CN113488584A - FePt material-based magnetization switching device, external magnetic field-free switching method and application - Google Patents

FePt material-based magnetization switching device, external magnetic field-free switching method and application Download PDF

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CN113488584A
CN113488584A CN202110695410.2A CN202110695410A CN113488584A CN 113488584 A CN113488584 A CN 113488584A CN 202110695410 A CN202110695410 A CN 202110695410A CN 113488584 A CN113488584 A CN 113488584A
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fept
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CN113488584B (en
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游龙
李若凡
郭喆
张帅
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Huazhong University of Science and Technology
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Abstract

The invention discloses a magnetization switching device based on a FePt material, a switching method without an external magnetic field and application, belonging to the field of spin electronic devices, wherein the magnetization switching device comprises a single crystal substrate and a FePt layer grown on the single crystal substrate and used for realizing current-driven magnetization switching; or, from bottom to top include in proper order: the single crystal substrate, the FePt layer and one or more composite overturning layers are used for realizing overturning without an external magnetic field; the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current; compound upset layer is from supreme including in proper order down: an isolation layer and an inducing layer; the induction layer is used for providing a stray field or ferromagnetic exchange coupling in the plane direction so as to break the symmetry of the system and realize deterministic magnetic moment overturning without an external magnetic field; the isolation layer is used for preventing the atomic penetration between the FePt layer and the inducing layer. The invention can simplify the structure and the preparation process of the magnetization switching device based on the SOT effect and improve the perpendicular magnetic anisotropy and the thermal stability of the device.

Description

FePt material-based magnetization switching device, external magnetic field-free switching method and application
Technical Field
The invention belongs to the field of spin electronic devices, and particularly relates to a magnetization switching device based on a FePt material, a switching method without an external magnetic field and application.
Background
Since the 21 st century, society has grown at a high pace and demands for memory and logic computing devices have become higher and higher. With the continuous reduction of feature size, the performance of the conventional nonvolatile memory represented by a flash memory and the conventional volatile memory represented by a dynamic random access memory have gradually developed to the limit, and the development and research of new process nodes continuously using silicon-based materials need high cost, so that new materials, new structures and new methods are required to develop new memory logic technologies in order to meet the demand of rapid social development. Magnetic Random Access Memory (MRAM) is expected to become the next generation of universal memory due to its non-volatility, low power consumption, long lifetime, high durability, strong radiation resistance, low cost and fast read/write speed.
In recent years, Spin Transfer Torque (STT) based on Spin-polarized current and Spin Orbit Torque (SOT) based on Spin Orbit Coupling (SOC) are considered as effective methods for implementing MRAM. However, STT can subject ultra-thin insulating layers in Magnetic Tunnel Junctions (MTJs) to large write current densities, which can easily break down during constant read, write, and erase processes, leading to significant stability and lifetime issues. In contrast, the read/write path of MRAM based on SOT effect (SOT-MRAM) is separated, and no write current is needed to pass through MTJ, which effectively improves the defect of STT. Therefore, it is more promising for the fabrication of next-generation high-speed, high-integration, low-power-consumption MRAM and logic devices.
The current-induced magnetization reversal realized by the spin orbit torque provides a wide application prospect for the next generation of magnetic random gapless memories and logic devices. In past studies of SOT-MRAM, a film structure composed of a Heavy metal layer (HM) having strong spin-orbit coupling and a perpendicular magnetization ferromagnetic material layer (FM) is generally used. When charge flows through the HM layer, the magnetization of the magnetic material layer is switched due to Spin Hall Effect (SHE) which generates Spin-polarized current and/or inversion asymmetry of the interface resulting in the Rashba Effect. Because the film layer structure contains the heavy metal layer, the existing magnetization reversal structure based on the SOT effect is relatively complex, the preparation process is relatively complex, the requirement on manufacturing equipment is high, the cost is high, the FM layer is mostly Co-based material, the coercive force field is small, and the Perpendicular Magnetic Anisotropy (PMA) is low, so that when the size of the device is reduced to a nanometer level, the good PMA and the high thermal stability are difficult to maintain. In addition, the conventional magnetization switching based on the SOT effect usually requires an external planar magnetic field in the same direction or opposite direction to the current direction to achieve the current-induced deterministic magnetization switching, which is very disadvantageous for the fabrication of large-scale integrated circuits and ultra-low power devices, and is a difficult problem and research hotspot in the development process of MRAM. Several SOT-induced magnetization switching schemes without external magnetic field assistance have been proposed and demonstrated so far, such as using exchange-bias coupling with antiferromagnetic materials, preparing a wedge-type oxidized cap layer to break the inversion symmetry, fabricating tilted easy-magnetization axes in the FM layer, using polarization ferroelectric substrate-induced in-plane spin current gradients, and special low-symmetry WTe2 half-metals. However, these solutions have the problems of complicated structure, complicated preparation process, and poor thermal stability.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a magnetization switching device based on a FePt material and a method for switching without an external field, and aims to simplify the structure and the preparation process of the magnetization switching device based on the SOT effect and improve the perpendicular magnetic anisotropy and the thermal stability of the device.
To achieve the above object, according to a first aspect of the present invention, there is provided a magnetization switching device based on FePt material for realizing current-driven magnetization switching, comprising: the single crystal substrate and the FePt layer are grown on the single crystal substrate;
the FePt layer is a single-layer FePt thin film of an L10 phase and is used for generating partial magnetization reversal under the induction of current.
According to the magnetization switching device based on the FePt material, provided by the invention, only the single-layer FePt thin film of the L10 phase is contained, and the SOT effect exists in the single-layer FePt thin film, so that local current-induced magnetization switching can be realized. Because the magnetization switching device based on the FePt material only contains the single-layer FePt film and does not contain the heavy metal layer, the structure is simpler, the preparation process is relatively simple, and the device still has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to the nanometer size.
According to the magnetization switching device based on the FePt material, the size of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer, so that the control of the switching ratio can be realized by controlling the growth temperature of the FePt layer in the preparation process of the device.
Further, the thickness of the FePt layer is 5nm-40 nm.
According to the invention, the thickness of the FePt layer in the magnetization switching device based on the FePt material is limited to 5nm-40nm, so that the difficulty in controlling the quality of a film due to the fact that the FePt layer is too thin can be prevented, and the defect of no good perpendicular magnetic anisotropy and SOT effect due to the fact that the FePt layer is too thick can be prevented, thereby ensuring that the magnetization switching device based on the FePt material has excellent performance.
Further, the FePt layer is in a Hall strip shape;
two crossed channels in the Hall strip shape are a current channel and a voltage channel respectively, and electrodes are deposited at four ends of the Hall strip shape respectively; the current path is used to apply current and the voltage path is used to measure hall voltage.
According to the invention, the FePt layer is prepared into the Hall strip shape formed by intersecting the current channel and the voltage channel, and the electrodes are respectively deposited at four ends of the Hall strip shape, so that the conductivity of the device can be improved, the uniformity of applied current can be improved, the current can be conveniently applied to the device, the Hall voltage of the device can be conveniently detected, and the magnetization overturning process of the device can be conveniently controlled.
According to a second aspect of the present invention, there is provided a magnetization switching device based on FePt material, for implementing switching without external magnetic field, which sequentially includes, from bottom to top: the device comprises a single crystal substrate, a FePt layer and one or more composite overturning layers;
the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current;
compound upset layer is from supreme including in proper order down: an isolation layer and an inducing layer;
the induction layer is used for providing a stray field or ferromagnetic exchange coupling in the plane direction so as to break the symmetry of the system and realize deterministic magnetic moment overturning without an external magnetic field;
the isolation layer is used for preventing the atomic penetration between the FePt layer and the inducing layer.
The magnetization switching device based on the FePt material provided by the invention can realize the switching without an external magnetic field by utilizing the SOT effect in the FePt layer and the stray field or ferromagnetic exchange coupling action in the plane direction provided by the induction layer, thereby improving the integration level of the device and leading the device to be applied to large-scale integrated circuits and ultra-low power consumption storage and logic devices.
Compared with other existing devices for realizing switching without an external magnetic field, the FePt material-based magnetization switching device provided by the invention does not contain a heavy metal layer, has a simple structure and a simple preparation process, and still has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to a nanometer size.
According to the magnetization switching device based on the FePt material, the size of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer, so that the growth temperature of the FePt layer can be controlled in the preparation process of the device, the control of the switching ratio is realized, and the device with better performance is prepared.
Further, the thickness of the FePt layer is 5nm-40 nm.
According to the invention, the thickness of the FePt layer in the magnetization switching device based on the FePt material is limited to 5nm-40nm, so that the difficulty in controlling the quality of a film due to the fact that the FePt layer is too thin can be prevented, and the defect of no good perpendicular magnetic anisotropy and SOT effect due to the fact that the FePt layer is too thick can be prevented, thereby ensuring that the magnetization switching device based on the FePt material has excellent performance.
Further, the material of the isolation layer is TiN.
The invention uses TiN material to prepare the isolating layer, and can obtain good non-external magnetic field overturning characteristic.
Further, the material of the inducing layer is NiFe.
Further, the thickness of the inducing layer does not exceed 10 nm.
According to the invention, the thickness of the inducing layer prepared from the NiFe material is limited to be not more than 10nm, so that the phenomenon that the AHE (abnormal Hall effect) loop of the device cannot be measured due to the generation of huge PHE (planar Hall effect) effect and AMR (anisotropic magnetic resistance) effect can be avoided.
Furthermore, all the film layers on the single crystal substrate are in the same Hall strip shape;
two crossed channels in the Hall strip shape are a current channel and a voltage channel respectively, and electrodes are deposited at four ends of the Hall strip shape respectively; the current path is used to apply current and the voltage path is used to measure hall voltage.
According to the invention, each film layer on the single crystal substrate is prepared into the Hall strip shape intersected by the current channel and the voltage channel, and the electrodes are respectively deposited at four ends of the Hall strip shape, so that the conductivity of the device can be improved, the uniformity of applied current can be improved, the current can be conveniently applied to the device, the Hall voltage of the device can be conveniently detected, and the magnetization overturning process of the device can be conveniently controlled.
According to a third aspect of the present invention, there is provided an external magnetic field-free switching method for a FePt material-based magnetization switching device according to the second aspect of the present invention, comprising:
calibrating the relationship between the switching ratio and the maximum switching current in the FePt material-based magnetization switching device in advance after the induction layer realizes magnetization saturation;
and determining corresponding pulse current according to the relation between the switching ratio and the maximum switching current density and combining with the switching ratio requirement, and applying the pulse current to the FePt material-based magnetization switching device to realize the switching without the external magnetic field.
According to a fourth aspect of the present invention there is provided the use of a FePt material based magnetization switching device as provided in the second aspect of the present invention in an integrated circuit, a memory device or a logic device.
The method for turning over the device without the external magnetic field provided by the invention does not need to apply a plane magnetic field in the process of making the device generate deterministic magnetization turning, only needs to apply corresponding pulse current to the device, does not depend on an external magnetic field, is simpler to control and is easier to realize integration.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the FePt material-based magnetization switching device provided by the invention is used for realizing the current-driven magnetization switching, only comprises the L10 phase single-layer FePt film, realizes the local current-induced magnetization switching by utilizing the SOT effect existing in the single-layer FePt film, does not contain a heavy metal layer, realizes the function of the existing HM/FM multilayer film structure by using a single-layer film structure, has simpler structure and relatively simple preparation process, and still has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to the nanometer size.
(2) The magnetization switching device based on the FePt material is used for realizing the switching without an external field, and realizes the switching without the external field by utilizing the SOT effect in the FePt layer and the stray field or ferromagnetic exchange coupling action in the plane direction provided by the induction layer, thereby improving the integration level of the device and being applicable to large-scale integrated circuits and ultra-low power consumption storage and logic devices. Compared with other existing devices for realizing switching without an external magnetic field, the device does not contain a heavy metal layer, is simple in structure and simple in preparation process, and still has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to a nanometer size.
(3) According to the magnetization switching device based on the FePt material, the size of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer, so that the control of the switching ratio, namely the control of the SOT effect performance of the device, can be realized by controlling the growth temperature of the FePt layer in the preparation process of the device.
(4) The external magnetic field-free turning method provided by the invention does not need to apply a plane magnetic field in the process of making the device generate deterministic magnetization turning, only needs to apply corresponding pulse current to the device, does not depend on an external magnetic field, is simpler to control, is easier to realize high integration, and completely accords with the trend of future social development.
Drawings
Fig. 1 is a schematic structural diagram of a magnetization switching device based on FePt material and an analysis diagram of torque effect provided in embodiment 1 of the present invention;
FIG. 2 is a schematic diagram showing the AHE measurement results of FePt layers prepared under different growth temperature conditions according to example 1 of the present invention;
FIG. 3 is an x-ray diffraction (XRD) pattern of FePt layers prepared at different growth temperatures as provided in example 1 of the present invention;
FIG. 4 is a graph of current-induced magnetization switching of FePt layers prepared at different growth temperatures according to example 1 of the present invention, i.e., a graph of magnetization switching achieved based on the SOT effect method; wherein (a) - (c) are current-induced magnetization reversal graphs of FePt layers prepared at 300 ℃,400 ℃ and 500 ℃ respectively;
FIG. 5 is a harmonic Hall voltage measurement of FePt layers prepared at different growth temperatures provided by embodiments of the present invention; wherein (a) and (b) are harmonic hall voltage measurements of FePt layers prepared at 400 ℃ and 500 ℃, respectively;
FIG. 6 is a schematic diagram showing the relationship between SOT effect and current density of FePt layers prepared at different growth temperatures according to example 1 of the present invention;
fig. 7 is a schematic structural diagram of an external field-free magnetization switching device based on a FePt material according to embodiment 2 of the present invention;
FIG. 8 is a schematic diagram of the read/write operation of the FePt-based magnetization switching device shown in FIG. 7;
FIG. 9 is a graph showing the AHE measurement of the FePt material based magnetization switching device of FIG. 7;
FIG. 10 is an x-ray diffraction (XRD) pattern of the magnetization switching device based on FePt material in example 2 at different TiN layer thicknesses;
FIG. 11 is a graph of current-induced magnetization switching for the FePt material-based magnetization switching device of example 2 at different TiN layer thicknesses; wherein, (a) to (d) are respectively current-induced magnetization switching graphs of the FePt material-based magnetization switching device in example 2 when the thickness of the TiN layer is 0nm, 1nm, 2nm, and 3 nm;
FIG. 12 is a graph showing the relationship between the switching curve and the maximum pulse current density of the magnetization switching device based on the FePt material in example 2 under different TiN layer thicknesses; wherein (a) - (d) are respectively a schematic diagram of the relationship between the switching curve and the maximum pulse current density of the FePt material-based magnetization switching device in the embodiment 2 when the thickness of the TiN layer is 0nm, 1nm, 2nm and 3 nm;
FIG. 13 is the switching curve without external magnetic field of the magnetization switching device based on FePt material in example 2 under different TiN layer thicknesses; wherein, (a) to (c) are respectively the inversion curves of the magnetization inversion device based on the FePt material in the embodiment 2 when the thickness of the TiN layer is 1nm, 2nm and 3 nm;
FIG. 14 is a schematic diagram of a magnetization switching device based on FePt material according to embodiment 3 of the present invention; wherein, (a) is a film layer structure schematic diagram of the device, (b) is a three-dimensional structure diagram of the device, and (c) is a top view of the device;
FIG. 15 is an AHE curve for the FePt material based magnetization switching device provided in example 3 at different composite switching layer quantities and different fabrication temperatures;
FIG. 16 is an x-ray diffraction (XRD) pattern of the FePt material based magnetization switching device provided in example 3 at different composite switching layer number and different fabrication temperatures;
fig. 17 is a graph showing the inversion curves of abnormal hall resistances with current under the assistance of different external magnetic fields for devices with different numbers of composite inversion layers prepared at normal temperature; the abnormal Hall resistance of the device with 3 layers of composite turnover layers prepared at normal temperature is a turnover curve along with current under the assistance of different external magnetic fields, and the abnormal Hall resistance of the device with 5 layers of composite turnover layers prepared at normal temperature is a turnover curve along with current under the assistance of different external magnetic fields;
FIG. 18 is a graph of the flip of abnormal Hall resistance with current under the assistance of different external magnetic fields for devices of different composite flip layer numbers fabricated at high temperature; the abnormal Hall resistance of the device with 3 layers of composite turnover layers prepared at high temperature is a turnover curve along with current under the assistance of different external magnetic fields, and the abnormal Hall resistance of the device with 5 layers of composite turnover layers prepared at high temperature is a turnover curve along with current under the assistance of different external magnetic fields.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Example 1:
a magnetization switching device based on FePt material for realizing current-driven magnetization switching, as shown in fig. 1, comprising: the single crystal substrate and the FePt layer are grown on the single crystal substrate;
the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current;
in the present embodiment, since the FePt thin film is (001) oriented, in order to facilitate epitaxial growth of the FePt thin film on the substrate, the substrate material is MgO, and the orientation thereof is (001); it should be noted that this is only an alternative embodiment, and that other materials that facilitate epitaxial growth of a single-layer FePt film of the L10 phase, such as MgO, Pt, KTaO with a face-centered cubic (FCC) structure3、SrTiO3Etc., can also be used as a substrate material in the present invention;
in the magnetization switching device based on the FePt material provided in this embodiment, only the single-layer FePt thin film of the L10 phase is included, and the SOT effect exists in the single-layer FePt thin film, under the effect of different SOT effective fields, the magnetization state changes, and macroscopically, abnormal hall resistances with different sizes are shown, and the direction of applying current to the device and the moment generated by the SOT effect based on the single-layer FePt thin film of the L10 phase are shown in fig. 1; in order to conveniently apply current to the device and detect the Hall voltage of the device, so as to conveniently control the magnetization overturning process of the device, in the embodiment, the FePt layer is etched into a Hall strip shape; two crossed channels in the Hall strip shape are a current channel with the length of 20-45 mu m and the width of 15 mu m and a voltage channel with the length of 20-45 mu m and the width of 6 mu m respectively, four ends of the Hall strip shape are deposited with wide square Pt electrodes respectively, and the width of the electrodes is not more than 200 mu m; the current channel is used for applying current, and the voltage channel is used for measuring Hall voltage;
in the embodiment, the thickness of the FePt layer is 5nm-40nm, so that the difficulty in controlling the quality of the film due to the fact that the FePt layer is too thin is prevented, and the situation that the FePt layer is too thick and does not have good perpendicular magnetic anisotropy and SOT effect is prevented, and therefore the FePt material-based magnetization switching device is guaranteed to have excellent performance.
In the above magnetization switching device based on the FePt material provided in this embodiment, the size of the SOT effect in the FePt layer is affected by the growth temperature of the FePt layer, and experiments show that as the growth temperature of the FePt layer increases, the intensity of peaks of XRD curves corresponding to (001) and (002) orientations of FePt is greater, which indicates that as the growth temperature of the FePt layer increases, the anisotropy of FePt corresponding to crystal orientation is stronger; the AHE measurement results and x-ray diffraction (XRD) patterns of the FePt layers prepared at different growth temperatures are shown in fig. 2 and 3, respectively;
the perpendicular magnetization can be induced by an abnormal Hall resistance (R)H) Is characterized by RHThe Perpendicular Magnetic Anisotropy (PMA) of the film can be analyzed, as shown in fig. 2, the coercive field and PMA of the sample increase with increasing preparation temperature; the sample deposited at 500 ℃ has a huge coercive field up to 6000Oe, showing good PMA; in addition, the sample deposited at 300 ℃ has an abnormal Hall resistanceMaximum variation, about 24 ohms;
the XRD morphology of the FePt layer is shown in figure 3; the thin films deposited on the MgO single crystal substrate at 300 deg.C, 400 deg.C and 500 deg.C, respectively, have crystal orientations of both (001) and (002), and have strength decreasing as the preparation temperature increases.
The measurement of current-induced magnetization switching was further performed on the above-mentioned magnetization switching device based on FePt material provided in this example. During the measurement, a series of different pulse currents were applied to the current path of the hall bar, the pulse duration being 12 ms; measuring abnormal Hall resistance (R) by applying small current (i.e. read current, 100uA) after each pulse currentH). At different external magnetic fields Hx(x is the direction of pulse current and y is the direction of Hall voltage) and an abnormal Hall resistance (R)H) The relationship with the pulse current density (J) can characterize the current-induced magnetization switching behavior of the device and its dependence on external magnetic fields. As shown in (a) to (c) of fig. 4, graphs showing magnetization reversal with current density of devices made of materials grown at 300 ℃,400 ℃ and 500 ℃ are given based on the SOT effect, respectively; as can be seen from FIG. 4, the single layer of L10FePt material grown on the MgO substrate layer has the SOT effect, and the related performance is influenced by the growth temperature; the turnover rate of the sample prepared at 300 ℃ is very small, about 0.8% under an optimal magnetic field of 200 Oe; the sample prepared at 400 ℃ has a larger turnover rate of about 2.7% under the optimal magnetic field of 500 Oe; the sample prepared at 500 ℃ has the largest turnover rate of about 6.6% under the optimal magnetic field of 1000 Oe; when the external magnetic field deviates from the optimal value, the overturning ratio is gradually reduced; when the direction of the applied magnetic field is reversed, the inversion direction of the inversion curve is also reversed.
The magnetization switching device based on the FePt material provided in this example was further subjected to harmonic hall voltage measurement. During measurement, low-frequency alternating current is applied to a current circuit of the Hall bar. The frequency of the alternating current is 317.3Hz, and the input channel and the reference channel of the phase-locked amplifier are locked by using the external trigger function of the current source phase generator. The voltage path of the Hall bar is connected to two phase-locked amplifiers to respectively measure the harmonic HallThe first harmonic component and the second harmonic component of the voltage. The second harmonic component can be used to characterize the effective field of the SOT. Effective field (H) generated by using SOT damping-like torque/field-like torqueDL/HFL) The relationship with the applied alternating current density (J) allows the SOT efficiency of the device to be analyzed. As shown in (a) and (b) of fig. 5, the upper left graph represents the first harmonic voltage graph measured while scanning the magnetic field in the x direction; the upper right hand graph represents the first harmonic voltage profile measured while scanning the magnetic field in the y direction; the bottom left graph represents the second harmonic voltage profile measured while scanning the magnetic field in the x-direction; the bottom right hand graph represents the second harmonic voltage profile measured while scanning the magnetic field in the y-direction. According to the data in the graph and a formula, the effective field of the structural device can be calculated, and the effective field can represent the size of the SOT effect. The results shown in fig. 5 indicate that the SOT effective field exists in the single-layer FePt prepared under the conditions of 400 ℃ and 500 ℃, and in addition, the SOT effective field prepared at 500 ℃ is significantly larger than that of the material device prepared at 400 ℃, which indicates that the larger PMA is helpful for improving the SOT effective field.
Based on the measurement results of fig. 5, it is possible to utilize
Figure BDA0003128111000000111
And
Figure BDA0003128111000000112
the result of the harmonic test is calculated, and the effective field size is calculated. In the first formula, a molecular term represents a first derivative of a variation curve of second harmonic voltage along with an external magnetic field in the x direction; the denominator term represents the second derivative of the variation curve of the first harmonic voltage along with the external magnetic field in the x direction; in the second formula, the molecular term represents the first derivative of the variation curve of the second harmonic voltage along with the external magnetic field in the y direction; the denominator term represents the second derivative of the variation curve of the first harmonic voltage along with the external magnetic field in the y direction; the planar Hall resistance Δ R is defined herePHEAnd abnormal Hall resistance DeltaRAHEIs xi ═ Δ RPHE/ΔRAHEConsidering that the planar hall resistance of FePt is negligible, let us take ξ as 0 here, from which we can calculateDamping-like Torque (DT) H of SOTDLAnd Field-like Torque (FL) H of SOTFLRespectively as follows:
Figure BDA0003128111000000121
Figure BDA0003128111000000122
further, based on the measurement results of fig. 5, the relationship between the SOT effective field and the current density in the FePt layer can be obtained, as shown in fig. 6, which indicates that the FePt monolayer has good SOT performance.
From the measurement results shown in fig. 2 to 6, it can be seen that in the present embodiment, the FePt monolayer has good SOT performance, and the magnitude of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer.
The embodiment provides the FePt material-based magnetization switching device which only contains a single-layer FePt film and does not contain a heavy metal layer, so that the FePt material-based magnetization switching device is simple in structure and simple in preparation process, and has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to a nanometer size.
In this embodiment, the preparation method and conditions of the device are specifically as follows:
depositing an L10FePt (10) single-layer film on an MgO (001) single-crystal substrate by adopting an ultrahigh vacuum magnetron sputtering technology;
depositing a series of FePt single-layer films at 300 ℃,400 ℃ and 500 ℃ respectively, and preserving heat for 30 minutes;
characterizing the crystal structure of the film by x-ray diffraction (XRD);
the film is respectively etched into Hall strips with a length of 20-45 mu m, a length of 15 mu m of current channel and a width of 6 mu m of voltage channel by ultraviolet lithography and argon ion etching.
Example 2:
a magnetization switching device based on FePt material, for realizing switching without external magnetic field, as shown in fig. 7, which comprises, from bottom to top: the device comprises a single crystal substrate, a FePt layer and a composite overturning layer;
the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current;
compound upset layer is from supreme including in proper order down: an isolation layer and an inducing layer;
the induction layer is used for providing a stray field or ferromagnetic exchange coupling effect in the plane direction so as to break the symmetry of the system and realize deterministic magnetic moment overturning without an external magnetic field;
the isolation layer is used for preventing atomic penetration between the FePt layer and the inducing layer;
alternatively, in order to facilitate epitaxial growth of a (001) -oriented FePt thin film on a substrate, in the present embodiment, the substrate material is MgO, and its orientation is (001); it should be noted that this is only an alternative embodiment, and that other materials that facilitate epitaxial growth of a single-layer FePt film of the L10 phase, such as MgO, Pt, KTaO with a face-centered cubic (FCC) structure3、SrTiO3Etc., can also be used as a substrate material in the present invention;
optionally, in this embodiment, the material of the inducing layer is NiFe, and it should be noted that, in some other embodiments of the present invention, the inducing layer may also be replaced by other materials capable of generating a stray field or an exchange coupling field in a planar direction;
preferably, in this embodiment, the material of the isolation layer is TiN, and it should be noted that, in some other embodiments of the present invention, the isolation layer may also be replaced by other materials capable of performing an isolation function, but experiments show that, compared to other materials, when TiN is used as the material of the isolation layer, this embodiment can obtain a more excellent external magnetic field-free switching characteristic;
in order to apply current to the device and detect the hall voltage of the device conveniently, so as to control the magnetization switching process of the device conveniently, in this embodiment, as shown in fig. 8, the FePt layer and the composite switching layer are etched into a hall bar shape; two crossed channels in the Hall strip shape are a current channel with the length of 20-45 mu m and the width of 15 mu m and a voltage channel with the length of 20-45 mu m and the width of 6 mu m respectively, four ends of the Hall strip shape are deposited with wide square Pt electrodes respectively, and the width of the electrodes is not more than 200 mu m; the current channel is used for applying current, and the voltage channel is used for measuring Hall voltage;
the magnetization switching device based on the FePt material provided by this embodiment can realize switching without an external magnetic field by utilizing the SOT effect in the FePt layer and the stray field or ferromagnetic exchange coupling effect in the planar direction provided by the inducing layer;
the magnetization switching device based on the FePt material provided in this embodiment is a three-layer film structure, as shown in fig. 7, in which the FePt layer has a thickness of 10nm, and the inducing layer made of a NiFe material has a thickness of 5 nm; in order to measure the switching of the perpendicular magnetization in the NiFe/TiN/FePt three-layer film structure without an external magnetic field and simultaneously measure the influence of the isolation effect of TiN in the three-layer film structure on the switching characteristics of the entire device, the results of measuring the AHE and the x-ray diffraction (XRD) patterns of the single-layer FePt layer in example 1 and the different TiN layer thicknesses in example 2 were respectively measured, as shown in fig. 9 and 10, respectively, and it can be seen from the results of measuring the AHE shown in fig. 9 that the abnormal hall resistance of the three-layer film structure is smaller than that of the single-layer film; the coercive field and PMA of the three-layer sample increase with the increase of the thickness of the TiN layer; when the TiN layer thickness was 3nm, the coercive field was about 2000Oe and the abnormal hall resistance was about 14 ohms. From the XRD patterns shown in fig. 10, it can be seen that the three thin films deposited on the MgO single crystal substrate each have the crystal orientations of FePt (001), FePt (002), and NiFe (200); the intensity of NiFe (200) is greatest when the TiN thickness is 2 nm.
Further, the current-induced magnetization switching characteristics of the FePt material-based magnetization switching device in example 2 were measured for different TiN layer thicknesses, and as shown in fig. 11, (a) to (d) are graphs of current-induced magnetization switching curves of the FePt material-based magnetization switching device in example 2 for TiN layer thicknesses of 0nm, 1nm, 2nm, and 3nm, respectively. As can be seen from the measurement results shown in fig. 11, the turn-over ratio of the sample without the TiN layer was very small, and no field-free turn-over could not be observed, as shown in (a) of fig. 11; when the thickness of the TiN layer is not less than 1nm, no external magnetic field inversion is observed for all three layers of samples, as shown in (b) to (d) of fig. 11. It should be noted that when the thickness of the TiN layer is 0 or 1nm, the switching curve has only one switching direction change under different applied magnetic fields, similar to the single-layer FePt, as shown in (a) and (b) of fig. 11; under different applied magnetic fields, there are three flip direction changes in the flip curve when the TiN layer thickness is 2 or 3nm, as shown in (c) and (d) of fig. 11. The reason is that exchange coupling exists between FePt and NiFe, when the TiN layer is thin, the FePt is influenced by the NiFe from the inside, fixed inclination occurs during vertical magnetization, and the turning direction of the turning curve changes once; when the TiN layer is thick, the exchange coupling between FePt and NiFe disappears, the FePt layer is influenced by the stray field generated by NiFe from the outside, and the equivalent field is superposed, so that the turning curve shows three-time rotation direction change.
Further, the relationship between the switching curve and the maximum pulse current density of the magnetization switching device based on the FePt material in example 2 was measured for different TiN layer thicknesses, and the measurement results are shown in fig. 12, where (a) to (d) are respectively schematic diagrams of the relationship between the switching curve and the maximum pulse current density of the magnetization switching device based on the FePt material in example 2 when the TiN layer thicknesses were 0nm, 1nm, 2nm, and 3 nm. The measurement results shown in fig. 12 indicate that the critical switching current densities of the three-layer film structures with different TiN layer thicknesses are not greatly different, and the switching ratio has a strong correlation with the maximum switching current density. When the TiN layer is not added, the turnover rate is very small and is only 0.3 percent at most. The turnover was up to 2%, 1.3% and 4.3% when the TiN layer thicknesses were 1, 2 and 3nm, respectively. Obviously, the presence of the TiN layer helps to improve the switching rate, making the three-layer film sample more suitable for multi-state memory, storage and logic device applications.
The measurements shown in fig. 11 and 12 also show that the TiN barrier layer improves the SOT performance of the device, and that the tri-layer structure achieves current-induced magnetization switching without the assistance of an external magnetic field when the thickness of the TiN barrier layer is not less than 1 nm. Furthermore, the perpendicular magnetization switching in the tri-layer structure has a strong dependence on TiN thickness: with the increase of the thickness of the TiN layer, the change times of the turning direction of the turning curve (in terms of R) under the action of different external magnetic fieldsHallAnd IPulseIs characterized in that R isHallAbnormal hall current of a representative deviceResistance, IPulseRepresenting the magnitude of the applied pulse current) is gradually increased from one time to three times. The reason for this is that the former is dominated by NiFe/FePt exchange coupling and the latter by NiFe stray fields. The research result has further knowledge on the physical properties of SOT, and a field-free magnetization switching scheme based on high PMA and high coercivity materials is provided. Compared with the traditional field-free overturning scheme based on magnetic materials such as CoFeB and the like, the scheme is simple in device structure, good in thermal stability, and good in performance when the size of the device is reduced to the nanometer size, and is beneficial to development of miniaturization and integration.
The switching characteristics without external magnetic field of the magnetization switching device based on the FePt material in example 2 were further measured at different TiN layer thicknesses, and the measurement results are shown in fig. 13, where (a) to (c) are the switching curves of the magnetization switching device based on the FePt material in example 2 when the TiN layer thickness is 1nm, 2nm, and 3nm, respectively. The measurement results shown in fig. 13 indicate that the three-layer sample having the TiN layer thickness of not less than 1nm has a definite magnetization reversal without an external magnetic field. When the thickness of the TiN layer is 1nm, 2nm and 3nm respectively, the turnover rate without external magnetic field is 0.7 percent, 0.2 percent and 1.6 percent respectively.
Based on the measurement results of the single-layer FePt thin film in example 1, it can be seen that, in this example as well, the FePt single layer has good SOT efficiency, and the magnitude of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer.
According to the measurement results shown in fig. 9 to 13, the embodiment can realize magnetization reversal without an external magnetic field, and improve the integration level of the device, so that the device can be applied to large-scale integrated circuits and ultra-low power consumption storage and logic devices. The embodiment does not contain a heavy metal layer, has simple structure and easy preparation compared with other existing devices for realizing the switching without external magnetic field, and still has good perpendicular magnetic anisotropy and thermal stability when the size of the device is reduced to the nanometer size. In addition, the control of the turn-over ratio can be achieved by controlling the growth temperature of the FePt layer during the device fabrication process.
In this embodiment, the preparation method and conditions of the device are specifically as follows:
an ultrahigh vacuum magnetron sputtering technology is adopted, and three layers of films of NiFe (5)/TiN (x)/FePt (10) (from top to bottom) are deposited on a MgO (001) single crystal substrate;
TiN layers of different thicknesses (0-3nm) were deposited on the FePt monolayer film at 300 deg.C, and a NiFe layer (5nm) was deposited at the end, forming a three-layer film structure (for simplicity of description, if TiN layer is not present, it is also considered as a three-layer film structure shadow, when TiN layer thickness is 0 nm);
characterizing the crystal structure of the film by x-ray diffraction (XRD);
subsequently, the thin film on the single crystal substrate was etched by ultraviolet lithography and argon ion etching to form Hall stripes having a current channel length of 20-45 μm and a voltage channel width of 15 μm and 6 μm, respectively.
Example 3:
a magnetization switching device based on FePt material for realizing switching without external magnetic field, as shown in (a) of fig. 14, which comprises, from bottom to top: the device comprises a single crystal substrate, a FePt layer and an n-layer composite overturning layer;
the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current;
compound upset layer is from supreme including in proper order down: an isolation layer and an inducing layer;
the induction layer is used for providing a stray field or ferromagnetic exchange coupling effect in the plane direction so as to break the symmetry of the system and realize deterministic magnetic moment overturning without an external magnetic field;
the isolation layer is used for preventing atomic penetration between the FePt layer and the inducing layer;
alternatively, in order to facilitate epitaxial growth of a (001) -oriented FePt thin film on a substrate, in the present embodiment, the substrate material is MgO, and its orientation is (001); it should be noted that this is only an alternative embodiment, and that other materials that facilitate epitaxial growth of a single-layer FePt film of the L10 phase, such as MgO, Pt, KTaO with a face-centered cubic (FCC) structure3、SrTiO3Etc., can also be used as a substrate material in the present invention;
optionally, in this embodiment, the material of the inducing layer is NiFe, and it should be noted that, in some other embodiments of the present invention, the inducing layer may also be replaced by other materials capable of generating a stray field or an exchange coupling field in a planar direction;
preferably, in this embodiment, the material of the isolation layer is TiN, and it should be noted that, in some other embodiments of the present invention, the isolation layer may also be replaced by other materials capable of performing an isolation function, but experiments show that, compared to other materials, when TiN is used as the material of the isolation layer, this embodiment can obtain a more excellent external magnetic field-free switching characteristic;
as shown in fig. 14 (a), in the present example, the FePt layer was 10nm thick, the inducing layer made of NiFe material was 2nm thick, and the spacer layer made of TiN material was 1nm thick;
in order to apply current to the device and detect the hall voltage of the device conveniently, so as to control the magnetization switching process of the device conveniently, in this embodiment, as shown in (b) and (c) of fig. 14, the FePt layer and the composite switching layer are etched into a hall bar shape; two crossed channels in the Hall strip shape are a current channel with the length of 20-45 mu m and the width of 15 mu m and a voltage channel with the length of 20-45 mu m and the width of 6 mu m respectively, four ends of the Hall strip shape are deposited with wide square Pt electrodes respectively, and the width of the electrodes is not more than 200 mu m; the current channel is used for applying current, and the voltage channel is used for measuring Hall voltage;
the magnetization switching device based on the FePt material provided by this embodiment can realize switching without an external magnetic field by utilizing the SOT effect in the FePt layer and the stray field or ferromagnetic exchange coupling effect in the planar direction provided by the inducing layer.
Based on the measurement results of the single-layer FePt thin film in example 1, it can be seen that, in this example as well, the FePt single layer has good SOT efficiency, and the magnitude of the SOT effect in the FePt layer is influenced by the growth temperature of the FePt layer.
Taking n-3 and n-5 as examples, the AHE curves of the multilayer film structures of n-3 and n-5 prepared at High Temperature (HT) and the AHE curves of the multilayer film structures of n-3 and n-5 prepared at Room Temperature (RT) were measured, respectively, and the measurement results are shown in fig. 15; similarly, taking n-3 and n-5 as examples, x-ray diffraction (XRD) patterns of the multilayer film structures of n-3 and n-5 prepared at High Temperature (HT) and x-ray diffraction (XRD) patterns of the multilayer film structures of n-3 and n-5 prepared at normal temperature (RT) were measured, respectively, and the measurement results are shown in fig. 16. The measurement results shown in fig. 15 and 16 indicate that the above-described magnetization switching device based on the FePt material provided in this example has excellent magnetization switching characteristics.
Taking n-3 and n-5 as examples, the flip characteristics with current under the assistance of different external magnetic fields of multilayer film structures of n-3 and n-5 prepared at normal temperature were further measured, and in the measurement, an external magnetic field (H) was applied in the x directionx) The SOT effect is generated in an auxiliary manner, the magnetization switching measurement induced by the current is realized, and the measurement result is shown in fig. 17, wherein (a) is a switching curve of the abnormal hall resistance of the device with 3 layers of composite switching layers prepared at normal temperature along with the current under the assistance of different external magnetic fields, and (b) is a switching curve of the abnormal hall resistance of the device with 5 layers of composite switching layers prepared at normal temperature along with the current under the assistance of different external magnetic fields; similarly, taking n-3 and n-5 as examples, the current-dependent switching characteristics of the multilayer film structures of n-3 and n-5 prepared at high temperature were further measured, and during the measurement, an external magnetic field (Hx) was applied in the x direction to assist the generation of the SOT effect, thereby performing the current-induced magnetization switching measurement, and the measurement results are shown in fig. 18, where (a) is the current-dependent switching curve of the abnormal hall resistance of the device with 3 layers of composite switching layers prepared at high temperature, and (b) is the current-dependent switching curve of the abnormal hall resistance of the device with 5 layers of composite switching layers prepared at high temperature, under different external magnetic fields. The measurement results shown in fig. 17 and 18 indicate that the multilayer film structure provided by the present embodiment has a good SOT effect and achieves inversion without the assistance of an external magnetic field.
Example 4:
an external magnetic field-free switching method based on the FePt material-based magnetization switching devices provided in the above embodiments 2 and 3, comprising:
calibrating the relationship between the switching ratio and the maximum switching current in the FePt material-based magnetization switching device in advance after the induction layer realizes magnetization saturation;
determining corresponding pulse current according to the relation between the turnover ratio and the maximum turnover current density and combining with the requirement of the turnover ratio, and applying the pulse current to a FePt material-based magnetization turnover device to realize turnover without an external magnetic field;
generally, after the external magnetic field is applied in the x direction to saturate the NiFe layer when the device is manufactured, the device can be directly used to realize the external field-free switching.
The method for turning over the device without the external magnetic field provided by the invention does not need to apply a plane magnetic field in the process of making the device generate deterministic magnetization turning, only needs to apply corresponding pulse current to the device, does not depend on the external magnetic field, and is simpler to control.
Example 5:
the FePt material-based magnetization switching device provided in embodiment 2 is applied to an integrated circuit, a memory device or a logic device.
Example 6:
the FePt material-based magnetization switching device provided in embodiment 3 above is applied to an integrated circuit, a memory device, or a logic device.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A magnetization switching device based on FePt materials, which is used for realizing current-driven magnetization switching, and is characterized by comprising: the single crystal substrate and the FePt layer are grown on the single crystal substrate;
the FePt layer is a single-layer FePt film of an L10 phase and is used for carrying out partial magnetization reversal under the induction of current.
2. The FePt material-based magnetization switching device of claim 1, wherein the FePt layer has a thickness of 5nm to 40 nm.
3. The FePt material-based magnetization switching device according to claim 1 or 2, wherein the FePt layer is in a hall bar shape;
two crossed channels in the Hall strip shape are a current channel and a voltage channel respectively, and electrodes are deposited at four ends of the Hall strip shape respectively; the current channel is used for applying current, and the voltage channel is used for measuring Hall voltage.
4. The utility model provides a magnetization switching device based on FePt material for realize there is not external magnetic field upset, its characterized in that from supreme down includes in proper order: the device comprises a single crystal substrate, a FePt layer and one or more composite overturning layers;
the FePt layer is a single-layer FePt film of an L10 phase and is used for generating partial magnetization reversal under the induction of current;
compound upset layer is from supreme including in proper order down: an isolation layer and an inducing layer;
the induction layer is used for providing a stray field or ferromagnetic exchange coupling in the plane direction so as to break the symmetry of the system and realize deterministic magnetic moment overturning without an external magnetic field;
the isolation layer is used for preventing atomic penetration between the FePt layer and the inducing layer.
5. The FePt material-based magnetization switching device of claim 4, wherein the FePt layer has a thickness of 5nm to 40 nm.
6. The FePt material-based magnetization switching device of claim 4, wherein the material of the spacer layer is TiN.
7. The FePt material based magnetization switching device of claim 4, wherein the inducing layer is of NiFe.
8. The FePt material based magnetization switching device according to any one of claims 4-7, wherein each film layer on the single crystal substrate is in the shape of the same Hall bar;
two crossed channels in the Hall strip shape are a current channel and a voltage channel respectively, and electrodes are deposited at four ends of the Hall strip shape respectively; the current channel is used for applying current, and the voltage channel is used for measuring Hall voltage.
9. An external magnetic field-free switching method of a FePt material based magnetization switching device according to any of claims 4-8, comprising:
calibrating the relationship between the switching ratio and the maximum switching current in the FePt material-based magnetization switching device in advance after the induction layer realizes magnetization saturation;
and determining corresponding pulse current according to the relation between the switching ratio and the maximum switching current density and combining with the switching ratio requirement, and applying the pulse current to the FePt material-based magnetization switching device to realize the switching without the external magnetic field.
10. Use of a FePt material based magnetization switching device as claimed in any one of claims 4-8 in an integrated circuit, a memory device or a logic device.
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