EP0080521B1

EP0080521B1 - Low magnetostriction amorphous metal alloys

Info

Publication number: EP0080521B1
Application number: EP81109913A
Authority: EP
Inventors: Robert Charles O'handley
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1981-11-26
Filing date: 1981-11-26
Publication date: 1986-10-15
Also published as: DE3175475D1; EP0080521A1

Description

Background of the invention

Field of the invention

This invention relates to amorphous metal alloys and, more particularly, to cobalt rich amorphous metal alloys that. include certain transition metal and metalloid elements.

Description of the prior art

There are three physical parameters which can inhibit the easy magnetization and demagnetization of magnetic materials: strong anistropy, non-zero magnetostriction and, at high frequencies, low resistivity. Metallic glasses generally show resistivities greater than 100 micro ohm cm, whereas crystalline and polycrystalline magnetic metals generally show resistivities below 50 micro ohm cm. Also, because of their randomly disordered structures, metallic glasses are typically isotropic in their physical properties, including their magnetization. Because of these two characteristics, metallic glasses have an initial advantage over conventional magnetic metals. However, metallic glasses do not generally show zero magento- striction. When zero magnetostriction glasses can be found they are generally good soft magnetic metals (R. C. 0'Handley, B. A. Nesbitt, and L. I. Mendelsohn, IEEE Trans Mag-12, p. 942, 1976, U.S. Patents Nos. 4,038,073 and 4,150,981), because they satisfy the three approved criteria. For this reason, interest in zero magnetostriction glasses has been intense as indicated by the many publications on low magnetostriction metallic glasses (A. W. Simpson and W. G. Clements, IEEE Trans Mag-11, p. 1338, 1975; N. Tsuya, K. I. Arai, Y. Shiraga and T. Masumoto, Phys. Lett. A51, p. 121, 1975; H. A. Brooks, Jour. Appl. Phys. 47 p. 334, 1975; T. Egami, P. J. Flanders and C. D. Graham, Jr., Appl. Phys. Lett. 26, p. 128, 1975 and AIP Conf. Proc. No. 24, p. 697, 1975; R. C. Sherwood, E. M. Gyorgy, H. S. Chen, S. D. Ferris, G. Norman and H. J. Leamy, AIP Conf. Proc. No. 24, p. 745,1975; H. Fujimori, K. Arai, H. Shiraga, M. Yamada, T. Masumoto and N. Tsuya, Japan, Jour. Appl. Phys. 15, p. 705,1976; L. Kraus and J. Schneider, Phys Stat. Sol. a39, p. K161, 1977; R. C. O'Handley in Amorphous Magnetism, edited by R. Levy and R. Hasegawa (Plenum Press, New York 1977), p. 379; R. C. O'Handley,-Solid State Communications 21, p. 1119, 1977; R. C. O'Handley, Solid State Communications 22, p. 458, 1977; R. C. O'Handiey, Phys. Rev. 18, p. 930, 1978; H. S. Chen, E. M. Gyorgy, H. J. Leamy and R. C. Sherwood, U.S. Patent No. 4,056,411, Nov. 1, 1977).
The existence of a zero in the magnetostriction of Co-Mn-B glasses has been observed by H. Hiltzinger of Vacuumschmeltze A. G., Hanau, Germany.
Reference to Co-rich glasses containing 6 atom percent of Cr is made by N. Heiman, R. D. Hempstead and N. Kazama in Journal of Applied Physics, Vol. 49, p. 5663, 1978. Their interest was in improving the corrosion resistance of Co-B thin films. No reference to magnetostriction is made in that article.
Saturation moments and Curie temperatures of Co_80-xT_xP₁₀B₁₀ glasses (T=Mn, Cr, or V) were recently reported by T. Mizoguchi in the Supplement to the Scientific Reports of RITU (Research Institutes of Tonoku University), A June 1978, p. 117. No reference to their magnetostrictive properties was reported.
In Journal of Applied Physics, Vol. 50, p. 7597, 1979, S. Ohnuma and T. Masumoto outline their studies of magnetization and magnetostriction in Co-Fe-B-Si glasses with light transition metal (Mn, Cr, V, W, Ta, Mo and Nb) substitutions. They show that the coercivity decreases and the effective permeability increases in the composition range near zero magnetostriction.
The EP-A-00 50 479 discloses in Table 1 some amorphous cobalt rich alloys, these alloys contain necessarily silicon. Other cobalt rich amorphous alloys are shown by EP-A-0021 101, but they contain additionally either manganum and silicon or iron. Alloys containing additionally to cobalt and boron only chromium and/or vanadium are not disclosed by both references.
New applications requiring improved soft zero- magnetic materials that are easily fabricated and have excellent stability have necessitated efforts to develop further specific compositions.

Summary of the invention

The present invention provides low magnetostriction and zero magnetostriction glassy alloys that are easy to fabricate and thermally stable. The alloys are at least 50 percent glassy and consist essentially of compositions defined by the formula:
where T is at least one of Cr and V, B is boron and x ranges from about 0 to 16 atom percent.
A special magnetic alloy has the composition CO₆₆Cr₈V₆B₂₀.

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

Figure 1 is a graph showing saturation magnetization for compositions defined by the formula:
where T is at least one of Cr and V and x ranges up to about 16 atom percent;
Figure 2 is a graph showing Curie temperatures of compositions for which T is below the crystallization temperature T_X;
Figure 3 is a graph showing the relationships between saturation magnetostriction and composition for selected alloys of the invention;
Figure 4 is a graph showing the relationships between temperature and magnetostriction values for selected alloys of the invention;

Description of the preferred embodiments

The amorphous alloys of the invention can be formed by cooling a melt of the composition at a rate of at least about 10⁵°C/sec. A variety of techniques are available, as is now well-known in the art, for fabricating splat-quenched foils and rapid-quenched continuous ribbons, wire, sheet, etc. Typically, a particular composition is selected, powders of the requisite elements (or of materials that decompose to form the elements, such as nickel-borides, etc.) in the desired proportions are melted and homogenized, and the molten alloy is rapidly quenched either on a chill surface, such as a rotating cooled cylinder, or in a suitable fluid medium, such as a chilled brine solution. The amorphous alloys may be formed in air. However, superior mechanical properties are achieved by forming these amorphous alloys in a partial vacuum with absolute pressure less than about 5.5 cm of Hg, and preferably about 100 pm to 1 cm of Hg, as disclosed in U.S. Patent No. 4,154,283 to Ray et al.
The amorphous metal alloys are at least 50 percent amorphous, and preferably at least 80 percent amorphous, as measured by X-ray diffraction. However, a substantial degree of amorphousness approaching 100 percent amorphous is obtained by forming these amorphous metal alloys in a partial vacuum. Ductility is thereby improved, and such alloys possessing a substantial degree of amorphousness are accordingly preferred.
Ribbons of these alloys find use in soft magnetic applications and in applications requiring low magnetostriction, high thermal stability (e.g., stable up to about 100°C) and excellent fabricability.
The following example is presented to provide a more complete understanding of the invention.

Example

An alloy melt of known composition was rapidly quenched to form non-crystalline ribbons, presumably of the same composition as the melt. The ribbons, typically 40 micrometers (pm) by 2 mm in cross section, were cut into squares for vibration-sample magnetometer measurements of specific magnetization a (4.2K, 9 KOe) and o (T, 9 KOe) with 295 K<T<T_x, the crystallization temperature. Curie temperatures were obtained from the inflection points in the a (T, 9 KOe) curves.
The magnetostriction measurements were made in fields up to 4 KOe with metal foil strain gauges (as reported in more detail by R. C. O'Handley in Solid State Communications, Vol. 22, p. 485, 1977). The accurary of these measurements is considered to be within 10 percent of full strain and their strain sensitivity is on the order of 10-⁷.
Composition variations of the room temperature specific saturation magnetizations a (295 K, 9 KOe) as functions of composition x for CO_80-xT_xB₂₀ (T=Cr, V) glasses are shown in Figure 1. The trends in Figure 1 reflect the variations of both the saturation moments n_B and the Curie temperatures T_c of these alloys.
The Curie temperatures of Co-rich glasses are generally well above the temperatures for crystallization T_x but fall below T. for sufficiently large additions of Cr or V (Figure 2).
In order to be useful in magnetic devices, materials should show appreciable magnetization. Commercial zero magnetostriction crystalline metallic alloys of the class exemplified by Permalloy ((Ni₈₂Fe₁₈)_1-xX_x with x=Mo or Cu and x<.04) have saturation inductions
of about 0.6 to 0.8 tesla (6 to 8 kGauss). The specific magnetizations in Figure 1 can be converted to tesla by multiplying by the mass density times 4n/10,000.
Defining p_x to be the mass density of the crystalline material X and pg to be that of the glassy material X₈₀B₂₀, the ratios of the measured quantities ρ_g/ρ_x were found to be 0.92 and 0.94 for Co₈₀B₂₀ and Fe₈₀B₂₀ glasses. A similar trend holds for the hypothetical X₈₀B₂₀ glasses listed in Table I. The estimated densities of X₈₀B₂₀ (X=Mn, Cr, V) glasses are also set forth in Table I. The densities of C0₇₀X₁₀B₂₀ glasses were calculated by linearly combining the densities of C0₈₀B₂₀ and X_s0B₂₀,
In Figure 3, there is shown the effects of Cr and V substitutions on the saturation magnetostriction of Co₈₀B₂₀ glass. As is the case with the Fe substitutions for Co disclosed by U.S. Patent No. 4,038,073 to O'Handley et al., the lighter transition metals cause λ_s to increase through zero, positive below T_c for Mn and Cr substitutions and go to zero for V substitutions. In the case of Co₆₆V₁₄B₂₀ glass, T_c=300 K (Fig. 2). Thus, the room temperature magnetostriction is zero probably because of the low T_c. Co_80-xV_xB₂₀ glasses with x>14 may show positive magnetostriction at 4.2 K (see Fig. 4). These Co-Cr-B glasses are, therefore, non-magnetostrictive alloys.
The temperature dependence of λS is shown in Figure 4 for selected alloys. The sign of À_s was observed to change in two of the glasses. Such compensation temperatures have not previously been observed in metallic glasses. The vanadium containing glasses either become paramagnetic or they crystallize before any compensation can be realized. Thus, the negative magnetostriction glasses shown in Figure 3 may be used in applications requiring as=0 at some elevated temperature (up to approximately 200°C above room temperature, which is not uncommon in many electronic devices).
The new low magnetostriction metallic glasses disclosed herein (Co-Cr-B and Co-V-B) show relatively low 4nM_s (Fig. 1). As a result, their utility is limited to applications requiring superior mechanical properties or improved corrosion resistance relative to permalloys or other λ_s=0 crystalline or non-crystalline materials.
Co-rich glass compositions with positive and negative magnetostriction can be added linearly to give zero magnetostriction.
The rule of linear combination of opposing magnetostrictions (LCOM) has been applied to develop additional zero magnetostriction glasses from those measured and shown in Figure 3.
The magnetostriction of Co-rich glasses is small because of the near-cancellation of two independent mechanisms for the magnetostriction, a positive two-ion interaction and a negative single-TM-ion term (O'Handley, Phys. Rev. B 18, p. 930, 1978). As a result, the TM makeup for λ_s=O is nearly independent of TM/M ratio. That is, because λ_s=0 for observed trends in C0_100-xB. glasses (K. Narita, J. Yamasaki, and H. Fukunaga, Jour. Appl. Phys. Vol. 50, p. 7591, 1979 and J. Aboaf and B. Klokholm, ICM Munich Sept. 1979 to appear in Jour. Magnetism and Magnetic Materials), are best described by assuming the number of nearest neighbor TM pairs to be independent of x. This implies that the nearest- neighbor coordination of cobalt atoms by cobalt atoms does not vary strongly with x. Thus the compositional dependence of magnetostriction in Co-rich glasses is well described at room temperature by:
where the first term is the observed two-ion component of magnetostriction (independent of composition x) and the second is the single-ion component of magnetostriction (which varies linearly with the TM concentration). Thus the magnetostriction becomes less negative as metalloid content increases, the change in λ being +0.13x 10^-6 per atom percent more metalloid.

Claims

1. A magnetic alloy that is at least 50 percent glassy, said alloy having the formula Co_80-xT_xB₂₀ where T is at least one of Cr and V, B is boron, and x ranges from about 0 to 16 atom percent.

2. A magnetic alloy having the composition C0₆₆Cr₈V₆B₂₀,