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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a Ni--Zn base ferrite, and especially to a Ni--Zn base ferrite which is small in dielectric loss and high in saturation magnetization and is useful as a magnetic material in high-frequency fields.
Ni--Zn base ferrites are expected to find utility in many fields, for example, as core materials for screw cores, radios and other household electric appliances, high-frequency core materials, and magnetic materials for isolators, circulators and other high-frequency band products all of which make use of gyromagnetic effect. They are also examples of representative ferrite materials which are employed in devices such as circulators for microwave communication.
As a magnetic material usable for such application purposes, it is essential to select a material having a saturation magnetization (4.pi.Ms) of from 500 to 5,000 (gauss) and a small ferromagnetic resonance absorption half-value width (.DELTA.H) and, from the standpoint of assurance of reliability, a small dielectric loss ›tan .delta.(.epsilon.)!.
2. Description of the Related Art
The history of ferrites goes back many years. Developed as hard ferrites include Co-base ferrites, Ba-base ferrites, and Sr-base ferrites. As soft ferrites, on the other hand, Mg-base ferrites, Cu-base ferrites, Zn-base ferrites, Ni--Zn base ferrites and the like have been developed, followed by the development of Mn-Zn base ferrites.
Mg-base ferrites still remain as Mn-Mg-Zn base ferrites, which make use of rectangular hysteresis characteristics of the Mg-base ferrites and are used primarily in television sets (as deflection cores and flyback cores).
Concerning Cu-base ferrites, attempts were made at the time of their development to use them as memory elements in large scale computers. They were however accompanied by the problem that their structure at 1,000.degree. C. or higher had to be retained at room temperature. There was then a move toward the mass production of very small cores. As analog memory elements, they soon confronted their limitations.
Around that time, ICs, LSIs and the like were developed. A trend toward digital memories became a mainstream, and with this the era of analog memory elements came to an end.
Subsequent to the discovery of magnetic properties of Ni--Zn ferrites over a low frequency to high frequency range and their gyromagnetic effect, systematic and extensive research was conducted on them. They however had large magnetic losses. A great deal of efforts was hence concentrated on the improvement of their magnetic losses, but this problem has remained unresolved.
Ni--Zn ferrites offer the superior qualities as described above and specifically, they feature excellent magnetic properties over a low frequency to high frequency range, a small ferromagnetic resonance absorption half-value width AH, gyromagnetic effect, mild and flexible production conditions, and superior property reproducibility and stability. It is therefore clear that they will be used as primary magnetic materials in high-frequency fields once their dielectric losses tan .delta.(.epsilon.) are improved.
Conventional Ni--Zn ferrites have dielectric losses tan .delta.(.epsilon.) as large as 1.times.10.sup.-2 or so, thereby making their application in magnetic devices difficult.
SUMMARY OF THE INVENTION
With the foregoing problems in view, the present invention has as an object the provision of a Ni--Zn base ferrite having a small dielectric loss tan .delta.(.epsilon.) of the order of 10.sup.-3 or smaller.
To achieve the above-described object, the present invention provides a Ni--Zn base ferrite having a compositional formula represented by Ni.sub.X Zn.sub.1-X -Fe.sub.2-Y-Z Mn.sub.Y M.sub.Z O.sub.4 where M: at least one of Ge and Sn, 0.55.ltoreq.X.ltoreq.1.00, 0.001.ltoreq.Y.ltoreq.0.36, and 0.002.ltoreq.Z.ltoreq.0.36.
It is for the below-described reasons that X, Y and Z in the above compositional formula are limited as defined above.
Concerning X which indicates the proportion of nickel (Ni), a value smaller than 0.55 leads to a lower Curie temperature (T.sub.c) and in view of the temperature stability required for a magnetic device upon actual use, such a low X value cannot provide a Ni--Zn base ferrite suitable for actual use.
Turning next to Y which is indicative of the proportion of manganese (Mn), a value smaller than 0.001 results in a large dielectric loss tan .delta.(.epsilon.) (as large as 1.times.10.sup.-2) while a value greater than 0.36 leads to a saturation magnetization 4.pi.Ms as small as 300 (G) and also to a low Curie temperature (T.sub.c). A Y value outside the range of 0.001.ltoreq.Y.ltoreq.0.36 therefore has difficulty in providing a Ni--Zn base ferrite suitable for actual use.
Z indicates the proportion of M (=Ge and/or Sn). A Z value within the range of 0.002.ltoreq.Z.ltoreq.0.36 can suppress a loss associated with an electric conduction which in turn takes place within the material. The dielectric loss tan .delta.(.epsilon.) is therefore reduced to the order of 10.sup.-3 or less.
Further, it is necessary to use Mn and M (=Ge and/or Sn) in combination.
The present invention is therefore limited to the Ni--Zn base ferrite of the above compositional formula in which, as described above, X, Y and Z fall within the following ranges: 0.55.ltoreq.X.ltoreq.1.00, 0.001.ltoreq.Y.ltoreq.0.36, and 0.002.ltoreq.Z.ltoreq.0.36.
Incidentally, when proportioned to give a compositional formula represented by Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.54 -Mn.sub.0.1 M.sub.0.36 O.sub.4, a Ni--Zn base ferrite having a still smaller dielectric loss tan .delta.(.epsilon.) (1.times.10.sup.-4) can be obtained.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will hereinafter be described based on certain working examples to be described subsequently herein.
Table 1 shows the compositional formulas of the embodiments and the saturated magnetizations 4.pi.Ms, dielectric losses tan .delta.(.epsilon.) and Curie temperatures (T.sub.c) of ferrites of the various compositions prepared in the respective invention examples in comparison with those of non-invention examples (comparative examples).
As described above, each Ni--Zn base ferrite according to the present invention is represented by the compositional formula Ni.sub.X Zn.sub.1-X Fe.sub.2-Y-Z Mn.sub.Y M.sub.Z O.sub.4 where M: at least one of Ge and Sn. Moreover, X, Y and Z should fall within the following specific ranges: 0.55.ltoreq.X.ltoreq.1.00, 0.001.ltoreq.Y.ltoreq.0.36, and 0.002.ltoreq.Z.ltoreq.0.36.
In Table 1, the ferrites having the compositions designated by Test Nos. 1 to 23 are examples according to the present invention, whereas Test Nos. 24 to 30 are comparative examples directed to compositions outside the scope of the present invention.
The above ferrites of the various compositions were each prepared as will be described next.
As raw materials for the ferrite material, a manganese carbonate was chosen as a manganese source and oxides were selected as sources for the remaining elements. Subsequent to proportioning of these raw materials, the resulting powder batch was mixed for 64 hours in an iron-made ball mill, pre-calcined at 850.degree. C. for 2 hours in an oxygen atmosphere, and then ground and mixed again.
A binder (polyvinyl alcohol) was then added. The resulting mixture was press-formed into a predetermined shape under a pressure of 2.0 tons per unit area (cm.sup.2). The green body so obtained was degreased, followed by sintering at 1,200.degree. to 1,450.degree. C. for 2 hours in an oxygen atmosphere.
The saturation magnetization 4.pi.Ms was determined by preparing a sample of 10 mm in diameter and 1.5 mm in thickness in the above-described manner, obtaining a hysteresis curve up to a maximum magnetic field of 10 kilogauss by using a vibrating sample magnetometer (VSM), and then determining magnetization at a magnetic field of 0 from the resultant hysteresis curve by extrapolation.
The dielectric loss tan .delta.(.epsilon.) was determined by preparing a measuring sample of 16 mm in diameter and 0.2 mm in thickness in the above-described manner and then measuring its dielectric loss in an electromagnetic radiation of 9 GHz by the TE112 mode cavity resonance method. Further, the Curie temperature T.sub.c was determined by preparing a ball of 1 to 2 mm in diameter in the above-described manner and then measuring its Curie temperature by a magnetic balance.
EXAMPLES
(Test Nos. 1 to 23)
Test Nos. 1 to 5 in Table 1 show that a value of X, which is indicative of the proportion of Ni, in the range of 0.55.ltoreq.X.ltoreq.1.00 gives a Curie temperature T.sub.c of from 100.degree. to 580.degree. C., a saturation magnetization 4.pi.Ms of from 1,600 to 4,400 (G) and a dielectric loss tan .delta.(.epsilon.) of the order of 10.sup.-3 or less.
Further, Test Nos. 6 to 23 in Table 1 show that values of Y and Z, which indicate the proportions of Mn and M (M: Ge and/or Sn), in the ranges of 0.001.ltoreq.Y.ltoreq.0.36 and 0.002.ltoreq.Z.ltoreq.0.36, respectively, give a dielectric loss tan .delta.(.epsilon.) of the order of 10.sup.-3 or less, a Curie temperature T.sub.c of from 110.degree. to 440.degree. C. and a saturation magnetization 4.pi.Ms of from 500 to 5,200 (G).
COMPARATIVE EXAMPLES
(Test Nos. 24 to 30)
In each of Test Nos. 24 to 30 in Table 1, one or more of the X, Y and Z values fall outside the above-described specific ranges (comparative examples), that is, one or more of the Curie temperature T.sub.c, saturation magnetization 4.pi.Ms and dielectric loss tan .delta.(.epsilon.) do not show any values within the prescribed ranges. The samples of these test numbers are therefore not suited for practical applications.
By limiting in a Ni--Zn base ferrite the proportion ranges of Ni, Zn, Fe, Mn and M (M: Ge and/or Sn) as described above, the present invention can provide the Ni--Zn base ferrite with a dielectric loss tan .delta.(.epsilon.) of the order of 10.sup.-3, which is smaller than those of conventional products, while assuring a high value as its saturation magnetization 4.pi.Ms. The Ni--Zn base ferrite according to the present invention can therefore be used in low-loss magnetic devices, thereby bringing about a significant industrial value.
TABLE 1
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Compositional Formula
T. c(.degree.C.)
4.pi.Ms(G)
tan.delta.(.epsilon.)
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1 Ni.sub.0.55 Zn.sub.0.45 Fe.sub.1.84 Mn.sub.0.06 Ge.sub.0.05 Sn.sub.0.05
O.sub.4 100 2500 4 .times. 10.sup.-4
2 Ni.sub.0.7 Zn.sub.0.3 Fe.sub.1.84 Mn.sub.0.06 Ge.sub.0.05 Sn.sub.0.05
O.sub.4 250 3100 9 .times. 10.sup.-4
3 Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.84 Mn.sub.0.06 Ge.sub.0.05 Sn.sub.0.05
O.sub.4 370 4400 9 .times. 10.sup.-4
4 Ni.sub.1.0 Zn.sub.0.4 Fe.sub.1.84 Mn.sub.0.06 Ge.sub.0.05 Sn.sub.0.05
O.sub.4 480 2200 2 .times. 10.sup.-3
5 Ni.sub.0.6 Fe.sub.1.84 Mn.sub.0.06 Ge.sub.0.05 Sn.sub.0.005
580ub.4
1600 3 .times. 10.sup.-3
6 Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.997 Mn.sub.0.001 Ge.sub.0.001
Sn.sub.0.001 O.sub.4
440 5200 8 .times. 10.sup.-3
7 Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.92 Mn.sub.0.02 Ge.sub.0.03 Sn.sub.0.03
O.sub.4 370 4800 4 .times. 10.sup.-3
8 Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.84 Mn.sub.0.01 Ge.sub.0.03 Sn.sub.0.03
O.sub.4 340 4400 5 .times. 10.sup.-3
9 Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.7 Mn.sub.0.1 Ge.sub.0.1 Sn.sub.0.1
O.sub.4 280 3500 9 .times. 10.sup.-4
10
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.63 Mn.sub.0.11 Ge.sub.0.13 Sn.sub.0.13
O.sub.4 250 3100 5 .times. 10.sup.-4
11
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.5 Mn.sub.0.20 Ge.sub.0.09 Sn.sub.0.21
O.sub.4 200 2200 1 .times. 10.sup.-4
12
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.5 Mn.sub.0.25 Ge.sub.0.2 Sn.sub.0.05
O.sub.4 190 2100 2 .times. 10.sup.-4
13
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.184 Mn.sub.0.3 Ge.sub.0.1 Sn.sub.0.2
O.sub.4 160 1400 1 .times. 10.sup.-4
14
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.28 Mn.sub.0.36 Ge.sub.0.22 Sn.sub.0.14
O.sub.4 110 500 1 .times. 10.sup.-4
15
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.44 Mn.sub.0.2 Ge.sub.0.18 Sn.sub.0.18
O.sub.4 130 1700 1 .times. 10.sup.-4
16
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.54 Mn.sub.0.11 Ge.sub.0.3 Sn.sub.0.05
O.sub.4 200 2500 5 .times. 10.sup.-4
17
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.54 Mn.sub.0.11 Ge.sub.0.05 Sn.sub.0.3
O.sub.4 210 2500 4 .times. 10.sup.-4
18
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.54 Mn.sub.0.1 Sn.sub.0.36
230ub.4
2700 1 .times. 10.sup.-4
19
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.54 Mn.sub.0.1 Ge.sub.0.36
240ub.4
2700 1 .times. 10.sup.-4
20
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.94 Mn.sub.0.05 Sn.sub.0.01
360ub.4
400 3 .times. 10.sup.-3
21
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.88 Mn.sub.0.05 Sn.sub.0.07
340ub.4
4700 6 .times. 10.sup.-3
22
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.94 Mn.sub.0.05 Ge.sub.0.01
370ub.4
400 2 .times. 10.sup.-3
23
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.88 Mn.sub.0.05 Ge.sub.0.07
350ub.4
4700 5 .times. 10.sup.-3
24
Ni.sub.0.5 Zn.sub.0.4 Fe.sub.1.7 Mn.sub.0.1 Ge.sub.0.1 Sn.sub.0.1
O.sub.4 50 2300 2 .times. 10.sup.-4
25
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.9975 Mn.sub.0.0005 Ge.sub.0.001
Sn.sub.0.001 O.sub.4
440 5200 1 .times. 10.sup.-2
26
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.998 Mn.sub.0.001 Ge.sub.0.0005
Sn.sub.0.0005 O.sub.4
440 5200 2 .times. 10.sup.-2
27
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.26 Mn.sub.0.46 Ge.sub.0.14 Sn.sub.0.14
O.sub.4 90 300 1 .times. 10.sup.-4
28
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.26 Mn.sub.0.26 Ge.sub.0.1 Sn.sub.0.38
O.sub.4 70 300 1 .times. 10.sup.-4
29
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.1.26 Mn.sub.0.26 Ge.sub.0.38 Sn.sub.0.1
O.sub.4 90 300 1 .times. 10.sup.-4
30
Ni.sub.0.6 Zn.sub.0.4 Fe.sub.2 O.sub.4
450 5250 1 .times. 10.sup.-2
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