JPS6029204B2 - Manufacturing method of high-density Ni-Zn ferrite - Google Patents

Description

[Detailed Description of the Invention] In recent years, with the increase in the amount of information, improving recording density has become an important issue.In order to meet this demand in the field of magnetic recording, the recording frequency has shifted to higher frequencies. It is being done.

As a result, materials used in magnetic heads are required to have even better high frequency characteristics. In this way, materials are required to exhibit properties that are close to their limits, so their stability becomes even more important. Currently, the main materials used for magnetic heads are permalloy, Mn--Zn ferrite, Ni--Zn ferrite, etc., but they have traditionally had problems in terms of stability. For example, in Mn-Zn ferrite, a phenomenon called disaccommodation (hereinafter referred to as DA) is well known, in which the initial magnetic permeability changes over time, and after a long period of time it decreases by 10% from the initial value. may also decrease.

However, in this case, it is possible to reduce the DA to 1% or less by heat treatment in nitrogen. Ni-Zn
DA is also observed in ferrite, although it is small, but in this case, the change in initial magnetic permeability due to thermal demagnetization is a greater factor in inhibiting the stability of the material than DA. In the case of Ni-Zn ferrite, the magnetization mechanism in the frequency band actually used as a magnetic head is M
Similar to h-Zn ferrite, it is thought that the main cause is domain wall movement.

Therefore, the magnitude of the initial magnetic permeability is determined by the difficulty of domain wall movement, but in this case, the factors that hinder domain wall movement are:
Examples include crystal anisotropy inherent to the substance, vacancies, and grain boundaries. Among these, the crystal anisotropy is determined by the composition, and after hot isostatic pressing (mP), the pores are also extremely reduced, resulting in a sintered material with a density close to the theoretical density. The effect of vacancies is also thought to be small because a large body is obtained. Therefore, when the compositions of such high-density Ni-Zn ferrites are the same, it can be considered that the main factor that influences the initial magnetic permeability is the grain boundary. The initial magnetic permeability (particularly the initial magnetic permeability in the frequency band where domain wall motion is considered to be king) is greatly influenced by the crystal grain size, that is, the number of grain boundaries, and even in Ni-Zn ferrite, the crystal grain size generally It is known that the smaller the particle size, the lower the initial magnetic permeability, and the larger the particle size, the higher the initial magnetic permeability. However, it is known that when the particle size is several microns or more, the initial magnetic permeability remains almost constant. When the magnetization mechanism is based on wall movement, the external magnetic field moves the domain walls and magnetization occurs as a whole, but generally in polycrystalline materials, the crystal axes of the polycrystalline grains, that is, the easy axis of magnetization, are arranged isotropically. Therefore, domain wall movement is not easy compared to single crystals. In order to improve the inherent disadvantages of polycrystals, conventional anti-sintering powder was not made into a spinel-type single phase, but the activity of the powder was increased by leaving the heat reactants, and each crystal grain in the dawn stripe was Researchers have been searching for ways to grow crystal grains so that their crystal axes are aligned to some extent, thereby facilitating domain wall movement and increasing initial magnetic permeability. However, the Ni-Zn ferrite obtained by this method is magnetically unstable because the positions where domain walls can stably exist, that is, the positions of potential minimum are not uniformly distributed.
Therefore, there is a strong possibility that the initial magnetic permeability will change if the material is heated above the Curie humidity, such as during bonding processing in the manufacture of a magnetic head, or if it is magnetized for some reason. In the method of the present invention, in order to improve these drawbacks, high density can be achieved by using spinel-type single-phase calcined powder with low activity, which has been considered difficult with normal calcining powder, by applying hot isostatic pressure. This is achieved by pressing, and by taking advantage of the features of this calcined powder, a competitive compact can be obtained that is extremely uniform both magnetically and in terms of crystal structure.

In the Ni-Zn ferrite obtained by this method,
Since the crystal axis direction of each crystal grain is isotropically distributed, domain wall movement is mainly stopped at the grain boundaries, which determines the initial magnetic permeability. In this case, the position of the potential minimum is Because it is uniformly distributed, it is magnetically very stable and has excellent high frequency characteristics. Furthermore, according to this method, a good polycrystalline body with an isotropic distribution of crystal axis directions can be obtained, so that it has excellent uniformity of strength and is advantageous when performing precision processing. The present invention has been made based on the above facts, and will be described in detail below with reference to Examples. Example 1 In both cases, the blending composition is Ni018.0 mol%, Zn032
．． 2 consisting of 5 mol% and Fe20349.5 mol%
Seed samples A, B, were prepared.

Sample A is a sample prepared by the method of the present invention using a false soybean powder that was calcined at 130,000 C and made into a spinel-type single phase, and sample B was calcined at 90,000 C and contains a phase other than the spinel phase. This is a sample made using a conventional technique using calcined powder. After pulverization and molding, all samples were subjected to secondary sintering at 1240 oo, followed by hot isostatic pressing at 1200 oo and 100 pia, and the resulting high-density compacts were annealed at 100,000. Yes, the theoretical density is 99.
It has a dawn compaction density of 8%. Figure 1 shows the frequency dependence of the initial permeability of A, B. At low frequencies, the initial permeability of B is slightly higher than that of A, but the high frequency characteristics of A are better. much better.

Table 1 shows the change in initial permeability due to thermal demagnetization.
This was held at each temperature for 10 minutes and then cooled to 0.
These are the results of measuring the initial magnetic permeability at 9 MHz. Note that the Curie temperature of both A and B is 13500. A
, there is almost no effect of thermal demagnetization, and the effect of the present invention is large, but in B. The effects of thermal demagnetization begin to appear even below the Curie temperature, and Kiko. Above the Lee temperature, the change becomes even larger. Due to thermal demagnetization, the initial magnetic permeability of B increases at low frequencies, but on the contrary, the high frequency characteristics deteriorate and the difference with A becomes even larger. In this way, in B, the initial magnetic permeability changes greatly due to the influence of heat, and the high frequency characteristics also deteriorate, but in contrast, A, which uses spinel-type single-phase calcined powder, has high uniformity. , it is stable with almost no change in initial magnetic permeability due to heat, and has excellent high frequency characteristics, demonstrating the effects of the present invention. Table 1 Example 0 Table 2 shows that the compositions are Ni020 mol%, Zn
These are the results of measuring the initial magnetic permeability change due to heat in a sintered body containing 0.030 mol% and Fe20350 mol% using the same method as in Example 1.

A2 and & are respectively subjected to calcination and primary binding in the same manner as A, B of Example 1, and then subjected to hot isostatic pressing under the conditions of 110,000 and 100 p atm to obtain 1,000 oo
These are sintered bodies obtained by heat treatment at a temperature of about 99.
It has a relative sintered density of 7% and a Curie temperature of about 190o
It is o. Similar to Example 1, in A2 using spinel-type single-phase calcined powder, almost no change in initial magnetic permeability due to heat was observed, and the high frequency characteristics were also excellent, so the effects of the present invention are obvious. . As is clear from Examples 1 and D, the sintered body obtained by the method of the present invention is very stable with almost no change in magnetic properties due to heat, and also has excellent high frequency properties.

In addition, since the crystal structure is uniform, precision machining is easy, and from an industrial perspective, the results are very significant.If the magnetic material of the present invention is applied to magnetic heads, it will be greatly improved. Expected to improve performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a characteristic curve diagram showing the frequency dependence of the initial magnetic permeability of sample A prepared according to the present invention and sample B prepared according to the conventional method. Table 2 Diagram

Claims (1)

[Claims] 1. A step of calcining at least the raw material, and a step of sintering the calcined powder to perform primary sintering to the extent that open pores (pores communicating from the surface of the sample to the center) are eliminated;
A method for producing Ni-Zn ferrite, which comprises the steps of hot isostatic pressing the ferrite material after the primary sintering, and annealing the ferrite material after the hot isostatic pressing under appropriate conditions, A method for producing Ni--Zn ferrite, characterized in that in the calcination step, a spinel-type single-phase calcined powder is produced.