KR20210043956A - Spin device including 2-dimentional magnetic material - Google Patents

Abstract

According to the present invention, provided is a spin element which comprises: a first electrode layer; a second electrode layer; an insulating layer positioned between the first electrode layer and the second electrode layer; and a two-dimensional magnetic material layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer, and capable of doping control. Therefore, a magnetization direction of the two-dimensional magnetic material layer can be easily controlled with little power.

Description

Spin device including a two-dimensional magnetic body TECHNICAL FIELD {SPIN DEVICE INCLUDING 2-DIMENTIONAL MAGNETIC MATERIAL}

The present invention relates to a spin element including a two-dimensional magnetic body, and in particular, to easily control magnetic anisotropy of a two-dimensional magnetic body.

Recently, a technique using a spin element of a method of storing information by controlling the magnetization direction of a magnetic material has been widely used.

In this regard, Korean Patent Registration No. 10-1967352 includes lower magnetic patterns arranged in a first direction and a second direction perpendicular to each other on a substrate; An upper magnetic layer covering at least two or more of the lower magnetic patterns arranged in the first direction and at least two or more of the lower magnetic patterns arranged in the second direction in common; And a tunnel barrier layer interposed between the lower magnetic patterns and the upper magnetic layer.

Apart from this, research on two-dimensional materials such as graphene has been actively conducted in recent years, and it is showing innovative achievements in nanotechnology and device research. With the discovery of two-dimensional materials of various properties such as metals, non-conductors, semiconductors, and superconductors, various electronic devices and optical devices using two-dimensional materials are being developed.

However, few attempts have been made to apply a two-dimensional magnetic material to a spin device among two-dimensional materials.

In particular, since the two-dimensional magnetic body has a high magnetic anisotropy, a large amount of power is consumed during spin switching, which may become an obstacle to using the two-dimensional magnetic body in a spin device. For example, as shown in FIG. 1, about 0.4 to 1T is required for spin switching of _{Fe 3} GeTe _2.

An object of the present invention is to provide a spin device including a two-dimensional magnetic body that facilitates control by lowering the magnetic anisotropy of the two-dimensional magnetic body.

A spin device according to an embodiment of the present invention includes: a first electrode layer; A second electrode layer; An insulating layer positioned between the first electrode layer and the second electrode layer; And a two-dimensional magnetic layer positioned between the first electrode layer and the insulating layer, or between the insulating layer and the second electrode layer, and capable of controlling doping.

The first electrode layer, the second electrode layer, and the insulating layer each have a two-dimensional layered structure, and planes of the first electrode layer, the second electrode layer, the insulating layer, and the magnetic layer may be parallel to each other.

The first electrode layer and the second electrode layer may be graphene.

The insulating layer may be hexagonal boron nitride (hBN).

The magnetic layer may be hole doped with an element that determines the magnetism of the magnetic layer, thereby causing deficiency in an element that determines the magnetism of the magnetic layer.

The magnetic layer is a material that can be separated in two dimensions with a layered structure, and may be made of any one of _{CrI 3} , Cr ₂ (Si, Ge) ₂ Te ₆ , MSe ₂ (where M is V or Mn) and Fe ₃ GeTe _2. have.

A voltage is applied between the first electrode layer and the second electrode layer, and magnetic anisotropy of the magnetic material layer may be reduced by an electric field generated by the voltage.

A spin device according to an embodiment of the present invention includes: a first electrode layer and a second electrode layer to which a voltage is applied; An insulating layer positioned between the first electrode layer and the second electrode layer; And a two-dimensional magnetic material layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer and reducing magnetic anisotropy by an electric field generated by the voltage.

A spin device according to an embodiment of the present invention includes: a first electrode layer having a two-dimensional structure; A second electrode layer having a two-dimensional structure; An insulating layer positioned between the first electrode layer and the second electrode layer and having a two-dimensional structure; And a two-dimensional magnetic layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second metal layer, wherein the first electrode layer, the second electrode layer, the insulating layer, and the magnetic layer are The faces are arranged parallel to each other to form a heterojunction at the interface.

According to the embodiment of the present invention, since the magnetic anisotropy of the two-dimensional magnetic layer is reduced, the magnetization direction of the two-dimensional magnetic layer can be easily controlled with little power.

1 is a graph showing the magnetic resistance according to the magnetic field _{of Fe 3} GeTe _{2 by temperature.}
2 is a diagram schematically showing the structure of a spin element 1 according to an embodiment of the present invention.
3 is a view for explaining the basic atomic structure and symmetry _{of Fe 3} GeTe _2.
4 is a view for explaining the magnetic properties _{of thinly peeled Fe 2.7} GeTe _2.
5, 6 and 7 are diagrams showing the magnetic properties _{of thinly peeled Fe 2.7} GeTe _{2 compared to Fe 3} GeTe _2.
8 is a table showing magnetization (M), local magnetic moment, and magnetocrystalline anisotropy energy (MAE) according to hole doping.

Terms or words used in this specification and claims are limited to their usual or dictionary meanings and should not be interpreted, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

In the specification and claims, the use of a singular word when used with the term “comprising” may mean “one”, or “one or more”, “at least one”, and “one or more than one”. May be.

The use of the term "or" in the claims indicates that although the present disclosure supports only selectables and definitions representing "and/or", selectables are mutually exclusive or are only expressly indicated to represent selectables " And/or is used to mean ".

Features and advantages of the present invention will become apparent from the following detailed description. However, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description, the detailed description and specific examples represent specific embodiments of the present invention, but only It should be understood that it is given as an example. Various exemplary embodiments of the invention are discussed in detail below with respect to the accompanying drawings, in which exemplary embodiments of the invention are shown. While specific implementations are discussed, this is done for illustrative purposes only. Those skilled in the art will recognize that other components and configurations may be used without departing from the spirit and scope of the present invention. The same numbers represent the same elements throughout.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram schematically showing the structure of a spin element 1 according to an embodiment of the present invention.

Referring to FIG. 2, the spin element 1 includes a first electrode layer 100, a two-dimensional magnetic layer 200, an insulating layer 300, and a second electrode layer 400.

The insulating layer 300 is positioned between the first electrode layer 100 and the second electrode layer 400. The two-dimensional magnetic layer 200 is positioned between the first electrode layer 100 and the insulating layer 300 as shown in FIG. 2.

According to an embodiment, the two-dimensional magnetic layer 200 may be positioned between the insulating layer 300 and the second electrode layer 400. Alternatively, although FIG. 2 shows that one insulating layer 300 is positioned between the two-dimensional magnetic layer 200 and the second electrode layer 400, between the first electrode layer 100 and the two-dimensional magnetic layer 200 An insulating layer may be additionally located on the.

The two-dimensional magnetic material layer 200 has a layered structure and is made of a magnetic material that can be separated in two dimensions. The two-dimensional magnetic layer 200 may be formed of, for example, one of CrI ₃ , Cr ₂ (Si, Ge) ₂ Te ₆ , MSe ₂ (wherein M is V or Mn) and Fe ₃ GeTe ₂ .

According to an embodiment, the two-dimensional magnetic material layer 200 may be formed by hole doping a magnetic material having a two-dimensional structure. The two-dimensional magnetic layer 200 may be doped with holes or electrons due to a lack or excess of an element that determines magnetism. Here, the element that determines the magnetism refers to an element that dominates the magnetism of the two-dimensional magnetic layer 200 when the material constituting the two-dimensional magnetic layer 200 is a compound composed of a plurality of elements. For example, when the two-dimensional magnetic layer 200 is made of Fe ₃ GeTe ₂ , Te is involved in the structure of the two-dimensional magnetic layer 200, and Fe and Ge determine magnetism. However, since the degree of Ge affects the magnetism of the two-dimensional magnetic layer 200 is very small compared to Fe, in the case of the two-dimensional magnetic layer 200 made of _{Fe 3} GeTe _{2, Fe is an element that dominantly affects the magnetism.}

According to the present embodiment, the magnetic anisotropy of the two-dimensional magnetic layer 200 is reduced by using the hole-doped two-dimensional magnetic layer 200, thereby facilitating control of the spin element 1. The effect of reducing the magnetic anisotropy will be described later in detail together with the experimental results.

In addition to the two-dimensional magnetic layer 200, the first electrode layer 100, the insulating layer 300, and the second electrode layer 400 have a two-dimensional structure, and the first electrode layer 100, the two-dimensional magnetic layer 200, and the insulating layer The surfaces of the 300 and the second electrode layer 400 may be parallel to each other. The interface between the first electrode layer 100 and the two-dimensional magnetic layer 200, the interface between the two-dimensional magnetic layer 200 and the insulating layer 300, and the interface between the insulating layer 300 and the second electrode layer 400 form a heterojunction can do.

Graphene may be used as a material forming the first electrode layer 100 and the second electrode layer 400 having a two-dimensional structure. In addition, hBN may be used as a material for forming the insulating layer 300 having a two-dimensional structure.

Depending on the embodiment, the materials forming the first electrode layer 100 and the second electrode layer 400 may be the same or different from each other.

A voltage is applied between the first electrode layer 100 and the second electrode layer 400, and the two-dimensional magnetic layer is caused by an electric field generated between the first electrode layer 100 and the second electrode layer 400 by the applied voltage. The magnetic anisotropy of (200) is reduced. As described above, magnetic anisotropy of the two-dimensional magnetic layer 200 may be reduced even when hole doping is performed on the material forming the two-dimensional magnetic layer 200. Depending on the embodiment, an electric field may be applied to the hole-doped two-dimensional magnetic layer 200, and in this case, the effect of reducing magnetic anisotropy may be increased.

_{Next, the effect of reducing magnetic anisotropy when hole-doped Fe 3-x} GeTe ₂ (FGT, 0<x<3) is used as the two-dimensional magnetic layer 200 will be described in detail with reference to the experimental results.

3A to 3E are diagrams for explaining the basic atomic structure and symmetry of FGT.

3A is a diagram showing the crystal structure _{of Fe 3-x} GeTe _{2 (FGT).} The crystal structure of Fe _3-x GeTe _{2 (FGT) belongs to the P6 3} /mmc spatial group with lattice parameters of a=0.3954(2)nm and c=1.6372(2)nm.

Referring to FIG. 3A, a single layer of FGT is formed by bonding of five atomic layers having Fe atoms occupying two unequal wick-off positions (Fe1 and Fe2). At the center of each layer, the planar atomic arrangement of Fe2 and Ge in a 1:1 ratio forms a hexagonal lattice similar to hBN. Fe1 atoms are located in a horizontal position along the center of the Fe2-Ge hexagon forming a triangular lattice, above and below 1.3Å of the Fe2-Ge surface. The outermost layer is formed of two Te planes about 1.3Å apart from the Fe1 layer in the c-axis, each located at the center of the adjacent Fe1 layer (or at the same horizontal position of Fe2). The unit cell of the FGT consists of two layers of an Fe-Ge-Te complex, and the layers are stacked so as to be 0.3Å apart from the upper layer rotated by 60 degrees with respect to the Fe1 atomic layer for the lower layer. Here, the number of flake layers is calculated as the thickness t of a unit cell (1.6 nm or less) composed of two single layers.

Referring to FIG. 3B, the average stoichiometry determined by EDX extracted from several single crystals having a plurality of measurement points is, when Te is fixed to 2, the crystals are Fe:Ge:Te=2.64(6):0.87(4). ): 2.00 indicates uniformity by a stoichiometric amount. The FGT measured in this experiment has Fe deficiency. That is, in FGT (Fe ₃ GeTe ₂ ) without Fe deficiency, the ratio of Fe atoms is Fe1:Fe2=2:1, and Fe deficiency has been reported to favor the Fe2 position.

3C is an optical microscope image of a mechanically exfoliated FGT piece placed on a _{SiO 2 /Si substrate.} The thickness and surface roughness of the pieces are defined by atomic force microscopy (AFM) measurements.

3D is an AFM image of an FGT fragment corresponding to the square dotted area of FIG. 3C.

FIG. 3E shows that the height profile along the green line of FIG. 3D has a relatively flat surface without any large defects or thickness gradients, and the thickness of the piece is 12.5 nm (8 unit cells or less).

4 is a view for explaining the magnetic properties _{of thinly peeled Fe 3-x} GeTe _2.

4a to 4c are temperature-dependent out-of-plane (H//c) magnetic hysteresis loops of _{Fe 3-x} GeTe ₂ pieces measured by MOKE (magneto-optical Kerr effect), FIG. 4a is 9.3 nm, and FIG. 4b is 13.6. nm, Fig. 4c representatively shows the thickness of 16 nm (corresponding to 6, 9, and 10 unit cells, respectively). Error bars are determined by the MOKE signal noise.

4D to 4F are drawn by fitting experimental data using the following equation (1). _{Curie temperatures Tc of 2} pieces of 10nm, 13.6nm, and 16nm Fe _3-x GeTe determined by the fitting curve were 101K, 102K, and 121K, respectively. The inset images of FIGS. 4D to 4F show an optical image of the measured piece together with a 5 μm white scale bar.

4A to 4C, _{the out-of-plane magnetic hysteresis loop of the Fe 3-x} GeTe ₂ flake shows a square loop having a full residual magnetism and a well-defined coercivity at a low temperature (T≤80K), which is thin. It is shown that the Fe _3-x GeTe ₂ layer has a uniaxial out-of-plane magnetic easy axis, that is, it has perpendicular magnetic anisotropy (PMA). As the temperature increases, the magnetic coercivity decreases, which is common in magnetic systems approaching two-dimensional systems.

)은 정규화된 자화이고 β는 임계 지수이다.Referring to FIGS. 4D to 4F, as the temperature increases, the saturation magnetization (Ms) also decreases, and a phase transition from a ferromagnetic state to a paramagnetic state is observed at a Curie temperature (Tc). The Tc of the flake can be determined by fitting the MT curves of FIGS. 4D to 4F by the following equation (1). In equation (1), m(

) Is the normalized magnetization and β is the critical exponent.

…(1)

… (One)

The Tc of the Fe _3-x GeTe ₂ flake is judged to be 101K~121, and it slightly increases with the thickness.

Thin (aqueous) Fe-deficient Fe _3-x GeTe ₂ flakes, _{similar to Fe 3} GeTe2, have strong PMA, but there are two major differences between _{Fe 3-x} GeTe ₂ and Fe ₃ GeTe _2. First, the Curie temperature of Fe-deficient Fe _3-x GeTe ₂ (100K or less for a piece of thickness less than 10 nm) is lower than that _{of Fe 3} GeTe _{2 (150K or less for a piece of thickness less than 10 nm).} Second, the Fe-deficient Fe _3-x GeTe ₂ piece has a relatively small magnetic coercivity (300 Oe or less for a layer with a thickness of 10 nm or less at T=10K), which is _{the magnetic coercivity of Fe 3} GeTe ₂ (10 nm in thickness at T=10K). Is much less than 4000 Oe or less) for the following layers. For micron-sized _{pieces of Fe 3-x} GeTe ₂ , the easy axis magnetic coercivity is largely proportional to the uniaxial magnetic anisotropy. Thus, a large decrease in coercivity indicates that Fe-deficient Fe _3-x GeTe ₂ has a significantly smaller, but still perpendicular magnetic anisotropy, compared to _{Fe 3} GeTe _2.

5 and 6 are diagrams showing the magnetic properties _{of thinly peeled Fe 2.7} GeTe _{2 compared to Fe 3} GeTe ₂ , and FIG. 7 shows the result of changing the coercive force _{of Fe 2.7} GeTe _{2 by doping.} As can be seen from this, the vertical magnetic anisotropy and switching field of the _{thinly peeled Fe 2.7} GeTe ₂ , that is, Fe-deficient Fe _3-x GeTe ₂ , are reduced compared _{to Fe 3} GeTe _2. That is, it can be seen that the magnetic anisotropy of _{Fe 3-x} GeTe _{2 can be controlled by hole doping.}

From the standpoint that magnetic anisotropy is an important parameter in the performance of the spintronic device, the significant reduction in coercivity with hole doping was further investigated by the first principle calculation.

8 is a table showing magnetization (M), local magnetic moment, and magnetocrystalline anisotropy energy (MAE) according to hole doping. x=0 corresponds to 0h/f.u., x=0.19 corresponds to 0.5h/f.u., and x=0.38 corresponds to 1h/f.u.

In a wide range of hole doping (0 to 1 h per formula unit (f.u.)), the magnetization along the c-axis takes precedence over the in-plane [210] direction, which is consistent with the PMA observed from MOKE measurements. In contrast to a gentle reduction in magnetization of about 10% down to x=0.38 (1h doping per fu), MAE with x=0.19 (0.5h doping per fu) showed a surprising reduction of about 33%, and x It was shown that MAE with =0.38 (1h doping per fu) decreased to a value of 7% or less compared to FGT (x=0) as it was in the formula. This indicates that the reduced magnetization is independent of the softening of the forced field.

From the above experiment and calculation results, it can be seen that the perpendicular magnetic anisotropy of _{hole-doped Fe 3-x} GeTe _{2 decreases.}

In addition, applying an electric field to the two-dimensional magnetic layer 200 can be expected to have the same effect as hole doping, that is, the effect of perpendicular magnetic anisotropy. To maximize the effect of perpendicular magnetic anisotropy reduction, both hole doping and electric field application may be used.

According to the embodiment of the present invention, spin information can be well preserved by the configuration in which each layer has a two-dimensional structure. In spintronic phenomena, interfacial magnetism and interfacial spin transport characteristics play a very important role. If the interface is not well defined, most of the spin information is destroyed on the surface, and predicted device performance may not be observed. In addition, two-dimensional magnetic bodies and heterojunction structures having a layered structure have a much better defined interface than magnetic thin films deposited by sputter or molecular ray epitaxy (MBE), so systematic analysis and physical understanding of spintronic phenomena Can make a big contribution to

According to an embodiment of the present invention, by using a flexible two-dimensional magnetic body, it is also possible to use it as a flexible spin device.

As described above, the present invention has been described in detail through preferred embodiments, but the present invention is not limited thereto, and various changes and applications can be made without departing from the technical spirit of the present invention. It is self-explanatory to the technician. Therefore, the true scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (9)

A first electrode layer;
A second electrode layer;
An insulating layer positioned between the first electrode layer and the second electrode layer; And
A two-dimensional magnetic layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer and capable of controlling doping;
Spin element comprising a. The method of claim 1,
The first electrode layer, the second electrode layer, and the insulating layer each have a two-dimensional structure,
The first electrode layer, the second electrode layer, the insulating layer and the magnetic material layer (planes) of the spin element, characterized in that parallel to each other. The method of claim 2,
The first electrode layer and the second electrode layer is a spin device, characterized in that graphene. The method of claim 2,
The insulating layer is a spin element, characterized in that the hBN (hexagonal boronate). The method of claim 1,
The magnetic material layer is a spin element, characterized in that the deficiency (deficiency) occurs in the element that determines the magnetism of the magnetic material layer by hole doping with an element that determines the magnetism of the magnetic material layer. The method of claim 1,
The magnetic layer is a spin element, characterized in that consisting of any one of _{CrI 3} , Cr ₂ (Si, Ge) ₂ Te ₆ , MSe ₂ (wherein M is V or Mn) and Fe ₃ GeTe _2. The method of claim 1,
A spin element, wherein a voltage is applied between the first electrode layer and the second electrode layer, and magnetic anisotropy of the magnetic material layer is reduced by an electric field generated by the voltage. A first electrode layer and a second electrode layer to which a voltage is applied;
An insulating layer positioned between the first electrode layer and the second electrode layer; And
A two-dimensional magnetic layer disposed between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer and having magnetic anisotropy reduced by an electric field generated by the voltage;
Spin element comprising a. A first electrode layer having a two-dimensional structure;
A second electrode layer having a two-dimensional structure;
An insulating layer positioned between the first electrode layer and the second electrode layer and having a two-dimensional structure; And
A two-dimensional magnetic layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second metal layer;
Including,
Surfaces of the first electrode layer, the second electrode layer, the insulating layer, and the magnetic layer are arranged parallel to each other to form a heterojunction at an interface.

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