KR102310181B1 - Spin device including 2-dimentional magnetic material - Google Patents

Abstract

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 material layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer, the doping of which is controllable.

Description

Spin element containing two-dimensional magnetic material {SPIN DEVICE INCLUDING 2-DIMENTIONAL MAGNETIC MATERIAL}

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

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

In this regard, Korean Patent Registration No. 10-1967352 discloses, on a substrate, lower magnetic patterns arranged in a first direction and a second direction perpendicular to each other; an upper magnetic layer that commonly covers the at least two or more lower magnetic patterns arranged in the first direction and the at least two or more lower magnetic patterns arranged in the second direction; and a tunnel barrier layer interposed between the lower magnetic patterns and the upper magnetic layer.

Separately, research on two-dimensional materials, such as graphene, has been actively conducted recently, and innovative results are shown in nanotechnology and device research. With the discovery of two-dimensional materials with various properties, such as metals, insulators, 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 among two-dimensional materials to a spin device.

In particular, since the two-dimensional magnetic material has high magnetic anisotropy, a large amount of power is consumed during spin switching, which may become an obstacle to using the two-dimensional magnetic material for a spin device. For example, as shown in Figure 1, Fe ₃ GeTe _{2 For} spin switching of about 0.4 ~ 1T is required.

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

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 may 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 have a deficiency in the element determining the magnetism of the magnetic layer by doping holes with the element determining the magnetism of the magnetic layer.

The magnetic layer has a layered structure and is a material that can be peeled off in two dimensions, CrI ₃ , Cr ₂ (Si, Ge) ₂ Te ₆ , MSe ₂ (where M is V or Mn) and Fe ₃ GeTe ₂ Can be made of any one have.

A voltage may be applied between the first electrode layer and the second electrode layer, and magnetic anisotropy of the magnetic 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 layer positioned between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer, the magnetic anisotropy being reduced by the 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 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 for each temperature.}
2 is a diagram schematically showing the structure of a spin device 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 exfoliated 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.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

The use of the word singular when used in conjunction with the term "comprising" in the specification and claims may mean "a," or "one or more," "at least one," and "one or more than one." may be

The use of the term “or” in the claims means that, although this disclosure supports a definition indicating only the selectables and “and/or,” the selectable are mutually exclusive or unless expressly indicated as indicating merely the selectable. and/or".

The features and advantages of the present invention will become apparent from the following detailed description. However, the detailed description and specific examples represent specific embodiments of the invention, but only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. It should be understood that they are given as examples. 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 illustration purposes only. A person skilled in the art will recognize that other elements and configurations may be used without departing from the spirit and scope of the present invention. Like numbers refer to like elements throughout.

Hereinafter, 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 device 1 according to an embodiment of the present invention.

Referring to FIG. 2 , the spin device 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 it is shown in FIG. 2 that one insulating layer 300 is positioned between the two-dimensional magnetic material layer 200 and the second electrode layer 400 , the first electrode layer 100 and the two-dimensional magnetic material layer 200 are located between the two-dimensional magnetic material layer 200 . An insulating layer may be additionally located.

The two-dimensional magnetic material layer 200 has a layered structure and is made of a two-dimensionally peelable magnetic material. The two-dimensional magnetic layer 200 may be formed of, for example, 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 .

According to an embodiment, the two-dimensional magnetic material layer 200 may be formed by doping holes in a magnetic material having a two-dimensional structure. The two-dimensional magnetic material layer 200 may be doped with holes or electrons due to a deficiency or excess of an element determining magnetism. Here, the element determining the magnetism means an element that predominantly affects the magnetism of the two-dimensional magnetic layer 200 when the material constituting the two-dimensional magnetic layer 200 is a compound made 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 to the magnetism of the two-dimensional magnetic layer 200 is very small compared to that of Fe, in the case of the two-dimensional magnetic layer 200 made of _{Fe 3} GeTe _{2 , the element that predominantly affects the magnetism is Fe.}

According to this embodiment, the magnetic anisotropy of the two-dimensional magnetic material layer 200 is reduced by using the hole-doped two-dimensional magnetic material layer 200, and accordingly, the control of the spin element 1 is facilitated. The effect of reducing the magnetic anisotropy will be described later in detail along with the experimental results.

In addition to the two-dimensional magnetic material layer 200, the first electrode layer 100, the insulating layer 300, and the second electrode layer 400 also have a two-dimensional structure, and the first electrode layer 100, the two-dimensional magnetic material layer 200, and the insulating layer Surfaces of 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 for forming the first electrode layer 100 and the second electrode layer 400 having a two-dimensional structure. Also, hBN may be used as a material for forming the insulating layer 300 having a two-dimensional structure.

According to an embodiment, 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 by the electric field generated between the first electrode layer 100 and the second electrode layer 400 by the applied voltage, the two-dimensional magnetic material layer The magnetic anisotropy of (200) is reduced. As described above, the magnetic anisotropy of the two-dimensional magnetic layer 200 may be reduced even when holes are doped into the material forming the two-dimensional magnetic layer 200 . According to an embodiment, an electric field may be applied to the hole-doped two-dimensional magnetic material layer 200, and in this case, the effect of reducing the 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 views for explaining the basic atomic structure and symmetry of FGT.

Figure 3a is a view 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 space group with lattice parameters of a=0.3954(2)nm and c=1.6372(2)nm.

Referring to FIG. 3A , a monolayer of FGT is formed by bonding of five atomic layers with Fe atoms occupying two unequal wick-off positions (Fe1, 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. Above and below 1.3 Å of the Fe2-Ge plane, Fe1 atoms are located in horizontal positions along the center of the Fe2-Ge hexagons forming the triangular lattice. The outermost layer is formed of two Te planes about 1.3 Å away from the Fe1 layer in the c-axis, each centered in the adjacent Fe1 layer (or at the same horizontal position of Fe2). The unit cell of FGT is composed of two layers of Fe-Ge-Te complex, the layers are stacked 0.3 Å apart from the upper layer rotated 60 degrees with respect to the Fe1 atomic layer with respect to the lower layer. Here, the number of layers of the flake 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 multiple measurement points is, when Te is fixed at 2, the crystals are Fe:Ge:Te=2.64(6):0.87(4 ):2.00 stoichiometry, indicating uniformity. 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 it is reported that Fe deficiency favors the Fe2 position.

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

Figure 3d is an AFM image of the FGT fragment corresponding to the rectangular dotted line region of Figure 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, while 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 exfoliated Fe 3-x} GeTe _{2 .}

4A-4C are temperature-dependent out-of-plane (H//c) magnetic hysteresis loops of _{Fe 3-x} GeTe ₂ fragments measured by the magneto-optical Kerr effect (MOKE). nm, FIG. 4c represents a representative thickness of 16 nm (corresponding to 6, 9, and 10 unit cells, respectively). The error bars are determined by the MOKE signal noise.

4D to 4F are drawn by fitting experimental data using Equation (1) below. The Curie temperatures Tc of the 10 nm, 13.6 nm, and 16 nm Fe _3-x GeTe ₂ fragments determined by the fitting curves are 101K, 102K, and 121K, respectively. The inset images of Figures 4d-4f show the optical image of the measured piece with a 5 μm white scale bar.

4a to 4c, _{the out-of-plane magnetic hysteresis loop of Fe 3-x} GeTe ₂ flakes exhibits a square loop with full residual magnetism and well-defined coercivity at low temperature (T≤80K), which is a thin This indicates 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 coercive force decreases, which is common in magnetic systems approaching two-dimensional systems.

)은 정규화된 자화이고 β는 임계 지수이다.4D to 4F , as the temperature increases, the saturation magnetization (Ms) also decreases, and a phase transition from the ferromagnetic state to the paramagnetic state is observed at the Curie temperature (Tc). The Tc of the lamella can be determined by fitting the MT curves of FIGS. 4D to 4F with 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 flakes is determined 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 (less than 100K for thin slices of _{10 nm or less) is lower than the Curie temperature of Fe 3} GeTe ₂ (less than 150K for slices of thickness less than 10 nm). Second, the Fe-deficient Fe _3-x GeTe ₂ fragments have a relatively small magnetic coercivity (300 Oe or less for layers up to 10 nm thick at T=10K), which is _{the magnetic coercivity of Fe 3} GeTe ₂ (10 nm thick at T=10K). much less than 4000 Oe for the layers below). For a micron-sized _{piece of Fe 3-x} GeTe ₂ , the easy-axis magnetic coercive force is roughly 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 views showing the magnetic properties _{of thinly exfoliated 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 perpendicular magnetic anisotropy and switching field of _{thinly exfoliated Fe 2.7} GeTe ₂ , ie, 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 point of view that magnetic anisotropy is an important parameter in the performance of spintronic devices, the significant reduction of coercive force with Hall doping was further investigated by first-principle calculations.

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.

Over a wide range of hole doping (0–1 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 observed PMA from MOKE measurements. In contrast to the gentle decrease in magnetization of about 10% up to x = 0.38 (1 h doping per fu), with x = 0.19 (0.5 h doping per fu) MAE showed a surprising decrease of about 33%, x MAE with =0.38 (1 h doping per fu) was shown to be reduced to a value of 7% or less compared to FGT without chemical formula (x=0). This indicates that the reduced magnetization is independent of the softening of the forced field.

It can be seen that the perpendicular magnetic anisotropy of _{hole-doped Fe 3-x} GeTe ₂ is reduced by the above experiments and calculation results.

In addition, applying an electric field to the two-dimensional magnetic layer 200 can expect the same effect as the 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 a configuration in which each layer has a two-dimensional structure. In spintronics 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 on the plane is destroyed, and the predicted device performance may not be observed. In addition, two-dimensional magnetic materials and heterojunction structures having a layered structure have a much better defined interface than a magnetic thin film deposited by sputtering or molecular beam epitaxy (MBE). Therefore, systematic analysis and physical understanding of spintronic phenomena can make a great contribution to

According to an embodiment of the present invention, by using a two-dimensional magnetic material having flexibility, it can be utilized 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 it is common in the art that various changes and applications can be made without departing from the technical spirit of the present invention. self-explanatory to the technician. Therefore, the true protection scope of the present invention should be construed 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 material layer located between the first electrode layer and the insulating layer or between the insulating layer and the second electrode layer, the doping of which is controllable;
including,
The magnetic layer has a deficiency (deficiency) in the element determining the magnetism of the magnetic layer by doping holes with respect to the element determining the magnetism of the magnetic layer,
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. According to claim 1,
The first electrode layer, the second electrode layer and the insulating layer each have a two-dimensional structure,
and planes of the first electrode layer, the second electrode layer, the insulating layer, and the magnetic layer are parallel to each other. 3. The method of claim 2,
The first electrode layer and the second electrode layer is a spin device, characterized in that the graphene. 3. The method of claim 2,
The insulating layer is a spin device, characterized in that hBN (hexagonal boron nitride). delete According to claim 1,
The magnetic layer is CrI ₃ , Cr ₂ (Si, Ge) ₂ Te ₆ , MSe ₂ (where M is V or Mn) and Fe ₃ GeTe ₂ Spin device, characterized in that made of any one. According to claim 1,
A voltage is applied between the first electrode layer and the second electrode layer, and the magnetic anisotropy of the magnetic layer is reduced by an electric field generated by the voltage. delete delete

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