CN112242221A - Iron nitride-based multiferroic heterostructure with exchange bias effect and preparation method thereof - Google Patents

Iron nitride-based multiferroic heterostructure with exchange bias effect and preparation method thereof Download PDF

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CN112242221A
CN112242221A CN202011149704.7A CN202011149704A CN112242221A CN 112242221 A CN112242221 A CN 112242221A CN 202011149704 A CN202011149704 A CN 202011149704A CN 112242221 A CN112242221 A CN 112242221A
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米文博
刘祥
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Tianjin University
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Abstract

The invention relates to an iron nitride-based multiferroic heterostructure with exchange bias effect and a preparation method thereof; by magnetron sputtering of ferromagnetic Fe4N and SrRuO3Film and multiferroic BiFeO3The films are combined together to form Fe4N/BiFeO3/SrRuO3/SrTiO3A multiferroic heterostructure of SrTiO in sequence from bottom to top3(111) Single crystal substrate, 50nm thick SrRuO3Layer, BiFeO 30nm thick3Layer and 20nm thick Fe4N layers; fe4N and SrRuO3Being a ferromagnetic layer, BiFeO3Is an antiferromagnetic layer. When a cooling magnetic field of 50kOe is applied, the exchange bias field of the heterostructure reaches-527 Oe at 3K; the magnetron sputtering method adopted by the invention can prepare high-quality single-phase Fe4The N film has high surface flatness and has obvious advantages in industrial production.

Description

Iron nitride-based multiferroic heterostructure with exchange bias effect and preparation method thereof
Technical Field
The invention relates to a multiferroic heterostructure with exchange bias effect and a preparation method thereof. More specifically, it is prepared byExchange bias effect of iron nitride (Fe)4N) based multiferroic heterostructure and method of preparation; by magnetron sputtering of ferromagnetic Fe4N and SrRuO3Film and multiferroic BiFeO3The films are combined together to form Fe with exchange bias effect4N/BiFeO3/SrRuO3/SrTiO3Multiferroic heterostructures.
Background
In the magnetic tunnel junction with the sandwich structure, the magnetization directions of the upper and lower ferromagnetic films affect the resistance of the tunnel junction. The ferromagnetic thin film and the antiferromagnetic thin film are compounded, and the pinning effect of the antiferromagnetic thin film is utilized to fix the magnetic moment direction of the adjacent ferromagnetic thin film. When a small magnetic field is applied, the magnetic moment direction of the ferromagnetic thin film which is not pinned by the antiferromagnetic thin film changes along with the magnetic field, so that the tunnel junction can be in a high resistance state and a low resistance state, and the method is applied to spintronics devices such as a memory, a magnetic sensor and the like.
Cubic anti-perovskite Fe4The N has the advantages of simple structure, corrosion resistance, oxidation resistance, good thermal stability, high saturation magnetization, high Curie temperature, high spin polarizability and the like, and has important application value in the spin electronics device. Perovskite BiFeO at room temperature3The ferroelectric material has ferroelectricity and antiferromagnetism, and the Curie temperature and the antiferromagnetic Neel temperature of the ferroelectricity are far higher than room temperature, so that the ferroelectric material can be applied to multiferroic heterostructures. Perovskite SrRuO3Has the characteristics of simple structure, good conductivity, good thermal stability and the like, and is compatible with BiFeO3And SrTiO3The perovskite material is lattice matched, so that the perovskite material is often used as a buffer layer or a metal electrode of a heterostructure and has wide application value in the field of spintronics. At the same time, cubic anti-perovskite Fe4N and BiFeO3Has better lattice matching, so that Fe can be formed4N/BiFeO3/SrRuO3/SrTiO3And (3) epitaxial heterostructure.
At present, there is no Fe internationally4N/BiFeO3/SrRuO3Preparation of heterostructures and reports of exchange bias due to single phase Fe4The existence window of N is narrower, soThis epitaxial Fe4The preparation of N becomes difficult. In addition, the molecular beam epitaxy method is not suitable for industrial production due to high cost. Single-phase epitaxial Fe prepared by using opposite-target magnetron sputtering method4N film, can reduce preparation cost. Furthermore, the ferromagnetic thin films in the reported multiferroic heterostructures are mostly polycrystalline or amorphous alloy thin films [ MATTER LETTERS 156,125, 125 (2015); ADVANCED MATERIALS 28,363, 363 (2016); JOURNAL OF PHYSICS D APPLIED PHYSICS 51,125308, 125308(2018)]There has been little research on a material having a high spin polarizability as a ferromagnetic thin film, and the exchange bias field generated is small. In spintronics devices, multiferroic heterostructures with greater exchange bias effects are desired. The invention adopts a magnetron sputtering method to SrTiO through a large amount of experimental research3(111) Fe polarized with high spin is prepared on the substrate4Fe based on N4N/BiFeO3/SrRuO3The epitaxial heterostructure shows that a +/-50 kOe polarizing magnetic field is applied in the cooling process, and the exchange bias field can reach-527 Oe under 3K, so that the heterostructure has important application value in a spin electronics device.
Disclosure of Invention
From the industrial production and practical application perspective, a low-cost magnetron sputtering method is needed to prepare the multiferroic heterostructure with the exchange bias effect. Meanwhile, in the multiferroic heterostructure, if obvious exchange bias is generated, lattice matching among layers is required, epitaxial growth can be realized, higher requirements on the thickness and the interface flatness of each layer are met, and the preparation conditions are harsh. In addition, single phase Fe4The existing window of N is narrow, the preparation condition is harsh, and single-phase Fe can be prepared only under specific conditions4And (6) N thin films. The invention designs and prepares Fe through a large number of experiments based on the five purposes4N/BiFeO3/SrRuO3/SrTiO3Multiferroic heterostructures.
The specific invention contents are as follows.
An iron nitride-based multiferroic heterostructure with exchange bias effect; structure of Fe4N/BiFeO3/SrRuO3/SrTiO3Multiferroic heterostructures.
Said Fe4N/BiFeO3/SrRuO3/SrTiO3SrTiO is sequentially arranged from bottom to top3(111) Single crystal substrate, 50nm thick SrRuO3Layer, BiFeO 30nm thick3Layer and 20nm thick Fe4N layers; wherein Fe4N and SrRuO3Being a ferromagnetic layer, BiFeO3Is an antiferromagnetic layer. Said Fe4N/BiFeO3/SrRuO3/SrTiO3SrTiO is sequentially arranged from bottom to top3(111) Single crystal substrate, 50nm thick SrRuO3Layer, BiFeO 30nm thick3Layer and 20nm thick Fe4N layers; wherein Fe4N and SrRuO3Being a ferromagnetic layer, BiFeO3Is an antiferromagnetic layer.
The substrate is SrTiO3(111) A single crystal substrate having a thickness of 500 μm and an area of 5mm by 5 mm.
Said Fe4N/BiFeO3/SrRuO3/SrTiO3Heterostructure the exchange bias field of the heterostructure is-527 Oe at 3K when the cooling field is 50 kOe.
The invention relates to Fe with exchange bias effect4A preparation method of an N-based multiferroic heterostructure; the method comprises the following steps:
(1) by magnetron sputtering with SrRuO3The target is the raw material, in the sputtering process, the mixed gas of argon (99.999) and oxygen (99.999) is introduced, and the sputtering power, the sputtering pressure, the substrate temperature and the cooling rate are controlled to be in SrTiO3(111) SrRuO with the thickness of 50nm is prepared on a substrate3(111) A film;
(2) by radio frequency magnetron sputtering with Bi1.1FeO3The target is the raw material, in the sputtering process, the mixed gas of argon (99.999) and oxygen (99.999) is introduced, and the sputtering power, the sputtering pressure, the substrate temperature and the cooling rate are controlled to be in SrRuO3/SrTiO3BiFeO with the thickness of 30nm is prepared on the film3(111) A film;
(3) adopting a magnetron sputtering method, taking a pure Fe target as a raw material, and introducing argon (99.999) and nitrogen (99.999) in the sputtering processThe mixed gas is prepared by controlling sputtering current, sputtering voltage, sputtering pressure, substrate temperature and cooling rate in BiFeO3/SrRuO3/SrTiO3Preparation of 20nm thick Fe on a heterostructure4N (111) film.
In the step (1), the vacuum degree at the back bottom is better than 2 multiplied by 10–5Pa, direct current sputtering power of 40W, sputtering pressure of 1.1Pa, substrate temperature of 650 ℃, flow ratio of argon (99.999) and oxygen (99.999) of 5: 3, annealing in pure oxygen (99.999) at 200Pa, 650 deg.C for 30min, 10 deg.C/min for cooling at 3 deg.C/min, and 0.5nm/min for depositing film3(111) SrRuO with the thickness of 50nm is prepared on a substrate3(111) A film.
In the step (2), the vacuum degree of the back bottom is better than 2 multiplied by 10–5Pa, the radio-frequency sputtering power is 80W, the sputtering pressure is 1.3Pa, the substrate temperature is 650 ℃, and the flow ratio of argon (99.999) to oxygen (99.999) is 5: 4, under the conditions that the annealing environment is pure oxygen (99.999), the annealing pressure is 200Pa, the annealing temperature is 650 ℃, the annealing time is 30min, the heating rate is 10 ℃/min, the cooling rate is 3 ℃/min, and the deposition rate of the film is 1.7nm/min, under the conditions of SrRuO3/SrTiO3BiFeO with the thickness of 30nm is prepared on the film3(111) Film to obtain BiFeO3(111)(30nm)/SrRuO3(111)(50nm)/SrTiO3(111) A heterostructure.
In the step (3), the vacuum degree at the back bottom is better than 2 multiplied by 10–5Pa, sputtering current of 0.05A, sputtering voltage of 700V, sputtering pressure of 1.0Pa, substrate temperature of 475 ℃, flow ratio of argon (99.999) to nitrogen (99.999) of 5: 1, under the conditions that the temperature rising rate is 10 ℃/min, the temperature reduction rate is 3 ℃/min and the deposition rate of a film is 2.1nm/min, BiFeO3/SrRuO3/SrTiO3Preparation of 20nm thick Fe on a heterostructure4N (111) film to obtain Fe4N(111)(20nm)/BiFeO3(111)(30nm)/SrRuO3(111)(50nm)/SrTiO3(111) A heterostructure.
Fe according to the invention4N(111)/BiFeO3(111)/SrRuO3(111) The heterostructure has application value in the spintronics device, such as a storage unit of a memory and a magnetic sensor, and the magnetron sputtering method adopted by the invention is a common method for industrially producing thin film materials, and Fe and SrRuO are used3And Bi1.1FeO3The target has the advantages of simple target material selection, high utilization rate and the like.
FIG. 1 shows the results obtained in SrTiO3(111) Fe prepared on a substrate4N(111)/BiFeO3(111)/SrRuO3(111) Schematic structural diagram of the heterostructure.
To confirm the best embodiment of the invention, we have prepared Fe according to the invention4N(111)/BiFeO3(111)/SrRuO3(111)/SrTiO3(111) The heterostructure was subjected to X-ray diffraction, atomic force microscopy and magnetic measurements.
Fe prepared from the present invention4N(111)/BiFeO3(111)/SrRuO3(111) As can be seen from the X-ray diffraction pattern of the heterostructure, Fe is present4N、BiFeO3、SrRuO3And SrTiO3The diffraction peaks of (111) and (222) crystal planes of (B) indicate Fe4N、BiFeO3And SrRuO3Film edge [111 ]]Directionally oriented growth, as shown in fig. 2.
Fe prepared from the present invention4N/BiFeO3/SrRuO3The surface topography of the heterostructure can be seen on the Fe4N surface is relatively flat, Fe4N grows in islands as shown in fig. 3(a) and 3 (b); in BiFeO3The surface shows a fluctuation in the shape of particles as shown in FIGS. 3(c) and 3 (d); SrRuO3The surface appears granular undulation as shown in fig. 3(e) and 3 (f).
The invention measures Fe in different cooling magnetic field directions4N(111)/BiFeO3(111)/SrRuO3(111) The magnetization intensity of the heterostructure changes with the change of an external magnetic field, and the direction of the magnetic field is parallel to the surface of the film. The variation of the magnetization of the heterostructure with the magnetic field upon application of a cooling magnetic field of 50kOe is shown in FIG. 4(a), Fe at 3K4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure is 1595Oe, the exchange bias field is-527 Oe, the coercive field and the exchange bias field gradually decrease with increasing temperature, and the exchange bias field of the heterostructure is less than-25 Oe when the temperature increases to above 150K, as shown in FIGS. 4(b) and 4 (c); the variation of the magnetization of the heterostructure with the magnetic field upon application of a-50 kOe cooling field is shown in FIG. 4(d), Fe at 3K4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure is 1440Oe and the exchange bias field is 454Oe, with the coercive field and the exchange bias field decreasing gradually with increasing temperature, and with increasing temperature above 150K, the exchange bias field of the heterostructure is less than 15Oe, as shown in fig. 4(e) and 4 (f).
The invention measures the Fe under the cooling magnetic field of 50kOe and 3K4N(111)/BiFeO3(111)/SrRuO3(111) The heterostructure exchanges the exercise effect of bias, the magnetic field direction is parallel to the thin film surface. The variation of the magnetization of the heterostructure with magnetic field at different measurement times is shown in fig. 5 (a). As the number of measurements increases, the coercive field and the exchange bias field of the heterostructure decrease, and when the magnetization of the heterostructure is measured fifth time as a function of the magnetic field, the coercive field of the heterostructure is 1408Oe and the exchange bias field is-276 Oe, as shown in fig. 5(b) and 5 (c).
Advantageous effects
Compared with other multiferroic heterostructures with exchange bias effect, the heterostructure prepared by the invention has the advantages that the ferromagnetic films are prepared on the upper surface and the lower surface of the antiferromagnetic film, the exchange bias effect of the heterostructure can be enhanced, the adopted method is simple and practical, and the popularization in industrial production is facilitated. The method comprises the following specific steps:
1) although there are international reports on exchange biasing of multiferroic heterostructures, most ferromagnetic films prepared are alloy materials, and carriers do not have high spin polarizability characteristics, so that the application of the film in spintronics is limited.
2) In the multiferroic heterostructure with the exchange bias effect prepared internationally at present, the exchange bias field is small. Cooling by 50kOeFe produced in a magnetic field at 3K4N(111)/BiFeO3(111)/SrRuO3(111) The exchange bias field of the heterostructure reached-527 Oe;
3) because the main method adopted by the current industrial production is a sputtering method, the magnetron sputtering method adopted by the invention can prepare high-quality single-phase Fe compared with a molecular beam epitaxy method and a chemical method4The N film has high surface flatness and has obvious advantages in industrial production.
Drawings
Fe prepared in FIG. 14N(111)/BiFeO3(111)/SrRuO3(111) Schematic structural diagram of the heterostructure.
FIG. 2 preparation of Fe4N(111)/BiFeO3(111)/SrRuO3(111) X-ray diffraction pattern of the heterostructure.
FIG. 3(a) shows Fe4And (3) a two-dimensional surface topography of the N film.
FIG. 3(b) shows Fe4And (3) a three-dimensional surface topography of the N film.
FIG. 3(c) shows BiFeO3A two-dimensional surface topography of the film.
FIG. 3(d) shows BiFeO3Three-dimensional surface topography of the film.
FIG. 3(e) shows SrRuO3A two-dimensional surface topography of the film.
FIG. 3(f) shows SrRuO3Three-dimensional surface topography of the film.
FIG. 4(a) shows Fe when a cooling magnetic field of 50kOe is applied4N(111)/BiFeO3(111)/SrRuO3(111) The magnetization of the heterostructure varies with the magnetic field.
FIG. 4(b) shows Fe when a cooling magnetic field of 50kOe is applied4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure varies with temperature.
FIG. 4(c) shows Fe when a cooling magnetic field of 50kOe is applied4N(111)/BiFeO3(111)/SrRuO3(111) The exchange bias field of the heterostructure varies with temperature.
FIG. 4(d) shows Fe when a-50 kOe cooling magnetic field is applied4N(111)/BiFeO3(111)/SrRuO3(111) The magnetization of the heterostructure varies with the magnetic field.
FIG. 4(e) shows Fe when a-50 kOe cooling magnetic field is applied4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure varies with temperature.
FIG. 4(f) shows Fe when a-50 kOe cooling magnetic field is applied4N(111)/BiFeO3(111)/SrRuO3(111) The exchange bias field of the heterostructure varies with temperature.
FIG. 5(a) shows Fe at 3K with an applied cooling field of 50kOe4N(111)/BiFeO3(111)/SrRuO3(111) The change relation of the hysteresis loop of the heterostructure along with the measurement times.
FIG. 5(b) shows Fe at 3K with an applied cooling field of 50kOe4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure varies with the number of measurements.
FIG. 5(c) shows Fe at 3K with an applied cooling field of 50kOe4N(111)/BiFeO3(111)/SrRuO3(111) The exchange bias field of the heterostructure varies with the number of measurements.
Detailed Description
According to the results of our structural and property analyses on the samples prepared in the present invention, the following method will prepare flexible epitaxial Fe by the opposite-target reactive magnetron sputtering method4The best mode of the N film will be described in detail:
1) the ultrahigh vacuum facing target magnetron sputtering film coating machine produced by Shenyang scientific instrument development center of Chinese academy of sciences is adopted, and the base material is [111 ]]Oriented SrTiO3A single crystal substrate having a thickness of 500 μm. Two Fe targets with a purity of 99.99% and two SrRuO targets with a purity of 99.99% were used3Targets respectively arranged on the two groups of opposite target heads; the target material has a thickness of 3mm and a diameter of 60 mm. In each group of opposite targets, one end is used as the N pole of the magnetic force line, and the other end is used as the S pole; the distance between the two targets is 85mm, the axis of the targets is aligned with the SrTiO3Of a substrateThe distance between the substrate holders was 70 mm. A block of Bi of 99.99% purity is used1.1FeO3A target mounted on the radio frequency target head; the target material has a thickness of 3mm and a diameter of 60 mm. Magnetic lines of force are distributed on the surface of the target material; target material and SrTiO3(111) The distance between the substrate holders of the substrate was 70 mm;
2)SrRuO3preparing a film:
2.1) first, SrTiO3(111) Placing the substrate on a substrate holder, and adding SrTiO with silver colloid3(111) Four corners of the substrate are fixed on the substrate holder to make SrTiO3(111) The substrate is tightly attached to the substrate frame, is uniformly heated in the substrate heating process, is placed behind the baffle plate, and is closed to the vacuum chamber;
2.2) starting a vacuum system of the ultrahigh vacuum opposite target magnetron sputtering coating machine, vacuumizing until the vacuum degree of the vacuum chamber is better than 2 multiplied by 10–5Pa；
2.3) uniformly heating the substrate to 650 ℃, wherein the heating rate is 10 ℃/min, and when the substrate temperature is stable;
2.4) introducing a sputtering gas argon and a reaction gas oxygen with the purity of 99.999% into the vacuum chamber, wherein the flow ratio of the argon to the oxygen is 5: 3, keeping the air pressure at 1.1 Pa;
2.5) turning on the DC sputtering power supply, in a pair of SrRuO3Applying direct current with the power of 80W on the target, pre-sputtering for 5 minutes, and removing impurities on the surface of the target;
2.6) mixing a pair of SrRuO3The DC sputtering power on the target was adjusted to 40W and the shutter on the substrate holder was opened to start sputtering. In the sputtering process, SrTiO3Fixing the position of the substrate;
2.7) control of SrRuO by controlling sputtering time3The thickness of the film is 50 nm;
2.8) after sputtering is finished, closing a baffle plate on the substrate frame, completely closing a gate valve, introducing oxygen into the chamber to ensure that the air pressure is 200Pa, and keeping the substrate within 650 ℃ for 30min by using a temperature control system;
2.9) using a temperature control system to enable the substrate to be cooled to the room temperature at a constant speed, wherein the cooling rate is 3 ℃/min;
2.10) closing the vacuum system and opening the vacuumRoom, and taking out SrTiO 500 μm thick3(111) Srruo prepared on a substrate3(111) A film;
3)BiFeO3preparing a film:
3.1) in SrRuO3(111) A strip-shaped mask is arranged at the edge of the film and covers part of SrRuO3A film;
3.2) SrRuO to be covered with a mask plate3/SrTiO3Putting the sample on a substrate frame, putting the substrate frame behind a baffle plate, and closing the vacuum chamber;
3.3) starting a vacuum system of the ultrahigh vacuum opposite target magnetron sputtering coating machine, vacuumizing until the vacuum degree of the vacuum chamber is better than 2 multiplied by 10–5Pa；
3.4) uniformly heating the substrate to 650 ℃, wherein the heating rate is 10 ℃/min, and when the substrate temperature is stable;
3.5) introducing a sputtering gas argon and a reaction gas oxygen with the purity of 99.999 percent into the vacuum chamber, wherein the flow ratio of the argon to the oxygen is 5: 4, keeping the air pressure at 1.3 Pa;
3.6) starting a sputtering power supply, and supplying Bi with a radio frequency power supply1.1FeO3Applying 120W alternating current on the target, pre-sputtering for 5 minutes, and removing impurities on the surface of the target;
3.7) supplying power to Bi through radio frequency1.1FeO3Applying 80W AC power to the target, opening the baffle plate on the substrate holder to start sputtering, and reactively sputtering BiFeO3In the film forming process, the position of the substrate is fixed;
3.8) controlling BiFeO by controlling sputtering time3The thickness of the film is 30 nm;
3.9) after the sputtering is finished, closing the baffle plate on the substrate frame, completely closing the gate valve, introducing oxygen into the chamber to ensure that the air pressure is 200Pa, and keeping the substrate within the range of 650 ℃ for 30min by using a temperature control system;
3.10) using a temperature control system to enable the substrate to be cooled to the room temperature at a constant speed, wherein the cooling rate is 3 ℃/min;
3.11) closing the vacuum system, opening the vacuum chamber, and taking out BiFeO3(111)/SrRuO3(111)/SrTiO3(111) A heterostructure;
4)Fe4preparation of N film:
4.1) in BiFeO3(111) Placing a mask plate with a round hole on the film, wherein the diameter of the round hole is 200 and 400 mu m;
4.2) BiFeO to be covered with mask plate3(111)/SrRuO3(111)/SrTiO3(111) Putting the sample on a substrate frame, putting the substrate frame behind a baffle plate, and closing the vacuum chamber;
4.3) starting a vacuum system of the ultrahigh vacuum facing target magnetron sputtering coating machine, vacuumizing until the back vacuum degree of the vacuum chamber is better than 2 multiplied by 10–5Pa；
4.4) uniformly heating the substrate to 475 ℃, wherein the heating rate is 10 ℃/min, and the temperature of the substrate is stable;
4.5) introducing a sputtering gas argon and a reaction gas nitrogen with the purity of 99.999% into the vacuum chamber, wherein the flow ratio of the argon to the nitrogen is 5: 1, keeping the air pressure at 1.0 Pa;
4.6) starting a sputtering power supply, applying 0.30A current and 1000V direct current voltage on a pair of Fe targets, pre-sputtering for 5 minutes, and removing impurities on the surfaces of the targets;
4.7) A direct current of 0.10A and 700V was applied to the pair of Fe targets, and the shutter on the substrate holder was opened to start sputtering. In the sputtering process, the position of the substrate is fixed;
4.8) control of Fe by controlling sputtering time4The thickness of the N thin film is 20 nm;
4.9) after sputtering is finished, closing a baffle plate on the substrate frame, then closing a sputtering power supply, stopping introducing argon and nitrogen, completely opening a gate valve, continuously vacuumizing, and enabling the substrate to be cooled to room temperature at a constant speed by using a temperature control system, wherein the cooling rate is 3 ℃/min;
4.10) closing the vacuum system, opening the vacuum chamber and taking out the Fe4N(111)/BiFeO3(111)/SrRuO3(111)/SrTiO3(111) A heterostructure.
5) Structural characterization and magnetic measurements:
5.1) X-ray diffraction results show that the Fe prepared by the invention4N(111)/BiFeO3(111)/SrRuO3(111)/SrTiO3(111) Heterostructure rim [111]Directionally oriented growth, as shown in fig. 2.
5.2) FIG. 3 shows Fe prepared in the present invention4N/BiFeO3/SrRuO3Surface topography of heterostructures in Fe4N surface is relatively flat, Fe4N grows in an island shape; in BiFeO3The surface has particle shape fluctuation; SrRuO3The surface appears granular undulation.
5.3) the invention measures Fe under different cooling magnetic field directions4N(111)/BiFeO3(111)/SrRuO3(111) The magnetization of the heterostructure varies with the applied magnetic field, which is directed parallel to the surface of the thin film, as shown in fig. 4. Fe at 3K under application of a cooling magnetic field of 50kOe4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure is 1595Oe, the exchange bias field is-527 Oe, the coercive field and the exchange bias field are gradually reduced along with the temperature rise, and when the temperature rises to more than 150K, the exchange bias field of the heterostructure is less than-25 Oe; fe at 3K with application of a-50 kOe cooling field4N(111)/BiFeO3(111)/SrRuO3(111) The coercive field of the heterostructure is 1440Oe, the exchange bias field is 454Oe, the coercive field and the exchange bias field are gradually reduced along with the temperature rise, and when the temperature rises to be more than 150K, the exchange bias field of the heterostructure is less than 15 Oe.
5.4) the invention measures the Fe under the cooling magnetic field of 50kOe and 3K4N(111)/BiFeO3(111)/SrRuO3(111) The heterostructure exchanges the exercise effect of bias, the magnetic field direction is parallel to the thin film surface. As shown in FIG. 5(a), as the number of measurements increases, the coercive field and the exchange bias field of the heterostructure decrease, and when the magnetization of the heterostructure is measured fifth time as a function of the magnetic field, the coercive field of the heterostructure is 1408Oe and the exchange bias field is-276 Oe.
While the methods and techniques of the present invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and/or modifications of the methods and techniques described herein may be made without departing from the spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and content of the invention.

Claims (8)

1. An iron nitride based multiferroic heterostructure having an exchange bias effect; characterized in that the structure is Fe4N/BiFeO3/SrRuO3/SrTiO3Multiferroic heterostructures.
2. The structure of claim 1, wherein said Fe is4N/BiFeO3/SrRuO3/SrTiO3SrTiO is sequentially arranged from bottom to top3(111) Single crystal substrate, 50nm thick SrRuO3Layer, BiFeO 30nm thick3Layer and 20nm thick Fe4N layers; wherein Fe4N and SrRuO3Being a ferromagnetic layer, BiFeO3Is an antiferromagnetic layer.
3. The structure of claim 1 wherein the substrate is SrTiO3(111) A single crystal substrate having a thickness of 500 μm and an area of 5mm by 5 mm.
4. The structure of claim 1, wherein Fe4N/BiFeO3/SrRuO3/SrTiO3Heterostructure the exchange bias field of the heterostructure is-527 Oe at 3K when the cooling field is 50 kOe.
5. Fe with exchange bias effect4A preparation method of an N-based multiferroic heterostructure; the method is characterized by comprising the following steps:
(1) by magnetron sputtering with SrRuO3The target is the raw material, in the sputtering process, the mixed gas of argon (99.999) and oxygen (99.999) is introduced, and the sputtering power, the sputtering pressure, the substrate temperature and the cooling rate are controlled to be in SrTiO3(111) SrRuO with the thickness of 50nm is prepared on a substrate3(111) A film;
(2) by radio frequency magnetron sputtering with Bi1.1FeO3The target is the raw material, in the sputtering process, the mixed gas of argon (99.999) and oxygen (99.999) is introduced, and the sputtering power, the sputtering pressure, the substrate temperature and the cooling rate are controlled to be in SrRuO3/SrTiO3BiFeO with the thickness of 30nm is prepared on the film3(111) A film;
(3) adopting a magnetron sputtering method, taking a pure Fe target as a raw material, introducing mixed gas of argon (99.999) and nitrogen (99.999) in the sputtering process, and controlling sputtering current, sputtering voltage, sputtering pressure, substrate temperature and cooling rate to obtain BiFeO3/SrRuO3/SrTiO3Preparation of 20nm thick Fe on a heterostructure4N (111) film.
6. The method of claim 5, wherein in step (1), the degree of vacuum in the background is better than 2 x 10–5Pa, direct current sputtering power of 40W, sputtering pressure of 1.1Pa, substrate temperature of 650 ℃, flow ratio of argon (99.999) and oxygen (99.999) of 5: 3, annealing in pure oxygen (99.999) at 200Pa, 650 deg.C for 30min, 10 deg.C/min for cooling at 3 deg.C/min, and 0.5nm/min for depositing film3(111) SrRuO with the thickness of 50nm is prepared on a substrate3(111) A film.
7. The method of claim 5, wherein in step (2), the background vacuum is better than 2 x 10–5Pa, the radio-frequency sputtering power is 80W, the sputtering pressure is 1.3Pa, the substrate temperature is 650 ℃, and the flow ratio of argon (99.999) to oxygen (99.999) is 5: 4, under the conditions that the annealing environment is pure oxygen (99.999), the annealing pressure is 200Pa, the annealing temperature is 650 ℃, the annealing time is 30min, the heating rate is 10 ℃/min, the cooling rate is 3 ℃/min, and the deposition rate of the film is 1.7nm/min, under the conditions of SrRuO3/SrTiO3BiFeO with the thickness of 30nm is prepared on the film3(111) Film to obtain BiFeO3(111)(30nm)/SrRuO3(111)(50nm)/SrTiO3(111) A heterostructure.
8. The method of claim 5, wherein in step (3), the degree of vacuum in the background is better than 2 x 10–5Pa, sputtering current of 0.05A, sputtering voltage of 700V, sputtering pressure of 1.0Pa, substrate temperature of 475 ℃, flow ratio of argon (99.999) to nitrogen (99.999) of 5: 1, under the conditions that the temperature rising rate is 10 ℃/min, the temperature reduction rate is 3 ℃/min and the deposition rate of a film is 2.1nm/min, BiFeO3/SrRuO3/SrTiO3Preparation of 20nm thick Fe on a heterostructure4N (111) film to obtain Fe4N(111)(20nm)/BiFeO3(111)(30nm)/SrRuO3(111)(50nm)/SrTiO3(111) A heterostructure.
CN202011149704.7A 2020-10-23 2020-10-23 Iron nitride-based multiferroic heterostructure with exchange bias effect and preparation method thereof Pending CN112242221A (en)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20090037282A (en) * 2007-10-11 2009-04-15 한국과학기술원 Ferroelectric substance thin film element and manufacturing method thereof

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Publication number Priority date Publication date Assignee Title
KR20090037282A (en) * 2007-10-11 2009-04-15 한국과학기술원 Ferroelectric substance thin film element and manufacturing method thereof

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SHIZHE WU等: ""Electric-Field-Controlled Room Temperature AMR Switching in a NiFe/BiFeO3/SrRuO3/SrTiO3(111) Heterostructure"", 《IEEE TRANSACTIONS ON MAGNETICS》 *
刘伟达: ""BiFeO3及其磁电复合薄膜的制备与性能研究"", 《中国优秀硕士学位论文全文数据库 基础科学辑》 *

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