CN100386470C - A kind of preparation method of perovskite structure lanthanum strontium manganese oxide semimetal thin film - Google Patents

Abstract

The invention is a method for preparing a perovskite structure lanthanum strontium manganese oxide (La _0.7 Sr _0.3 MnO ₃ , LSMO) film by adopting a novel channel spark ablation method (Channel Spark Ablation, CSA). In the present invention, the LaAlO ₃ (001) single crystal substrate is used as the substrate, and the channel spark ablation technology is used at the substrate temperature of 700-850°C, and the La _0.7 Sr _0.3 MnO ₃ ceramic target is used under the appropriate oxygen pressure, substrate temperature, pulse Under current and pulse voltage, La _0.7 Sr _0.3 MnO ₃ films with high c-axis orientation were grown. The prepared film has a Curie temperature higher than room temperature, and has good electrical properties and ferromagnetic properties at room temperature. The thin film obtained by the method of the invention has good application potential in spintronic devices.

Description

A kind of preparation method of perovskite structure lanthanum strontium manganese oxide semimetal thin film

technical field

The invention belongs to the technical field of magnetic thin films, and in particular relates to a semimetal lanthanum strontium manganese oxide (La _0.7 Sr _0.3 MnO ₃ , LSMO) iron with a high degree of c-axis orientation growth using a novel channel spark ablation technology (ChannelSpark Ablation, CSA) Magnetic film method.

Background technique

Half-metal thin film materials are characterized by being metallic for spin-up electrons and insulating for spin-down electrons below the Curie temperature. The electronic density of states at the Fermi level is thus 100% spin polarized. Magnetic materials with high spin polarizability have attracted much attention because of their potential applications in nonvolatile magnetic random access memory, magnetic sensors, and spin field effect transistors. Perovskite manganese compound R _1-x A _x MnO ₃ is a semi-metal material widely studied, in which R is mostly La, and La ³⁺ ions are replaced by divalent alkaline earth element ions such as Sr ²⁺ , Ca ^{2 +} and Ba ²⁺ etc. for substitution. These compounds have high spin polarizability.

The half-metal and giant magnetoresistive perovskite manganese compounds that have been studied in the early stage are mainly La _1-x Ca _x MnO ₃ (LCMO). However, the Curie temperature Tc of this compound is around 250K, which greatly hinders its industrial application. The La _1-x Sr _x MnO ₃ (LSMO) material has a Curie temperature Tc (~350K) higher than room temperature. Therefore, research on how to prepare LSMO films with high electrical and magnetic properties is of great importance to the industrial application of magnetic thin film materials. important research significance.

The channel spark ablation method (CSA) is similar to the pulsed laser ablation method (Pulsed Laser Deposition, PLD) method, both are based on the process of ablation coating, that is, a very high energy is instantly transferred to a small part of the target surface , causing its temperature to be higher than the sublimation limit, so that the target is ablated and uses the remaining kinetic energy to move to the surface of the substrate to deposit a thin film. CSA has the same effectiveness and universality as PLD, but the operation is simpler and the equipment is cheaper.

Therefore, studying how to prepare high-quality LSMO thin films using CSA technology has become a research goal in this field because of its great application value.

Contents of the invention

The purpose of the present invention is to propose a new method for preparing high-quality semimetallic perovskite structure thin film (LSMO) which is easy to operate, relatively cheap in equipment price, and has large-scale production potential.

The method for preparing the La _0.7 Sr _0.3 MnO ₃ semi-metal thin film proposed by the present invention is to prepare the La _0.7 Sr _0.3 MnO ₃ thin film with a perovskite structure by using a novel channel spark ablation technology based on pulsed electron beams. The invention uses La _0.7 Sr _0.3 MnO ₃ ceramic target with stoichiometric ratio as the target material, and grows La _0.7 Sr _0.3 MnO ₃ thin film on the LaAlO ₃ crystal orientation as (001) substrate. The working gas is O ₂ , the air pressure is maintained at 2.0-2.5Pa, the substrate temperature is controlled at 700-850°C, the high-voltage DC power output power supply is set at -15--19KV, the working current is 3.0-6.0mA, and the pulsed electron beam The repetition frequency is 2.0-3.0 Hz, and after the deposition time is 0.5-30 minutes, a 10-800 nm thick La _0.7 Sr _0.3 MnO ₃ film with a perovskite structure is prepared.

The film thickness prepared by the invention is 50-500nm. The thickness of the film can be controlled by controlling the deposition time of the film, the repetition frequency of the pulsed electron beam, and the operating voltage and operating current of the DC power output power supply as required.

The better preparation conditions of the present invention are as follows:

In the present invention, the substrate temperature is 750-850°C.

In the present invention, the pressure of the _O2 working gas is 2.0-2.5Pa.

In the present invention, when the channel spark ablation technology is used for coating, the deposition conditions are: the high-voltage direct current power output power supply sets the working voltage to -16～-18KV, the working current is 3.0～5.0mA, and the pulse electron beam repetition frequency is 2.0～2.5Hz , Coating deposition time 0.5 to 10 minutes.

In the present invention, the _O2 gas is passed into the reaction chamber through a variable gas guide valve and a flow meter, which is the prior art for preparing thin films in vacuum.

The film thickness of the perovskite structure semimetal La _0.7 Sr _0.3 MnO ₃ prepared by the method of the invention is 10-800 nm, and the film thickness can be controlled by the deposition time as required.

The experimental results show that the LSMO films grown on LaAlO ₃ (001) substrates by CSA technology have the characteristics of high c-axis orientation. The prepared LSMO thin film has the characteristics of soft magnetic materials, has a low coercive force, and saturates at a low magnetic field, which is similar to the LSMO thin film prepared by the PLD method. The resistivity of the film is low, which is close to the epitaxial growth LSMO film prepared by PLD method. The CSA technology equipment used in the present invention is relatively cheap, easy to operate, and can prepare high-quality semi-metal LSMO thin films comparable to the PLD technology.

Description of drawings

Fig. 1 is the X-ray diffraction spectrogram of the LSMO thin film prepared by the method of the present invention.

Fig. 2 is a hysteresis loop diagram of the LSMO film prepared by the method of the present invention under an applied magnetic field parallel to the plane of the film.

Fig. 3 is a graph showing the relationship between the electronic density of states and energy of the LSMO film prepared by the method of the present invention.

Detailed ways

Concrete implementation steps of the present invention are as follows:

Example 1, a La _0.7 Sr _0.3 MnO ₃ circular target with a strict stoichiometric ratio was prepared according to the traditional ceramic target preparation method, with a target diameter of 17 mm and a thickness of 2 mm. The distance between the target surface and the quartz tube was fixed at 4mm. The inner diameter of the quartz catheter is 2mm. The substrate LaAlO ₃ (001) was polished on both sides, and then ultrasonically cleaned with deionized water, acetone and alcohol for 20 minutes each. The background pressure of the vacuum chamber before film deposition was 2.0×10 ^-3 Pa.

The mass flowmeter of Bronkhorst company is used to control the flow of _O2 so that the working pressure is 2.0Pa, the substrate is heated by an infrared lamp and the temperature of the substrate is maintained at 824°C, and the operating voltage and current of the HCL 140-20000 high-voltage DC power output power supply are set as -16.0KV and 4.8mA, pulse electron beam repetition frequency is 2.4Hz. The film deposition time is 10 minutes, and the film thickness is 450 nm.

Example 2, the same method as in Example 1, the LSMO film was prepared under the following conditions: the working pressure was 2.5Pa, the substrate temperature was 830°C, the working voltage and working current were respectively set to -18.0KV and 3.2mA, and the pulse electron The beam repetition frequency is 1.4-1.6 Hz. The film deposition time is 20 minutes, and the film thickness is 680 nm.

)为光源在10°～80°内扫描得到薄膜的XRD谱。采用在PPMS系统(Quantum Design)上的VSM方法测量室温下薄膜在外加平行磁场下的磁滞回线。采用传统的四探针方法测量薄膜室温时的方块电阻。采用自旋极化扫描探针显微镜测量薄膜的dI/dV谱图，并据此计算薄膜表面的能态密度。A Kosaka ET3000 surface profiler was used to measure the film thickness, and a Cu Kα1 (λ=1.5406

) is the XRD spectrum of the thin film obtained by scanning the light source within 10°-80°. The hysteresis loops of the thin films under an applied parallel magnetic field at room temperature were measured by the VSM method on a PPMS system (Quantum Design). The sheet resistance of the films at room temperature was measured using a conventional four-probe method. The dI/dV spectrum of the film was measured by a spin-polarized scanning probe microscope, and the density of states on the surface of the film was calculated accordingly.

The same method as in the examples can obtain films that meet the performance requirements within the scope of the preparation conditions of the present invention. Therefore, the content of the present invention is not limited to the above examples.

Claims (6)

1. a calcium titanium ore structure lanthanum strontium manganese oxygen is La _0.7Sr _0.3MnO ₃The preparation method of half metal film is characterized in that utilizing channel spark ablation to prepare film, and concrete preparation condition is as follows:

(1) target is by the La that mixes by the chemical dose proportioning _0.7Sr _0.3MnO ₃The compound sintering forms;

(2) adopting the crystal orientation is the LaAlO of (001) ₃Monocrystalline is as film substrate; Keep substrate temperature at 700～850 ℃;

(3) high voltage direct current power output source set operating voltage and be-15～-19KV, working current is 3.0～6.0mA, the pulsed electron beam repetition rate is 2.0～3.0Hz, the coated film deposition time is 0.5～30 minute;

(4) with working gas O ₂Feed vacuum chamber, making operating air pressure is 2.0～2.5Pa.

2. preparation method according to claim 1 is characterized in that substrate temperature is 750～850 ℃.

3. preparation method according to claim 1, it is characterized in that the operating voltage of high voltage direct current power output power supply is set at-16～-18KV, working current is 3.0～5.0 mA.

4. preparation method according to claim 1 is characterized in that the pulsed electron beam repetition rate is 2.0～2.5Hz.

5. preparation method according to claim 1 is characterized in that the coated film deposition time is 0.5～10 minute.

6. preparation method according to claim 1, the calcium titanium ore structure lanthanum strontium manganese oxygen half metal film thickness that is obtained is 10～800nm.

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