EP0291726B1 - Amorphous alloy for strip-shaped sensor elements - Google Patents

Description

The invention relates to an amorphous alloy according to the preamble of claim 1 and a strip-shaped sensor element.

Narrow and thin strips of a well soft magnetic material are required for security labels. So far commercial strips made of both crystalline and amorphous material have been used. The usual dimensions here are strip widths less than 3 mm, strip thicknesses less than 40 µm and label lengths from 50 to 100 mm, in individual cases even less. It is important for the functioning of such strips that the material can be completely magnetized or re-magnetized with the smallest possible exciting magnetic fields. Due to the non-linearity of the magnetization curve of the strip when magnetic saturation is reached, when the magnetization is reversed in a corresponding receiver coil of an anti-theft system, z. B. harmonics of the excitation frequency are generated, which are used to detect the strip and thus a possible thief.

wobei w die Breite, t die Dicke, 1 die Länge des Streifens, B_s die Sättigungsinduktion und H_A das magnetische Anisotropiefeld bedeuten. Der Faktor α hängt ebenfalls, allerdings nur sehr schwach, von der Streifengeometrie ab und darf im wesentlichen als konstant angesehen werden.The field strength H _s , which is necessary for the complete magnetization of the strip, is essentially determined by the geometry of the strip (magnetic shear effect) and the magnetic anisotropy energy transverse to the strip direction. Here applies in Strip direction

where w is the width, t is the thickness, 1 is the length of the strip, B _{s is} the saturation induction and H _{A is} the magnetic anisotropy field. The factor α also depends, albeit only very weakly, on the strip geometry and can essentially be regarded as constant.

In order to arrive at a detectable, significant signal, the magnetic excitation field strength in current systems must be about the order of magnitude or greater than the saturation field strength H _s , if possible. On the other hand, z. B. to avoid false alarms by other ferromagnetic objects or for reasons of power requirements for the excitation field strength, to reduce unnecessary losses or heating, the excitation field strength should not be too large.

Similar relationships are often also found in magnetic field sensors for detecting magnetic fields. The sensitivity of these sensors generally increases with increasing strip length, whereby a regularity of the above-mentioned equation is also decisive.

Due to the special choice of the strip geometry, ie small width and thickness and relatively long label length, the demagnetizing field in the strip direction is significantly reduced according to the equation. This has the desired effect that the magnetic stripe can be remagnetized in relatively small excitation fields and thus delivers the desired signal.

Furthermore, the saturation field strength H _{s can be} further reduced by making the anisotropy field H _A almost disappear by special heat treatments. This is e.g. B. the case for magnetic material with an intrinsically rectangular magnetization loop, which is why such a material turned out to be particularly suitable in many cases.

So far, the optimization of the magnetic strips for theft protection labels has been carried out by coordinating geometry and partial heat treatment on commercially available magnetic material, the heat treatment taking place in the magnetic field parallel to the longitudinal axis of the tape.

Problems arise, however, if the space available and thus the strip length 1 are limited for spatial reasons (e.g. miniaturization). In order to achieve a small shear field in such cases, w · t · B _s (see equation) must be reduced accordingly. To a certain extent, this can be done by reducing the width w and thickness t. With very small widths and thicknesses, however, problems arise in the manufacture and handling of tape (or wire) with such a small cross-section.

The invention has for its object to find an amorphous alloy with which, if necessary, the length of the strip-shaped sensor elements can be reduced in the sense of miniaturization, it must be ensured that the desired function can also be performed. This object is achieved by an amorphous alloy with the features of claim 1 and by the sensor element according to claim 5.

The present invention is based on the knowledge that for such special applications the saturation field strength H _s can be achieved not only by reducing the cross section but also by reducing the saturation magnetization. The known, commercially available alloys in the field of application according to the invention all have a saturation magnetization B _s of greater than 0.5 T. For example, reference is made to EP-OS 0 121 694, which shows that the saturation magnetization is far greater than 0.5 T, and it is noted that it is particularly advantageous if the saturation magnetization has a value equal to or greater than 1 T .

zu erreichen.A reduction in the saturation induction can always be achieved by dilution of known compositions by magnetically inactive atoms. However, it is generally found here that alloys with a low B _s often no longer respond in the desired manner to heat treatment in the magnetic field. However, you need good responsiveness to heat treatment in the longitudinal field to create a Z-shaped loop with a required remanence ratio of ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

to reach.

It has now been shown that this responsiveness is particularly good in the case of low-magnetostriction amorphous alloys is given on a co-basis. Nickel and, in some cases, niobium have emerged as particularly favored alloying elements for lowering B _s without giving up the required response to the heat treatment. Iron or manganese can usually be used to set small magnetostriction values in cobalt alloys. It has now additionally been shown that iron gives significantly better results, ie good responsiveness to magnetic field treatments, than manganese.

u =

4 - 10 At.-%

x =

20 - 50 At.-%

y =

0 - 18 At.-%

z =

5 - 30 At.-%

betragen und die Bedingung
$\text{S = x + 5,3 y + 4,1 z - 0,73 u ≃ 120 bis 135}$

erfüllt ist, wobei $\text{z + y > 20 At.-\%}$

und $\text{Nb + B > 6 At.-\%,}$

wobei das Element $\text{T = Nb}$

ist und dieses fallweise bis zu 3 At.-% (bezogen auf die Gesamtlegierung) durch Mo, Cr, V, Zr, Ti, W ersetzbar ist.The conditions according to the invention with regard to saturation induction and remanence ratio can be achieved with an amorphous alloy according to the invention, which is characterized by the empirical formula



Co _{100 - u - x - y - z} Fe _u Ni _x T _y (Si B) _z ,

in which

u =

4 - 10 at .-%

x =

20 - 50 at%

y =

0 - 18 at .-%

z =

5 - 30 at%

amount and the condition
$\text{S = x + 5.3 y + 4.1 z - 0.73 u ≃ 120 to 135}$

is fulfilled, whereby $\text{z + y> 20 at .-\%}$

and $\text{Nb + B> 6 at .-\%,}$

being the element $\text{T = Nb}$

is and in some cases up to 3 at% (based on the total alloy) can be replaced by Mo, Cr, V, Zr, Ti, W.

An amorous alloy of u = 4 to 10 at.%, X = 20 to 45 at.%, Y = 0 to 4 at.%, Z = 20 to 30 at.%, Wherein the the following condition is met:

$\text{S = x + 5.3 y + 4.1 z - 0.73 u ≃ 120 to 130.}$

erfüllt ist.An advantageous modification of this is that
u = 4 to 10 at%, x = 20 to 30 at%,
y = 12 to 18 at%, Z = 5 to 12 at% and the condition $\text{S = x + 5.3 y + 4.1 z - 0.73 u ≃ 120 to 130}$

is satisfied.

Another advantageous variant is that u = 4 to 10 at.%, X = 35 to 45 at.%, Y = 0 to 1 and z = 21 to 23 at.%.

erzielen.The attached table shows the results of a series of alloys which have been subjected to heat treatment in the longitudinal field. For economic reasons, such a heat treatment should not take too long, ie be shorter than about 1 day, and still be a remanence ratio ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

achieve.

erreicht werden). Andererseits sind eine Reihe von Legierungen wie z. B.

bekannt, welche zwar gut auf eine Wärmebehandlung ansprechen ( ${\text{B}}_{\text{r}}{\text{/B}}_{\text{s}}\text{> 0,6}$

erreichbar), welche jedoch alle ${\text{B}}_{\text{s}}\text{> 0,5 T}$

haben und für diese gewünschten Anwendungen nicht in Frage kommen. Geeignet sind jedoch die Legierungen 7 bis 11, welche sowoh ${\text{l B}}_{\text{s}}\text{≦ 0,5 T}$

und ${\text{B}}_{\text{r}}{\text{/B}}_{\text{s}}\text{> 0,6}$

erreichen.

The table shows that alloys 1 to 6 have a saturation induction in the desired range, but do not respond sufficiently to heat treatment at all temperatures used here (ie, no desired remanence ratio could be achieved ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

can be achieved). On the other hand, a number of alloys such as B.

known, which respond well to heat treatment ( ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

accessible), but all of them ${\text{B}}_{\text{s}}\text{> 0.5 T}$

have and are out of the question for these desired applications. Alloys 7 to 11 are suitable, however ${\text{l B}}_{\text{s}}\text{≦ 0.5 T.}$

and ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

to reach.

Claims (5)

1. An amorphous alloy for strip-shaped sensor elements with a low saturation induction for use in anti-theft security labels or magnetic field detectors, characterised in that the amorphous alloy is a magnetostriction-free alloy with a saturation induction of ${\text{B}}_{\text{s}}\text{≦ 0.5 T}$

   

   and with a good capability of response in the case of a tempering treatment in the magnetic field to achieve a remanence ratio of ${\text{B}}_{\text{r}}{\text{/ B}}_{\text{s}}\text{> 0.6}$

   

   

   , and that the alloy has the total formula
   
   
   
           Co_{100 - u - x - y - z} Fe_u Ni_x T_y (SiB)_z
   
   
   
   wherein

   u =   4 to 10 At.-%

   x =   20 to 50 At.-%

   y =   0 to 18 At.-%

   z =   5 to 30 At.-%

   and the condition
   $\text{S = x + 5.3 y + 4.1 z - 0.73 u≃120 to 135}$

   

   is fulfilled, where z + y > 20 At.-% and Nb + B > 6 At.-%, where the element T = Nb and the latter can from case to case be replaced by up to 3 At.-% (relative to the total alloy) with Mo, Cr, V, Zr, Ti, W.
2. An amorphous alloy as claimed in Claim 1, wherein
   u = 4 to 10 At.-%, x = 20 to 45 At.=96, y = 0 to 4 At.-%,
   z = 20 to 30 At.-%, and the condition
   $\text{S = x + 5.3 y + 4.1 z = 0.73 u≃120 to 130}$

   

   is fulfilled.
3. An amorphous alloy as claimed in Claim 1, wherein
   u = 4 to 10 At.=%, x = 20 to 30 At.-%, y = 12 to 18 At.-%,
   Z = 5 to 12 At.-%, and the condition
   $\text{S = x + 5.3 y + 4.1 z - 0.73 u≃120 to 130}$

   

   is fulfilled.
4. An amorphous alloy as claimed in Claim 2, wherein
   $\text{u = 4 to 10 At.-\%, x = 35 to 45 At.-\%, y = 0 to 1,}$

   

   
   $\text{Z = 21 to 23 At.-\%}$

   

   .
5. A strip-shaped sensor element composed of an alloy as claimed in one of the preceding clams for use in anti-theft security labels or magnetic field detectors.