MnZnCo-BASED FERRITE

Abstract

To provide MnZnCobased ferrite with small magnetic losses over a wide frequency range and a wide temperature range. Disclosed is MnZnCobased ferrite containing basic components and auxiliary components, in which the basic components are Fe.sub.2O.sub.3: 51.00 mol % or more and less than 58.00 mol %, ZnO:6.00 mol % or more and less than 13.00 mol %, and CoO:more than 0.10 mol % and 0.50 mol % or less, with the balance being MnO, and the auxiliary components are 50 mass ppm to 500 mass ppm of Si in terms of SiO.sub.2, 200 mass ppm to 2000 mass ppm of Ca in terms of CaO, 85 mass ppm to 500 mass ppm of Nb in terms of Nb.sub.2O.sub.5, and 5 mass ppm to 20 mass ppm of K, relative to the basic components.

Claims

1. MnZnCobased ferrite consisting of basic components, auxiliary components, and inevitable impurities, wherein the basic components are Fe.sub.2O.sub.3:51.00 mol % or more and less than 58.00 mol %, ZnO: 6.00 mol % or more and less than 13.00 mol %, and CoO:more than 0.10 mol % and 0.50 mol % or less, with the balance being MnO, and the auxiliary components are 50 mass ppm to 500 mass ppm of Si in terms of SiO.sub.2, 200 mass ppm to 2000 mass ppm of Ca in terms of CaO, 85 mass ppm to 500 mass ppm of Nb in terms of Nb.sub.2O.sub.5, and 5 mass ppm to 20 mass ppm of K, relative to the basic components.

2. The MnZnCobased ferrite according to claim 1, wherein an average grain size is 6.5 m or more and 9.0 m or less.

3. The MnZnCobased ferrite according to claim 1, wherein a percentage of crystal grains having a grain size of 6 m to 10 m is 51% or more.

4. The MnZnCobased ferrite according to claim 1, wherein a lowest magnetic loss value is 360 kW/m.sup.3 or less when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz.

5. The MnZnCobased ferrite according to claim 1, wherein a lowest magnetic loss value is 200 kW/m.sup.3 or less when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz.

6. The MnZnCobased ferrite according to claim 1, wherein an average grain size is 6.5 m or more and 9.0 m or less, a percentage of crystal grains having a grain size of 6 m to 10 m is 51% or more, a lowest magnetic loss value is 360 kW/m.sup.3 or less when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and a lowest magnetic loss value is 200 kW/m.sup.3 or less when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz.

Description

DETAILED DESCRIPTION

[0033] First, the basic components of the MnZnCobased ferrite according to the present disclosure will be specifically described.

[0034] Fe.sub.2O.sub.3:51.00 mol % or more and less than 58.00 mol % in the basic components.

[0035] If the content of Fe.sub.2O.sub.3 is less than 51.00 mol % in mole ratio in the basic components, the sintered density decreases and magnetic loss increases. Therefore, the content of Fe.sub.2O.sub.3 should be 51.00 mol % or more. The content of Fe.sub.2O.sub.3 is preferably 51.20 mol % or more, more preferably 51.30 mol % or more, and even more preferably 51.40 mol % or more. On the other hand, if the content of Fe.sub.2O.sub.3 is 58.00 mol % or more in mole ratio in the basic components, the magnetic loss becomes excessively large. Therefore, the content of Fe.sub.2O.sub.3 should be less than 58.00 mol %. The content of Fe.sub.2O.sub.3 is preferably 56.00 mol % or less, more preferably 54.00 mol % or less, and even more preferably 53.00 mol % or less.

[0036] ZnO: 6.00 mol % or more and less than 13.00 mol % of the basic components

[0037] In order to obtain a lowest magnetic loss value of 360 kW/m.sup.3 or less when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and a lowest magnetic loss value of 200 kW/m.sup.3 or less when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz, the content of ZnO should be 6.00 mol % or more and less than 13.00 mol % in the basic components. The content of ZnO is preferably 8.00 mol % or more, more preferably 10.00 mol % or more, and even more preferably 10.50 mol % or more. On the other hand, the content of ZnO is preferably 12.50 mol % or less, more preferably 11.90 mol % or less, and even more preferably 11.80 mol % or less.

[0038] CoO:more than 0.10 mol % and 0.50 mol % or less in the basic components

[0039] CoO acts to modulate the thermal behavior of magnetic loss, as mentioned above. However, an excess of CoO will lower the temperature at which the magnetic loss takes its lowest value, making it impossible to lower the lowest magnetic loss value. Therefore, the content of CoO is 0.50 mol % or less in the basic components. The content of CoO is preferably 0.49 mol % or less, more preferably 0.48 mol % or less, and even more preferably 0.47 mol % or less. On the other hand, if the content of CoO is low, the improvement in temperature coefficient becomes less significant and the magnetic loss value cannot be improved. Therefore, the content of CoO is more than 0.10 mol % in the basic components. The content of CoO is preferably 0.20 mol % or more, more preferably 0.30 mol % or more, and even more preferably 0.35 mol % or more. The present disclosure is directed to the MnZnCobased ferrite, in which the remainder of the basic components other than the above-described Fe.sub.2O.sub.3, ZnO, and CoO is manganese oxides. In other words, the total amount of such basic components is 100.00 mol %. When all manganese oxides are converted as MnO, the content of MnO is preferably 30.00 mol % or more and 38.00 mol % or less in the basic components. The content of MnO is more preferably 31.00 mol % or more, more preferably 33.00 mol % or more, and most preferably 35.10 mol % or more. On the other hand, the content of MnO is more preferably 37.50 mol % or less, more preferably 37.00 mol % or less, and most preferably 36.50 mol % or less.

[0040] The MnZnCobased ferrite disclosed herein contains SiO.sub.2, CaO, and Nb.sub.2O.sub.5 as auxiliary components in addition to the above basic components.

[0041] Si: 50 mass ppm to 500 mass ppm in terms of SiO.sub.2 relative to the basic components

[0042] SiO.sub.2 segregates at the grain boundaries together with CaO to form a highly resistive phase, which has the effect of reducing eddy current loss and overall magnetic loss. If the content of Si is less than 50 mass ppm in terms of SiO.sub.2, the effect of Si addition is not sufficient. On the other hand, if the content of Si exceeds 500 mass ppm in terms of SiO.sub.2, crystal grains grow abnormally during sintering, which in turn significantly increases magnetic loss. Therefore, the content of Si should be in the range of 50 mass ppm to 500 mass ppm in terms of SiO.sub.2 relative to the basic components. Furthermore, to more reliably suppress abnormal grain growth, the content of Si, in terms of SiO.sub.2, is preferably 70 mass ppm or more, more preferably 80 mass ppm or more, and even more preferably 90 mass ppm or more. To more reliably suppress abnormal grain growth, the content of Si, in terms of SiO.sub.2, is preferably 480 mass ppm or less, more preferably 450 mass ppm or less, and even more preferably 420 mass ppm or less.

[0043] Ca: 200 mass ppm to 2000 mass ppm in terms of CaO relative to the basic components

[0044] CaO, when coexisting with SiO.sub.2, contributes to the reduction of magnetic loss by segregating at grain boundaries and increasing resistance. However, if the content of Ca is less than 200 mass ppm in terms of CaO, the effect of Ca addition is not sufficient. On the other hand, if the content of Ca is more than 2000 mass ppm in terms of CaO, magnetic loss increases. Therefore, the content of Ca should be in the range of 200 mass ppm to 2000 mass ppm in terms of CaO relative to the basic components. Furthermore, to more reliably suppress abnormal grain growth, the content of Ca, in terms of CaO, is preferably 300 mass ppm or more, and more preferably 500 mass ppm or more. Furthermore, to more reliably suppress abnormal grain growth, the content of Ca, in terms of CaO, is preferably 1800 mass ppm or less, and more preferably 1500 mass ppm or less.

[0045] Nb: 85 mass ppm to 500 mass ppm in terms of Nb.sub.2O.sub.5 relative to the basic components

[0046] Nb.sub.2O.sub.5 effectively contributes to the increase in specific resistivity in coexistence with SiO.sub.2 and CaO. If the content of Nb is less than 85 mass ppm in terms of Nb.sub.2O.sub.5, the effect is not sufficient. On the other hand, if the content of Nb exceeds 500 mass ppm in terms of Nb.sub.2O.sub.5, the magnetic loss increases. Therefore, the content of Nb should be in the range of 85 mass ppm to 500 mass ppm in terms of Nb.sub.2O.sub.5 relative to the basic components. The content of Nb, in terms of Nb.sub.2O.sub.5, is preferably 90 mass ppm or more, and more preferably 95 mass ppm or more. The content of Nb is preferably 400 mass ppm or less in terms of Nb.sub.2O.sub.5, and more preferably 350 mass ppm or less.

[0047] Furthermore, it is important that the MnZnCobased ferrite contain K in an amount ranging from 5 mass ppm to 20 mass ppm as additional auxiliary components in addition to the above-described basic components and auxiliary components. K has the effect of segregating additives at grain boundaries, and acts to increase the specific resistivity. K also has the effect of refining and homogenizing the size of crystal grains, and acts to reduce magnetic loss at high frequencies through the refinement and improve magnetic properties through the homogenization. The actual amount of K to be added to the raw material varies depending on the firing conditions and environment because the amount of K volatilized varies depending on the firing conditions and environment.

[0048] Here, if the content of K in the MnZnCobased ferrite is less than 5 mass ppm, the effect of K addition is not sufficient. Therefore, the content of K in the MnZnCobased ferrite is 5 mass ppm or more, preferably 6 mass ppm or more. On the other hand, when the content of K in the MnZnCobased ferrite exceeds 20 mass ppm, the magnetic loss begins to increase because the grain size becomes smaller than the optimum size for magnetic loss at a frequency of 100 kHz. Furthermore, excessive addition of K results in regions where crystal grains are excessively refined and abnormally grow during sintering, which significantly increases magnetic loss. Therefore, the content of K in the MnZnCobased ferrite is 20 mass ppm or less, preferably 18 mass ppm or less.

[0049] The MnZnCobased ferrite consists of the basic components, auxiliary components, and inevitable impurities as described above. In the present disclosure, the inevitable impurities include Cl, Sr, Ba, etc., which are contained in the raw materials of the basic components. An acceptable total content of the inevitable impurities is about 0.01 mass % or less relative to the entire MnZnCobased ferrite.

[0050] Next, the method of producing the MnZnCobased ferrite according to the present disclosure will be described. Raw material powder of the basic components that have been weighed so that the compositional ratio of Fe.sub.2O.sub.3, MnO, ZnO, and CoO, which are the basic components in the MnZnCobased ferrite after subjection to sintering, is within the specified range of the present disclosure, is thoroughly mixed and then calcined. To this powder after subjection to the calcination, SiO.sub.2, CaO, Nb.sub.2O.sub.5, and K, which are the auxiliary components, are weighed and added so that their contents in the sintered MnZnCobased ferrite are within the specified range of the disclosure, and then thoroughly mixed and ground. The powder thus mixed and ground is granulated with a binder and compacted with a press mold. The formed body thus compacted is fired to make sintered ferrite body (product).

[0051] In this way, the sintered ferrite body provides the MnZnCobased ferrite according to the present disclosure that has a lowest magnetic loss value of 360 kW/m.sup.3 or less when measured at a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and a lowest magnetic loss value of 200 kW/m.sup.3 or less when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz, which have been extremely difficult to achieve with conventional MnZnCobased ferrites.

[0052] Furthermore, the sintered ferrite body has a magnetic loss value of 400 kW/m.sup.3 or less at 40 C. and 500 kW/m.sup.3 or less at 120 C. when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and a magnetic loss value of 200 kW/m.sup.3 or less at 40 C. and 300 kW/m.sup.3 or less at 120 C. when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz.

[0053] If the lowest magnetic loss value is 360 kW/m.sup.3 or less, the magnetic loss value at 40 C. is 400 kW/m.sup.3 or less, and the magnetic loss value at 120 C. is 500 kW/m.sup.3 or less when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and if the lowest magnetic loss value is 200 kW/m.sup.3 or less, the magnetic loss value at 40 C. is 200 kW/m.sup.3 or less, and the magnetic loss value at 120 C. is 300 kW/m.sup.3 or less when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz, loss is low over a wide frequency range, making it possible to handle a variety of frequencies.

[0054] As used herein, the lowest magnetic loss value means the magnetic loss value (iron loss value) at the temperature at which the magnetic loss value (iron loss value) takes its minimum value (magnetic-loss-minimum temperature).

[0055] Average grain size: 6.5 m or more and 9.0 m or less The MnZnCobased ferrite according to the present disclosure preferably has an average grain size of 6.5 m or more and 9.0 m or less. If the average grain size is less than 6.5 m, the magnetic loss measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz may worsen. On the other hand, if the average grain size exceeds 9.0 m, the magnetic loss measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz may worsen.

[0056] Proportion of crystal grains having a grain size of 6 m to 10 m: 51% or more

[0057] From the viewpoint of achieving low magnetic loss over a wide frequency range and a wide temperature range, in the MnZnCobased ferrite disclosed herein, a percentage of crystal grains having a grain size of 6 m to 10 m that are present in the MnZnCobased ferrite is preferably 51% or more.

[0058] If the average grain size of MnZnCobased ferrite is 6.5 m or more and 9.0 m or less and the percentage of crystal grains having a grain size of 6 m to 10 m is 51% or more, the size of crystal grains can be adjusted such that both the magnetic loss measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz and the magnetic loss measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz are low, and the size uniformity of the crystal grains thus obtained reduces residual loss. As a result, the magnetic loss properties according to the present disclosure can be achieved.

[0059] Other methods of producing the sintered body (MnZnCobased ferrite) not mentioned above are not limited in terms of conditions or equipment used, for example, and so-called conventional methods may be followed.

EXAMPLES

[0060] Next, examples of the present disclosure will be described.

Example 1

[0061] First, Fe.sub.2O.sub.3, ZnO, MnO, and CoO, as basic components, were weighed in powder form to obtain the compositional ratio (mol %) presented in Table 1, and the raw material powder thus weighed was mixed for 16 hours using a wet ball mill, and then calcined for 3 hours at 925 C. in air to obtain calcined powder. SiO.sub.2, CaO, Nb.sub.2O.sub.5, and K(K.sub.2CO.sub.3 in this example) were added as auxiliary components to the calcined powder in the ratio (mass ppm) presented in Table 1, ground for 16 hours using a wet ball mill, and then dried to obtain ground powder. To the ground powder, polyvinyl chloride was added as a binder and granulated through a sieve to obtain granulated powder. The granulated powder was formed into a ring shape with an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm, then subjected to firing for 2 hours in mixed gas of nitrogen and air with oxygen partial pressure controlled in the range of 1 vol % to 5 vol % to obtain a ring-shaped sample (sintered ferrite body). The maximum temperature of the atmosphere during the firing was set in the range of 1300 C. to 1350 C. Such firing was performed in a lab-scale batch furnace.

[0062] The ring-shaped sample was subjected to 5 primary and 5 secondary windings, and the magnetic loss (iron loss) was measured with an alternating-current (AC) BH loop tracer when the sample was excited to a magnetic flux density of 200 mT at 100 kHz and to a magnetic flux density of 50 mT at 500 kHz, at temperatures of 23 C. to 130 C. The temperature at the time of measurement of magnetic properties, etc., means the value measured by a thermocouple on the surface of the sintered ferrite body to be measured. More specifically, the ambient temperature of the measurement environment was set to a predetermined temperature, and magnetic and other properties were measured after confirming that the surface temperature of the sintered ferrite body was the same as the ambient temperature.

[0063] The average grain size and the percentage of crystal grains having a grain size of 6 m to 10 m were measured as follows. That is, the prepared ring-shaped sample was fractured, and the cross section after the fracture was observed under an optical microscopy (at 400 magnification, the number of crystal grains in this field of view was 1000 to 2000). The crystal grain size was calculated assuming each crystal grain to be a perfect circle, and the average value was obtained. For such calculations, an image interpretation software, A-ZO KUN (A-ZO KUN is a registered trademark in Japan, other countries, or both of Asahi Kasei Engineering Co., Ltd.), was used. Next, the particle size distribution of crystal grains was calculated to determine the percentage of crystal grains (percentage of number of grains) having a grain size of of 6 m to 10 m.

[0064] Based on the results of the above measurements, the magnetic-loss-minimum temperature, the lowest magnetic loss value, and the magnetic loss values at 40 C. and 120 C. when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, the magnetic-loss-minimum temperature, the lowest magnetic loss value, and the magnetic loss values at 40 C. and 120 C. when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz, the average grain size, and the percentage of crystal grains having a grain size of 6 m to 10 m are listed in Table 1. Here, Nos. 1-15 in Table 1 are our examples conforming to the present disclosure, while Nos. 16-21 in Table 1 are comparative examples where the content of K of the sintered body is outside the range of the present disclosure, and Nos. 22-39 in Table 1 are comparative examples where the content of basic components or auxiliary components other than K is outside the range of the present disclosure. In both our examples and comparative examples in Table 1, the total content of inevitable impurities is 0.01 mass % or less.

[0065] As can be seen in Table 1, the MnZnCobased ferrite of our examples, in which the compositions of the basic components, Fe.sub.2O.sub.3, ZnO, MnO, and CoO, and of the auxiliary components, SiO.sub.2. CaO, and Nb.sub.2O.sub.5, were appropriately selected and an appropriate amount of K was contained, has a lowest magnetic loss value of 360 kW/m.sup.3 or lower when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, and a lowest magnetic loss value of 200 kW/m.sup.3 or lower when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz, indicating low loss over a wide frequency range and a wide temperature range.

[0066] These properties, where the average grain size is in an appropriate range of 6.5 m to 9.0 m, or where the percentage of crystal grains having a grain size of 6 m to 10 m is 51% or more, are the result of the effect of inclusion of K, providing more uniform crystal grains.

[0067] These results indicate that, according to the present disclosure, the addition of K can produce low-loss MnZnCobased ferrite in a wide frequency range from 100 kHz to 500 kHz and in a wide temperature range.

[0068] In contrast, in those cases where at least one of the basic components, Fe.sub.2O.sub.3, ZnO, MnO, and CoO, or the auxiliary components, SiO.sub.2, CaO, Nb.sub.2O.sub.5, and K, was outside the scope of the present disclosure, at least one of the following two conditions was not achieved: a lowest magnetic loss value of 360 kW/m.sup.3 or lower when measured with a highest magnetic flux density being 200 mT and at a frequency of 100 kHz, or a lowest magnetic loss value of 200 kW/m.sup.3 or lower when measured with a highest magnetic flux density being 50 mT and at a frequency of 500 kHz.

TABLE-US-00001 TABLE 1 Chemical composition Magnetic property Auxiliary component (mass ppm) 100 kHz-200 mT K Magnetic- (*content loss- Lowest Magnetic Magnetic of minimum magnetization loss value loss value Basic component (mol %) sintered temp. loss value at 40 C. at 120 C. No. Fe.sub.2O.sub.3 MnO ZnO CoO SiO.sub.2 CaO Nb.sub.2O.sub.5 body) ( C.) (kW/m.sup.3) (kW/m.sup.3) (kW/m.sup.3) 1 51.86 36.08 11.64 0.42 100 1000 250 6 80 330 342 425 2 51.86 36.08 11.64 0.42 100 1000 250 8 60 314 335 419 3 51.86 36.08 11.64 0.42 100 1000 250 10 70 334 359 414 4 51.86 36.08 11.64 0.42 100 1000 250 11 60 316 333 417 5 51.86 36.08 11.64 0.42 100 1000 250 14 70 353 369 467 6 51.86 36.08 11.64 0.42 100 1000 250 18 60 356 370 458 7 51.45 36.43 11.67 0.45 100 1000 250 12 50 260 281 352 8 52.80 35.12 11.69 0.39 100 1000 250 6 90 316 358 354 9 51.86 36.08 11.64 0.42 150 1000 250 10 70 341 370 42.5 10 51.86 36.08 11.64 0.42 300 1000 250 10 70 348 375 432 11 51.86 36.08 11.64 0.42 400 1000 250 10 70 355 384 449 12 51.86 36.08 11.64 0.42 100 500 250 10 70 351 372 471 13 51.86 36.08 11.64 0.42 100 1500 250 10 60 357 387 485 14 51.86 36.08 11.64 0.42 100 1000 100 10 70 346 381 457 15 51.86 36.08 11.64 0.42 100 1000 300 10 70 347 385 461 16 51.86 36.08 11.64 0.42 100 1000 250 0 60 341 360 442 17 51.86 36.08 11.64 0.42 100 1000 250 2 60 323 345 414 18 51.86 36.08 11.64 0.42 100 1000 250 25 60 398 419 496 19 51.86 36.08 11.64 0.42 100 1000 250 43 60 581 601 685 20 51.86 36.08 11.64 0.42 100 1000 250 55 40 677 677 827 21 51.86 36.08 11.64 0.42 100 1000 250 60 40 693 693 840 22 50.00 37.48 12.08 0.44 100 1000 250 8 70 382 400 483 23 61.00 30.98 7.91 0.11 100 1000 250 11 30 365 352 463 24 57.47 37.04 5.00 0.49 100 1000 250 9 60 501 522 590 25 51.13 32.46 16.00 0.41 100 1000 250 10 90 428 469 476 26 52.12 36.16 11.72 0.00 100 1000 250 13 100 400 471 456 27 51.55 35.93 11.52 1.00 100 1000 250 12 50 381 409 480 28 51.86 36.08 11.64 0.42 20 1000 250 6 60 432 452 535 20 51.86 36.08 11.64 0.42 800 1000 250 8 60 471 489 571 30 51.86 36.08 11.64 0.42 100 50 250 13 70 517 538 615 31 51.86 36.08 11.64 0.42 100 3000 250 5 80 498 529 579 32 51.86 36.08 11.64 0.42 100 1000 10 10 70 421 440 520 33 51.86 36.08 11.64 0.42 100 1000 700 12 60 403 424 498 34 51.86 36.08 11.64 0.42 0 1000 250 10 50 439 442 621 35 51.86 36.08 11.64 0.42 600 1000 250 10 50 376 379 531 36 51.86 36.08 11.64 0.42 100 0 250 10 0 675 830 1856 37 51.86 36.08 11.64 0.42 100 3000 250 10 50 497 498 708 38 51.86 36.08 11.64 0.42 100 1000 0 10 50 468 475 699 39 51.86 36.08 11.64 0.42 100 1000 600 10 30 533 536 759 Magnetic property 500 kHz-50 mT Crystal property Magnetic- Percentage loss- Lowest Magnetic Magnetic Average of grain minimum magnetization loss value loss value grain size temp. loss value at 40 C. at 120 C. size 6-10 m No. ( C.) (kW/m.sup.3) (kW/m.sup.3) (kW/m.sup.3) (m) (%) Remarks 1 60 191 195 250 7.7 52 Example 2 60 178 182 248 8.4 54 Example 3 50 186 186 237 7.3 56 Example 4 60 166 170 229 7.0 56 Example 5 50 167 167 232 7.1 54 Example 6 50 158 160 210 6.6 52 Example 7 50 150 162 199 7.1 57 Example 8 60 194 195 257 8.0 52 Example 9 50 189 191 242 7.3 55 Example 10 50 191 195 257 7.5 53 Example 11 50 196 198 266 7.5 52 Example 12 50 188 189 255 7.3 55 Example 13 40 198 198 294 7.2 57 Example 14 50 188 192 253 7.3 54 Example 15 50 189 195 259 7.2 56 Example 16 60 276 278 338 9.3 50 Comparative example 17 60 201 208 280 9.2 50 Comparative example 18 60 159 163 219 6.1 49 Comparative example 19 60 251 252 320 8.2 47 Comparative example 20 80 309 311 377 9.1 45 Comparative example 21 80 381 385 429 9.3 41 Comparative example 22 70 273 277 325 Comparative example 23 30 301 299 398 Comparative example 24 60 316 318 372 Comparative example 25 90 247 217 296 Comparative example 26 100 211 238 264 Comparative example 27 50 203 204 282 Comparative example 28 60 222 224 281 Comparative example 20 60 236 238 292 Comparative example 30 50 388 390 459 Comparative example 31 60 362 364 420 Comparative example 32 50 238 240 299 Comparative example 33 60 204 206 273 Comparative example 34 50 213 214 378 Comparative example 35 50 156 160 244 Comparative example 36 0 532 801 1906 Comparative example 37 20 273 276 512 Comparative example 38 40 270 270 483 Comparative example 39 40 233 234 406 Comparative example Note: means not measured.

Example 2

[0069] Granulated powder produced by the same method as in Example 1 using the compositions of basic components and auxiliary components listed in Table 2 was formed into a ring shape as in Example 1 to make a formed ring. The continuous firing furnace was then adjusted so that the firing conditions were the same as in Example 1, and the formed ring was fired. Multiple formed rings of the same composition were also fired on different days (multiple days) under the same firing conditions using the same continuous firing furnace. The magnetic loss (iron loss) of these fired products with different firing dates (specifically, magnetic loss (iron loss) under the conditions of frequency: 100 kHz, highest magnetic flux density: 200 mT, temperature: 80 C., and magnetic loss (iron loss) under the conditions of frequency: 500 kHz, highest magnetic flux density: 50 mT, and temperature: 80 C.) were measured by the method described above, and the mean and standard deviation were determined. The results are listed in Table 2.

TABLE-US-00002 TABLE 2 Chemical composition Magnetic loss value Auxiliary component (mass ppm) 100 kHz, 200 mT, 80 C. 500 kHz, 50 mT, 80 C. K Standard Standard Basic component (mol %) (*content of Mean deviation Mean deviation No. Fe.sub.2O.sub.3 MnO ZnO CoO SiO.sub.2 CaO Nb.sub.2O.sub.5 sintered body) (kW/m.sup.3) (kW/m.sup.3) (kW/m.sup.3) (kW/m.sup.3) Remarks 1 51.86 36.08 11.64 0.42 100 1000 250 7 335 7.9 221 5.9 Example 2 51.86 36.08 11.64 0.42 100 1000 250 12 341 5.7 181 4.8 Example 3 51.86 36.08 11.64 0.42 100 1000 250 1 392 10.1 252 9.5 Comparative example

[0070] In general, it was recognized that the use of the continuous firing furnace tends to increase the variation of magnetic loss and other parameters, but as seen in Table 2, it was confirmed that the variation of magnetic loss values is reduced by following the present disclosure.