JPH07120596B2 - Method of forming ferromagnetic thin film - Google Patents

Description

The present invention relates to a ferromagnetic thin film used in a magnetic recording medium, a high-performance small motor, etc., and relates to a forming method for increasing the maximum energy product (BH) max.

(Prior art) Nd-F with large coercive force and maximum energy product (BH) max
The use of e-B magnets is being promoted in order to contribute to the miniaturization of equipment. However, since this magnet is difficult to form and work, it cannot be thinned or used in a special shape. Therefore, research has been conducted to form thin films of arbitrary shape by liquid quenching, sputtering, spraying, etc.
For example, the sputtering method is described in J. Magn. Magn. Mat. 54-57.
(1986) P535, or Japanese Patent Application No. Sho 61 filed by the applicant.
−229130 and the like.

(Problems to be solved by the invention) In order to improve the performance and size of a device using magnetism, the maximum energy product (BH) max is large, for example, a value of 10 MGOe or more is required. In the present situation, as shown in the above-mentioned literature, the one having anisotropy in the film thickness direction and the maximum energy product (BH) max exceeding the above value has not been obtained at present.

An object of the present invention is to provide a method for forming a film having a high maximum energy product (BH) max and having anisotropy in the film thickness direction, which solves the above problems.

(Means for solving the problem) For this reason, an alloy thin film consisting of 13 to 27 atomic% of Nd, 3 to 17 atomic% of B, 28 atomic% or more of Fe, and the balance of at least one of Co and Al is sputtered. After being formed by the method, a film having a squareness ratio in the film thickness direction of 0.7 or more is annealed at a predetermined temperature for a predetermined time in a vacuum or a non-oxidizing gas atmosphere (for example, N ₂ gas).

(Function) A state in which a film having anisotropy in the film thickness direction by the sputtering method is annealed under the above conditions to be crystallized and the magnetic layer is surrounded by the non-magnetic layer formed at the grain boundary. Therefore, the movement of the domain wall is prevented even when an external magnetic field is applied, so that a film having a high energy product and having anisotropy in the film thickness direction is obtained.

〔Example〕

FIG. 1 is a sectional view of a multipole magnetron sputtering apparatus for forming a perpendicularly magnetized film of the present invention. A target 2 is provided in a vacuum container 1, and a substrate 3 is placed on a substrate mounting base 4 facing the target 2 with a space of 25 mm.

The substrate can be heated by the heater 6, and the temperature of the substrate is controlled by the heater power supply 13. A shutter 5 is provided between the target 2 and the substrate 3 to prevent particles scattered in the initial stage of sputtering from adhering to the substrate, and a DC voltage or a high frequency voltage can be applied to the target 2 by a target power supply 7. I am doing it. The filament 8 and the anode electrode 10 are arranged in the vicinity of the target, and the filament power source 9 heats the filament to generate thermoelectrons and collect them in the anode electrode 10. The filament power source 9 and the anode power source 11 allow the target current to be arbitrary. The target voltage and the target current can be changed independently.

Target 2 is 15 at% Nd, 5 at% B in the thin film, Fe
Was mixed in such a manner that the powder content was 63 atomic%, Co was 10 atomic%, and Al was 7 atomic%, and the powder was sintered in vacuum. This target was attached to the sputtering electrode, and the substrate 3 was mounted on the substrate table 4. 2 x 10 inside the vacuum container by the exhaust system 14
Exhaust below ^-6 Torr. The substrate is heated to 300 ° C. while adjusting the heater power supply 13, the filament power supply 9 is adjusted to heat the filament 8, and then the argon gas introduction valve 12 is opened to introduce the argon gas, and the pressure is 8 × 10 5. ^-3
Adjusted to be Torr. After adjusting the anode power supply to a target current of 0.5 A, the target power supply 7 applies a negative DC voltage of 300 V with the shutter 5 closed.
Pre-sputtering was performed for minutes to remove oxides and the like on the target surface, the shutter was opened, and sputtering was performed for 20 minutes to form a film having a thickness of about 2 μm. After that, the inside of the vacuum vessel was evacuated again to 2 × 10 ⁻⁶ Torr or less and cooled to the substrate temperature of room temperature. Select a squareness ratio of 0.7 or more in the film thickness direction, set it in an infrared image furnace capable of rapid heating and cooling, exhaust the inside of the furnace to 2 × 10 ^-6 Torr or less, and then rapidly heat it to 640 ° C. After heating for 10 seconds to anneal, it was immediately cooled. As a result, a ferromagnetic film with an energy product of more than 10 MGOe was obtained. Fig. 2 shows the distribution of the measured values of the film characteristics when annealing was performed at various temperatures and times, divided into 10 MGOe and above. The circles indicate that the maximum energy product (BH) max in the film thickness direction after annealing was 10 MGOe or more. That is, if annealing is performed under the conditions of the shaded region, a maximum energy product (BH) max in the film thickness direction of 10 MGOe or more can be obtained. When the annealing temperature exceeds 800 ° C, the magnetic properties are impaired by the growth of the paramagnetic phase. Conversely, when the annealing temperature is less than 400 ° C, crystallization is not promoted and the magnetic properties do not improve no matter how long it takes.

The annealing holding time differs depending on the annealing temperature. For example, when the annealing temperature is 640 ° C to 800 ° C, the holding time is 10 seconds, but when the annealing temperature is 600 ° C, the holding time is 45 seconds.
The lower the annealing temperature is, such as 1700 seconds at 500 ° C, the longer the holding time becomes, but when the holding time exceeds 20 hours, the annealing temperature between 400 and 800 ° C gives 10MGOe.

When the composition of the alloy thin film was changed and examined, a good result was obtained as a result of selecting a composition having a squareness ratio of 0.7 or more and performing the experiment under the above annealing conditions. That is, a film having a composition of 13 to 27 atomic% of Nd, 3 to 17 atomic% of B, 28 atomic% or more of Fe, and the balance of one or more of Co and Al is annealed under the above annealing conditions to obtain the maximum energy product ( A film having a BH) max of 10 MGOe or more and having anisotropy in the film thickness direction can be obtained.

(Effects of the Invention) As described above, according to the present invention, there is an effect that a vertically magnetized film having a maximum energy product (BH) max of 10 MGOe or more can be obtained. Therefore, a device using magnetism has high performance and is small in size. Can be converted.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a multi-pole magnetron sputtering apparatus for forming a perpendicularly magnetized film of the present invention, and FIG. 2 is a characteristic diagram showing annealing conditions of the present invention. In the figure, 2 is a target, 3 is a substrate, and 5 is a shutter.

Claims (1)

[Claims] 1. Nd of 13 to 27 atomic%, B of 3 to 17 atomic%, Fe
Is 28 atomic% or more and the balance is at least one of Co and Al on the substrate by sputtering, and select a substrate with an alloy thin film with a squareness ratio of 0.7 or more in the film thickness direction in vacuum. Or, in an atmosphere of non-oxidizing gas, when the annealing holding time s (sec) is taken as log (s) on the X axis and the annealing holding temperature (° C) is taken on the Y axis, a straight line Y = 80
0, straight line X = 1, straight line Y = 400, straight line X = 6 and point (1,
640) and the point (4.8,400) are annealed in a range surrounded by a straight line.