melt alloy. When such inclusions are incorporated in the ribbon, they form additional defects deteriorating the magneto-mechanical properties of the ribbon. Some casting technology improvements are desirable which reduce the number and sizes of these inclusions and so improving the magnetoelastic properties of the ribbon.

The efficiency of the energy transfer is also dependent on the elasticity of magnetostrictive material. Higher material elasticity results in higher efficiency of the energy transfer. Therefore, introducing such heavy elements into the alloy composition, which increase the modulus of elasticity of magnetostrictive strips, one can improve the detection ability of the produced magneto- mechanical markers. However, the alloys containing high levels of heavy elements like Mo, Cr, and Mn have reduced ribbon cast ability owing to the higher melting temperatures and melt viscosity, which can result in the ribbon quality deterioration.

A broad range of alloys containing elements improving elastic properties of the amorphous magnetostrictive ribbons have been claimed in patents suitable for the marker material for the acoustomagnetic detection systems . For example, Hasegawa et al (U.S. Pat Nos. 5,495,231 and 6,187,112) disclose amorphous magnetostrictive alloys with Mn, Mo and Cr bearing good magnetoelastic properties. In these alloys the content of Mn, Mo and Cr is less than 3 atomic %.

Other metallic glasses containing up to 5 atomic % of Nb, Ta, Mo, Cr, and Mn, and exhibiting good magnetoelastic properties are disclosed by Herzer et al in US Pat. Nos. 6,171,694 and 6,359,563. These patents also disclose a multiple resonator for use in a marker said resonator comprising at least two ferromagnetic elements disposed in registration each having a length and a width and the respective widths of said at least two ferromagnetic elements being substantially equal and the respective lengths of said at least two ferromagnetic elements being substantially equal. Using of at least two ferromagnetic elements of equal length and equal width allows increasing the signal compared to a single resonator; it is clear that the improved signal is accompanied by elevated cost of the marker.

Various amorphous magnetostrictive alloys defined by the formula Fe_aCθ_bNi_cSi_xB_yM_z wherein M denotes one or more elements of groups IV through VII of the periodic table and z lies between 0 and 5 atomic % and suitable for the production of magneto-mechanical markers are also claimed by Herzer et al in US Patents No. RE38, 098, No. 6,171,694 and No. 5,728,237. These patents state that high content of these elements in the marker alloy results in reduced ribbon casting ability owing to the higher melting point temperature of the metal and that is why the content of the elements improving magneto- mechanical properties of the alloys is limited. As alloys containing high levels of molybdenum, chromium, or manganese have reduced ribbon casting ability owing to the higher viscosity of liquid metal, some other modifications of the alloy composition are needed to prevent the growth of the melt viscosity and therefore deterioration of the casting ability.

High quality of the quench ribbon surface can be achieved using a casting wheel made of alloys having high thermal conductivity, high mechanical strength and low wheel erosion. However even with a good selection of mechanical and thermal properties (e.g., Cu-Cr and Cu-Be type alloys) the deterioration of the casting wheel's quench surface progresses rapidly resulting in low quality of the quench ribbon surface.

To improve the surface quality of the ribbon one needs to decrease chemical interaction between the wheel surface and liquid metal during the ribbon casting. It is well known that interaction between solid and liquid metals is increased with temperature growth. Therefore improving the ribbon surface quality is favoured by reduction of the casting temperature to the extent possible. As the commercially most significant process for amorphous materials fabrication in the form of ribbons is the rapid solidification of molten metal via melt-spinning processes where a liquid metal is sprayed through a nozzle having very small dimensions the ribbon casting temperature is mainly determined by viscosity of the liquid metal.

So introduction into the alloy composition of elements, which considerably decrease viscosity of the molten metal, allows casting the amorphous ribbon even with high content of Mo, Cr, and Mn at relatively low temperature. A number of annealing techniques is known in the prior art which are used for annealing amorphous ribbons for EAS markers .

US Pat. 5,469,140 discloses a heat treatment process in which a ribbon-shaped strip of an amorphous magnetic alloy is heat-treated, while applying a transverse saturating magnetic field. The treated strip is used in a marker for a pulsed-interrogation electronic article surveillance system.

United States Patent 5,676,767 discloses a magnetostrictive element for use in a magneto-mechanical electronic article surveillance marker, which is formed by annealing a continuous ribbon of an amorphous metal alloy. The alloy ribbon is transported from reel to reel through an oven in which a transverse saturating magnetic field is applied to the ribbon. The annealed ribbon is cut into discrete strips, which are suitable for use as magnetostrictive elements.

United States Patent 5,684,459 discloses a process in which a longitudinal curvature in an amorphous metal alloy ribbon is formed by heat-treatment. While the heat- treatment occurs, the alloy ribbon is bent "backwards" against the longitudinal curvature. The process is carried out continuously by transporting the alloy ribbon from reel to reel, while wrapping the ribbon around a heated roller. Using a discrete strip cut from the alloy ribbon subjected to the curvature-reducing process, a magneto-mechanical EAS marker is constructed that has a relatively low profile, while retaining desired magnetic properties . United States Patent 5,891,270 discloses a mechanically resonant marker, which comprises a strip of magnetic glassy metal alloy that has been annealed in a furnace for a predetermined time at a plurality of temperatures. A first of the temperatures is high enough to relieve quenched-in and post fabrication stresses. The second of the temperatures is near the Curie temperature of the strip. Annealing is carried out in the presence of an external magnetic field applied perpendicular to the strip's length and in the plane of the strip. The second of the temperatures is applied sequentially of the first temperature and is operative to induce magnetic anisotropy along the direction of the magnetic field. Annealing is continuous and the velocity of the strip passing through the annealing furnace determines the annealing time.

United States Patent 6,011,475 discloses a ferromagnetic resonator for use in a marker in a magneto-mechanical electronic article surveillance system which has improved magnetoresonant properties and/or reduced eddy current losses by virtue of being annealed so that the resonator has a fine domain structure with a domain width less than about 40 . μm, or less than about 1.5 times the thickness of the resonator. This produces in the resonator an induced magnetic easy axis, which is substantially perpendicular to the axis along which the resonator is operated magnetically by a magnetic bias element also contained in the marker. The annealing which produces these characteristics can take place in a magnetic field of at least 1000 Oe, oriented at an angle with respect to the plane of the material being annealed so that the magnetic field has a significant component perpendicular to this plane, a component of at least about 20 Oe across the width of the material, and a smallest component along the direction of transport of the material through the annealing oven.

United States Patents 6,254,695, 6,299,702 6, and 551,416 disclose a ferromagnetic resonator for use in a marker in a magneto-mechanical electronic article surveillance system, which has improved properties and can be manufactured at higher annealing speeds and reduced raw material cost by virtue of being continuously annealed in the simultaneous presence of a magnetic field perpendicular to the ribbon axis and a tensile stress applied along the ribbon axis and by providing an amorphous magnetic alloy containing iron, cobalt and nickel in which the portion of iron is more than about 15 at % and less than about 30 at %.

United States Patent 6,645,314 discloses a ferromagnetic resonator for use in a marker in a magneto-mechanical electronic article surveillance system which is manufactured at reduced cost by being continuously annealed with a tensile stress applied along the ribbon axis and by providing an amorphous magnetic alloy containing iron, cobalt and nickel and in which the portion of cobalt is less than about 4 at % .

United States Patent 6,830,634 presents a method and device for continuous annealing metallic ribbons in which a thin metallic ferromagnetic alloy ribbon is annealed by continuously transporting it through an oven in order to induce specific magnetic characteristics and in order to remove a production-inherent longitudinal curvature of the ribbon. While the heat-treatment occurs, a channel in a substantially straight annealing fixture guides the ribbon. The channel is characterized by slight curvatures along portions of its length, in particular where the ribbon enters into the annealing oven. The curved channel provides an improved thermal contact between the ribbon and the heat reservoir. Consequently the process can be conducted at particularly high annealing speeds without degrading the desired characteristics.

U. S. Pat.5, 568,125 issued to Liu disclose procedure in which a two-step annealing process is applied to an amorphous magnetostrictive metal alloy ribbon. During the first step, a continuous amorphous ribbon is annealed at

420°C for 22 seconds in a saturating transverse magnetic field. After the first (transverse-field) annealing step, the ribbon is cut into strip pieces and the cut strip pieces are then further annealed at 340°C for 1 minute while being maintained in a stationary position in a separate oven. During the second annealing step, the saturating magnetic field was not imposed. After the two annealing steps, the material is cut into discrete strip pieces suitable for use as active elements in pulsed- field magneto-mechanical EAS markers. The resulting markers exhibit satisfactory total frequency shift and ring-down signal amplitude characteristics. United States Patent 5,786,762 presents a magnetostrictive element for use in a magneto-mechanical electronic article surveillance marker formed by first annealing a strip of amorphous metal alloy in the presence of a saturating transverse magnetic field and, subsequent to said first annealing, second annealing said strip in the presence of a longitudinal magnetic field to reduce a rate at which said resonant frequency varies in dependence on changes in said biasing magnetic field. Said first annealing is performed at a temperature in the range of about 380 °Cto about 400 ⁰C and second annealing is performed at a temperature in the range of about 250 ⁰C to about 450 ⁰C.

The above-referenced 5,568,125 patent discloses also the continuous annealing process in which the continuous ribbon passes through the first transverse magnetic field zone at the temperature of 380°C and then it enters the second magnetic field free zone at the temperature of 360°C.

The technique disclosed in the 5,568,125 patents represents advantages over previously known techniques. However, it would be desirable to modify the techniques mentioned above as to provide active elements for EAS markers having a resonant frequency that is relatively insensitive to variations in the biasing magnetic field.

It is therefore the major object of the present invention to provide magneto-mechanical EAS markers having a highly efficient magnetic characteristics and good stability in terms of resonant frequency relative to change in bias magnetic field.

It is a further object of the present invention to offer a new composition of the alloy for magneto-mechanical EAS markers, which provides improved magnetoelastic properties to the amorphous ribbon.

It is another object of the present invention to introduce into the alloy composition additional elements, which prevent the growth in the alloy melt viscosity due to introduction of the elements improving the magnetoelastic properties of the amorphous alloy and thus deteriorate the casting ability of the melt alloy.

It is still one more object of the present invention to provide the alloy composition allowing casting at relatively low temperature in order to reduce interaction between the melt and to avoid deterioration of the casting wheel's quench surface, which result in higher quality of the ribbon surface.

It is yet another object of the present invention to provide a two-stage heat treatment process for the ribbon alloy with the new composition, which results in improved magnetoelastic properties of the annealed material.

It is yet one more object of the present invention to provide process of overheating the melted alloy to a precise temperature prior to rapid quenching, to achieve more reliable ribbons with more reproducible characteristics, better surface quality, and better magnetoelastic properties.

It is still one more object of the invention to provide a reduced cost multi-resonant EAS marker using new alloy composition resonant strip pieces having substantially same lengths and substantially different widths.

DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will now be described by way of examples. The magnetostrictive elements for use in magneto- mechanical EAS systems were fabricated from amorphous 20- 25 microns thick and 4, 5, and 6 mm wide ribbons formed by melt spinning quench technique. Using the ribbons with reduced width allows to reduce the marker cost.

Prior to casting, the melted alloy is treated with "overheating" technique. This technique was disclosed in an article by Manov et al . entitled "The Influence Of Quenching Temperature On The Structure And Properties Of Amorphous Alloys," published in Materials Science and Engineering, A133 (1991) 535-540. As used herein, the term overheated metallic alloy ribbon refers to a metallic alloy ribbon made from a melt, which had been overheated as described by Manov et al . By overheating the melt and then lowering the temperature before actually forming an amorphous metallic ribbon from it, it is possible to produce a ribbon with improved characteristics. Overheating Technique in the sense of the present invention means to heat the alloy considerably above its melting temperature, to keep the melt at a temperature considerably above the melting temperature for a while and to lower the temperature to casting temperature. The ribbon produced by this technique is characterized by higher uniformity and surface quality due to fewer defects caused by foreign inclusions, e.g., due to wear products of ceramic crucibles resulting in foreign inclusions. These inclusions form local defects in the rapid-quenched ribbon, which reduce the magnetoelastic properties of the ribbon. Overheating technique favors dissolving of these effects, reduction of their sizes and allows formation of more uniform ribbon with fewer defects due to these inclusions. In addition, such inclusions can serve as centers of cluster formation causing local deviations in the alloy concentration, which results in higher energy damping during transformation of the magnetic energy into mechanical and vice versa. The present invention describes the production of amorphous ribbons for magneto-mechanical markers using the melted alloy overheating process detailed by Manov, with the unexpected benefits of achieving better magnetoelastic properties as detailed above; these benefits were not described in the Manov article. Thus, until now the above detailed process was not known to be advantageous to magneto-mechanical markers made of amorphous metallic alloys .

The amorphous ribbons were cast at different temperatures. To reduce the casting temperature to the extent possible, surface-active elements were added to the alloy composition. Such elements are as follows: Sn, Pb, Bi, and others. The goal of adding these elements to the alloy is reduction of the melt viscosity and consequently of the casting temperature. The reduced viscosity provides better ribbon casting ability, which in its turn results in the reduced casting temperature. Another goal of adding the surface-active elements is to compensate the melt viscosity growth due to elevated concentration of Mo, Cr, and Mn. Adding Mo, Cr, and Mn allows significant improvement of magnetoelastic properties of the amorphous ribbon.

The casting temperature of the alloys containing tin was decreased by 70-100⁰C due to reduced liquid metal viscosity. The cast amorphous ribbons having the composition described by the following formula: Ni_aFe_bCo_cM' _kM' '_mB_dSi_e; wherein M' is at least one element from the group consisting of Cr, Mo, and Mn, and M' ' is at least one element from the group consisting of surface active elements like Sn, Pb and Bi, and " a "ranges from 15 to 32, "b" ranges from 22 to 29, "c " ranges from 24 to 29.5, "d" ranges from 15 to 25 , "e" ranges from 0 to 3, "k" is the sum of amount of elements of group M' and ranges from 5.1 to 10, "m" is the sum of amount of elements of group M'' and ranges from 0.001 to 0.04 and sum "a-m" is 100, and "a-m "are in atomic %, were continuously heat treated in a tube-type two zone heat treatment unit (Fig. Ib, 2b, 3b) by transporting the ribbon 23 from one reel 22 to another reel 21 at a certain speed to get time of the ribbon heat treatment of about 5-30 seconds. The unit was consisting of two zones. The first one or annealing zone 33 was about 120 or 170 cm long. The second or cooling zone 31 was about 80 or 30 cm long. Distribution of temperatures in the unit is shown in Fig. Ia, Fig.2a and Fig.3a.

The temperature in the annealing zone was 350-440°C. The temperature at the center of cooling zone was mainly 50 - 70°C. During the heat treatment process, the ribbon was exposed to 2.5 kOe strength magnetic field 32 oriented perpendicularly to the long ribbon axis. In some experiments, the length of the region exposed to the magnetic field 32 perpendicularly oriented to the longitudinal axis of the ribbon was changed. The amorphous ribbons so heat-treated were then cut into 36- 39 mm long pieces. Then two 36-39 mm long strip pieces having width 4, 5, and 6 mm stacked together were exposed to a burst of exciting signal of constant amplitude tuned to the frequency of mechanical resonance of the strip pieces material. The strip pieces responded to the exciting pulse and generated output signal in the receiving coil. At time tO=O excitation is terminated and the marker starts to ring-down, reflected in the output signal which is reduced from AO to zero over a period of time. At time tl, which is one millisecond after the termination of excitation, output signal being measured and denoted by the quantity Al. Thus, AO /Al is a measure of the ring-down or oscillation damping. The lower value of A0/A1 results in higher detection rate of the marker.

According to a first aspect of the invention the inventive amorphous metallic alloy for a magnetoristrictive element has the following composition:

Ni_aFe_bCo_cM \M ' ' _mB_dS i_e

wherein M' is at least one element from the group consisting of Cr, Mn, and Mo, and M' ' is at least one element from the group consisting of surface active elements Sn, Pb and Bi, and "a" ranges from 10 to 32, "b" ranges from 22 to 29,5, "c" ranges from 15 to 35, "d" ranges from 15 to 25 , "e" ranges from 0 to 3, "k" and is the sum of amount of elements of group M' and ranges from 5.1 to 10, "m" is the sum of amount of elements of group M'' and ranges from 0,001 to 0,04 and sum "a" to ,,m" is 100. As described said composition provides improved magnetoelastic properties of a magnetoristrictive element made of said alloy.

An advantageous embodiment of the inventive alloy contains 0,001 to 0,03 at % Sn. On the one hand adding Sn to the inventive alloy allows to reduce casting temperature due to a reduction of melt viscosity. On the other hand the reduced melt viscosity allows to add higher amounts of Mo, Cr and/or Mn in orde to achieve significant improvement of magentoelastic properties.

A further advantageous embodiment of the inventive alloy contains 0,005 at % Sn. It has been found that such an amount of Sn is sufficient to reduce melt viscosity and to reduce casting temperature significantly.

Good magentoelastic and mechanical properties are provide by embodiments of the inventive alloy which have the following composition:

Ni₂₀Co_{3 O}Fe_{2 G}Mo₃Cr₃Bi_{7 - 99} Sn₀. oi or Ni₂₄Co₂₆Fe₂₇Mo_{21 6}Cr_{2 - 5}Bi_{7 - 89}Sn_{0 -} Oi or Ni_{2I - 5}Co_{29 - 5}Fe₂₆Mo_{2 - 6}Cr_{2 - 5}Bi_{7 - 895}Sn_{0 - 005} .

According to a second aspect of the invention the aforementioned objects are solved by a magneto-mechanical marker for use in a theft detection system comprising at least one magnetoristrictive element at least partially made of an inventive amorphous metallic alloy. This magneto-mechanical marker shows an improved detection capability due to its improved magnetoelastic properties causing a high amplitude signal.

According to another embodiment of the inventive marker contains at least one magnetostrictive element and at least one ferromagnetic element, whereby said magnetoristrictive element and said ferromagnetic element are arranged in a way that said magnetostrictive element is biased with dc magnetic field ranging from 3,0 to 10,0 Oe. The biasing field allows to use one, two or three magnetostrictive strip pieces in a magnetostrictive element . According to another embodiment of the inventive marker the magnetostrictive element comprises at least one magnetostrictive strip having a length and width and the respective width ranging from 1 to 10 mm.

According to another embodiment of the inventive marker the magnetostrictive element comprises at least two magnetostrictive strip pieces disposed in a stack each having a length and a width, and respective widths of said strip pieces being substantially equal or different and not exceeding 10 mm and the respective lengths of said at least two magnetostrictive elements being substantially equal.

According to another embodiment of the inventive marker the magnetostrictive element comprises three magnetostrictive strip pieces disposed in a stack, two of them having substantially equal widths and the third one having substantially different width and the respective lengths of all of them are substantially equal.

According to another embodiment of the inventive marker two magnetoristrictive strip pieces have a width of 4 mm and the third one has a width of 5 mm.

According to another alternative embodiment of the inventive marker the two magnetoristrictive strip pieces have a width of 4 mm and the third one has a width of 6 mm.

According to another alternative embodiment of the inventive marker the two magnetoristrictive strip pieces have a width of 5 mm and the third one has a width of 4 mm.

According to another alternative embodiment of the inventive marker the two magnetoristrictive strip pieces have a width of 5 mm and the third one has a width of 6 mm.

According to another alternative embodiment of the inventive marker the two magnetoristrictive strip pieces have a width of 6 mm and the third one has a width of 4 mm.

According to another alternative embodiment of the inventive marker the two magnetoristrictive strip pieces have a width of 6 mm and the third one has a width of 5 mm.

According to another alternative embodiment of the inventive marker the marker consists of three magnetostrictive strip pieces disposed in a stack, all three strip pieces having substantially different widths and substantially equal lengths.

In another alternative embodiment of the inventive marker the three strip pieces have a width of 4 mm, 5 mm, and 6 mm, respectively.

According to another alternative embodiment of the inventive marker the marker consists of two magnetostrictive strip pieces disposed in a stack having substantially equal widths and the same length.

According to another alternative embodiment of the inventive marker the marker consists of two magnetostrictive strip pieces disposed in a stack having substantially different widths and the same length.

According to another alternative embodiment of the inventive marker said two magnetoristrictive strip pieces have a width of 4 mm and 5 mm.

According to another alternative embodiment of the inventive marker said two magnetoristrictive strip pieces have a width of 4 mm and 6 mm.

According to another alternative embodiment of the inventive marker the two said two magnetoristrictive strip pieces have a width of 5 mm and 6 mm.

With regard to a third aspect of the invention it is provided a method of manufacturing a magnetoristrictive strip of an inventive marker comprising the steps of

- providing an inventive alloy

- treatment of the melt with overheating technique prior to casting and

- casting an amorphous ribbon at a temperature equal or below 1250⁰C. ^• Overheating Technique in the sense of the present invention means to heat the alloy above its melting temperature and keeping the melt at a temperature considerably above the melting temperature for a while and lowering the temperature to casting temperature.

A first embodiment of the inventive method further comprises the steps of

- heat-treating said ribbon in a continuous mode in two consecutive hot and cold regions,

- the first region having temperature of 350°C-440°C while the second region having length suitable to cool the ribbon down to room temperature and

- a magnetic field directed perpendicularly to the longitudinal axis of the ribbon in the both regions

- cutting said annealed ribbons into the strip pieces of substantially equal and predetermined lengths,

- disposing at least two strip pieces of different or equal widths from set of strip pieces having width not exceeding 10 mm in a stacked manner to form a multiple magnetostrictive element.

According to another embodiment of the inventive method the alloy has the composition:

Ni ₂1 . 5C029 . 5 Fe26M02 . eCr2 . 5B17 . 895 S n₀ . o o5 , and said al loy i s cast at temperature of 1220⁰C . According to another embodiment of the inventive method the magnetic field directed perpendicularly to the longitudinal axis of the ribbon in the cold region is partly in the first region neighboring the cold zone.

According to another embodiment of the inventive method said ribbon is heat treated in a continuous mode in two consecutive hot and cold regions the first region having a temperature of 420 C while the second region having a temperature below 300 ⁰C, preferably of 20-60 C.

With the aforementioned embodiments of the inventive method magnetostrictive ribbons, respectively strip pieces can be manufactured with very good magnetostrictive properties. Additionally due to the improved magnetostrictive properties of the ribbon or strip piece the production costs can be lowered additionally. This applies to the following alternative embodiments of the inventive method, too.

According to another embodiment of the inventive method two strip pieces are disposed in a stacked manner having widths of 4 mm and 5 mm.

According to another embodiment of the inventive method two strip pieces are disposed in a stacked manner having widths of 4 mm and 6 mm.

According to another embodiment of the inventive method two strip pieces are disposed in a stacked manner having widths of 5 mm and 6 mm.

According to another embodiment of the inventive method two strip pieces are disposed in a stacked manner having the same widths of 6 mm. According to another embodiment of the inventive method the magnetostrictive element consists of three ferromagnetic magnetostrictive strip pieces disposed in a stack two of them having substantially equal widths and the third one having substantially different width and the respective lengths of all of them are substantially equal .

According to another alternative embodiment of the inventive method the two strip pieces have a width of 4 mm and the third one has a width of 5 mm.

According to another alternative embodiment of the inventive method the two have a width of 4 mm and the third one has a width of 6 mm.

According to another alternative embodiment of the inventive method the two strip pieces have a width of 5 mm and the third one has a width of 4 mm.

According to another alternative embodiment of the inventive method the two strip pieces have a width of 5 mm and the third one has a width of 6 mm.

According to another alternative embodiment of the inventive method the two strip pieces have a width of 6 mm and the third one has a width of 4 mm.

According to a last alternative embodiment of the inventive method the two strip pieces have a width of 6 mm and the third one has a width of 5 mm.

BRIEF DESCRIPTION OF THE DRAWING

FIG. Ia, FIG.2a and FIG.3a illustrates temperature distribution in two-zone heat treatment unit. FIG. Ib, FIG.2b and FIG.3b illustrate schematic representation of different technology of the heat treatment processes.

FIG.4 shows magnetoelastic properties of the amorphous ribbon made from alloy not containing tin (Ni₂1.5Cθ29.5Fe₂6Mo₂.6Cr₂.5B17.9) and cast at high temperature and heat treated according to the inventive technology.

FIG.5 shows magnetoelastic properties of the amorphous ribbon made from alloy containing tin (Ni₂L₅Co_29-5Fe₂₆Mo_2-6Cr_2-5Bi_7-SgSnCOi) and cast at low temperature and heat-treated according to the inventive technology.

FIG.6 shows magnetoelastic properties of the inventive alloy amorphous ribbon annealed at 420⁰C with partial exposition of cooling zone to perpendicular magnetic field (Exp .No2, Table2) .

FIG.7 shows magnetoelastic properties of the inventive alloy amorphous ribbon annealed at 420⁰C with full exposition of cooling zone to perpendicular magnetic field (Exp .N06, Table2) .

FIG.8 shows dependence of the resonant amplitude signal value on the biasing magnetic field for the inventive resonators containing magnetostrictive strip pieces having different width.

FIG.9 shows dependence of the resonant amplitude signal value on the biasing magnetic field for the inventive resonators made from magnetostrictive ribbons of different chemical compositions.

FIG.10 shows dependence of the resonant amplitude signal value on the biasing magnetic field for the inventive resonators containing one, two and three strip pieces respectively for amorphous alloy AM-I (Fe₂4Ni24Cθ27Mn₂Cr5

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EXAMPLE 1

Glassy metal alloys in the Ni_aFe_bCo_cM' _kM' '_mB_dSi_e series were rapidly quenched using well-known method supplemented with overheating technique. Silicon content in the alloys was defined by its content in ferroboron used for alloying metal with boron was equal to 0.2-0.4 atomic %. All casts were made in an inert gas, using 1000 g melts. The ribbons, typically 25 μm thick and 6 mm wide, were cast at lowest possible temperatures (Tc) and they were strong and ductile. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit (see Fig. Ib) . In the cooling zone the ribbon 23 was exposed to 2.5 kOe strength magnetic field 32 oriented perpendicularly to the longitudinal ribbon axis. The casting and annealing temperatures are given at Table 1. Temperature distribution in the heat treatment unit when annealing temperature was about 420 T °C is given in Fig. Ia. The annealing time of the ribbon was about 14-15 seconds. When the hot ribbon enters the cooling zone it is cooled to temperature kept there. The cooling of the ribbon in the cold zone takes for 9-10 seconds. The heat- treated ribbons for magneto-mechanical resonance characterization were cut to a length of about 36-39 mm and typical magnetoresonant properties of the two amorphous strip pieces stacked together. Typical magnetoresonant properties of the magnetosrictive elements consisting of two amorphous strip pieces stacked together containing Mo and Cr with and without tin are shown in Table 1. The following designations were accepted: Taz is the temperature of the annealing zone in 0C; AO is the maximum amplitude signal at time t=0;Al is the amplitude signal at time t=l ms at HOmax; Hk is the anisotropy field; HOmax is the bias field where the resonant amplitude has its maximum; Fr is resonant frequency; HFrmin is the bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr(H); KAo/Al is the ring-down coefficient.

Table 1 Magnetoelastic properties of the amorphous ribbons cast at different temperatures

As one can see from Table 1 and Fig.4 and 5 the magnetostrictive strip pieces made from alloys containing tin and cast at low temperature demonstrate higher amplitude signal and lower value of the ring-down coefficient KA0/A1 than those not containing tin or cast at relatively high temperature (>1250°C). The slope value, dFr/dH, preferably, should be as small as possible. As the resonant frequency of the marker can be changed due to the orientation of the marker in the earth's magnetic field and/or due to scatter in the bias magnet's properties it is highly desirable, for EAS markers that the resonant frequency in the activated state (i.e. when the bias magnet is magnetized) varies as little as possible Thus in US Patent 6,254,695 it is recommended to have the slope less than 0.7 kHz/Oe. As it follows from Table 1 this can be achieved when the resonator alloy is cast into the amorphous ribbon at temperature below 1250⁰C, then annealed at temperature close to Curie temperature and cooled in the presence of magnetic field oriented perpendicularly to longitudinal axis of the ribbon.

Good sensitivity (dFr/dH) and large magneto-mechanical resonance response signal (Aomax) of the magnetostrctive strip pieces made of the metallic glasses of this invention gives a possibility to produce markers especially suitable for use in article surveillance system that employ excitation and detection of magneto- mechanical resonance.

EXAMPLE 2

Glassy metal alloy having composition as

Ni₂1.5Co₂9.5Fe₂6Mo₂.6Cr₂.5B17. SgSn₀. oi was prepared in the s ame manner as in example 1. The ribbons, typically 25 μm thick and about 6 mm wide, were cast at temperatures 1220⁰C and they were strong and ductile. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit by transporting the ribbon 23 from one reel 22 to another reel 21 at speed 5 m/min. Schematically the heat treatment process and temperature distribution in the unit are shown in FIG. Ia and FIG. Ib. After annealing at temperature 420⁰C ribbon 23 enters a cooling zone 31 where it was exposed to 2.5 kOe strength magnetic field 32 oriented perpendicularly to the longitudinal ribbon axis. The annealing zone having length of about 120 mm and created by heating element 33 was not exposed to magnetic field. In some experiments by taking out some magnets, the part of cooling zone of length Lczfm to annealing zone was free from magnetic field. In some other experiments by adding some magnets the part of annealing zone close to cooling zone was exposed to the magnetic field as well. The temperature Tmz where the ribbon enters a magnetic zone is given at Table 2. The annealing time of the ribbon was about 14-15 seconds. The cooling of the ribbon exposed to a perpendicular magnetic field took 9-10 seconds. So heat- treated ribbons for magneto-mechanical resonance characterization were cut to a length of about 36-39 mm and typical magnetoresonant properties of the two amorphous strip pieces stacked together are shown in Table 2. The following designations were accepted: Lmz is the magnetic zone length; Tmz is the temperature of the unit working space where the ribbon enters a magnetic zone; Lczfm is the length of cooling zone not exposed to the magnetic field; Lazm is the length of the annealing zone exposed to the magnetic field; AO is maximum amplitude signal at time t=0; Al is amplitude signal at time t=lmsec at HOmax; Hk is the anisotropy field; HOmax is the bias field where the resonant amplitude has its maximum; Fr is resonant frequency; H_Frmin is bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr(H); KAo/Al is the ring-down coefficient .

Table 2 Magnetoelastic properties of the heat-treated ribbon exposed to the magnetic field only in the cooling zone

Magnetoresonant properties of the heat-treated amorphous ribbons No2 and No6 from Table 2 are shown in Figβ and Fig.7. As one can see from Table 2, Fig.6 and Fig.7 the magneto-mechanical markers containing magnetostrictive elements annealed with followed immediate cooling of the ribbon in the presence of a perpendicular magnetic field demonstrate high amplitude signal and lower value of the ring-down coefficient KA0/A1 than those cooled with partial exposition of the ribbon to perpendicular magnetic field in the cooling zone. Moreover, if the heated ribbon enters the magnetic zone having temperature below 300⁰C it does not resonate at all. Additionally, saturating magnetic field of anisotropy increases by 1.5- 2.5 Oe when cooling of the heat-treated ribbon takes place in the presence of a perpendicular magnetic field. It is also well known that the saturating magnetic field of the ribbon anisotropy is increased with increase of heat treatment time and therefore, application of inventive alloys and heat treatment technology results in raise of the ribbon thermal treatment productivity as in this case the magnetoresonance properties of the amorphous strip pieces are determined by cooling time in magnetic field.

EXAMPLE 3

Amorphous alloy ribbon having composition as Ni₂1.5Co₂9.5Fe₂6Mo₂.6Cr₂.5B17. SgSn₀. oi was prepared in the same manner as in example 1. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit by transporting it at speed 5 m/min. Schematically the heat treatment process and distribution temperature in the unit are shown in FIG.2a and FIG.2b. The annealing zone having length of about 120 mm and created by heating element 33 was exposed to 2.5 kOe strength magnetic field 32 oriented perpendicularly to the longitudinal ribbon axis. In cooling zone 31, the ribbon 23 was not exposed to the magnetic field. In some experiments, the part of cooling zone close to annealing zone was exposed to the magnetic field. The annealing temperature was about 420⁰C. The annealing time of the ribbon was about 14-15 seconds. The temperature Tmzl where the ribbon leaves a magnetic zone is given at Table 3. The cooling of the ribbon in the cold zone took 9-10 seconds. So heat- treated ribbons for magneto-mechanical resonance characterization were cut to a length of about 36-39 mm and typical magnetoresonant properties of the two amorphous strip pieces stacked together are shown in Table 3. The following designation were accepted: Tmzl is the temperature of the unit working space where the ribbon leaves a magnetic zone ⁰C; Lmz is the magnetic zone length, cm; Lczm is the length of cooling zone exposed to the magnetic field, cm; AO is maximum amplitude signal at time t=0;Al is amplitude signal at time t=l ms at HOmax; Hk is the anisotropy field; HOmax is the bias field where the resonant amplitude has its maximum; Fr is resonant frequency; HFrmin is bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr(H).

Table3 Magnetoelastic properties of the heat-treated ribbon exposed to the magnetic field in the annealing zone and not exposed or partially exposed in the cooling zone .

As it follows from Table3, the magneto-mechanical markers containing magnetostrictive elements made from ribbon annealed with exposition to a perpendicular magnetic field and cooled in a space free from magnetic field have no output signal amplitude at all, and only the markers made from the ribbon cooled with partial exposition to magnetic field produce amplitude signal. Moreover, at the heat treatment conditions mentioned above, when the heated ribbon leaves the magnetic zone having temperature below 280⁰C it had very good magnetoelastic properties. So to get quality products at given conditions of the ribbon heat treatment, the cooling of the ribbon from 420 to 280⁰C must proceed under exposition to magnetic field.

EXAMPLE 4

Amorphous alloy ribbon having composition as Ni₂1.5Co₂9.5Fe₂6Mo₂.6Cr₂.5B17. SgSn₀. oi was prepared in the same manner as in example 1. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit by transporting it at speed 5 and 7.6 m/min. Schematically the heat treatment process and distribution temperature in the unit are shown in FIG.3a and FIG.3b. In annealing 33 and cooling 31 zones the ribbon 23 was exposed to 2.5 kOe strength magnetic field 32 oriented perpendicularly to the longitudinal ribbon axis and only a small part (about 10 cm long) of the cooling zone close to the unit outlet was not exposed to magnetic field. The ribbon was annealed at 420⁰C. Cooling temperatures are given at Table 4. The annealing and cooling time of the ribbon are also given in Table 4. The heat-treated ribbons for magneto-mechanical resonance characterization were cut to a length of about 36-39 mm and typical magnetoresonant properties of the 2 amorphous strip pieces stacked together are shown in Table 4. The following designations were accepted : is the transport ribbon speed, m/min; Tmzl is the temperature of the unit working space where the ribbon leaves a magnetic zone ⁰C; Lcz is the length of cooling zone, cm; Tcz is the temperature at the center of cooling zone , ⁰C ; Lmz is the magnetic zone length, cm; Lczm is the length of cooling zone exposed to the magnetic field , cm; tczm is time of cooling under magnetic field, sec; AO is maximum amplitude signal at time t=0;Al is amplitude signal at time t=l ms at HOmax; Hk is the anisotropy field; HOmax is the bias field where the resonant amplitude has its maximum; Fr is resonant frequency; HFrmin is bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr(H).

Table 4 Magnetoelastic properties of the heat-treated ribbon exposed to magnetic field in an annealing zone and partly in a very short cooling zone with dramatic fall of temperature

Table 4 shows that decrease of the cooling time under magnetic field due to increase of the ribbon transport speed results in the raise of the slope coefficient KsI , the ring-down coefficient KA0/A1 and decrease of the anisotropy field Hk. It means that the ribbon transport speed and therefore the heat treatment productivity are mainly determined by the length of cooling zone where the ribbon is cooled down room temperature. EXAMPLE 5

Glassy metal alloy having composition as Ni₂o.5Co₂9.5Fe₂6 Mo₃Cr₃Bi_7-99Sn_0-Oi was prepared in the same manner as in example 1. The ribbons, typically 25 μm thick and about 4, 5 and 6 mm wide, were cast at temperatures 1220⁰C and they were strong and ductile. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit by transporting the ribbon 23 from one reel 22 to another reel 21 at speed 5 m/min. All three types of the ribbons were heat treated at 420 ⁰C in the same way as the amorphous ribbon in Example 2, Exp. No 7. So heat-treated ribbons for magneto-mechanical resonance characterization were cut to a length of about 36-39 mm and three types of magnetoelastic markers were prepared.

The first one consisted of two strip pieces disposed in a stacked manner having widths 4 mm and 6 mm. The second marker consisted of two strip pieces disposed in a stacked manner having widths 5 mm and 6 mm and the third marker consisted of two strip pieces disposed in a stacked manner having widths 6 mm. Typical magnetoresonant properties of the two amorphous strip pieces having different width stacked together are shown in Table 5 and Fig.8.

Table 5 Magnetoelastic properties of the two amorphous strip pieces heat treated with exposition of them to the magnetic field only in the cooling zone

As it follows from Table 5 and Fig.8 the magneto- mechanical markers containing magnetostrictive elements produced in accordance with the inventive technology and consisting of the strip pieces having different width have output signal amplitude lower by 15-20% than those made of the two 6mm wide strips. But, nevertheless, the markers made of the two strip pieces of different width have high enough output signal amplitude and due to good sensitivity (dFr/dH) , low value of the ring-down coefficient KA0/A1 and lower consumption of the amorphous ribbon there is a possibility to produce markers with lower production cost.

Therefore, markers made from magnetostrictive strip pieces of different width are especially suitable for use in article surveillance system that employs excitation and detection of magneto-mechanical resonance.

EXAMPLE 6

Glassy metal alloys having different compositions as indicated in Table 6 were prepared in the same manner as in example 5. The ribbons, typically 22 μm thick and about 6 mm wide, were cast at temperatures 1220⁰C and they were strong and ductile. The cast ribbons were annealed and cooled in continuous mode in two-zone heat treatment unit by transporting the ribbon 23 from one reel 22 to another reel 21 at speed 5 m/min. All ribbons were heat treated in the same way as the amorphous ribbon in Example 2, Exp. No 9. Temperature and time of ribbons annealing are shown in Table 6 as well.

For magneto-mechanical resonance of characterization, so heat-treated ribbons of different compositions were cut to a length of about 36-39 mm and the two strip pieces magnetostrictive resonators were prepared.

Typical magneto- resonant properties of the inventive resonators made from ribbon of different compositions are shown in Table 7 and Fig.9. For comparison, the magnetic properties of the two 6 mm amorphous magnetostrictive strip pieces stacked together produced by Sensormatic Electronics Corporation are shown as well.

The following designations were accepted : AO is maximum amplitude signal at time t=0;Al is amplitude signal at time t=l ms at HOmax; Hk is the anisotropy field; HOmax is the bias field where the resonant amplitude has its maximum; HFrmin is bias field where the resonant frequency has its minimum; KsI or dFr/dH is the slope of Fr(H), KAO /Al is the ring-down coefficient.

Table 7 Magnetoelastic properties of the two strip pieces resonators made from different alloys ribbons

As it follows from data given in table 7 and Fig.9 the magnetostrictive resonators made from almost all inventive alloys containing tin and cast at low temperature demonstrate higher amplitude signal than that of the Sensormatic resonators. Moreover the maximum value of the amplitude signal is produced when the magnetostrictive strip pieces are biased with dc magnetic field of strength ranging from 6 to 8 Oe. All resonators, but AM- 6, have good slope value, dFr/dH, which ranges from 0.60 to 0.72 kHz/Oe. Resonator AM - 6 can be used in electronic surveillance system if its magnetostrictive element contains three amorphous strip pieces as with increase of number of strip pieces in the resonator, the maximum value of the amplitude signal is shifted to the higher value of the biasing field strength and the slope coefficient (KAO /Al) value is decreased as well. In addition, in case of resonator AM-7, when maximum value of the amplitude signal is about 10 Oe and it is recommended to use one strip resonator to shift it to the lower value of the bias field strength. Fig.10 illustrates in what way the position of maximum value of the resonance amplitude is changed with an increase of strip pieces number in the resonator.

Finally, the magneto-mechanical markers containing magnetostrictive elements of the present invention are a significant improvement over conventional materials used in the prior art.

Claims

1. Amorphous metallic alloy for a magnetoristrictive element characterized in that, the alloy has the following composition:

Ni_aFe_bCo_cM \M ' ' _mB_dS i_e

wherein M' is at least one element from the group consisting of Cr, Mn, and Mo, and M' ' is at least one element from the group consisting of surface active elements Sn, Pb and Bi, and "a" ranges from 10 to 32, "b" ranges from 22 to 29.5, "c" ranges from 15 to 35, "ά" ranges from 15 to 25 , "e" ranges from 0 to 3, "k" and is the sum of amount of elements of group M' and ranges from 5.1 to 10, "m" is the sum of amount of elements of group M'' and ranges from 0.001 to 0.04 and sum "a" to "m" is 100.

2. Alloy of claim 1, wherein the alloy contains 0.001 to 0.3 at % Sn.

3. Alloy of claim 2, wherein the alloy contains 0.005 at % Sn.

4. Alloy according claim 1, wherein the alloy has the following composition:

Ni₂OCo₃OFe₂GMo₃Cr₃Bi_{7 - 99}Sn₀. oi or Ni₂₄Co₂₆Fe₂₇Mo_{2 - 6}Cr_{2 - 5}Bi_{7 - 89}Sn_{0 -} Oi or Ni ₂L ₅Co₂₉.5 Fe₂₆Mo_{2 - 6}Cr_{2 - 5}Bi₇ . 895 S n₀ . o o5 .

5. Magneto-mechanical marker for use in a theft detection system comprising at least one magnetoristrictive element at least partially made of an alloy according to claims 1 to 4.

6. Marker of claim 5, wherein the magneto-mechanical marker contains at least one magnetostrictive element and at least one ferromagnetic element, whereby said magnetoristrictive element and said ferromagnetic element are arranged in a way that said magnetostrictive element is biased with dc magnetic field ranging from 3,0 to 10,0 Oe.

7. Marker of claim 5 or 6, wherein the magnetostrictive element comprises at least one magnetostrictive strip having a length and width and the respective width ranging from 1 to 10 mm.

8. Marker of claim 5 to 7, wherein the magnetostrictive element comprises at least two magnetostrictive strip pieces disposed in a stack each having a length and a width, and respective widths of said strip pieces being substantially equal or different and not exceeding 10 mm and the respective lengths of said at least two magnetostrictive elements being substantially equal.

9. Marker of claim 5 to 8, wherein the magnetostrictive element comprises three magnetostrictive strip pieces disposed in a stack, two of them having substantially equal widths and the third one having substantially different width and the respective lengths of all of them are substantially equal.

10. Marker of claim 5 to 9, wherein two magnetoristrictive strip pieces have a width of 4 mm and the third one has a width of 5 mm.

11. Marker of claim 5 to 9, wherein the two magnetoristrictive strip pieces have a width of 4 mm and the third one has a width of 6 mm.

12. Marker of claim 5 to 9, wherein the two magnetoristrictive strip pieces have a width of 5 mm and the third one has a width of 4 mm.

13. Marker of claim 5 to 9, wherein the two magnetoristrictive strip pieces have a width of 5 mm and the third one has a width of 6 mm.

14. Marker of claim 5 to 9, wherein the two magnetoristrictive strip pieces have a width of 6 mm and the third one has a width of 4 mm.

15. Marker of claim 5 to 9, wherein the two magnetoristrictive strip pieces have a width of 6 mm and the third one has a width of 5 mm.

16. Marker of claim 5 to 9, wherein the marker consists of three magnetostrictive strip pieces disposed in a stack, all three strip pieces having substantially different widths and substantially equal lengths.

17. Marker of claim 5 to 9, the three strip pieces have a width of 4 mm, 5 mm, and 6 mm, respectively.

18. Marker of claim 5 to 8, wherein the marker consists of two magnetostrictive strip pieces disposed in a stack having substantially equal widths and the same length.

19. Marker of claim 5 to 8, wherein the marker consists of two magnetostrictive strip pieces disposed in a stack having substantially different widths and the same length.

20. Marker of claim 5 to 8, wherein said two magnetoristrictive strip pieces have a width of 4 mm and 5 mm.

21. Marker of claim 5 to 8, wherein said two magnetoristrictive strip pieces have a width of 4 mm and 6 mm .

22. Marker of claim 5 to 8, wherein the two said two magnetoristrictive strip pieces have a width of 5 mm and 6 mm.

23. Method of manufacturing a magnetoristrictive strip of a marker according to claims 5 to 22, comprising the steps of

- providing an alloy with a composition according to claim 1 to 4

- treatment of the melt with overheating technique prior to casting and

- casting an amorphous ribbon at temperature equal or below 1250⁰C. ^•

24. Method of claim 23, further comprising the steps of

- heat-treating said amorphous ribbon in a continuous mode in two consecutive hot and cold regions,

25. Method of claim 23 or 24, wherein the alloy has the composition :

Ni₂L₅Co₂₉.5Fe₂₆Mo₂.6Cr_2-5Bi₇.895Sn₀. oo5,

said alloy is cast at temperature of 1220⁰C.

26. Method of claim 23 to 25, wherein the magnetic field is directed perpendicularly to the longitudinal axis of the ribbon in the cold region and partly in the first region neighboring the cold zone.

27. Method of claim 23 to 26, wherein said ribbon is heat treated in a continuous mode in two consecutive hot and cold regions the first region having temperature of 420⁰C while the second region having temperature below 300⁰C.

28. Method of claim 27, wherein said second region having temperature of 20 to 6O⁰C.

29. Method of claim 23 to 28, wherein two strip pieces are disposed in a stacked manner having widths of 4 mm and 5 mm .

30. Method of claim 23 to 28, wherein two strip pieces are disposed in a stacked manner having widths of 4 mm and 6 mm.

31. Method of claim 23 to 28, wherein two strip pieces are disposed in a stacked manner having widths of 5 mm and 6 mm.

32. Method of claim 23 to 28, wherein two strip pieces are disposed in a stacked manner having the same widths of 6 mm.

33. Method of claim 23 to 28, wherein the magnetostrictive element consists of three magnetostrictive strip pieces disposed in a stack two of them having substantially equal widths and the third one having substantially different width and the respective lengths of all of them are substantially equal.

34. Method of claim 33, wherein the two strip pieces have a width of 4 mm and the third one has a width of 5 mm.

35. Method of claim 33, wherein the two strip pieces have a width of 4 mm and the third one has a width of 6 mm.

36. Method of claim 33, wherein the two strip pieces have a width of 5 mm and the third one has a width of 4 mm.

37. Method of claim 33, wherein the two strip pieces have a width of 5 mm and the third one has a width of 6 mm.

38. Method of claim 33, wherein the two strip pieces have a width of 6 mm and the third one has a width of 4 mm.

39. Method of claim 33, wherein the two strip pieces have a width of 6 mm and the third one has a width of 5 mm.