JPH04154697A - Mn-zn ferrite single crystal and its production - Google Patents

Abstract

PURPOSE:To obtain the subject single crystal having a uniform composition, free from remarkable contamination of platinum and excellent in crystallinity at a low cost by thoroughly fusing the raw material and subsequently allowing the fused raw material to stand for one hour or longer in growing the single crystal. using a crucible made of Pt or Pt-Rh alloy. CONSTITUTION:A crucible 1 made of Pt or Pt-Rh alloy is set to a supporting unit 7 linked to an elevating unit 10 and placed in an electric furnace 5. A prescribed amount of raw material powder is then charged to the crucible 1, heated to form a fused liquid 4 and allowed to stand in that state for one hour or longer. The crucible 1 is then slowly lowered so that an Mn-Zn ferrite single crystal may be produced from the bottom of the crucible 1 taking a long time. A sintered ZnO rod 2 is suspended from a sintered rod-elevating unit 3 arranged over the electric furnace 5 to a position right above the surface of the fused liquid 4 and ZnO is sublimed to prevent evaporation of ZnO from the fused liquid 4. Composition variation of the single crystal can be prevented thereby, thus obtaining the objective Mn-Zn ferrite single crystal having <=500ppm contamination of Pt and/or Rh.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an improvement in a method for growing Mn--Zn ferrite single crystals using the Bridgman method.

(Prior Art) Conventionally, the Bridgman method using platinum or a metal crucible in which rhodium or the like is added to platinum has been used to manufacture Mn-Zn ferrite single crystals. Single crystal growth using the Bridgman method has the advantage that large single crystals can be obtained relatively easily.On the other hand, crucible component metal particles such as platinum or platinum-rhodium may be mixed into the single crystal and precipitated. However, when the obtained single crystal is microfabricated into magnetic heads, etc., the metal particles peel off and the dimensional accuracy deteriorates. Due to the sublimation of ZnO from the Mn-Zn ferrite melt, the composition changes along the growth direction of the single crystal. There was a problem that only a small portion of the single crystal obtained was usable.

(Problems to be solved by the invention) To solve these problems, hitherto the main focus has been on Mn with a uniform composition.
- Research has been conducted to obtain Zn ferrite. In other words, as a countermeasure against compositional fluctuations, a method has been proposed and researched in which single crystals are grown while continuously supplying raw materials into a crucible. However, there is a problem that platinum contamination is not eliminated, and since the raw material is supplied into the melt during growth, the melt is disturbed and the crystallinity of the single crystal is lower than that of the conventional method where no measures are taken to change the composition. There was also the problem that the mechanism for supplying the raw materials and the raw materials to be supplied required the raw materials to be formed into a rod shape and sintered. Countermeasures against compositional fluctuations were implemented with the aim of reducing costs by increasing the number of parts that can be used, etc., but since the cost required to counteract compositional fluctuations is by no means low, even if the countermeasures against compositional fluctuations are implemented, the costs will not be significantly reduced. did not become.

(Means for Solving the Problems) In order to solve the above-mentioned drawbacks, the present inventors investigated the route of platinum penetration and the causes of compositional fluctuations, researched countermeasures therefor, and arrived at the present invention. According to Mn-
It is possible to provide Zn ferrite, and the gist of the present invention is to provide a Mn-Zn ferrite single crystal grown using a crucible made of platinum or platinum-rhodium alloy,
Using an Mn-Zn ferrite single crystal characterized by a platinum and/or rhodium content of 500 ppm or less and a crucible made of pt or Pt-Rh alloy, the entire raw material is completely melted, and the state is further reduced to 1. Mn-Zn characterized in that single crystal growth is performed after holding for a period of time or more.
During the manufacturing method of ferrite single crystal and the growth of Mn-Zn ferrite single crystal, Z is separated from the melt in the crucible in an electric furnace.
A method for producing an Mn--Zn ferrite single crystal, characterized by growing a single crystal while sublimating nO.

The present invention will be explained in detail below.

The present inventors first discovered platinum (hereinafter platinum refers to platinum (Pt)).
We conducted research on the mechanism of contamination (which refers to both platinum and rhodium alloys (Pt-Rh)). In other words, regarding platinum contamination, most of the platinum in the melt sinks to the bottom of the crucible, and what does not sink conversely collects near the surface of the melt (
It was found that the behavior of Therefore, Mn-Zn
By completely melting the entire raw material before growing ferrite and leaving it in that state for a sufficient period of time, the platinum that was conventionally mixed in the single crystal is collected at the bottom and top of the single crystal ingot, and the single crystal is We succeeded in drastically reducing the amount of platinum mixed in to 500 ppm or less. The time required to collect platinum from the time the raw materials are completely melted until the single crystal growth begins is 1.
It is better if the time is longer than that, and if it is less than that, the platinum separation will be insufficient and the present invention will not be effective.

On the other hand, with regard to measures against compositional fluctuations, the method of supplying raw materials into the melt during growth, which has been studied previously, involves supplying the raw materials in solid or liquid form, and the raw materials are not allowed to fall or drip. During this process, the liquid level is disturbed and the platinum that has collected on the melt surface is scattered as mentioned above, and the scattered platinum gets mixed into the single crystal and precipitates, so it is not possible to reduce platinum contamination. found. Therefore, a method that does not disturb the liquid level is required. Generally, the main cause of compositional fluctuations in Mn--Zn ferrite single crystals is a decrease in ZnO from the melt due to sublimation, and therefore, as the single crystal grows, ZnO in the single crystal also decreases. The present invention focuses on this phenomenon, and generates ZnO vapor by evaporating and sublimating ZnO separately from the melt in the atmosphere where the single crystal is grown, and generates ZnO vapor near the melt surface. By increasing the vapor pressure of ZnO, sublimation of ZnO from the melt is suppressed, thereby taking measures against compositional fluctuations. According to this method, there is no need to supply solid or liquid raw materials to the melt, so the melt surface is not disturbed, and the platinum that has gathered near the melt surface is not scattered. It is possible to reduce platinum contamination. Also, since the melt is not disturbed, a single crystal with good crystallinity can be obtained.

The ZnO steam generator required for the present invention has various embodiments as described below, and may be appropriately selected in consideration of the scale of the single crystal growth apparatus, heating method, temperature control method, etc. This will be illustrated below with reference to the drawings.

1) Figure 1 shows an apparatus that can carry out the invention most effectively.
Platinum crucible 1 is placed in electric furnace 5 (heater 6) on support stand 7 interlocked with crucible lifting device 1O, a predetermined amount of raw material powder is charged into the crucible, and the temperature is raised to produce melt 4 for over 1 hour. After holding, single crystal growth begins. Single crystal growth conditions are 5 m
The crucible is lowered at a speed of m/Hr, and a single crystal is produced from the bottom of the crucible over 50 hours. On the other hand, when single crystal growth begins, the ZnO sintered rod 2 is suspended directly above the melt surface from the sintered rod lifting device 3 installed at the top of the electric furnace, and the ZnO is sublimated and evaporated from the melt. and suppress compositional fluctuations in single crystals.

FIG. 2 shows a conventional and very common Bridgman method single crystal growth apparatus (hereinafter, the symbols are the same as in FIG. 1).

Fig. 3 shows a type of conventional composition variation countermeasure method, in which a melt 4 is first prepared at about 10% of the total amount of the single crystal, and a sintered rod 8 having the same composition as the Mn-Zn ferrite single crystal is suspended in a crucible. This is a method in which single crystals are grown by dripping melt from the tip of a sintered rod.

2) Separately from the crucible containing the melt shown in Fig. 1, a small platinum container 21 is hung above the crucible with a platinum wire, and ZnO powder is placed in it ((Fig. 4).

3) Make a ZnO sintered disk 22 and attach it to the upper edge of the crucible with platinum wire (Fig. 5).

4) Attach the ZnO sintered disk to the inside of the crucible lid with platinum wire and make M9 (Figure 6).

5) In the platinum crucible hanging method, the ZnO sintered rod 2 is hooked on a hanging hook (FIG. 7).

A simple method of equal degrees is fine. Therefore, according to these methods, there is almost no increase in the cost of growing single crystals according to the present invention.
Since the composition is uniform, it is possible to reduce costs by improving the yield of single-crystal ingots, reduce platinum contamination, and have excellent crystallinity, making it possible to significantly reduce costs and improve quality.

The scope of application of the present invention is Mn0-ZnO-Fe20g as an Mn-Zn ferrite single crystal, or Sn,
Examples include ferrite single crystals to which oxides such as In, Ca, and A1 are added.

Hereinafter, specific embodiments of the present invention will be described with reference to Examples, but the present invention is not limited thereto.

(Example 1) A Mn-Zn ferrite single crystal was grown by the improved Bridgman method of the present invention.

Platinum crucible (70mmφX 250mm1 (total length))
As raw materials, powdered Mn0595g, Zn0455g,
Prepare 2,450g of Fezes and heat it to 1.70g in an electric furnace.
The temperature was raised to 0°C and the composition ratio MnO/ZnO/Fe2O,=
A 28.6/19.1152.3 mol % Mn-Zn ferrite melt was prepared, and after being completely melted and held for 1 hour, single crystal growth was started. Single crystal growth conditions are 5mm/Hr
The crucible was lowered at a speed of 50 hours to form a single crystal from the bottom of the crucible. A diameter of 1 am prepared for this opening,
A ZnO sintered rod with a length of 5 cm is suspended from a sintered rod elevator installed at the top of the electric furnace 1 cm above the melt surface of the crucible using a heat-resistant platinum wire to sublimate ZnO and remove Z from the melt.
Evaporation of nO was suppressed. This ZnO replenishment rate (= Z
The nO sublimation rate) was controlled by setting a sintered rod elevator at an appropriate position taking into account the temperature distribution in the electric furnace. The variation in the obtained Mn-Zn ferrite single crystal composition is due to MnO/
ZnO/Fe20x = 0.510.510.6 mol%
Met. Figure 8 shows the analysis values of each component (mol%) of the single crystal and the number of platinum particles mixed in (observed in the diameter direction cross section of the single crystal and expressed as number per square centimeter (n)) in the longitudinal direction of the single crystal. Ta. The X axis in this figure represents the distance (mm) from the bottom of the crucible to the top from left to right. In addition, in the ingot after the growth was completed, no platinum precipitation was observed inside the ingot, but a large amount of platinum crystallized in the form of needles was observed on the upper surface.

(Comparative Example 1.2) In Comparative Example 1, raw material powder of Mn-Zn ferrite was placed in a platinum crucible and melted as usual, except that it was grown without taking the measures against compositional fluctuation (sublimation of ZnO) of the present invention. It was grown under the same conditions as in Example 1. In Comparative Example 2, a small amount of the raw material Mn-Z was initially
After melting n-ferrite powder (10% by weight of the total single crystal) in a platinum crucible and holding it in that state for 1 hour, Mn-Zn ferrite rods were sintered using the same mounting equipment as in Example 1. Gradually put the solid into the furnace and melt it from the bottom of the rod, supply droplets into the crucible and then move towards the top of the crucible.
Single crystals were grown. The apparatus used in Comparative Example 1 is shown in FIG. 32, and the apparatus used in Comparative Example 3 is shown in FIG.

The compositional deviation along the growth direction of the single crystal obtained on each side and the platinum content are also shown in FIG. As is clear from Section 8B, in Comparative Example 1, in which no measures against compositional fluctuations were taken, Zn and Feze3 decreased along the growth direction of the single crystal.
It can be seen that nO increases and compositional fluctuations occur.

However, platinum contamination is low, and this is because there is almost no turbulence in the melt surface. On the other hand, measures were taken to change the composition of the raw material necessary for growing the single crystal in Comparative Example 2 during growth (the composition of the single crystal is relatively constant, but the number of platinum mixtures is large. It can be seen that compositional fluctuations in Example 1 according to the present invention are suppressed more than in Comparative Example 2.Also, the number of platinum mixed tends to be concentrated in the first part and the upper part of the crucible than in Comparative Example 1, but it is very , which is significantly less than that of Comparative Example 2.Also, regarding single crystal C crystallinity, Example 1 and Comparative Example 1 were good with no grain boundaries or small-angle grain boundaries.
Comparative example.

) In No. 2, there were no grain boundaries, but the occurrence of small-angle grain boundaries was observed, indicating that the melt was disturbed due to the long raw material supply time.

2 (Example 2) In addition to the ZnO sublimation device shown in Example 1, 1) In addition to the crucible containing the melt shown in Figure 1, a small platinum wire was attached to the top of the crucible. Hang the container 21 and place Z inside it.
Add nO powder (Figure 4).

2) Make a sintered disk 22 of ZnO and place platinum on the upper edge of the crucible.
Connect them with lines (Figure 5).

3) Attach a ZnO sintered disk to the inside of the crucible lid with platinum wire and cover it with a lid 9' (Fig. 6). The same effect was obtained with 80% of the weight compared to the case without it.

4) In the platinum crucible hanging method, the ZnO sintered rod 2 is hooked on a hanging hook (FIG. 7). Single crystals were grown under the same conditions as in Example 1 except that ZnO was sublimed using four types of equipment. The results were similar to those of Example 1 in terms of compositional analysis value and platinum count, indicating that the measures against compositional fluctuations were effective. Furthermore, when a ZnO sintered body is placed on top of a crucible, by covering the crucible with a lid, compositional fluctuations can be taken care of using a small amount of sintered body.

(Effects of the Invention) According to the present invention, a high-quality Mn--Zn ferrite single crystal with a uniform composition, low platinum contamination, and good crystallinity can be obtained at low cost. Furthermore, it is possible to take measures against compositional fluctuations even in the hanging Bridgman method, which was conventionally thought to be difficult to deal with compositional fluctuations, so it has extremely great industrial value.

[Brief explanation of drawings]

Figures 1 and 4 to 7 are explanatory diagrams showing an example of the Bridgman method single crystal growth apparatus used in the present invention, and Figures 2 and 3 are explanatory diagrams of a conventional Bridgman method single crystal growth apparatus. It is a diagram. FIG. 8 is a graph showing the growth direction composition analysis values of Mn--Zn ferrite single crystals produced by the method of the present invention and the conventional method. 1... Platinum crucible, 2... ZnO sintered rod 3.
... Sintered rod lifting device, 4... Melt 5... Electric furnace,
6... Heater 7... Crucible support stand, 8...
Ferrite sintered rod 9...lid, 1o...crucible lifting device 21...small platinum container, 22...Zn
O sintered disk・J3≧1/

Claims (1)

[Claims] 1. Mn-Zn ferrite single crystal grown using a crucible made of platinum or platinum-rhodium alloy, characterized in that the amount of platinum and/or rhodium mixed is 500 ppm or less Zn ferrite single crystal. 2. A method for producing an Mn-Zn ferrite single crystal, which is characterized by completely melting the entire raw material using a crucible made of Pt or Pt-Rh alloy, and further maintaining that state for one hour or more before growing a single crystal. . 3. Mn-Zn ferrite single crystal production according to claim 2, characterized in that during the Mn-Zn ferrite single crystal growth, the single crystal is grown while sublimating ZnO separately from the melt in the crucible in an electric furnace. Method.