DE1062611B - Process for the production of a ferrite material for magnetic cores with an almost rectangular hysteresis loop - Google Patents

Description

GERMAN

The invention relates to a method for producing a ferrite material for magnetic cores which have an almost rectangular hysteresis loop and a coercive force <2 Oe and which consist of MgO, 50 to 70 percent by weight Fe ₂ O ₃ and MnO ₂ .

Magnetic cores with an almost rectangular hysteresis loop are important for various applications. This type of nucleus is used, among other things, for so-called "magnetic memories" (see e.g. W. N. Papian, Proceedings of the I. R. L, April 1952, ίο Pp. 475 to 478, and D. R. Brown and E. Albers-Schoenberg, "Electronics", April 1953, pp. 146 to 149). Such magnetic memories are used, among other things, in calculating machines and for automatic ones Controls. These cores are also used in magnetic switches.

The degree of squareness of the hysteresis loop can be expressed quantitatively in various ways. A measure of the squareness is e.g. B. the quotient B _r / B _d . To explain the meaning of this quotient, reference is made to FIG. 1, which is a schematic representation of part of a saturation magnetization curve. In this figure, B _r denotes the remanent induction and B _d denotes the induction at which the hysteresis loop is just closing. In practice, it is often not easy to measure B _d with great accuracy. However, it is easy to find an approximately correct value for B _d on the basis of the mean value of the inductions after partial magnetization or partial demagnetization (with intermittent saturation), the two inductions being measured at the same field strength, which is selected in such a way that the inductions differ by more than 1%, but by less than 3 ° / _0. The samples measured in the making of the present invention were carried out in this manner. The quotient B _r / B _d was always measured on a ring-shaped magnetic core with a constant cross-section of the ferromagnetic material over the entire circumference of the ring and with an outer diameter that is at most 1.6 times the inner diameter.

Another measure of the squareness of the hysteresis loop of the ferromagnetic material is the so-called squareness ratio {R _{s) m} ax · F ^or the importance of this size is referred to the above-mentioned literature. For the sake of completeness, a brief explanation follows with reference to FIG. 2, likewise a schematic representation of part of a magnetization curve which relates to a case in which the demagnetization was started before the magnetic saturation was reached. The size [R _s ) _max is called

Method of manufacture

a ferrite material for magnetic cores

with almost rectangular

Hysteresis loop

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Netherlands 7 October 1953.

Pieter Geldermans and Pieter van den Ban,

Eindhoven (Netherlands),
have been named as inventors

Are defined. The quotient

* (- l / 2 H _m )

-BRA

m)

is a function of the applied field strength H _m . It turns out that this quotient has a maximum value for a certain value of H _m , which usually deviates little from the coercive force H _0. This maximum value of the quotient is indicated with the symbol (R _s ) _max . The measurements of B (H _m ) and # (- 1/2 H _m ) required to determine (Rsjmax ) would also be carried out on ring-shaped magnetic cores with a constant cross-section of the ferromagnetic material along the entire circumference of the ring and with an outer diameter carried out with a maximum of 1.6 times the inner diameter.

A material with an almost rectangular hysteresis loop is to be understood in the context of the invention as one in which the value of the quotient B _r jB _{d is} at least 0.7 and / or the (i? _S ) _Aail . Value is at least 0.5.

Magnetic cores with an almost rectangular hysteresis loop should also have the lowest possible coercivity

909 579/379

power to reduce the energy consumption when switching the core from a state of remanence to to keep others small.

Magnetic cores with an almost rectangular hysteresis loop are already known which consist of 10 to 30 percent by weight MgO, 50 to 70 percent by weight Fe ₂ O ₃ and the remainder MnO ₂ . However, these magnetic cores have coercive forces of over 2 Oe, in some cases even over 3 Oe.

It has now been found, surprisingly, that magnetic cores with an almost rectangular hysteresis loop and very small coercive force can be obtained in a method of the type mentioned at the outset by using a mixture of magnesium, manganese and iron compounds, preferably in a low-oxygen, in particular in a nitrogen atmosphere, is heated to a temperature of 1150 to 145O ⁰ C, preferably to 1250 to 1350 ⁰ C, the proportions of magnesium, manganese and iron compounds are chosen so that in the end product 3 to 8 percent by weight Mg O, 50 to 70 percent by weight Fe ₂ O ₃ and the remainder MnO ₂ are present.

It should also be mentioned that manganese ferrites are also known which do not contain magnesium. These well-known Manganese ferrites do not have a rectangular hysteresis loop.

The invention is explained in more detail using a few exemplary embodiments.

A mixture of Fe ₂ O ₃ , MnCO ₃ and MgO is ground for 2 hours with alcohol in a rotating ball mill, then dried and ^{pre-sintered by heating to about 700 °} C. for 1 hour; the presintered mass is cooled and ground for 16 hours with alcohol in a vibratory mill. The powder obtained in this way is dried and sieved and, after the addition of a binder, is made granular and pressed into rings ^{at a pressure of 4 t / cm 2.} This is followed by final sintering.

For the measurements of B _r jB _d and {R _{s) m} ax> ^aue carried out at room temperature, the rings thus obtained, which had mm an internal diameter of 3.8 mm and an outer diameter of 5.9 were wire with twenty secondary windings strands and four primary turns of thin copper wire. The rings were previously demagnetized by passing an alternating current of steadily decreasing strength through the primary winding. The measurements are made according to the so-called " ballistic " method (cf. B ο ζ ο rth, »Ferromagnetisrru, 1951, p. 843, etc.).

Table 1 shows B _r / B _a and {R _s ) _max of some materials according to the invention with the corresponding compositions, converted to percentages by weight of MgO, MnO ₂ and Fe ₂ O ₃ .

Table 1 Table 2

35

45

Raw materials,
according to the
below Mn Fe Composition,
converted to MgO MnO ₂ Fe ₂ O ₃ (■ "- *) max (Hm) max atomic ^ 0.75 2 Weight percent 8.2 26.6 65.2 ^ he 1.00 2 the oxides 7.5 32.6 59.9 proportion weighed 1.25 2 7.0 37.6 55.4 0.53 1.6 Mg 1.50 2 6.5 42.0 51.5 0.77 1.2 0.50 0.61 1.4. 0.50 0.61 1.4 0.50 0.50

When producing the samples to which Table 2 relates, ^{sintering was always carried out at 1320 °} C. in air.

Table 3

Raw materials,
according to the
below Mn Fe Composition,
converted to MgO MnO ₂ Fe ₂ O ₃ [Rs) ma x (Egg m) max 2O _{1 drop}
atomic ver 1.00 2 Weight percent 3.9 33.8 62.3 proportion weighed 1.25 2 the oxides 3.6 39.3 57.2 Mg 1.50 2 3.3 43.5 53.2 0.78 1.3 0.25 1.75 2 3.1 47.3 49.6 0.82 1.3 ²⁵ 0.25 0.76 1.2 0.25 0.61 1.2 0.25

When producing the samples to which Table 3 relates, ^{sintering was always carried out at 1300 °} C. in nitrogen.

The values of (H _m ) _max are shown in the tables. Since, as already noted earlier, (H _m ) _r deviates only slightly from the coercive force H ₀ , these numerical values give an impression of the magnitude of the coercive force.

It has also been found according to the invention that (R _s ) _{max is influenced} by the choice of the final sintering temperature. Table 4, which proves this, relates to samples with a composition corresponding to 7.5 percent by weight of MgO, 32.6 percent by weight of MnO ₂ and 59.5 percent by weight of Fe ₂ O ₃ . These samples were obtained by sintering in air at various temperatures.

Table 4

Sintering temperature
⁰ C (Rs) max (Hm) max 1250 0.65 2.0 1320 0.77 1.2 1355 0.65 1.2 1390 0.55 1.2 1400 0.54 1.4

Together 32.5 Fe ₂ O ₃ Sinter Sinter Br / Ba (- "s) max (Hm) max settlement
Weight percent 41.9 59.9 tempe atmo MgO I MnO ₂ 39.0 51.6 temperature ° C sphere 0.98 0.84 1.2 7.6 47.2 57.4 1320 air 0.96 0.80 1.5 6.5 49.7 1300 N ₂ 0.91 0.76 1.2 3.6- 1275 air 0.95 0.74 1.0 3.1 1250 O ₂

The invention preferably relates to materials as manganese-magnesium ferrites with a Excess manganese are to be understood. These ferrites are given in Tables 2 and 3.

It was found that sintering in a nitrogen atmosphere at a temperature of about 1300 ^° C. is particularly favorable in order to achieve a high [Rg) _{max value.} A sample with a composition corresponding to 7.0 percent by weight of MgO, 37.6 percent by weight of MnO ₂ and 55.4 percent by weight of Fe ₂ O ₃ , which was obtained by sintering in nitrogen at 1300 ^° C., had a (/? _S ) _maa . Value of 0.80 with an (H _m ) _max -WeTt of 1.5, while a sample with a composition corresponding to 3.6 percent by weight of MgO, 39.3 percent by weight of MnO ₂ and 57.1 percent by weight of Fe ₂ O ₃ , is below sintered to the same conditions, an (R _s ) _max -Width of 0.82 with an (i? _m ) _maa! -Value of 1.3.

From the above it follows that a sintering temperature of 1250 to 135O ⁰ C in general

is cheap; the composition naturally influences the level of the most favorable sintering temperature. Sintering in nitrogen at a temperature of about 1300 ^° C. can lead to high (R _s ) _max values, even of 0.80 and higher, at least with a sufficient excess of manganese, which, however, must not be too large.

Claims (1)

PATENT CLAIM: Process for the production of a ferrite material for magnetic cores which have an almost rectangular hysteresis loop and a coercive force <2 Oe and which consist of MgO, 50 to 70 percent by weight Fe ₂ O ₃ and MnO ₂ , characterized in that, that a mixture of magnesium, manganese and iron compounds, is preferably heated in a low-oxygen, in particular in a nitrogen atmosphere, to a temperature of 1150 to 145 ° ⁰ C, .vorzugsweise to 1250 to 135o ⁰ C, wherein the proportions of magnesium , Manganese and iron compounds are chosen so that 3 to 8 percent by weight of MgO, 50 to 70 percent by weight of Fe ₂ O ₃ and the remainder MnO ₂ are present in the end product. Considered publications:
French Patent No. 983,712;
Physica, III, 1936, pp. 470/71, Figs. 2 and 3;
German patent application St 4840 IVc / 806 (published on July 9, 1953). 1 sheet of drawings