JP3411663B2 - Permanent magnet alloy, permanent magnet alloy powder and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to alloys and alloy powders for bond magnets optimal for various motors, speakers and meters and focus convergence rings, and a method for producing the same, and Fe of a specific composition containing a small amount of a rare earth element. -B-R-M (M = Al, Si, S , Cu,
Zn, Ga, Ag, Pt, Au, Pb) alloy melt is made into an amorphous structure or a structure in which fine crystals and amorphous are mixed by a super quenching method using a rotating roll, a splat quenching method, a gas atomizing method or a combination thereof.
Fe ₃ B type compound as well as α-iron and Nd _{2 by} specific heat treatment
By obtaining an alloy powder consisting of a fine crystal aggregate with the constituent phases of the Fe ₁₄ B type crystal structure and binding this with a resin,
Fe-B having a residual magnetic flux density Br of 8 kG or more, which was not obtained with a hard ferrite magnet, and excellent temperature characteristics.
Permanent magnet alloy powder in the permanent magnet alloy sequence <br/> can get -R based bonded magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art In fields requiring a high residual magnetic flux density Br and permanent magnets required to be used at high and low temperatures, Br is mainly 10 kG or more and an intrinsic coercive force iHc is 0.
An alnico magnet having a magnetic characteristic of 5 kOe to 2 kOe,
Or S with Br of 8 kG or more and iHc of 6 kOe or more
m-Co magnets are used.

These magnets are mainly made of Co, which is difficult to obtain stably because the supply amount from the country of origin is unstable. In the case of Alnico magnet, 20 to 30 wt%, Sm-C
It also contains 50 to 65 wt% of a magnet. Also, Sm
There is a problem that Sm contained in a Co magnet is extremely expensive because it is contained in a rare earth mineral in a small amount and is difficult to obtain stably. However, magnets used for motors and speedometers for automobile electrical components may be used in an environment of 80 ° C. or higher, so Alnico magnets and Sm-Co magnets are much cheaper for such applications. It occupies the mainstream over the available hard ferrites.

In particular, the Sm-Co magnet is an expensive magnet due to the demand for improving the fuel efficiency of today's automobiles, but has excellent magnetic characteristics, so that it is suitable for a magnetic circuit that requires a small size and high performance. It is used. So Co and S
There is a demand for a permanent magnet material that does not contain m and has excellent magnetic characteristics and temperature characteristics. At present, however, a magnetic material that can be mass-produced and can be provided at low cost and has a Br of 8 kG or more has been found. Absent.

[0005]

Recently, in an Nd-Fe-B system magnet containing no Co or Sm, Nd ₄ Fe _{77 was used.}
A magnetic material having a Fe ₃ B type compound as a main phase in the vicinity of B ₁₉ (at%) is proposed (R. Coehorn et al., J. de P.
hys. , C8, 1988, pp. 669-670). This magnet material is a metastable structure permanent magnet material having a crystal texture in which Fe ₃ B phase and Nd ₂ Fe ₁₄ B phase are mixed by heat-treating an amorphous ribbon.
Although it has Br of about 0 kG and iHc of 2 to 3 kOe,
The heat treatment conditions for becoming a hard magnetic material are narrowly limited, which is not practical in industrial production.

Further, a study has been published to improve iHc to 3 to 5 kOe by substituting a part of Nd of the Nd-Fe-B system magnet having the Fe ₃ B type compound as a main phase with Dy and Tb. However, in addition to the problem of adding an expensive element, there is a problem that the magnetic moment of the rare earth element added is coupled antiparallel to the magnetic moments of Nd and Fe, and the squareness of the magnetization and demagnetization curve is reduced (R Coehoorn, J .;
Magn, Magn, Mat. , 83 (1990) 22
8 to 230).

In any case, Fe ₃ B type Nd-Fe-B
The system magnet can be made into a hard magnetic material by heat treatment after being made amorphous by the ultra-quenching method, but iHc is low and the heat treatment conditions are narrow, and stable industrial production cannot be performed. As an alternative, it cannot be provided inexpensively.

The present invention focuses on an iron-based permanent magnet material in which a soft magnetic phase and a hard magnetic phase are mixed in the same structure and has a low rare earth concentration, and the iHc of this magnet is improved to enable stable industrial production. Establishing a manufacturing method, and having a residual magnetic flux density Br of 10 kG or more, having cost performance comparable to that of a hard ferrite magnet, providing a permanent magnet alloy that can be provided at low cost, and a permanent magnet alloy powder and a manufacturing method thereof. It is intended to be provided.

[0009]

According to the present invention, a soft magnetic phase and a hard magnetic phase are mixed in the same structure, and the rare earth concentration is 4 at%.
As a result of various studies aimed at improving the iHc of the iron-based permanent magnet, which is as low as a degree, and enabling stable industrial production,
The content of rare earth elements is low, and Al, Si, S , Cu,
A specific heat treatment is performed by using an ultra-quenching method or the like to form an alloy melt having a specific composition of an iron base to which a small amount of at least one of Zn, Ga, Ag, Pt, Au, and Pb is added as an amorphous structure or a structure in which fine crystals and amorphous are mixed. To obtain an alloy powder composed of a Fe ₃ B type compound and a fine crystal aggregate of α-iron and a constituent phase of the Nd ₂ Fe ₁₄ B type crystal structure,
The inventors have found that an optimum rare earth magnet alloy powder can be obtained for a bond magnet having a residual magnetic flux density Br of 10 kG or more, which is comparable to an alnico magnet or an Sm-Co magnet, and completed the present invention.

The present invention uses the composition formula Fe _100-xyz B _x
R _y M _z (where R is one or two of Pr or Nd,
M is Al, Si, S , Cu, Zn, Ga, Ag, Pt,
Au, Pb 1 type or 2 types or more), and the symbols x, y, z that limit the composition range satisfy the following values, and Fe ₃ B type compounds and α-iron, and Nd ₂ Fe ₁₄ B type crystals It is a fine crystal aggregate in which a compound having a structure coexists in the same powder particle, and the average crystal grain size of each constituent phase is in the range of 1 nm to 50 nm , and the magnetic characteristics are iHc ≧ 3.0 kOe, Br ≧
It is a permanent magnet alloy characterized in that 11 kG and (BH) max ≧ 16 MGOe . 10 ≦ x ≦ 30 at% , 3 ≦ y ≦ 5 at% , 0.1 ≦ z ≦ 3 at%

The present invention uses the composition formula Fe _100-xyz B _x R
_y M _z (where R is one or two of Pr or Nd, M
Is Al, Si, S 2 , Cu, Zn, Ga, Ag, Pt, A
u or Pb), and the symbols x, y and z for limiting the composition range satisfy the following values, and Fe ₃ B type compounds and α-iron and Nd ₂ Fe ₁₄ B type crystal structures And a constituent phase having a coexistence in the same powder particle, and each constituent phase is composed of a fine crystal aggregate having an average crystal grain size in the range of 1 nm to 50 nm, and has magnetic properties of iHc ≧ 3.0 kOe and Br ≧ 1.
It is a permanent magnet alloy powder characterized in that 0 kG and (BH) max ≧ 9 MGOe. 10 ≦ x ≦ 30 at% , 3 ≦ y ≦ 5 at% , 0.1 ≦ z ≦ 3 at%

The present invention also provides (1) the composition formula: Fe _100-xyz B _x R _y M _z (where R is P
1 or 2 of r or Nd, M is Al, Si, S 2 ,
Cu, Zn, Ga, Ag, Pt, Au, and Pb), and symbols x and y for limiting the composition range.
A molten alloy having z satisfying the above-mentioned value is quenched by a super-quenching method using a rotating roll, a splat quenching method, a gas atomizing method or a combination of these methods to obtain an amorphous structure or a structure in which fine crystals and amorphous are mixed. ) Further, from a temperature around the point where crystallization starts, 600 ° C ~
The temperature rising rate up to the processing temperature of 700 ° C. is 15 ° C./min to 50
(3) Fe ₃ B type compound and α-iron, and Nd ₂ Fe ₁₄ B
A compound having a type crystal structure coexists in the same powder particle, and a fine crystal aggregate in which the average crystal grain size of each constituent phase is in the range of 1 nm to 50 nm is obtained, and then (4) , Average particle size 3 μm to 500 μm
It is a method for producing a rare earth alloy powder, which is characterized by pulverizing to m to obtain a magnet alloy powder.

Reasons for limiting the composition The rare earth element R has high magnetic properties only when it contains one or two of Pr or Nd in a specific amount.
For example, in the case of Ce and La, the characteristic that iHc is 2 kOe or more cannot be obtained, and medium rare earth elements and heavy rare earth elements after Sm cause deterioration of magnetic characteristics and make the magnet expensive, which is not preferable. If R is less than 3 at%, iHc of 3 kOe or more cannot be obtained, and if it exceeds 5 at%, it is 10 k.
Since Br of G or more cannot be obtained, the range is 3 to 5 at%.

If B is less than 10 at%, an amorphous structure cannot be obtained even if the ultra-quenching method is used, and even if a heat treatment is applied, it becomes 3
Only iHc less than kOe can be obtained. Also, 30 at%
If it exceeds, the squareness of the demagnetization curve will be significantly reduced and 10 kG
Since the above Br cannot be obtained, the range is 10 to 30 at%. It is preferably 15 to 20 at%.

Al, Si, S , Cu, Zn, Ga, A
g, Pt, Au, and Pb improve the squareness of the demagnetization curve, and B
has the effect of increasing r and (BH) max,
If it is less than 0.1 at%, such an effect cannot be obtained, and 3 at%
Exceeding 10 kG, no Br of 10 kG or more can be obtained.
The range is 1 to 3 at%. Preferably 0.5-1.
5at% is good.

Fe occupies the remaining content of the above-mentioned elements.

Reasons for limiting manufacturing conditions In the present invention, the molten alloy having the above-mentioned specific composition is formed into an amorphous structure or a structure in which fine crystals and amorphous are mixed by the ultra-quenching method, and the temperature is about 6 from the temperature at which crystallization starts.
The temperature rising rate from the processing temperature of 00 ° C to 700 ° C is 15 ° C /
By performing the crystallization heat treatment at a temperature of min.
Fe ₃ B type compounds and α-iron, and a compound phase having an Nd ₂ Fe ₁₄ B type crystal structure coexist in the same powder, and the average crystal grain size of each constituent phase is in the range of 1 nm to 50 nm It is most important to obtain an aggregate, and a super-quenching method using a known rotating roll can be adopted for the super-quenching treatment of the molten alloy, but it is possible to obtain a structure in which amorphous or fine crystals are substantially mixed. For example, a splat quenching method, a gas atomizing method, or a quenching method combining these methods may be adopted in addition to the super quenching method using a rotating roll. For example, when a Cu roll is used, a roll surface peripheral velocity in the range of 10 to 50 m / sec is preferable because a suitable quenched structure can be obtained. That is, the roll peripheral speed is 1
When it is less than 0 m / sec, an amorphous structure is not formed, which is not preferable. On the other hand, if it exceeds 50 m / sec, it is not preferable because it does not form a fine crystal aggregate capable of obtaining good hard magnetic properties during crystallization. However, even if a small amount of α-Fe phase is present in the quenched structure, it does not significantly deteriorate the magnetic properties and is acceptable.

In the present invention, after the molten alloy having the above-mentioned specific composition is made into an amorphous structure or a structure in which fine crystals and amorphous are mixed by the ultra-quenching method, the heat treatment condition that maximizes the magnetic characteristics depends on the composition. Heat treatment temperature is 6
If the temperature is less than 00 ° C, the Nd ₂ Fe ₁₄ B phase does not precipitate, so iH
c is not expressed. Further, when the temperature exceeds 700 ° C., grain growth is remarkable, iHc, Br, and the squareness of the demagnetization curve are deteriorated, and the above-mentioned magnetic properties cannot be obtained.
Limit to 700 ° C. Since the heat treatment atmosphere prevents oxidation, it is preferably in an atmosphere of an inert gas such as Ar gas or N ₂ gas or in a vacuum of 10 ^-2 Torr or more. Magnetic properties are not dependent on heat treatment time, when the 6 hours that obtain super, since the Br with the passage of some time tends to decrease, preferably less than 6 hours.

An important feature of the present invention is the rate of temperature increase from around the temperature at which crystallization starts during heat treatment, and at a rate of temperature increase of less than 15 ° C./min, grain growth occurs during temperature increase, which is good. It is not preferable because it does not form a fine crystal aggregate having excellent hard magnetic properties and iHc of 3 kOe or more cannot be obtained. Also, in the ultra-El heating rate is 50 ° C. / sec, 60
The Nd ₂ Fe ₁₄ B phase generated after passing 0 ° C. is not sufficiently precipitated, and not only the iHc decreases, but also the demagnetization with a decrease in the magnetization in the second quadrant of the demagnetization curve near the Br point. It becomes a curve and (BH) max decreases, which is not preferable.
The temperature at which crystallization starts is the temperature at which Fe ₃ B and Fe crystallize in the amorphous alloy of the present magnet composition, and it is clearly measured using a method such as DTA or DSC as an exothermic reaction in the temperature rising process. it can. In the heat treatment, the temperature rising rate up to the crystallization start temperature is arbitrary, and rapid heating or the like can be applied to increase the processing efficiency.

[0020] The crystal structure crystalline phase of the permanent magnet alloy according to the present invention, a soft magnetic phase consisting of Fe ₃ B type compound and α- iron having ferromagnetic,
A hard magnetic phase having an Nd ₂ Fe ₁₄ B type crystal structure coexists in the same powder, and the average crystal grain size of each constituent phase is 1 nm to 50.
It is characterized by comprising a fine crystal aggregate in the range of nm. In the present invention, the average crystal grain size of the magnet alloy is 5
If it exceeds 0 nm, the squareness of Br and the demagnetization curve deteriorates, and the magnetic characteristics of Br ≧ 10 kG and (BH) max ≧ 9 MGOe cannot be obtained. Further, the smaller the average crystal grain size is, the more preferable, but it is difficult to obtain the average crystal grain size of less than 1 nm in industrial production. Therefore, the lower limit is set to 1 nm.

Magnetization Method A molten alloy having a specific composition is made into an amorphous structure or a structure in which fine crystals and amorphous are mixed by the above-mentioned rapid quenching method, and 600 ° C. to 700 ° C. near the temperature at which crystallization starts.
The present invention provides a fine crystal aggregate having an average crystal grain size in the range of 1 nm to 50 nm by performing a crystallization heat treatment at a temperature rising rate up to a treatment temperature of 15 ° C of 15 ° C / min to 50 ° C / sec. To magnetize using the permanent magnet alloy powder by
Any known sintered magnetizing method and bond magnetizing method capable of solidifying and compacting at 700 ° C. or less can be adopted, and if necessary, the alloy has an average crystal grain size of 3 to 50.
After crushing to 0 μm and mixing with a known binder to form a required bonded magnet, a bonded magnet having a residual magnetic flux density Br of 8 kG or more can be obtained.

[0022]

The present invention is characterized in that Fe-B-R-M (R is Pr or Nd, M is A) of a specific composition containing a small amount of rare earth elements.
1, Si, S 2 , Cu, Zn, Ga, Ag, Pt, Au,
The molten alloy of Pb (one or more kinds of Pb) is formed by an ultra-quenching method into an amorphous structure or a structure in which fine crystals and amorphous are mixed, and the obtained ribbons, flakes and spherical powders are heated from around the temperature at which crystallization starts. 600-700 ° C
The Fe ₃ B type compound having soft magnetism and α-iron, and Nd ₂ Fe ₁₄ B type are obtained by performing a crystallization heat treatment at a temperature rising rate up to the temperature treatment of 15 ° C./min to 50 ° C./sec. A hard magnetic phase having a crystal structure coexists in the same powder, and a fine crystal aggregate having an average crystal grain size of each constituent phase in the range of 1 nm to 50 nm is obtained. At this time, M (= Al, Si, S , C
When u, Zn, Ga, Ag, Pt, Au, and Pb) are added, the crystal grains become finer by about 1/2 to 1/3 as compared with the composition not containing M. Improvement of Br and squareness is obtained by this fine crystallization, iHc ≧ 3.0 kOe, Br ≧ 11 k
G, has magnetic properties of (BH) max ≧ 16 MGOe
Permanent magnet alloy, and iHc ≧ 3kOe, Br ≧ 10k
A permanent magnet alloy powder having magnetic properties of G, (BH) max ≧ 9 MGOe can be obtained.

[0023]

Example 1 No. 1 in Table 1 Purity of 99.
5% or more of Fe, Al, Si, S 2 , Cu, Zn, Ga,
Metals of Ag, Pt, Au, Pb, B, Nd, and Pr were weighed so that the total amount was 30 gr, put into a quartz crucible having an orifice with a diameter of 0.8 mm at the bottom, and Ar at a pressure of 56 cmHg. It is melted by high frequency heating in an atmosphere, and the melting temperature is set to 1300 ° C.
A molten metal is jetted from a height of 0.7 mm onto the outer peripheral surface of a room temperature Cu roll that is pressurized with a gas and rotates at a roll peripheral speed of 20 m / sec, and has a width of 2 to 3 mm and a thickness of 20 to 40 μm.
The ultra-quenched ribbon of was produced. The obtained ultra-quenched ribbon is CuK
It was confirmed to be amorphous by the characteristic X-ray of α.

The ultra-quenched ribbon was heated in Ar gas at a temperature rising rate shown in Table 1 above 580 ° C. to 600 ° C. at which crystallization begins, and held at the heat treatment temperature shown in Table 1 for 7 minutes. After cooling to room temperature, the thin strip was taken out, and a sample having a width of 2 to 3 mm, a thickness of 20 to 40 μm, and a length of 3 to 5 mm was prepared.
Magnetic property using M and B at 25 ° C to 140 ° C
The temperature coefficient of r and iHc was measured. The measurement results are shown in Table 2. No. For the sample No. 2, a demagnetization curve (sample shape; width 3 mm, thickness 30 μm, length 3 mm) is shown in FIG. In addition, No. The sample of 4 shows a reference example. As a result of investigating the constituent phases of the sample with the characteristic X-ray of CuKα, α-F
It had a multiphase structure in which the e phase, the Fe ₃ B phase and the Nd ₂ Fe ₁₄ B phase were mixed. In addition, Al, Si, S 2 , Cu, Zn, Ga,
Ag, Pt, Au, and Pb replace part of Fe in each of these phases. The average crystal grain size was 30 nm or less in all cases.

Comparative Example No. 1 in Table 1 Purity of 99.
An ultra-quenched ribbon was produced under the same conditions as in Example 1 using 5% or more of Fe, B, and R. The obtained ribbon was subjected to heat treatment under the same conditions as in Example 1, and after cooling, sampled under the same conditions as in Example 1 (Comparative Examples Nos. 14 to 16), and magnetic properties and 25 ° C to 140 ° C were measured using VSM. The temperature coefficient of Br and iHc in ° C was measured. The measurement results are shown in Table 2. No. 15
For the sample of Fig. 1, the demagnetization curve (sample shape; width 3 m
m, thickness 30 μm, length 3 mm). The constituent phases of the sample are α-Fe phase having Fe ₃ B phase as a main phase and Nd ₂ Fe phase.
₁₄ It has a multi-phase structure of B phase, and the average crystal grain size is around 50 nm, and it is 1-No. It was coarser than the 13 samples.

Example 2 Composition No. of Table 1 obtained in Example 1 After the heat treatment of Table 1, the ultra-thin quenched ribbon of No. 2 was ground to an average powder particle size of 150 μm or less, and a binder made of an epoxy resin was mixed at a ratio of 3 wt%, and then a bond magnet having a size of 12 mm × 12 mm × 8 mm was prepared. did. The magnetic properties of the obtained bonded magnet have a density of 6.0 g / cm ³ , iHc = 3.5 kOe,
Br = 9.2 kG and (BH) max = 8.7 MGOe.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

INDUSTRIAL APPLICABILITY The present invention has a specific composition of Fe-B-RM (where R is Pr or N) with a low content of rare earth elements.
d and M are Al, Si, S 2 , Cu, Zn, Ga, Ag,
A molten alloy of Pt, Au, Pb (one or more kinds) is formed by an ultra-quenching method into an amorphous structure or a structure in which fine crystals and amorphous are mixed, and the obtained ribbons, flakes and spherical powders are heat-treated under specific conditions. The Fe ₃ B type compound and α-iron and the compound phase having the Nd ₂ Fe ₁₄ B type crystal structure coexist in the same powder, and the average crystal grain size of each constituent phase is 1 nm to 50 nm. Obtain a crystallite aggregate within the range. At this time, M (= Al, Si, S 2 ,
By adding Cu, Zn, Ga, Ag, Pt, Au, Pb), the structure is refined to 1/2 to 1/3 as compared with the composition not containing M, so that the squareness of Br and the demagnetization curve is improved. Improved, as is clear from the examples, iHc ≧ 3.0k
Oe, Br ≧ 11 kG, (BH) max ≧ 16 MGOe
Permanent magnet alloy with magnetic properties of Hc ≧ 3 kO
e, Br ≧ 10 kG, (BH) max ≧ 9 MGOe, and permanent magnet alloy powder having excellent temperature characteristics can be obtained. In addition, the present invention does not contain Sm or Co, has a simple manufacturing method, and is suitable for mass production.
It is possible to stably provide an inexpensive bonded magnet having a residual magnetic flux density Br of G or more and having magnetic performance exceeding that of a hard ferrite magnet.

[Brief description of drawings]

FIG. 1 is a graph showing a demagnetization curve.

Continuation of front page (56) Reference JP-A-6-53019 (JP, A) JP-A-6-61026 (JP, A) JP-A-7-245208 (JP, A) JP-A-7-245207 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01F 1/053 B22F 1/00 B22F 9/04 C22C 38/00 303

Claims (3)

(57) [Claims] 1. The composition formula is Fe _100-xyz B _x R _y M _z
(However, R is one or two of Pr or Nd, M is A
1, Si, S 2 , Cu, Zn, Ga, Ag, Pt, Au,
Pb is one or two or more), and the symbols x, y, and z that limit the composition range satisfy the following values, and the Fe ₃ B type compound and α-iron and the Nd ₂ Fe ₁₄ B type crystal structure are represented. a reduction <br/> compound having coexist in the same powder particle, an average crystal grain size of each component phase is in the fine crystal aggregate in the range of 1nm~50nm
Yes, magnetic characteristics are iHc ≧ 3.0 kOe, Br ≧ 11 k
G, (BH) max ≧ 16 MGOe , a permanent magnet alloy. 10 ≦ x ≦ 30 at% , 3 ≦ y ≦ 5 at% , 0.1 ≦ z ≦ 3 at% 2. The composition formula is Fe _100-xyz B _x R _y M _z
(However, R is one or two of Pr or Nd, M is A
1, Si, S 2 , Cu, Zn, Ga, Ag, Pt, Au,
Pb is one or more of Pb), and the symbols x, y, and z that limit the composition range satisfy the following values, and Fe ₃ B type compounds and α-iron and Nd ₂ Fe ₁₄ B type crystal structures are represented. The compound having the compound coexists in the same powder particle, and is composed of a fine crystal aggregate in which the average crystal grain size of each constituent phase is in the range of 1 nm to 50 nm, and the magnetic characteristics are iHc ≧ 3.0 kOe and Br ≧ 10.
kG, (BH) max ≧ 9 MGOe, a permanent magnet alloy powder. 10 ≦ x ≦ 30 at% , 3 ≦ y ≦ 5 at% , 0.1 ≦ z ≦ 3 at% 3. The composition formula is Fe _100-xyz B _x R _y M _z (wherein R is one or two of Pr or Nd, M is Al, S
i, S , Cu, Zn, Ga, Ag, Pt, Au, Pb), and the symbols x, y, z for limiting the composition range satisfy the following values. Ultra-quenching method using splat, splat quenching method, gas atomizing method or a combination of these methods to obtain an amorphous structure or a structure in which fine crystals and amorphous are mixed.
Temperature rising rate up to processing temperature of 00 ° C 15 ° C / min to 50 ° C /
The Fe ₃ B type compound and α-iron and the compound having the Nd ₂ Fe ₁₄ B type crystal structure coexist in the same powder particle, and the average crystal grain size of each constituent phase is A method for producing a permanent magnet alloy powder, comprising obtaining a microcrystalline aggregate in the range of 1 nm to 50 nm, and then pulverizing the aggregate to have an average particle size of 3 μm to 500 μm, if necessary, to obtain a magnet alloy powder. 10 ≦ x ≦ 30 at% , 3 ≦ y ≦ 5 at% , 0.1 ≦ z ≦ 3 at%