Patent Description:
<FIG> is a conceptual diagram of a conventional magnetic nano-oscillating device.

Referring to <FIG>, a magnetic nano-oscillating device <NUM> uses a spin Hall spin torque, generated by in-plane current flowing through a conducting line, and an antiferromagnetic material <NUM>. The magnetic nano-oscillating device <NUM> includes a conductive line <NUM>/an antiferromagnetic layer <NUM>, and a precession motion of an antiferromagnetic layer <NUM> is induced by current flowing to the conductive wire <NUM> in an in-plane direction. An up-spin electron and a down-spin electron are polarized in opposite directions due to spin-orbit coupling. Thus, spin current is generated in a z direction perpendicular to a direction of externally applied current direction (an x direction). In this case, a spin transferred by the spin current has an element in a y direction perpendicular to both the external current direction (the x direction) and the spin current direction (the z direction). When the spin element flows into an adjacent ferromagnetic material, the ferromagnetic material receives a spin transfer torque. Such a torque is called a spin Hall spin torque. <CIT> discloses a magnetic memory element of the spin transfer torque method and <CIT> discloses a radiofrequency oscillator integrating a magnetoresistive device.

However, a nano-oscillating device using a spin Hall spin torque and an antiferromagnetic material is required to have significantly high current density. In addition, the nano-oscillating device has a limitation in frequency tunability. To overcome the limitation, a nano-oscillating device, oscillating even at low current density, is required.

An aspect of the present disclosure is to reduce current required for magnetic oscillation. To this end, a conductive line having a structure of a ferromagnetic layer and a nonmagnetic layer is introduced. When a structure of a ferromagnetic layer, a nonmagnetic layer, and an antiferromagnetic layer (or a ferrimagnetic layer) is used, low current density may be achieved and frequency tunability may be improved.

According to an aspect of the present disclosure, a magnetic nano-oscillating device includes a ferromagnetic layer disposed on a substrate, a nonmagnetic conductive layer stacked on the ferromagnetic layer, an antiferromagnetic layer stacked on the nonmagnetic conductive layer, and first and second electrodes, respectively being in contact with both side surfaces of the ferromagnetic layer and the nonmagnetic conductive layer. The antiferromagnetic layer is a thin film formed of a material magnetized in a perpendicular or in-plane direction to a layer surface. The ferromagnetic layer is in-plane magnetized on a layer surface of the ferromagnetic layer. In-plane current, injected into the ferromagnetic layer and the nonmagnetic conductive layer through the first and second electrodes, provides spin current, including a spin in a thickness direction of a thin film transferred to the antiferromagnetic layer, to cause magnetization precession of a sub-lattice of the antiferromagnetic layer.

In an example embodiment, the magnetic nano-oscillating device may further include a magnetic tunnel junction disposed on the antiferromagnetic layer. The magnetic tunnel junction may include a free layer/a tunnel insulating layer/a pinned layer, and the free layer of the magnetic tunnel junction may have an exchange interaction with the antiferromagnetic layer.

In an example embodiment, the ferromagnetic layer may be formed of one selected from Fe, Co, Ni, B, Si, Zr, and mixtures thereof.

In an example embodiment, the antiferromagnetic layer may be formed of one selected from Ir, Pt, Mn, Cr, FeMn, NiO, Fe<NUM>O<NUM>, and mixtures thereof.

In an example embodiment, the nonmagnetic conductive layer may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, and mixtures thereof.

In an example embodiment, each of the first and second electrodes may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, Ir, and mixtures thereof.

According to an aspect of the present disclosure, a magnetic nano-oscillating device includes a ferromagnetic layer disposed on a substrate, a nonmagnetic conductive layer stacked on the ferromagnetic layer, a ferrimagnetic layer stacked on the nonmagnetic conductive layer, and first and second electrodes, respectively being in contact with both side surfaces of the ferromagnetic layer and the nonmagnetic conductive layer. The ferrimagnetic layer is a thin film formed of a material magnetized in a perpendicular or in-plane direction to a layer surface. The ferromagnetic layer is in-plane magnetized on a layer surface of the ferromagnetic layer. In-plane current, injected into the ferromagnetic layer and the nonmagnetic conductive layer through the first and second electrodes, provides spin current, including a spin in a thickness direction of a thin film transferred to the ferrimagnetic layer, to cause magnetization precession of a sub-lattice of the ferrimagnetic layer.

In an example embodiment, the magnetic nano-oscillating device may further include a magnetic tunnel junction disposed on the ferrimagnetic layer. The magnetic tunnel junction includes a free layer/a tunnel insulating layer/a pinned layer, and the free layer of the magnetic tunnel junction may have an exchange interaction with the antiferromagnetic layer.

In an example embodiment, the ferrimagnetic layer may be formed of one selected from Co, Gd, Tb, Mn, Ir, Ge, Se, Cr, Y, Fe, garnet, a rare earth-transition metal (RE-TM) alloy, mixtures thereof.

According to an aspect of the present disclosure, a magnetic nano-oscillating device includes a first ferromagnetic layer disposed on a substrate, a first nonmagnetic conductive layer disposed on the first ferromagnetic layer, a second ferromagnetic layer disposed on the first nonmagnetic conductive layer, a second nonmagnetic conductive layer disposed on the second ferromagnetic layer, a third ferromagnetic layer disposed on the second nonmagnetic conductive layer, and first and second electrodes, respectively being in contact with both side surfaces of the first ferromagnetic layer and the first nonmagnetic conductive layer. The first ferromagnetic layer is a thin film formed of a material having a fixed magnetization direction and magnetized in a direction parallel to a layer surface. The second ferromagnetic layer and the third ferromagnetic layer are thin films, each having an antiferromagnetic exchange interaction due to the second nonmagnetic conductive layer. In-plane current, injected into the first ferromagnetic layer and the first nonmagnetic conductive layer through the first and second electrodes, provides spin current including a spin in a thickness direction of a thin film transferred to the second ferromagnetic layer and the third ferromagnetic layer to cause magnetization precession of each of the second ferromagnetic layer and the third ferromagnetic layer.

In an example embodiment, the magnetic nano-oscillating device may further include a magnetic tunnel junction disposed on the third ferromagnetic layer. The magnetic tunnel junction may include a tunnel insulating layer/a pinned layer.

In an example embodiment, each of the first ferromagnetic layer, the second ferromagnetic layer, and the third ferromagnetic layer may be formed of one selected from Fe, Co, Ni, B, Si, Zr, and mixtures thereof, the first nonmagnetic conductive layer may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, and mixtures thereof, and the second nonmagnetic conductive layer may be formed of one selected from Ru, Ta, Rh, Ir, Cr, Re, Mo, W, V, and mixtures thereof.

In a magnetic nano-oscillating device according to an example embodiment, spin-polarized spin current may be generated in an interface between a ferromagnetic layer and a nonmagnetic layer while in-plane current passes through the ferromagnetic layer and the nonmagnetic layer, the spin current may transfer an interfacial spin-orbit torque to an antiferromagnetic layer (or a ferromagnetic layer), and the interfacial spin-orbit torque may induce a magnetization precession motion of a sub-lattice of the antiferromagnetic layer (or ferromagnetic layer).

In a magnetic nano-oscillating device according to an example embodiment, a magnetization precession motion of a sub-lattice of the antiferromagnetic layer (or the ferromagnetic layer) may be induced to improve frequency tunability.

A magnetic nano-oscillating device according to an example embodiment may include a ferromagnetic layer, a nonmagnetic layer, and a layer having an antiferromagnetic exchange interaction. The ferromagnetic layer may have a fixed magnetization direction, and may be a thin film formed of a material magnetized in a direction parallel to a layer surface. In addition, a magnetization precession motion of the layer having an antiferromagnetic exchange interaction may be induced by spin current generated in an interface between the ferromagnetic layer and the nonmagnetic layer.

A ferromagnetic material refers to a material spontaneously magnetized even when a strong magnetic field is not externally applied. A resonant frequency of the ferromagnetic material is determined by a magnetic anisotropy field. At this point, a frequency f is given by Equation <NUM>.

In Equation <NUM>, γ (= <NUM> × <NUM><NUM> T-<NUM>s-<NUM>) denotes a gyromagnetic ratio, Bk denotes a magnetic anisotropy field of the ferromagnetic material. In a common ferromagnetic material, a magnetic anisotropy field magnetic field has a magnitude of about 1T. Accordingly, a frequency of the nano-oscillating device using a ferromagnetic material is limited to several tens of gigahertz (GHz).

In a spin valve structure in which a nonmagnetic material is inserted between two ferromagnetic materials (a first magnetic material/a nonmagnetic material/a second magnetic material) or a magnetic tunnel junction structure in which an insulating material is inserted between two ferromagnetic materials (a first magnetic material/an insulating material/a second magnetic material), when current is applied in a vertical (thickness) direction, current spin-polarized by the first magnetic material (a pinned magnetic layer) transfers its own spin-angular momentum while passing through the second magnetic material (a free magnetic layer). A torque felt by magnetization due to the transfer of the spin angular momentum is called a spin-transfer torque. Reversal of magnetization of the free magnetic layer or a magnetization precession, continuously rotating the magnetization, may be performed using a spin-transfer torque. However, a magnetic nano-oscillating device using a ferromagnetic material has a low operating frequency, which is a limitation.

An antiferromagnetic material refers to a material having an antiferromagnetic exchange interaction in which adjacent magnetic moments try to maintain opposite directions in atomic units. Also, an antiferromagnetic material refers to a material in which adjacent magnetic moments have the same size.

A ferrimagnetic material refers to a material in which adjacent magnetic moments have different sizes or directions to each other. Since some ferrimagnetic materials have antiferromagnetic exchange interactions between two adjacent magnetic moments, directions of the adjacent magnetic moments are opposite or substantially opposite each other, similarly to the antiferromagnetic material. In the present disclosure, the ferrimagnetic material refers to a ferrimagnetic material having antiferromagnetic characteristics.

When magnetic moments are coupled in an antiferromagnetic state in atomic units, a resonant frequency is given by Equation <NUM>.

In Equation <NUM>, Bex denotes an antiferromagnetic exchange field of an antiferromagnetic (ferrimagnetic) material. A magnetic anisotropy field is about 1T, while the antiferromagnetic exchange magnetic field is about 100T to about 1000T. Therefore, a frequency of the nano-oscillating device using an antiferromagnetic (ferrimagnetic) material has several a range of several terahertz (THz).

Currently, in a current electromagnetic spectrum, oscillation is performed in a range, in which a frequency is tens of GHz or less, using an electronic element. The oscillation is performed in a range, in which a frequency is several tens of THz or more, using an optical element. However, an appropriate element for generating, detecting, and regulating signals has not been found in the range from <NUM> THz to <NUM> THz. A signal in the range of <NUM> THz to <NUM> THz is harmless to a human body and has high material selectivity because characteristics such as transmittance of a THz signal are different depending on a material, and corresponds to resonant frequencies of various molecules. Therefore, the signal in the range of <NUM> THz to <NUM> THz may be used in molecular spectrum analysis. Thus, a magnetic oscillation element, including an antiferromagnetic layer (or a ferrimagnetic layer) corresponding to a resonant frequency in the range of <NUM> THz to <NUM> THz, needs to achieve low current density and improve frequency tunability.

A nano-oscillating device according to an example embodiment includes a ferromagnetic layer/a nonmagnetic conductive layer/ an antiferromagnetic layer (or a ferrimagnetic layer, which are sequentially stacked. A magnetization precession of a sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer) is induced by current flowing through the ferromagnetic layer and the nonmagnetic conductive layer in the in-plane direction. The magnetization direction of the sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer) is perpendicular to an in-plane parallel direction or the in-plane direction. Spin current, generated in an interface between the ferromagnetic layer and the nonmagnetic conductive layer induces a magnetization precession of the sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer).

A nano-oscillating device according to an example embodiment includes a first ferromagnetic layer/a first nonmagnetic conductive layer/a second ferromagnetic layer/a second nonmagnetic conductive layer/a third ferromagnetic layer, which are sequentially stacked. The second ferromagnetic layer and the third ferromagnetic layer have a structure in which magnetization directions of the second ferromagnetic layer and the third ferromagnetic layer are antiparallel to each other through an antiferromagnetic exchange interaction caused by the second nonmagnetic conductive layer interposed therebetween. The magnetization precession of the second ferromagnetic layer and the third ferromagnetic layer having the antiferromagnetic exchange interaction is induced by spin current generated in an interface between the first ferromagnetic layer and the first nonmagnetic conductive layer.

Hereinafter, the present disclosure will be described in more detail based on preferred embodiments. However, these embodiments are for better understanding of the present disclosure, and it is obvious to those skilled in the art that the scope of the present disclosure is not limited thereto. In addition, in the case in which detailed description of known functions or configurations in relation to the present disclosure is judged as unnecessarily making the essence of the present disclosure vague, the detailed description will be excluded.

<FIG> is a conceptual diagram of a magnetic nano-oscillating device according to an example embodiment of the present disclosure.

<FIG> is a perspective view illustrating oscillation of the magnetic nano-oscillating device in <FIG>.

Referring to <FIG> and <FIG>, a magnetic nano-oscillating device <NUM> includes a ferromagnetic layer <NUM>, a nonmagnetic conductive layer <NUM>, and an antiferromagnetic layer <NUM> sequentially stacked on a substrate <NUM>. First and second electrodes 240a and 240b, respectively being in contact with both side surfaces of the ferromagnetic layer <NUM> and the nonmagnetic layer <NUM>, provide in-plane current I. The in-plane current I provides spin current JS, including a spin σz polarized in a thickness direction, to the antiferromagnetic layer <NUM> due to interfacial spin orbital coupling between the ferromagnetic layer <NUM> and the nonmagnetic layer <NUM>. The ferromagnetic layer <NUM> has a fixed magnetization direction and is a thin film formed of a material magnetized in a direction parallel to a layer surface. The sub-lattice of the antiferromagnetic layer <NUM> has a fixed magnetization direction. The antiferromagnetic layer <NUM> is a thin film formed of a material magnetized in perpendicular or in-plane direction to a layer surface. The ferromagnetic layer <NUM> is magnetized on a layer surface of the ferromagnetic layer <NUM> in an in-plane direction. The in-plane current, injected into the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM> through the first and second electrodes 240a and 240b, provides the spin current <NUM>, including a spin of the thin film in a thickness direction transferred to the antiferromagnetic layer, to cause magnetization precession of the antiferromagnetic layer <NUM>.

The spin current JS is generated by an interfacial effect between the ferromagnetic material and the nonmagnetic material, and the spin current has both a y-direction spin and a z-direction spin.

An interfacial spin orbit torque, generated by the spin of the spin current Js, allows magnetization of the antiferromagnetic layer (or the ferrimagnetic layer) to move in precession.

The antiferromagnetic layer <NUM> may be replaced with a ferrimagnetic layer. A magnetization precession of the sub-lattice in the antiferromagnetic layer (or the ferrimagnetic layer) is induced by current flowing through the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM> in the in-plane direction. The magnetization direction of the ferromagnetic layer <NUM> is aligned in a +x direction. Current flows through the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM>, and spin current flows to the antiferromagnetic layer (or the ferrimagnetic layer) due to interfacial spin orbital coupling present on the interface.

When the current flows through the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM>, spin current JS having a y-direction spin σy and a z-direction spin σz and flowing in a thickness direction (the z direction) is generated by spin orbit coupling in a structure of the ferromagnetic layer <NUM>/the nonmagnetic conductive layer <NUM> having magnetization parallel to a layer surface. The spin current JS transfers the y-direction spin σy and the z-direction spin σz to the antiferromagnetic layer (or the ferrimagnetic layer) to cause precession of the magnetization of the antiferromagnetic layer (or the ferrimagnetic layer).

That is, the spin current JS flows in a direction perpendicular to the interface. In this case, the antiferromagnetic layer (or the ferrimagnetic layer) has the y-direction spin σy and the z-direction spin σz due to an interaction of a spin of electrons, passing through the interface, and a spin polarization accumulated in the interface. That is, in the spin currents JS flowing in a z-axis direction, the z-direction spin σz may reduce threshold current density, as compared with the case in which there is no z-direction spin.

In the present disclosure, a spin torque, generated by an interfacial effect between a ferromagnetic layer and a nonmagnetic conductive layer and having both a y-direction spin and a z-direction spin as described above, will be referred to as an interfacial spin orbit torque to be distinguished from an existing spin Hall toque generated by a y-direction spin σy.

Current density, required for the magnetization precession of the sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer), varies depending on sizes of the y-direction spin σy and the z-direction spin σz transferred to the antiferromagnetic layer (or the ferrimagnetic layer) and frequency tunability also varies.

The substrate <NUM> may be a semiconductor substrate. The substrate <NUM> may be a silicon substrate.

The ferromagnetic layer <NUM> is patterned on the substrate <NUM> in a line shape and may be formed of one selected from Fe, Co, Ni, B, Si, Zr, and mixtures thereof.

The nonmagnetic conductive layer <NUM> may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, and mixtures thereof. The ferromagnetic layer and the nonmagnetic conductive layer may be vertically aligned with each other.

The antiferromagnetic layer <NUM> may be locally disposed on the nonmagnetic conductive layer <NUM>. Alternatively, the antiferromagnetic layer <NUM> may be transformed to be vertically aligned with the nonmagnetic conductive layer <NUM>. The antiferromagnetic layer <NUM> may be formed of one selected from Ir, Pt, Mn, Cr, FeMn, NiO, Fe<NUM>O<NUM>, and mixtures thereof. The sub-lattice of the antiferromagnetic layer <NUM> may be magnetized in a direction perpendicular to a surface.

The first electrode 240a and the second electrode 240b may be made of a material selected from Cu, Ta, Pt, W, Ti, Bi, Ir, and mixtures thereof. The first electrode 240a and the second electrode 240b may be respectively connected to both ends of the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM> to inject current. The current may flow along a conducting line including the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM>.

A magnetic tunnel junction <NUM> is disposed on the antiferromagnetic layer <NUM>. The magnetic tunnel junction <NUM> includes a free layer <NUM>/a tunnel insulating layer <NUM>/a pinned layer <NUM>, and the free layer <NUM> of the magnetic tunnel junction has an exchange interaction with the antiferromagnetic layer <NUM>. The magnetic tunnel junction <NUM> may output an oscillating signal due to tunneling resistance. The free layer <NUM> and the pinned layer <NUM> may be perpendicular magnetized on an arrangement plane.

The third electrode <NUM> may be disposed on the magnetic tunnel junction <NUM>. The third electrode <NUM> may be connected to a wiring for connecting an oscillating signal to another circuit. The third electrode <NUM> may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, Ir, and mixtures thereof.

An equation of motion of the sub-lattice magnetization of the antiferromagnetic (or the ferrimagnetic) is given by Equation <NUM>.

In Equation <NUM>, Mi denotes a magnetization vector of an i-th sub-lattice of an antiferromagnetic layer (or a ferrimagnetic layer), γ denotes a gyromagnetic ratio, Ms,i denotes a magnetization value of the i-th sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer), Heff,i denotes all effective magnetic field vectors of the i-th sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer), and α denotes a Gilbert damping constant. The sub-lattice may be a first sub-lattice or a second sub-lattice. Also, in Equation <NUM>, η denotes a ratio of spin current, transferring a y-direction spin σy, to applied current generated in an interface between the ferromagnetic layer and the nonmagnetic conducive layer, and δ denotes a ratio of spin current, transferring a z-direction spin σz, to applied current generated in an interface between the ferromagnetic layer and the nonmagnetic conducive layer. Also, in Equation <NUM>, h (= <NUM> × <NUM>-<NUM> Jsec) denotes a value obtained by a Planck constant by 2n, J denotes applied current density, and e (= <NUM> x <NUM>-<NUM> C) is the amount of charge of an electron, and t denotes a thickness of the antiferromagnetic layer (or the ferrimagnetic layer). An x direction is a direction in which the antiferromagnetic layer (or the ferrimagnetic layer) extends on the substrate, and a z direction is a thickness direction of the antiferromagnetic layer (or the ferrimagnetic layer).

When the z-direction spin σz is not transferred to the antiferromagnetic layer (or the ferrimagnetic layer) and only the y-direction spin σy is transferred thereto, threshold current density Jth is given by Equation <NUM>.

where h denotes a value obtained by diving a Planck constant by 2π, e denotes the amount of charge of an electron, t denotes a thickness of the antiferromagnetic (or the ferrimagnetic) layer, K denotes magnetic anisotropy energy density and a magnetic anisotropy constant of the antiferromagnetic layer (or the ferrimagnetic layer), and η denotes a ratio of the spin current, transferring the y-direction spin σy to the applied current.

An oscillation frequency of the antiferromagnetic layer (or the ferrimagnetic layer), induced by current density higher than threshold current density corresponding to Equation <NUM>, is described as Equation <NUM>. <MAT> where γ denotes a gyromagnetic ratio, J denotes current density, h denotes a value obtained by dividing a Planck constant by 2n, e denotes the amount of charge of an electron, t denotes a thickness of the antiferromagnetic layer (or the ferrimagnetic layer), Ms denotes a saturated magnetization value of the sub-lattice of the ferrimagnetic layer (or the ferrimagnetic layer), α denotes a Gilbert damping constant, and η denotes a ratio of spin current, transferring the y-direction spin σy, to the applied current.

When the z-direction spin σz is not transferred to the antiferromagnetic layer (or the ferrimagnetic layer) and only the y-direction spin σy is transferred thereto, normalized magnetization N rotates in an x-z plane. The ratio η of the spin current, transferring the y-direction spin σy, to the applied current is not zero and the ratio δ of the spin current, transferring the z-direction spin σz, to the applied current is zero.

The spin current JS has a z-direction spin (σz) component. When the y-direction spin σy is not transferred to the antiferromagnetic layer (or the ferrimagnetic layer) and only the z-direction spin σz is transferred thereto, the threshold current density is given by Equation <NUM>. <MAT> where h denotes a value obtained by dividing a Planck constant by 2π, e denotes the amount of charge of an electron, t denotes a thickness of the antiferromagnetic layer (or the ferrimagnetic layer), K denotes magnetic anisotropy energy density of the antiferromagnetic layer (or the ferrimagnetic layer), A denotes an antiferromagnetic exchange interaction constant, α denotes a Gilbert damping constant, d denotes a distance between sub-lattices of the antiferromagnetic layer (or the ferrimagnetic layer), and δ denotes a ratio of the spin current, transferring the z-direction spin σz, to the applied current.

An oscillation frequency of the antiferromagnetic layer (or the ferrimagnetic layer) for current density higher than threshold current density corresponding to Equation <NUM> is described as Equation <NUM>. <MAT> where γ denotes a gyromagnetic ratio, J denotes current density, h denotes a value obtained by dividing a Planck constant by 2π, e denotes the amount of charge in an electron, t denotes a thickness of the antiferromagnetic (or the ferrimagnetic) layer, Ms denotes the amount of saturated magnetization of a sub-lattice of the antiferromagnetic layer (or the ferrimagnetic layer), α denotes a Gilbert damping constant, and η denotes a ratio of the spin current, transferring the z-direction spin σz, to the applied current.

According to an example embodiment, both the y-direction spin σy and the z-direction spin σz are transferred to the antiferromagnetic layer (or the ferrimagnetic layer) by an interfacial spin orbital torque. In this case, the threshold current density is determined as lower threshold current density, among threshold current densities corresponding to Equation <NUM> and Equation <NUM>. In this case, a frequency which may oscillate is described as Equation <NUM>.

The ratio η of the spin current, transferring the y-direction spin σy, to applied current is not zero, and the ratio δ of the spin current, transferring the z-direction spin σz, to the applied current is not zero. When both the z-direction spin σz and the y-direction spin σy are transferred to the antiferromagnetic layer (or the ferrimagnetic layer), the normalized magnetization N is rotated to have an x-y plane component and an x-z plane component.

<FIG> is a simulation result showing a trajectory of normalized magnetization of an antiferromagnetic layer (or a ferrimagnetic layer) in a magnetic nano-oscillating device <NUM> according to an example embodiment of the present disclosure.

Referring to <FIG>, an effect of the magnetic nano-oscillating device was confirmed through macrospin micromagnetic simulation using an equation of motion of magnetization.

A structure and physical properties of the magnetic nano-oscillating device are as follows:.

The ratio η of the spin current, transferring the y-direction spin σy, to the applied current is <NUM>, and the ratio δ of the spin current, transferring the z-direction spin σz, to the applied current is <NUM>. In this case, normalized magnetization N includes an elliptical component projected in an x-y plane and an elliptical component projected in an x-z plane. Accordingly, when the normalized magnetization N is projected in a y-z plane, the normalized magnetization N is shown as a straight line having a constant slope.

<FIG> is a graph showing threshold current density depending on a ratio of spin current, transferring a z-direction spin σz, to applied current in the magnetic nano-oscillating device <NUM> in <FIG>.

<FIG> is a graph showing an oscillation frequency depending on current density in the magnetic nano-oscillating device <NUM> in <FIG>.

Referring to <FIG>, a ratio η of the spin current, transmitting the y-direction spin σy, to the applied current is <NUM>. The antiferromagnetic layer <NUM> has a sub-lattice magnetization in a direction perpendicular to an arrangement plane (a thickness direction). When an interfacial spin orbital torque is applied to the magnetic nano-oscillating device <NUM>, a ratio δ of the spin current, transferring the z-direction spin σz, and threshold current density Jth are shown.

When δ is zero, there is no z-direction spin σz and threshold current density Jth is <NUM> × <NUM><NUM> A/cm<NUM>. When δ is <NUM>, the threshold current density Jth is <NUM> X <NUM><NUM> A/cm<NUM>. As the ratio of the z-direction spin σz is increased, the threshold current density Jth is decreased. That is, when a ferromagnetic layer/a nonmagnetic conductive layer are designed to increase an interfacial spin orbital torque, the threshold current density Jth is decreased.

Referring to <FIG>, when the ratio η of the spin current, transferring the y-direction spin σy, to the applied current is fixed to <NUM> and the ratio δ of the spin current, transferring the z-direction spin σz, to the applied current is changed, applied current density J and an oscillation frequency are shown.

As δ is increased, a slope of a frequency to current density J is increased. Thus, a large frequency difference may be provided with a change in low current density J. When δ = <NUM>, an oscillation element may oscillate in the range of <NUM> THz to <NUM> THz depending on the current density.

<FIG> is a conceptual diagram of a magnetic nano-oscillating device according to another example embodiment of the present disclosure.

<FIG> is a graph showing threshold current density depending on a ratio δ of spin current, transferring a z-direction spin σz, to applied current in the magnetic nano-oscillating device in <FIG>.

<FIG> is a graph showing an oscillation frequency depending on current density.

Referring to <FIG>, a magnetic nano-oscillating device <NUM> includes a ferromagnetic layer <NUM> disposed on a substrate <NUM>, a nonmagnetic conductive layer <NUM> stacked on the ferromagnetic layer <NUM>, an antiferromagnetic layer <NUM> stacked on the nonmagnetic conductive layer <NUM>, and first and second electrodes 240a and 240b, respectively being in contact with both side surfaces of the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM>. The antiferromagnetic layer <NUM> is a thin film formed of a material magnetized in a direction horizontal to a layer surface, and the ferromagnetic layer <NUM> is horizontally magnetized on a layer surface of the ferromagnetic layer <NUM>. In-plane current, injected into the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM> through the first and second electrodes 240a and 240b, provides spin current, including a spin in a thickness direction of a thin film transferred to the antiferromagnetic layer <NUM>, to cause magnetization precession of a sub-lattice of the antiferromagnetic layer <NUM>. The antiferromagnetic layer <NUM> is magnetized in an in-plane direction.

The magnetic tunnel junction <NUM> is disposed on the antiferromagnetic layer <NUM>. The magnetic tunnel junction <NUM> includes a free layer <NUM>/a tunnel insulating layer <NUM>/a pinned layer <NUM>, and the free layer <NUM> of the magnetic tunnel junction has an exchange interaction with the antiferromagnetic layer <NUM>. The free layer <NUM> and the pinned layer <NUM> may be magnetized in an arrangement plane.

Referring to <FIG>, a ratio η of spin current, transferring a y-direction spin σy, to applied current is <NUM>. The antiferromagnetic layer <NUM> has sub-lattice magnetization in an arrangement plane. An easy magnetization axis of the antiferromagnetic layer <NUM> is a y axis. When an interfacial spin orbital torque was applied to the magnetic nano-oscillating device <NUM>, threshold current density Jth and an oscillation frequency f were simulated under the following conditions.

A structure and physical properties of magnetic nano-oscillating device <NUM> are as follows:.

When δ is zero, there is no z-direction spin σz and threshold current density Jth is <NUM> × <NUM><NUM> A/cm<NUM>. When δ is <NUM>, threshold current density Jth is <NUM> X <NUM><NUM> A/cm<NUM>. As the ratio of the z-direction spin σz is increased, the threshold current density Jth is decreased. That is, when a ferromagnetic layer/a nonmagnetic layer are designed to increase the interfacial spin trajectory torque, the threshold current density Jth is decreased.

Referring to <FIG>, when a ratio η of spin current, transferring a y-direction spin σy, to the applied current is fixed to <NUM> and a ratio δ of spin current, transferring a z-direction spin σz, to the applied current is changed, applied current density J and an oscillation frequency are shown.

As δ is increased, a slope of a frequency to the current density J is increased. Therefore, a large frequency difference may be provided with a change in low current density J.

<FIG> is a conceptual diagram of a magnetic nano-oscillating device 200a according to another example embodiment of the present disclosure.

<FIG> is a graph showing threshold current density depending on a ratio of spin current, transferring a z-direction spin, to applied current in the magnetic nano-oscillating device 200a in <FIG>.

<FIG> is a graph showing an oscillation frequency depending on current density in the magnetic nano-oscillating device 200a in <FIG>.

Referring to <FIG>, the magnetic nano-oscillating device 200a includes a ferromagnetic layer <NUM> disposed on a substrate <NUM>, a nonmagnetic conductive layer <NUM> stacked on the ferromagnetic layer <NUM>, a ferrimagnetic layer 230a stacked on the nonmagnetic conductive layer <NUM>; and first and second electrodes 240a and 240b, respectively being in contact with both side surfaces of the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM>. The ferrimagnetic layer 230a is a thin film formed of a material magnetized in a perpendicular or in-plane direction to a layer surface. The ferromagnetic layer <NUM> is in-plane magnetized on a layer surface of the ferromagnetic layer <NUM>. In-plane current, injected into the ferromagnetic layer <NUM> and the nonmagnetic conductive layer <NUM> through the first and second electrodes 240a and 240b, provides spin current, including a spin in a thickness direction of a thin film transferred to the ferrimagnetic layer <NUM>, to cause magnetization precession of a sub-lattice of the ferrimagnetic layer 230a.

A structure and physical properties of the nano-oscillating device 200a are as follows:.

The ferrimagnetic layer 230a may be formed of one selected from Co, Gd, Tb, Mn, Ir, Ge, Se, Cr, Y, Fe, garnet, a rare earth-transition metal (RE-TM) alloy, mixtures thereof.

When a ferromagnetic layer/a nonmagnetic conductive layer are designed to increase an interfacial spin orbital torque, threshold current density Jth is decreased.

When a ratio η of spin current, transferring a y-direction spin σy, to applied current is fixed to <NUM> and a ratio δ of spin current, transferring a z-direction spin σz, to the applied current is changed, applied current density J and an oscillation frequency are shown.

As δ is increased, a slope of a frequency to the current density J is increased. Therefore, a large frequency difference may be provided with a change in low current density J. When δ = <NUM>, an oscillation element may oscillate in the range of <NUM> THz to <NUM> THz depending on the current density.

Referring to <FIG>, a magnetic nano-oscillating device <NUM> includes a first ferromagnetic layer <NUM> disposed on a substrate <NUM>, a first nonmagnetic conductive layer <NUM> disposed on the first ferromagnetic layer <NUM>, a second ferromagnetic layer <NUM> disposed on the first nonmagnetic conductive layer <NUM>, a second nonmagnetic conductive layer <NUM> disposed on the second ferromagnetic layer <NUM>, a third ferromagnetic layer <NUM> disposed on the second nonmagnetic conductive layer <NUM>, and first and second electrodes 240a and 240b, respectively being in contact with both side surfaces of the first ferromagnetic layer <NUM> and the first nonmagnetic conductive layer <NUM>. The first ferromagnetic layer <NUM> is a thin film formed of a material having a fixed magnetization direction and magnetized in a direction parallel to a layer surface. The second ferromagnetic layer <NUM> and the third ferromagnetic layer <NUM> are thin films, each having an antiferromagnetic exchange interaction due to the second nonmagnetic conductive layer <NUM>. The second ferromagnetic layer <NUM> and the third ferromagnetic layer <NUM> are magnetized to be parallel or perpendicular to the layer surface. In-plane current, injected into the first ferromagnetic layer <NUM> and the first nonmagnetic conductive layer <NUM> through the first and second electrodes 240a and 240b, provides spin current including a spin in a thickness direction of a thin film transferred to the second ferromagnetic layer <NUM> and the third ferromagnetic layer <NUM> to cause magnetization precession of each of the second ferromagnetic layer <NUM> and the third ferromagnetic layer <NUM>.

The first ferromagnetic layer <NUM> and the first nonmagnetic conductive layer <NUM> may be vertically aligned.

In addition, the second ferromagnetic layer <NUM>, the second nonmagnetic conductive layer <NUM>, and the third ferromagnetic layer <NUM> may be vertically aligned and coupled by an antiferromagnetic exchange interaction. The second ferromagnetic layer <NUM> and the third ferromagnetic layer <NUM> may always move in precession while maintaining antiparallel coupling.

A magnetic tunnel junction <NUM> is disposed on the third antiferromagnetic layer <NUM>. The magnetic tunnel junction <NUM> may include a tunnel insulating layer <NUM>/a pinned layer <NUM>, and the pinned layer <NUM> of the magnetic tunnel junction may interact with the third ferromagnetic layer <NUM> to generate a tunnel magnet resistance signal. The fixed layer <NUM> may be magnetized to be parallel or vertical in a plane.

Each of the first ferromagnetic layer <NUM>, the second ferromagnetic layer <NUM>, and the third ferromagnetic layer <NUM> may be formed of one selected from Fe, Co, Ni, B, Si, Zr, and mixtures thereof. The first nonmagnetic conductive layer <NUM> may be formed of one selected from Cu, Ta, Pt, W, Ti, Bi, and mixtures thereof. The second nonmagnetic conductive layer <NUM> may be formed of one selected from Ru, Ta, Rh, Ir, Cr, Re, Mo, W, V, and mixtures thereof.

Claim 1:
A magnetic nano-oscillating device (<NUM>, <NUM>) comprising:
a ferromagnetic layer (<NUM>) disposed on a substrate (<NUM>);
a nonmagnetic conductive layer (<NUM>) stacked on the ferromagnetic layer;
an antiferromagnetic layer (<NUM>, <NUM>) stacked on the nonmagnetic conductive layer; and
first and second electrodes (240a, 240b), respectively being in contact with both side surfaces of the ferromagnetic layer and the nonmagnetic conductive layer,
wherein the antiferromagnetic layer is a thin film formed of a material magnetized in a perpendicular or in-plane direction to a layer surface,
the ferromagnetic layer is in-plane magnetized on a layer surface of the ferromagnetic layer, and
in-plane current, injected into the ferromagnetic layer and the nonmagnetic conductive layer through the first and second electrodes, provides spin current, including a spin in a thickness direction of a thin film transferred to the antiferromagnetic layer, to cause magnetization precession of a sub-lattice of the antiferromagnetic layer.