JPH10208208A - Micro magnetic device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To form an atomic cluster or atomic wire array on a non-magnetic solid surface by microfabrication technology such as STM and lithography, and to artificially apply ferromagnetism to this minute surface structure. Provided is a micromagnetic device developed. SOLUTION: ST is formed on a surface of a nonmagnetic crystal substrate 32.
Utilizing microfabrication technology such as M, atomic clusters or atomic wires composed of the nonmagnetic atoms 31 are arranged and arranged such that a sharp peak of the electronic state density exists near the Fermi level. By applying a voltage to the gate electrode 33 formed on a part of the substrate, the magnitude of the magnetization of the atom cluster or the atom wire is controlled. The magnetic disk drive can be used as a magnetic recording head capable of performing ultra-high-density magnetic recording of 10 giga bits / square inch to 1 peta bit / square inch or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro magnetic device having a size as small as an atomic size on a solid surface by using STM (scanning tunneling microscope) and its peripheral microfabrication and integration technologies. Are used as magnetic recording heads constituting a magnetic disk drive.

[0002]

2. Description of the Related Art In recent years, miniaturization and high recording density of magnetic disk drives have been rapidly progressing, and a magnetic recording head of a minute size has been required in response to the high recording density.
Currently, magnetic heads widely used are of the electromagnetic induction type, and are mainly electromagnets formed by winding a conductor coil such as Cu around a Mn-Zn ferrite core.

Here, as a recording method, a method of writing data on a magnetic recording medium by an induced magnetic field generated when a recording current is applied to a conductor coil is employed.

[0004] However, as the magnetic recording density increases, it is expected that a minute size magnetic cluster composed of several to several hundred atoms will serve as a recording unit as a future image of the magnetic recording medium. However, the minimum limit of the writing size of the conventional electromagnetic induction type magnetic head is about 0.1 μm, and it is difficult to process and manufacture a minute conductor coil having a space size smaller than this. Therefore, it is very difficult for an electromagnetic induction type magnetic head to record magnetic information on individual minute-sized magnetic clusters, which are recording units of a future high-density magnetic recording medium.

On the other hand, as a non-magnetic recording method realizing an atomic size level, for example, Nature, Vol. 344 (1990), pp. 524 to 526 (Nature, Vol. 344 (19)
90), pp. 524-526), using STM,
Artificially arranged more than one Xe atom on Ni solid surface,
2. Description of the Related Art A technique for writing a character or a graphic with one atom as a constituent element has been developed.

Further, according to recent advances in microfabrication technology using STM, for example, Japanese Journal
Applied Physics Letters, Vol. 35 (1996), pp. 1085 to 1088 (Jpn. J. Appl. Phys. Vol. 35
(1996) pp. L 1085-L 1088).
By arranging Ga atoms in a one-dimensional direction on the surface of the i-substrate, it is possible to fabricate structurally stable Ga atom wires with high conductivity.

However, in these ultrafine surface structures, the ferromagnetic function, that is, spontaneous magnetization is extracted, and switching between ferromagnetic (state where spontaneous magnetization is non-zero) / paramagnetism (state where spontaneous magnetization is zero) is artificially performed. At present, an atomic-size magnetic device which can be used as a magnetic recording head has not been realized until now. In particular, there is no technology that actively applies atomic manipulation technology to part or all of the magnetic recording system.

As a model for describing a bulk ferromagnetic material such as Fe, Co, and Ni having non-zero spontaneous magnetization, a Stoner model is often used. Condensed Matter Science Dictionary (The Institute of Condensed Matter, The University of Tokyo, Tokyo Book, 1996)
As described on pages 198-200 of
Conditions for ferromagnetic expression in this model (Stoner condition)
Is expressed as U × D (Ef)> 1 using the electron correlation energy or energy U, which represents the Coulomb repulsion between electrons, and the electron density of states D (Ef) at the Fermi level. Therefore, for a material to be ferromagnetic, it must have a very large density of states D (Ef) on the Fermi surface.

However, even when a ferromagnetic material such as Fe, Co, and Ni that satisfies the above Stoner condition is used to form an atomic cluster system or an atomic wire system having a small size, a small space size similar to the atomic size is obtained. In the system, the density of states D (Ef) is extremely reduced due to the finite size effect, so that the Stoner condition is not satisfied, and the spontaneous magnetization of the system may disappear. Therefore, it can be said that it is not always appropriate to use a substance group that becomes a ferromagnetic material in bulk in order to obtain ferromagnetism in an atomic size. Conversely, even for a substance group that does not show ferromagnetism in bulk, the Stoner condition U
If the atoms are arranged and configured so as to satisfy × D (Ef)> 1, it can be expected that ferromagnetism can be expressed at the atomic level.

For example, despite the fact that graphite is bulk and has no spontaneous magnetization, Journal of Physical Society of Japan, Vol. 65 (1996)
As described in pages 1920 to 1923, it was theoretically predicted that spontaneous magnetization appears on the atomic scale at the end of the ribbon-shaped graphite. However, this carbon atom structure has not yet been actually synthesized.

[0011]

As described above, the STM
It is possible to control and arrange atoms on the surface of a solid substrate to a certain degree by microfabrication technology, etc. By using this atom manipulation technology, a substrate / surface atom combination consisting of non-magnetic atoms can be used. In, it is expected that surface atoms can be arranged and configured to have a large electronic state density near the Fermi level. Furthermore, it can be expected to artificially and forcibly extract the function as an atomic-level ferromagnetic material. The Fermi level can change the level of the Fermi level Ef by applying a gate voltage Vg by adding a gate electrode structure similar to that of a normal field-effect transistor. Therefore, Vg
, The Stoner condition U × D (Ef)> 1
To obtain ferromagnetism (non-zero magnetization),
Or, conversely, it is possible to artificially control the change that makes the system paramagnetic (the state of zero magnetization) by forcibly breaking the Stoner condition.

That is, it is expected that the magnitude of magnetization can be artificially controlled only by the electric field effect in an invariant atomic structure.

An object of the present invention is to arrange an atomic cluster or atomic wire composed of non-magnetic atoms on a non-magnetic solid surface by using a fine processing technique such as STM or lithography, and to construct this extremely fine surface structure. An object of the present invention is to provide a micromagnetic device that artificially expresses ferromagnetism.

In the present invention, the non-magnetic atoms used in the arrangement include Cr, which shows ferromagnetism as a single substance in the periodic table of elements.
Mn, Fe, Co, Ni, and Ce in the lanthanoid series,
Defined as elements that exclude Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and He, Ne, Ar, Kr, Xe, and Rh, which are inert elements. .

[0015]

Here, a magnetic field of a micro magnetic head consisting of atomic clusters and atomic wires on a solid surface is applied to a solid surface, in contrast to a recording method using current application of an electromagnetic induction type magnetic head. The system is controlled by the applied voltage.

First, an STM is placed on a nonmagnetic crystal substrate surface.
Atomic clusters or atomic wires composed of non-magnetic atoms are produced using microfabrication techniques such as those described above. In this case, as the electronic state of the surface structure, atoms are arranged so that an energy band in which a part or the whole is almost flat appears near the Fermi level. At this time, when the electronic density of states (DOS) is viewed as a function of the electron energy (E), a feature is that a sharp peak exists near the Fermi level. Next, a gate electrode portion is provided in another portion of the substrate.

In such a structure, an electric field is applied to the surface structure including the atomic clusters or the atomic wires by applying a voltage to the gate electrode portion. The magnetization is controlled by raising and lowering the Fermi level using the electric field effect of the gate electrode. Here, as shown in FIG.
When the Fermi level just crosses the flat band (sharp peak of DOS), ferromagnetic (magnetization) appears in the surface structure, and the Fermi level becomes flat band (sharp peak of DOS).
If it is deviated, the ferromagnetism (magnetization) is lost and the state becomes paramagnetic. Thus, it is possible to control the onset of ferromagnetism (magnetization) by the electric field effect.

Here, the main feature is that the atoms to be arranged on the substrate are non-magnetic atoms. However, even if atoms other than non-magnetic atoms are contained as impurities, as long as the Stoner condition for ferromagnetic expression is not violated. In addition, spontaneous magnetization can occur.

The operation as a magnetic recording head is based on writing bit information (magnetization direction) in a recording unit of a magnetic recording medium by artificially developing or erasing the surface structure by changing the gate voltage.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) FIG. 2 shows an atomic arrangement structure of a micromagnetic device according to the present invention. In this example, a non-magnetic Si substrate is used, as shown in FIG.
All unbonded bonds of atom 21 are terminated by hydrogen atoms 22. Thereby, a chemically inert and stable surface structure is obtained. The substrate may be a Ge semiconductor crystal other than Si. Next, Japanese Journal Applied Physics Letters Vol. 35 (1996)
85 to 1088 (Jpn. J. Appl. Phys. Vol. 35 (1996)
pp. L 1085-L 1088).
Approach the hydrogen-terminated Si substrate surface and apply an appropriate voltage pulse to the
One line is extracted, and a one-dimensional thin line-shaped hydrogen-unbonded
I made a row of Si bonds. This non-hydrogen bonded Si bond train is chemically active compared to other hydrogen bonded Si surface structures. Thus, in the present embodiment, Ga atoms 23, which are trivalent metal atoms, are adsorbed to the above-mentioned hydrogen-unbonded Si bond array using a thermal evaporation source. The adatom is
It may be another trivalent metal atom B, Al, In, Tl, a non-trivalent atom, or a combination of these plural types of atoms.

In this embodiment, the number of Ga atoms 23 adsorbed on the substrate surface is set to 1.5 times the number of unbonded bonds. FIG. 2B shows an example of a surface structure on an atomic scale obtained by the above-described atomic operation and vapor deposition operation. In this embodiment, as shown in FIG. 2C, the basic unit is two Si atoms 2
One atomic group composed of one and three Ga atoms 23. Any Ga atomic wire composed of this basic unit is the object of this embodiment.

A scanning tunneling spectroscopy (ST) is performed on the Ga atomic wire using an STM probe.
When S) was performed and the electronic state density was examined as a function of the electron energy, it was found that there was a sharp peak structure near the Fermi energy as shown in FIG.

FIG. 3 shows an example of a micro magnetic device according to the present invention. As shown in the figure, an Au thin film was evaporated on the back surface of a Si (100) substrate 32 on which a thin wire of Ga atoms 31 was evaporated, and this Au thin film was used as a back gate electrode 33.

FIG. 4 shows another example of the micromagnetic device according to the present invention. In this example, the gate electrode 43 is formed not on the back surface of the substrate 42 but on the surface of the substrate in the vicinity of the fine lines of the Ga atoms 41. FIG. 5 shows that when a voltage Vg is applied to the gate electrode in a range of -10 volts to +10 volts, G
(a) An example in which the state of change of the magnetization value M of an atomic wire is measured by a scanning magnetic force microscope (MFM). As is clear from FIG. 5, the presence or absence of magnetization of the Ga atomic wire can be controlled by appropriately selecting the gate voltage Vg. At this time, the direction of the spontaneous magnetization (spin) was found to be in the direction along the Ga atomic wire, and it was found that the magnet could operate as a micro magnet of the atomic size level.

By using the above-described magnetization control method based on the gate voltage effect, a minute magnetic recording spot of about several hundred angstroms could be written on the surface of the magnetic recording medium by the same operation as a normal bulk magnetic recording head. . This fact was confirmed by scanning the surface of the magnetic recording medium after the writing operation with a scanning magnetic force microscope (MFM) or a spin-scanning electron microscope.

(Embodiment 2) FIG. 6 shows an atomic arrangement structure of a micro magnetic device according to the present invention. In the present embodiment, as shown in FIG.
The (111) surface is used to construct a ferromagnetic device without forming unbonded bond rows as described in Example 1. First, the surface of the hydrogen-terminated Si atoms 61 is maintained at a temperature of 80 K, and after supplying Ga atoms 62 thereto, individual Ga atoms are moved using an STM probe to form Ga atom clusters. The basic units in this embodiment are, as shown in FIG. 6B, two Si atoms as substrate atoms and one Ga atom as an adsorbed atom. Using these as basic units, an atomic cluster constituted by a combination of arbitrary basic units is an object of this embodiment.

For this Ga atom cluster, STM
Scanning tunneling spectroscopy (STS) was performed on a Ga atom cluster using the probe shown in FIG. 1, and the electronic state density of the cluster was examined as a function of the electron energy. As shown in FIG. It was found that there was a sharp peak structure. Further, for this atomic cluster structure, a back gate electrode similar to that shown in FIG. 3 or a side gate electrode similar to that shown in FIG. 4 is formed. The spontaneous magnetization can be controlled. In this case, the direction of spontaneous magnetization (spin) was perpendicular to the Si surface.

As described above, in order to obtain spontaneous magnetization, the adsorbed atoms on the solid surface do not necessarily need to have a one-dimensional atomic wire structure, and may have an atom cluster shape. Rather, it is important to arrange the adatoms so that the electron state density has a sharp peak structure near the Fermi energy, which facilitates field-effect-type magnetization control. .

Furthermore, in order to obtain a peak structure having a sharp electronic state density, atoms are formed so that an energy band in which a part or the whole is flat appears near the Fermi level as an electronic state of the surface structure. It is important to arrange them in an array.

Also, in the case of this embodiment, the combination of the substrate and the adsorbed atoms is not limited to Si and Ga.

[0031]

By using the magnetic device of the present invention having a structure as small as an atomic size, in an appropriate magnetic recording medium, an extremely small area in which the spatial size of a recording unit is in the range of 2 to 500 angstroms. , Magnetic writing and recording are possible.

As a result, it is possible to perform ultra-high density magnetic recording of 10 giga bits / square inch to 1 peta bit / square inch or more. Further, this magnetic device can be used as a magnetic recording head constituting a normal magnetic disk drive.

[Brief description of the drawings]

FIG. 1 is a diagram showing electronic density of states (DOS) as a function of electron energy (E).

FIG. 2 (a) is a micromagnetic device according to the present invention, Si (100)
FIG. 1B is a diagram showing the arrangement structure of atoms on the surface, FIG. 2B is a cross-sectional view of the atomic arrangement structure near the surface, and FIG.

FIG. 3 is a diagram showing an embodiment of a micromagnetic device having a back gate electrode.

FIG. 4 is a diagram showing an embodiment of a micromagnetic device having a side gate electrode.

FIG. 5 is a diagram showing a relationship between the magnetization M (per two Ga atoms) of a Ga atom wire and a gate voltage Vg.

FIG. 6 (a) is a micromagnetic device according to the present invention, Si (111)
FIG. 2 is a diagram showing an arrangement structure of atoms on a surface, and FIG.

[Explanation of symbols]

Ef: Fermi energy, DOS: Electronic density of states, 2
1: silicon (Si) atom, 22: hydrogen (H) atom, 23:
Garyum (Ga) atom, 31: Garyum (Ga) atom, 3
2: silicon (Si) crystal substrate, 33: back gate electrode,
41: gallium (Ga) atom, 42: silicon (Si) crystal substrate, 43: side gate electrode 61: silicon (Si) atom, 62: gallium (Ga) atom.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshimasa Ono 2520 Akanuma-cho, Hatoyama-cho, Hiki-gun, Saitama Prefecture Inside Hitachi, Ltd. Hitachi Basic Research Laboratory (72) Inventor Yasuo Wada 2520 Akanuma, Hatoyama-cho, Hiki-gun, Saitama Prefecture Hitachi Research Laboratory, Ltd.

Claims (8)

[Claims] 1. A micromagnetic device having a surface structure in which nonmagnetic atoms are arranged in atomic size and adsorbed on the surface of a nonmagnetic substrate, and one or more gate electrodes are separately provided on the substrate portion. A micromagnetic device having a function of changing the electron spin state of the surface structure between a paramagnetic state and a ferromagnetic state by applying a voltage to a gate electrode portion. 2. The microstructure according to claim 1, wherein said surface structure is constituted by arranging atoms so as to have a basic unit of an atomic arrangement in which a peak of an electronic state density appears near a Fermi level. Magnetic device. 3. The method according to claim 1, wherein said two atoms of the same kind constituting said substrate and atoms of the same kind or different kinds of adsorbed atoms or atomic groups are arranged and bonded so as to constitute one basic unit. The micromagnetic device according to claim 1. 4. The micromagnetic device according to claim 1, wherein the basic units are two identical atoms constituting a substrate and one atom or an atomic group constituting an adsorbed atom group. 5. A structure in which an electron energy band involving an adsorbed non-magnetic atom is partially or entirely flat, wherein atoms are arranged so as to appear near the Fermi level. The micromagnetic device according to claim 1. 6. A semiconductor crystal containing Si or Ge or a semiconductor crystal containing GaAs is used for the non-magnetic substrate, and the non-magnetic atoms adsorbed on the surface have an ionic value of B, Al, Ga, In, and Tl of 3. The micromagnetic device according to any one of claims 1 to 4, wherein one or a combination of a plurality of the metal atoms is used. 7. A first atom, a second atom of the same kind as the first atom, and a third atom or group of atoms of the same kind or different from the first atom and the third atom or atom of the first atom. A chemical bond is formed between the first atom and the second atom, and between the first atom and the second atom. Alternatively, a micromagnetic device in which one or a plurality of structures exhibiting ferromagnetism are formed by forming a structure arranged on a substrate surface as a basic unit such that an electron transfer path that does not pass through an atomic group is formed. 8. A micro magnetic device according to claim 1, wherein bit recording is written on a magnetic recording medium by utilizing a switching function between paramagnetic / ferromagnetic by a gate voltage in the micro magnetic device. Magnetic recording head.