JPH0145968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing single crystal ferrite suitable as a material for recording/reproducing heads for VTR video.

Conventional Structures and Their Problems In general, single crystal ferrite used in magnetic heads is required to have high magnetic permeability and high magnetic properties such as saturation magnetic flux density.

Conventionally, the method for manufacturing single crystal ferrite that satisfies the above characteristics involves moving a crucible containing melted raw materials vertically in an electric furnace with a certain appropriate temperature gradient, and gradually starting from the tip of the crucible. The Bridgeman method of solidifying and turning into a single crystal, and the bonding of polycrystalline ferrite onto a single crystal ferrite substrate,
There is a solid phase reaction method that uses solid phase reaction to convert the entire material into a single crystal by firing at a certain temperature range.

However, these manufacturing methods have drawbacks, such as the former having a large compositional segregation, and the latter having an extremely small compositional segregation, but the polycrystalline raw material does not completely become a single crystal, leaving crystal grains in some places. .

Purpose of the Invention It is an object of the present invention to provide a method for growing high-quality single crystals by solving the above-mentioned conventional problems.

Composition of the Invention The present invention has been made to achieve the above object, and includes a step of bringing a single crystal ferrite substrate and a polycrystalline ferrite with a fine crystal grain size into close contact, and a step between the single crystal ferrite substrate and the polycrystalline ferrite. The present invention provides a method for producing single-crystal ferrite, in which the polycrystalline ferrite is made into a single crystal by continuously passing a rectangular wave-like current through the polycrystalline ferrite.

DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic cross-sectional view for explaining a method for manufacturing single crystal ferrite, which is an embodiment of the present invention. In the figure, 1 is a single crystal ferrite substrate;
2 is polycrystalline ferrite, 3 is an electrode made of graphite, and 4 and 4' are electrode terminals. Polycrystalline ferrite 2 is provided in contact with one surface of single-crystalline ferrite substrate 1, and polycrystalline ferrite 2 and single-crystalline ferrite substrate are connected to each other. A graphite electrode 3 is provided as an electrode for passing a current between the electrode 1 and the electrode 1. Electrode terminals 4, 4'
A platinum wire was used for the wire, and a silver paste was used for connection to the electrode 3. The single crystal ferrite substrate 1 is cut from an ingot produced by the Bridgeman method, and the polycrystalline ferrite 2 has a crystal grain size of 20 μm or less and a porosity of 0.01% or less. The mirror-polished surfaces of the single-crystal ferrite substrate 1 and the polycrystalline ferrite 2 are brought into close contact with each other. In such a configuration, the single crystal ferrite substrate 1
The electrode terminal 4' on the side of the polycrystalline ferrite 2 is grounded, and a rectangular wave current with a peak value of 8 A/cm ² is passed through the electrode terminal 4 on the side of the polycrystalline ferrite 2 at a temperature range of 1300℃ to 1450℃ in an electric furnace. As a result of firing in an atmosphere close to the equilibrium oxygen partial pressure, polycrystalline ferrite 2 completely became a single crystal without leaving a single crystal grain size.

In this case, it goes without saying that the direction of current flow may be reversed.

Although the reason why this phenomenon occurs is not necessarily clear, it can be considered as follows. Since a fixed value of interfacial energy per unit area is attached to the boundary surfaces of crystal grains, the smaller the area, the smaller the total interfacial energy. Therefore, the smaller the crystal grain size, the smaller the total interfacial energy of the crystal grain, and therefore, the smaller the crystal grain, the easier it is to become a single crystal by solid phase reaction. On the other hand, large crystal grains have a large interfacial energy and are difficult to form into single crystals. In addition, it is known that if the temperature at which a solid phase reaction occurs is too high, the crystal grains will increase in the polycrystal, and the rectangular wave will remain until the end. Needs to be fired.

Therefore, if the size of the crystal grains is not constant, there may be cases where large crystal grains do not become single crystals and remain. At this time, energy is given to the crystal grains by passing a rectangular wave current through the polycrystal, and when the energy reaches enough to annihilate the interface of the crystal grains, the large crystal grains also disappear, forming a complete single crystal. It is estimated that it becomes a crystal. When the applied current is a sinusoidal wave, the energy changes gradually, so it is assumed that the effect is not as strong as that of a rectangular wave, and there have also been cases in which crystal grains remain.

As another example, as shown in FIG. 2, even when polycrystalline ferrite 2 is sandwiched between monocrystalline ferrite substrates 1 from both sides and fired, current is passed through graphite electrodes 3 during firing. As a result, the same effect as in the first example was obtained.

Effects of the Invention In summary, the present invention provides a continuous bond between the single crystal ferrite substrate and the polycrystalline ferrite when polycrystalline ferrite is laminated onto a single crystal ferrite substrate and the whole is made into a single crystal by firing at a certain temperature range. This method provides a method for producing single crystal ferrite in which polycrystalline ferrite is made into a single crystal by applying an electric current from the side or from the polycrystalline side.This method produces a high quality single crystal with extremely small compositional segregation and no residual crystal grains. can be obtained, which is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a method for manufacturing single-crystal ferrite according to one embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a method for manufacturing single-crystal ferrite according to another embodiment of the present invention. 1... Single crystal ferrite substrate, 2... Polycrystalline ferrite, 3... Graphite electrode, 4, 4'
...Platinum electrode terminal.

Claims (1)

[Claims] 1 At least a step of bringing a single crystal ferrite substrate and a polycrystalline ferrite made of fine crystal grains into close contact with each other, and a step of firing while continuously applying a rectangular wave current between the single crystal ferrite substrate and the polycrystalline ferrite. A method for producing single crystal ferrite, comprising: