CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of US Application Serial No.08/465,051 , filed

June 6, 1995 which, in turn, is a continuation-in-part of Serial No. 08/421.094, filed April 13, 1995 entitled Metallic Glass Alloys for Mechanically Resonant Marker Surveillance Systems.

BACKGROUND OF THE INVENTION

L Field of the Invention

This invention relates to metallic glass alloys; and more particularly to metallic glass alloys suited for use in mechanically resonant markers of article surveillance systems.

2. Description of the Prior Art

Numerous article surveillance systems are available in the market today to help identify and/or secure various animate and inanimate objects. Identification of personnel for controlled access to limited areas, and securing articles of merchandise against pilferage are examples of purposes for which such systems are employed.

An essential component of all surveillance systems is a sensing unit or "marker", that is attached to the object to be detected. Other components of the system include a transmitter and a receiver that are suitably disposed in an "interrogation" zone. When the object carrying the marker enters the interrogation zone, the functional part of the marker responds to a signal from the transmitter, which response is detected in the receiver. The information contained in the response signal is then processed for actions appropriate to the application: denial of access, triggering of an alarm, and the like.

Several different types of markers have been disclosed and are in use. In one type, the functional portion of the marker consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit When placed in an electromagnetic field transmitted by the interrogation apparatus, the antenna-diode marker generates harmonics of the interrogation frequency in the receiving antenna. The detection of the harmonic or signal level change indicates the presence of the marker. With this type of system, however, reliability of the marker identification is relatively low due to the broad bandwidth of the simple resonant circuit Moreover, the marker must be removed after identification, which is not desirable in such cases as antipilferage systems

A second type of marker consists of a first elongated element of high magnetic permeability ferromagnetic material disposed adjacent to at least a second element of ferromagnetic material having higher coercivity than the first element. When subjected to an interrogation frequency of electromagnetic radiation, the marker generates harmonics of the interrogation frequency due to the non-linear characteristics of the marker The detection of such harmonics in the receiving coil indicates the presence of the marker Deactivation of the marker is accomplished by changing the state of magnetization of the second element, which can be easily achieved, for example, by passing the marker through a dc magnetic field. Harmonic marker systems are superior to the aforementioned radio-frequency resonant systems due to improved reliability of marker identification and simpler deactivation method Two major problems, however, exist with this type of system, one is the difficulty of detecting the marker signal at remote distances. The amplitude of the harmonics generated by the marker is much smaller than the amplitude of the interrogation signal, limiting the detection aisle widths to less than about three feet. Another problem is the difficulty of distinguishing the marker signal from pseudo signals generated by other ferromagnetic objects such as belt buckles, pens, clips, etc.

Surveillance systems that employ detection modes incorporating the fundamental mechanical resonance frequency of the marker material are especially advantageous systems, in that they offer a combination of high detection sensitivity, high operating reliability, and low operating costs Examples of such systems are disclosed in U S Patent Nos 4,510,489 and 4,510,490 (hereinafter the '489 and '490 patents)

The marker in such systems is a strip, or a plurality of strips, of known length of a ferromagnetic material, packaged with a magnetically harder ferromagnet (material with a higher coercivity) that provides a biasing field to establish peak magneto-mechanical coupling The ferromagnetic marker material is preferably a metallic glass alloy ribbon, since the efficiency of magneto-mechanical coupling in these alloys is very high. The mechanical resonance frequency of the marker material is dictated essentially by the length of the alloy ribbon and the biasing field strength When an interrogating signal tuned to this resonance frequency is encountered, the marker material responds with a large signal field which is detected by the receiver The large signal field is partially attributable to an enhanced magnetic permeability of the marker material at the resonance frequency Various marker configurations and systems for the interrogation and detection that utilize the above principle have been taught in the '489 and '490 patents

In one particularly useful system, the marker material is excited into oscillations by pulses, or bursts, of signal at its resonance frequency generated by the transmitter When the exciting pulse is over, the marker material will undergo damped oscillations at its resonance frequency, i e , the marker material "rings down" following the termination of the exciting pulse The receiver "listens" to the response signal during this ring down period Under this arrangement, the surveillance system is relatively immune to interference from various radiated or power line sources and, therefore, the potential for false alarms is essentially eliminated

A broad range of alloys have been claimed in the '489 and '490 patents as suitable for marker material, for the various detection systems disclosed. Other metallic glass alloys bearing high permeability are disclosed in U.S. Patent No. 4, 152, 144. A major problem in use of electronic article surveillance systems is the tendency for markers of surveillance systems based on mechanical resonance to accidentally trigger detection systems that are based an alternate technology, such as the harmonic marker systems described above The non-linear magnetic response of the marker is strong enough to generate harmonics in the alternate system, thereby accidentally creating a pseudo response, or "false" alarm. The importance of avoiding interference among, or "pollution" of, different surveillance systems is readily apparent. Consequently, there exists a need in the art for a resonant marker that can be detected in a highly reliable manner without polluting systems based on alternate technologies, such as harmonic re-radiance. There further exists a need in the art for a resonant marker that can be cast reliably in high yield amounts, is composed of raw materials which are inexpensive, and meets the detectability and non-polluting criteria specified hereinabove.

SUMMARY OF INVENTION The present invention provides magnetic alloys that are at least 70% glassy and, upon being cross-field annealed to enhance magnetic properties, are characterized by substantially linear magnetic responses in a frequency regime wherein harmonic marker systems operate magnetically. Such alloys can be cast into ribbon using rapid solidification, or otherwise formed into markers having magnetic and mechanical characteristics especially suited for use in surveillance systems based on magneto-mechanical actuation of the markers. As used herein, the term "cross-field annealed" means an anneal carried out on a strip having a length direction and a width direction, wherein the magnetic field used in the anneal is applied substantially in the plane of the ribbon across the width direction, and the

direction of the magnetic field is about 90 ° with respect to the length direction. Generally stated the glassy metal alloys of the present invention have a composition consisting essentially of the formula Fe _a Cθb Ni _c Mj B _e Sif C _g , where M is selected from molybdenum , chromium and manganese and "a", "b", "c", "d", "e", "f ' and "g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 8 to about 18 and "c" ranges from about 20 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 12 to about 20 , "f ranges from about 0 to about 5 and "g" ranges from about 0 to about 2. Ribbons of these alloys having dimensions of about 38mmxl2.7mmx20μm , when mechanically resonant at frequencies ranging from about 48 to about 66 kHz, evidence substantially linear magnetization behavior up to an applied field of 8 Oe or more as well as the slope of resonant frequency versus bias field between about 500 Hz/Oe and 750 Hz/Oe. Moreover, voltage amplitudes detected at the receiving coil of a typical resonant- marker system for the markers made from the alloys of the present invention are comparable to or higher than those of the existing resonant marker of comparable size. These features assure that interference among systems based on mechanical resonance and harmonic re-radiance is avoided

The metallic glasses of this invention are especially suitable for use as the active elements in markers associated with article surveillance systems that employ excitation and detection of the magneto-mechanical resonance described above. Other uses may be found in sensors utilizing magneto-mechanical actuation and its related effects and in magnetic components requiring high magnetic permeability

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the preferred embodiments of the invention and the accompanying drawings in which:

Fig. 1(a) is a magnetization curve taken along the length of a conventional resonant marker, where B is the magnetic induction and H is the applied magnetic field;

Fig. 1(b) is a magnetization curve taken along the length of the marker of the present invention, where H _a is a field above which B saturates;

Fig. 2 is a signal profile detected at the receiving coil depicting mechanical resonance excitation, termination of excitation at time t ₀ and subsequent ring- down, wherein V ₀ and V] are the signal amplitudes at the receiving coil at t = t ₀ and t = ti ( 1 msec after t _D ), respectively; and Fig. 3 is the mechanical resonance frequency, f _r , and response signal . V, , detected in the receiving coil at 1 msec after the termination of the exciting ac field as a function of the bias magnetic field, Hb, wherein H _b i and Hb ₂ are the bias fields at which V _! is a maximum and f _r is a minimum, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, there are provided magnetic metallic glass alloys that are characterized by substantially linear magnetic responses in the frequency region where harmonic marker systems operate magnetically. Such alloys evidence all the features necessary to meet the requirements of markers for surveillance systems based on magneto-mechanical actuation. Generally stated the glassy metal alloys of the present invention have a composition consisting essentially of the formula Fe _a Cθb Ni _c Md B _e Si _f C _g , where M is selected from molybdenum, chromium and manganese and "a", "b", "c", "d", "e", "f ' and "g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 8 to about 18 and "c" ranges from about 20 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 12 to about 20 , "f ranges from about 0 to about 5 and "g" ranges from about 0 to about 2. The purity of the above compositions is that found in normal commercial practice. Ribbons of

these alloys are annealed with a magnetic field applied substantially in the plane of the ribbon across the width of the ribbon at elevated temperatures below alloys' crystallization temperatures for a given period of time. The field strength during the annealing is such that the ribbons saturate magnetically along the field direction. Annealing time depends on the annealing temperature and typically ranges from about a few minutes to a few hours. For commercial production, a continuous reel-to-reel annealing furace is preferred. In such cases, ribbon travelling speeds may be set at about between 0.5 and about 12 meter per minute. The annealed ribbons having, for example, a length of about 38 mm. exhibit substantially linear magnetic response for magnetic fields of up to 8 Oe or more applied parallel to the marker length direction and mechanical resonance in a range of frequencies from about 48 kHz to about 66 kHz. The linear magnetic response region extending to the level of 8 Oe is sufficient to avoid triggering some of the harmonic marker systems. For more stringent cases, the linear magnetic response region is extended beyond 8 Oe by changing the chemical composition of the alloy of the present invention. The annealed ribbons at lengths shorter or longer than 38 mm evidence higher or lower mechanical resonance frequencies than 48-66 kHz range The annealed ribbons are ductile so that post annealing cutting and handling cause no problems in fabricating markers. Most metallic glass alloys that are outside of the scope of this invention typically exhibit either non-linear magnetic response regions below 8 Oe level or H. levels close to the operating magnetic excitation levels of many article detection systems utilizing harmonic markers. Resonant markers composed of these alloys accidentally trigger, and thereby pollute, many article detection systems of the harmonic re-radiance variety.

There are a few metallic glass alloys outside of the scope of this invention that do show linear magnetic response for an acceptable field range. These alloys, however, contain high levels of cobalt or molybdenum or chromium, resulting in increased raw material costs and/or reduced ribbon castability owing to the higher

melting temperatures of such constituent elements as molybdenum or chromium. The alloys of the present invention are advantageous, in that they afford, in combination, extended linear magnetic response, improved mechanical resonance performance, good ribbon castability and economy in production of usable ribbon Apart from the avoidance of the interference among different systems, the markers made from the alloys of the present invention generate larger signal amplitudes at the receiving coil than conventional mechanical resonant markers This makes it possible to reduce either the size of the marker or increase the detection aisle widths, both of which are desirable features of article surveillance systems

Examples of metallic glass alloys of the invention include Fe ₄ oCθi8 Ni ₂ 45 B ₍₅ Si ₂₅ , Fe ₄ o Co, ₈ Ni ₂₅ B _i5 Si ₂ , Fe ₄₀ Cθι ₈ Ni ₂ 48B|5 Si ₂₂ , Fe ₃₂ Cθ] _g Ni ₃₂₅ Bn Si ₄₅ , Fe ₄₀ Cθι ₆ Ni ₂₆ Bπ Sii, Fe ₄ o Cθι ₆ Ni ₂₇ Bι _? Si ₄ , Fe ₄ o Co i6 Ni _2g BH Si ₂ , Fe ₄ 5 Co _u Ni ₂₄ Bι ₆ Sii, Fe ₄₄ Cθι ₄ Ni ₂₄ Bι ₆ Si ₂ , Fe ₄ 4 Co _I4 Ni ₂₄ Bι ₈ , Fe ₄ 4 Cθ| ₂ Ni ₂₉ B( ₅ , Fe ₄ 4 Co ₎₂ Ni ₂₈ B _t3 Si ₃ , Fe ₄ ? Co ₎₂ Ni ₃₀ B _i3 Si ₂ , Fe ₄₂ Co ₎₂ Ni3o Bι ₆ , Fe ₄₂ Co^ Ni ₃₀ Bι ₅ Sii, Fe ₄₂ Co ₁₂ Ni _?0 B ₁₄ Si ₂ , Fe ₄₂ Cθj ₂ Nio Bι ₃ Si ₃ , Fe ₄ ι ₈ Cθn ₉ Ni ₂₉₈ B] ₆ Si ₀ 5, Fe ₄ i5 Co _π9 Ni _:9 6 B| ₆ Si, , Fe ₄₀ Co, ₂ Ni _?3 B| ₅ , Fe ₄₀ Co ₎₂ Ni ₃₂ B _!3 Si ₃ , Fe _?8 5 Co _π9 Ni _: , ₂ 6 B ₎₆ Si 1 , Fe _3g Cθι ₂ Ni ₃₅ B15, Fe ₃₆ Cθι ₂ Ni ₃ τ Bι ₅ , Fe ₃₅ 8 Cou ₉ Ni ₃₆ s B _I5 Sin 5, Fe ₃₅ 6 Cθn9Ni365 B ₎₅ Sii, Fe354Cθn ₈ Ni ₃₆ 3 B15 Sii 5, Fe ₄₄ Coio Ni ₃ ι B ₎₅ ,

Fe ₄₂ Coio Ni ₃₃ B15, Fe ₄ o Coio Ni ₃ s B _]5 , Fe ₄₀ Cθι ₀ Ni3 ₅ B _M Sii , Fe ₃₉ Coio Ni ₃ s B15 Sii, Fe ₃₉ Coio Ni ₃₄ B15 Si ₂ , Fe ₃ s Co _]0 Ni ₃₇ B _]5 , Fe _? 6 Coio Ni ₃₉ B _]5 , Fe _?6 Co ₁₀ Ni ₃ 8 B _iS Sii, Fe ₄ 5 Co ₈ Ni ₃₂ B15, Fe ₄₂ Co ₈ Ni ₃₄ Bι ₄ Si ₂ , Fe ₄₂ Co ₈ Ni ₃₄ Bι ₅ Siι, Fe4oCo _g Ni ₃₇ B,5, and Fe ₃ g.5 Cθ8Ni ₃₈ 5 B15 , wherein subscripts are in atom percent. The magnetization behavior characterized by a B-H curve is shown in Fig.

1 (a) for a conventional mechanical resonant marker, where B is the magnetic induction and H is the applied field. The overall B-H curve is sheared with a non¬ linear hysteresis loop existent in the low field region. This non-linear feature of the marker results in higher harmonics generation, which triggers some of the

harmonic marker systems, hence the interference among different article surveillance systems

The definition of the linear magnetic response is given in Fig I (b) As a marker is magnetized along the length direction by an external magnetic field. H, the magnetic induction, B, results in the marker The magnetic response is substantially linear up to H _a , beyond which the marker saturates magnetically The quantity H _a depends on the physical dimension of the marker and its magnetic anisotropy field To prevent the resonant marker from accidentally triggering a surveillance system based on harmonic re-radiance, H _a should be above the operating field intensity region of the harmonic marker systems

The marker material is exposed to a burst of exciting signal of constant amplitude, referred to as the exciting pulse, tuned to the frequency of mechanical resonance of the marker material The marker material responds to the exciting pulse and generates output signal in the receiving coil following the curve leading to V ₀ in Fig 2 At time t ₀ , excitation is terminated and the marker starts to ring- down, reflected in the output signal which is reduced from V _c to zero over a period of time At time t _t , which is 1 msec after the termination of excitation, output signal is measured and denoted by the quantity Vi Thus Vj / V ₀ is a measure of the ring-down Although the principle of operation of the surveillance system is not dependent on the shape of the waves comprising the exciting pulse, the wave form of this signal is usually sinusoidal The marker material resonates under this excitation

The physical principle governing this resonance may be summarized as follows: When a ferromagnetic material is subjected to a magnetizing magnetic field, it experiences a change in length. The fractional change in length, over the original length, of the material is referred to as magnetostriction and denoted by the symbol λ A positive signature is assigned to λ if an elongation occurs parallel to the magnetizing magnetic field. The quantity λ increases with the magnetizing

magnetic field and reaches its maximum value termed as saturation magnetostriction, λ _s .

When a ribbon of a material with a positive magnetostriction is subjected to a sinusoidally varying external field, applied along its length, the ribbon will undergo periodic changes in length, i.e., the ribbon will be driven into oscillations The external field may be generated, for example, by a solenoid carrying a sinusoidally varying current. When the half-wave length of the oscillating wave of the ribbon matches the length of the ribbon, mechanical resonance results. The resonance frequency f _r is given by the relation f _r = ( l/2L)(E/D) ^{0 5} , where L is the ribbon length, E is the Young's modulus of the ribbon, and D is the density of the ribbon.

Magnetostrictive effects are observed in a ferromagnetic material only when the magnetization of the material proceeds through magnetization rotation. No magnetostriction is observed when the magnetization process is through magnetic domain wall motion Since the magnetic anisotropy of the marker of the alloy of the present invention is induced by field-annealing to be across the marker width direction, a dc magnetic field, referred to as bias field, applied along the marker length direction improves the efficiency of magneto-mechanical response from the marker material. It is also well understood in the art that a bias field serves to change the effective value for E, the Young's modulus, in a ferromagnetic material so that the mechanical resonance frequency of the material may be modified by a suitable choice of the bias field strength. Fig. 3 explains the situation further: The resonance frequency, f _r , decreases with increasing bias field, H _b , reaching a minimum, (fr),™, at Hb ₂ . The quantity Hb ₂ is related to the magnetic anisotropy of the marker and thus directly related to the quantity H _a defined in Fig. lb. Thus use of Hb ₂ can be conveniently adopted as a measure of the quantity H _a . The signal response, Vi , detected , say at t = ti at the receiving coil, increases with Hb , reaching a maximum, V _m , at Hbi. The slope, df _r /dH _b. near the

operating bias field is an important quantity, since it related to the sensitivity of the surveillance system.

Summarizing the above, a ribbon of a positively magnetostrictive ferromagnetic material, when exposed to a driving ac magnetic field in the presence of a dc bias field, will oscillate at the frequency of the driving ac field, and when this frequency coincides with the mechanical resonance frequency, f _r , of the material, the ribbon will resonate and provide increased response signal amplitudes. In practice, the bias field is provided by a ferromagnet with higher coercivity than the marker material present in the "marker package" Table I lists typical values for V _m , H _b ι, (f _r ) _πun and H _b2 for a conventional mechanical resonant marker based on glassy Fe4o Ni ₃ g Mo ₄ Big . The low value of H _b2 , in conjunction with the existence of the non-linear B-H bahavior below Hb ₂ , tends to cause a marker based on this alloy to accidentally trigger some of the harmonic marker systems, resulting in interference among article surveillance systems based on mechanical resonance and harmonic re-radiance..

TABLE I Typical values for V _m , Hbi , (fr )mm and H _>2 for a conventional mechanical resonant marker based on glassy as cast Fe ₄ o Ni ₃ g Mo ₄ Big . This ribbon having a dimension of about 38.1mm x 12.7mm x 20 μm has mechanical resonance frequencies ranging from about 57 and 60 kHz.

Vn. (mV) HbiiOe) (f _t U (kHz) H^jOe)

150-250 4-6 57-58 5-7

Table II lists typical values for H _a , V _m , Hbi, (f _r ) _m ui . Hb ₂ and df _r /dHb Hb for the alloys outside the scope of this patent Field-annealing was performed at 380 °C in a continuous reel-to-reel furnace on 12.7 mm wide ribbon where ribbon speed was from about 0.6 m/min. to about 1.2 m/min. The dimension of the ribbon-shaped marker was about 38 1mm x 12.7 mm x 20 μm.

TABLE II

Values for H _a , V _m , H _b ι, (f _r ) _m ι _n , H _h2 and df _r /dH _b taken at H _b = 6 Oe for the alloys outside the scope of this patent. Field-annealing was performed in a continuous reel-to-reel furnace at 380 °C where ribbon speed was from about 0 6 m/min. to about 1.2 m/min with a magnetic field of about 1 4 kOe applied perpendicular to the ribbon length direction.

Composition jal %> H, (Oe) V„, (mV) JIulOe] αUn OJiz) H _h; (Qe) df, dfi, ( Hz Oe)

V Co^ Feio Bu Si, 22 400 7 0 -49 7 15.2 700

B Coj ₈ Fe« NuBuSi, 20 420 9 3 53 8 164 500

C Co; Fe4o N-,„ B,jSι, 10 400 3 0 50.2 6.8 2.080

D Co„.Fe ₄₀ Ni;Λln,BιjSι> 7 5 400 2 7 50 5 6 8 2.300

.Although alloys A and B show linear magnetic responses for acceptable magnetic field ranges, but contain high levels of cobalt, resulting in increased raw material costs. Alloys C and D have low Hbi values and high df _r /dHb values, combination of which are not desirable from the standpoint of resonant marker system operation.

EXAMPLES

Example 1 Fe-Co-Ni-B-Si metallic glasses

1 Sample Preparation

Glassy metal alloys in the Fe-Co-Ni-B-Si system were rapidly quenched from the melt following the techniques taught by Narasimhan in U S Patent No 4, 142.571. the disclosure of which is hereby incoφorated by reference thereto All casts were made in an inert gas, using 0 1 - 60 kg melts The resulting ribbons, typically 25 μm thick and about 12 7 - 50 5 mm wide, were determined to be free of significant crystallinity by x-ray diffractometry using Cu-Kα radiation and differential scanning calorimetry Each of the alloys was at least 70 % glassy and, in many instances, the alloys were more than 90 % glassy Ribbons of these glassy metal alloys were strong, shiny, hard and ductile

The ribbons for magneto-mechanical resonance characterization were heat treated with a magnetic field applied across the width of the ribbons and were cut to a length of about 38 mm The strength of the magnetic field wasl 4 kOe and its direction was about 90° respect to the ribbon length direction and substantially in the plane of the ribbon The speed of the ribbon in the reel-to-reel annealing furnace was changed from about 0 5 meter per minute to about 12 meter per minute

2 Characterization of magnetic properties

Each marker material having a dimension of about 38 1mm x 12 7mm x 20μm or 38 1mm x 6.0mm x 20 μm was tested by applying an ac magnetic field applied along the longitudinal direction of each alloy marker with a dc bias field changing from 0 to about 15 Oe The sensing coil detected the magneto-

mechanical response of the alloy marker to the ac excitation. These marker materials mechanically resonate between about 48 and 66 kHz. The quantities characterizing the magneto-mechanical response were measured and are listed in Table III and Table IV

TABLE III

Values of H _a , V _m , H _b ι , (f _r )mιn , H _>2 and df _r /dH _b taken at H _b = 6 Oe for the alloys of the present invention heat-treated at 360 °C in a continuous reel-to- reel furnace with a ribbon speed of about 8 m/minute. The annealing field was about 1.4 kOe applied peφendicular to the ribbon length direction and substantially within the plane of the ribbon The dimension of the ribbon-shaped marker was about 38.1mm x 12.7mm x 20μm. Asterisks indicate 'not measured' due to instrument limitation.

Aliov V _τ (mV) Hhi (Oe) (f\ _m (kHz) H _b: (Oe) df, /dH. (Hz/Oe)

Fe _4f) Co ₁₈ Ni _24.5 Bι ₅ Si ₂₅ 280 8.0 53.2 13.5 680

Fe ₄ n Coig Ni ₂₅ B ₎₅ Si ₂ 350 8.6 53.5 13.7 510

Fe ₄₀ Cθ| ₈ Ni ₂₄₈ Bis Si ₂₂ 480 9.6 52.9 14.6 620 Fe _3: Cθι ₈ Ni ₃₂₅ B _]3 Si ₄₅ 440 7.5 53.5 12.7 600

FcoCθi6 Ni ₂₆ Bi7 Si, 480 7.9 52.5 144 640

Fe ₄₀ Co, ₆ Ni ₂₇ Bι ₃ Si ₄ 520 8.4 51.0 13.8 740

Fe ₄ n Co,6 Ni ₂₈ B _M Si ₂ 480 10.2 * >15 500

Fe ₄₅ Co ₎₄ Ni ₂₄ B ₎₆ Sii 480 8.2 * >15 700 Fe ₄₄ Co ₎₄ Ni ₂₄ Bι ₆ Si ₂ 470 7.5 52.6 14.5 740

Fe ₄₄ Cθ| ₄ Ni ₂₄ Bι ₈ 450 7.5 * >15 670

Fe ₄₄ Co ₎₂ Ni ₂₉ Bis 470 9.8 * >15 530

Fe ₄₃ Con Ni ₃₀ B ₎₃ Si ₂ 420 8.5 * >15 520

Fe ₄₂ Cθι ₂ Ni ₃₀ Bι ₆ 470 8.7 * >15 550 Fe ₄₂ Cθι ₂ Ni ₃₀ B| ₅ Si, 450 9.0 51.6 15 620

Fe ₄₂ Co ₎₂ Ni _3n B ₎₄ Si ₂ 400 8.4 52.5 15 600

Fe ₄₂ Cθι ₂ Nι ₃₀ B _i3 Sι ₃ 500 73 506 145 730

Fe ₄ | 8 Cθ|| 9 Nl ₂₉₈ B|6 Sios 480 80 * >15 620

Fe ₄₀ Cθι: Nι ₃₃ B,s 430 98 * >15 500

Fe _4ϋ Cθι ₂ Nι ₃₂ B ₎₃ Sι ₃ 490 85 509 144 650

Fe ₃₈ s Cθιi ₉ Nι ₃₂₅ Bι ₆ SI, 420 73 533 146 600

Fe ₃₆ Co, ₂ Nι ₃ -B,s 410 90 526 145 510

Fe ₃ s ₈ Cθ|ioNl ₃ 6gBi5 Slθ5 390 87 523 142 500

Fe ₃ s ₄ Co,, β Nh ₆ 3 Bis Sl| 5 310 75 536 124 610

Fe ₄₄ Coio Nin B|, 440 90 * >15 530

Fe _4: Co,,j Nι ₃₃ Bis 420 88 * >15 560

Fe ₄₀ CθιnNι ₃ sB|, 440 87 * >15 540

Fe ₄₀ Co, ₀ Nι ₃ s B, ₄ Si| 340 75 533 125 630

Fe ₃₉ Co,oNι ₃₅ Bis Si, 420 80 510 130 700

Fe ₃₉ Coio Nι ₃₄ Bis Sι ₂ 420 87 528 125 640

Fe ₃₈ CθιoNι ₃ - B,s 410 92 515 148 550

Fe ₃₆ Cθι ₀ Nι ₃₉ B, ₅ 390 85 528 126 640

Fe ₃₆ CθιoNι ₃₈ B,s Si, 400 78 526 133 620

Fe ₄ s Co ₈ Nι ₃₂ Bιs 410 80 * >15 640

Fe ₄₂ Co ₈ NH ₄ B, ₄ Sι ₂ 440 71 503 145 700

Fe ₄₂ Co ₈ Nι ₃₄ B ₎₅ Si, 470 72 509 142 690

Fe ₄₀ Co ₈ Nι ₃ -B, ₅ 430 82 513 139 650

Fe ₃₈₅ Co ₈ Nι ₃₈₅ B, ₅ 370 55 532 12 I 700

All the alloys listed in Table III exhibit H _b2 values exceeding 8 Oe, which make them possible to avoid the interference problem mentioned above Good sensitivity ( df _r /dH _b ) and large response signal ( V _m ) result in smaller markers for resonant marker systems

As examples of smaller marker, markers having a width less than one-half that of the conventional marker were tested The quantities characterizing the magneto-mechanical resonance of the marker material having a dimension of about 381mm x 6 Omm x 20μm are summarized in Table IV

TABLE IV

Values of H. , V _m , H _b ι , (f _r )mιn , H _b2 and df _r /dH _b taken at H _b = 6 Oe for the alloys of the present invention were heat-treated at 360 °C in a continuous reel-to-reel furnace with a ribbon speed of about 8 m/minute and were cut to strips having a dimension of about 381mm x 6 Omm x 20μm The annealing field was about 14 kOe applied peφendicular to the ribbon length direction and substantially in the plane of the ribbon Askeπsks indicate 'not measured' due to instrument limitation

Allov V _m (mV) H _h , (Oe) (£)„,,„ (kHz) H^ (Oe) df, /dH„ (Hz/Oe)

Fe ₄₀ Co, ₈ Ni: ₅ Bi ₅ Sι _: 220 85 548 145 540

Fe ₄₄ Cθι ₂ Nι _:g B, ₃ Sι ₃ 240 92 * >15 570

Fe ₄₃ Co, _: Nι ₃₀ Bn Sι ₂ 210 92 526 >15 520

Fe ₄₂ Co, _: NboBit, 220 75 517 148 600

Fe ₄₀ Cθι: Nι ₃₃ B,s 220 92 * >15 530

Fe ₃₈ Cθι: Nι ₃ s Bis 220 94 * >15 510

Fe ₃₆ Cθι ₂ Nι ₃₇ B, ₅ 220 95 514 144 560

Fe ₃₅ 6 Cθι,9Nι ₃₆₅ B,s Si, 230 80 516 143 590

Fe ₄₄ Co, ₀ Nι ₃ , B,s 180 85 527 15 550

Fe4oCo,oNi ₃₅ Bi5 230 83 52.8 145 580

Fe ₃₈ Coio Nι _r Bis 170 85 532 138 580

All the alloys listed in Table IV exhibit H _b2 values exceeding 8 Oe, which make them possible to avoid the interference problems mentioned above Good sensitivity ( df _r /dH _b ) and large magneto-mechanical resonance response signal (

V _m ) result in smaller markers for resonant marker systems. The marker of the present invention having a width less than one-half that of the conventional marker of Table I can achieve the level of the magneto-mechanical resonance response signal of the conventional marker.

Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that further changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.