JP2003142315A - Organic magnetic film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic magnetic film that becomes a magnetic recording medium, capable of realizing a magnetic recording system which does not use changes in the direction of magnetization, a very small recording unit, and the multi-valued recording. SOLUTION: Magnetic recording is performed by not utilizing direction of magnetization, utilizing the presence/absence of magnetism. The presence/ absence of magnetism is realized by generating ion radicals by electrochemically oxidizing π-conjugated organic molecules and converting the radical into closed shell radicals through reduction. The π-conjugated organic molecules are arranged on the surface of a substrate by introducing a long-chain alkyl group. The multi-valued recording is performed, by dividing an oxidation-reduction reaction into multiple stages by connecting a plurality of π-conjugated sections, having oxidizing and reducing ability to each other by means of a ferromagnetic coupler. This organic magnetic film is composed of the π-conjugated organic molecules, coupled with at least one alkyl group and formed on a highly oriented substrate in a self-assembling state, so that the π-conjugated organic molecules may be electrochemically oxidized, independently from other π-conjugated organic molecules.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a two-dimensional self-assembled body in which a π-conjugated organic molecule which can be easily electrochemically oxidized is formed on a highly oriented substrate such as a graphite substrate and is oxidized by More specifically, the present invention relates to an organic magnetic film in which π electron portions having a doublet or triplet electronic state are separated and aligned, and more specifically, “writing” of information at a molecular level by a scanning tunneling microscope or the like. The present invention relates to an organic magnetic film that can be used in a magnetic recording medium based on the operating principle of "reading" by a magnetic force microscope. The substrate coated with this organic magnetic film can be used as a magnetic recording medium.

[0002]

2. Description of the Related Art Currently used magnetic recording disks (hard disks) are prepared by applying a coating material containing inorganic magnetic particles onto a glass or metal disk, and have a size of several tens of bits / square μm. Has recording density. When reading and writing information, a coil is used to locally apply and detect a magnetic field (a magnetoresistive element formed of a multilayer thin film of magnetic metal is also used for detection). In this recording, recording and reading are performed by changing the magnetization direction of the magnetic particles, but there is a lower limit to the size of the magnetic particles that can hold the recorded magnetization direction in a stable manner. Levels are already approaching their limits.

On the other hand, as a limit for realizing a high recording density, stable atoms such as a rare gas are carried on a clean surface by atomic operation using a scanning probe microscope and arranged at an arbitrary position. ing. However, a large amount of information cannot be processed at high speed because each atom is carried. Although a plurality of research examples are known as a π-conjugated system molecule that produces an ion radical by electrochemical oxidation as in the present invention and exhibits a ground triplet state by two-electron oxidation (MM Wienk, RAJ Janssen, Stabl
e Triplet-State Di (Cation Radicals) of a Meta-Para
Aniline Oligomer by "Acid Doping", J. Am. Chem. S
oc., 118, 10626-10628 (1996): MM Wienk, RA
J. Janssen, High-SpinCation Radicals of Meta-Para
Oligomers, J. Am. Chem. Soc., 119, 4492-4501 (199
7)), there is no example of introducing a long-chain alkyl group to perform the arrangement on the substrate.

[0004]

DISCLOSURE OF THE INVENTION The present invention realizes a magnetic recording system which does not use a change in the direction of magnetization, realizes a minute recording unit, and becomes an organic magnetic recording medium which realizes multi-valued recording. The purpose is to provide a magnetic film.

[0005]

The organic magnetic film of the present invention comprises:
The feature is that magnetic recording can be performed by utilizing the presence or absence of magnetism, not the direction of magnetization. The presence or absence of magnetism is π
It is realized by generating an ion radical by electrochemical oxidation of a conjugated organic molecule and converting it to a neutral closed shell species by reduction. Arrangement of π-conjugated organic molecules, which are the recording units, for oxidation / reduction on the surface of the substrate is realized by introducing long-chain alkyl groups to cause interaction with the substrate and intermolecular interaction. To do. Also,
The multi-valued recording is performed by connecting a plurality of π-conjugated parts having a redox ability to multi-step the redox reaction. In particular, cross-conjugated π such as metaphenylene
When the two-electron oxidant shows an electronic structure of a ground triplet species by introducing a conjugated system as a connecting portion, the magnetism shown at each stage of oxidation is singlet, doublet, triplet. And, three-step recording is realized.

That is, the present invention is an organic magnetic film comprising a π-conjugated organic molecule having at least one alkyl group bonded, wherein one π-conjugated organic molecule is independent of the other π-conjugated organic molecule. It is an organic magnetic film self-assembled on a highly oriented substrate so that it is electrochemically oxidized. The present invention is also a magnetic recording medium comprising a substrate coated with this organic magnetic film.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION
When a long-chain alkyl group is introduced into a conjugated organic molecule, a π-conjugated system as a spin active site and a long-chain alkyl group as a spacer are arranged in stripes on a graphite substrate at regular intervals. , A two-dimensional self-assembly is formed. A two-dimensional clean surface on a single crystal can be used as the highly oriented substrate. For example, it is preferable to use highly oriented pyrolytic graphite (HOPG).

The organic magnetic film of the present invention is an organic magnetic film comprising a π-conjugated organic molecule having at least one alkyl group bonded, wherein one π-conjugated organic molecule is different from another π-conjugated organic molecule. It is an organic magnetic film self-assembled on a highly oriented substrate so as to be independently electrochemically oxidized, and the π-conjugated organic molecule is converted into a doublet or triplet electronic state by electrochemical oxidation. It is an organic magnetic film capable of exhibiting a magnetic response by being converted into an ion radical type magnetic chemical species. This π-conjugated organic molecule is composed of two parts, 1) a π-conjugated part having redox properties and 2) a long-chain alkyl group part, for each function. This 1) introduction of a π-conjugated part having a redox property allows the non-oxidized species and 1
Since the electronically oxidized species are detected as the difference between the spin state of the singlet and the spin state of the doublet, the recording of one pit can be realized. By introducing 2) a long-chain alkyl group moiety into this molecule, it becomes possible to align the molecule on the substrate. The number of long-chain alkyl groups may be one or more with respect to one molecule, and when two or more are included, it is preferable to arrange them on opposite sides of the molecule. What is a long-chain alkyl group?
It has 8 to 20 carbon atoms and is preferably linear.

As the π-conjugated organic molecule, an electron-donating π-conjugated molecule such as paraphenylenediamine, pyrrole, thiophene and tetrathiafulvalene can be used. As the π-conjugated system that can be electrochemically oxidized, for example, a para-phenylenediamine skeleton is targeted. A derivative having a long-chain alkyl group introduced is used to control the molecular arrangement on the graphite substrate.

That is, the π-conjugated organic molecule to which at least one alkyl group is bonded, which is used in the organic magnetic film of the present invention, is one of the following molecules:

[Chemical 1]

[Chemical 2]

[Chemical 3]

[Chemical 4] (In the formula, at least one of R ^{1 to} R ⁴ has 8 to 2 carbon atoms.
0 straight-chain alkyl group, more preferably any one of R ^{1 to} R ⁴ is a straight-chain alkyl group having 8 to 20 carbon atoms or R ^1.
Alternatively, R ² and R ³ or R ⁴ have 8 to 20 carbon atoms.
At least one of R ⁵ or R ⁶ is a linear alkyl group having 8 to 20 carbon atoms, R ⁷ is a hydrogen atom, a methyl group or an ethyl group, and at least one of R ⁸ or R ⁹ has a carbon number. Is a linear alkyl group having 8 to 20, at least one of R ^{10 to} R ¹³ is a linear alkyl group having 8 to 20 carbon atoms,
More preferably, any one of R ^{10 to} R ¹³ is a linear alkyl group having 8 to 20 carbon atoms, or R ¹⁰ or R ¹¹
And R ¹² or R ¹³ represents a linear alkyl group having 8 to 20 carbon atoms, and n and m each represent an integer of 3 to 6. ) Is preferable. When R ^{1 to} R ¹³ are not linear alkyl groups having 8 to 20 carbon atoms, these are alkyl groups having 2 or less carbon atoms or hydrogen atoms. If the alkyl group has 3 or more carbon atoms, formation of a two-dimensional self-assembly of π-conjugated organic molecules may be hindered.

The π-conjugated organic molecule to which at least one alkyl group is bonded, which is used in the organic magnetic film of the present invention, includes, in addition to 1) a π-conjugated portion having redox properties and 2) a long-chain alkyl group portion. Further, 3) it may have a ferromagnetic coupler portion connecting a plurality of π-conjugated portions. Only one bit can be recorded with one π-conjugated part, but by connecting two π-conjugated parts with a ferromagnetic coupler,
Non-oxidized species, 1-electron oxidized species and 2-electron oxidized species are 1
It is detected as a difference in spin states in three stages such as a triplet, a doublet and a triplet. This state is shown in FIG. If a ferromagnetic coupler is not used, the two-electron oxidizing species will be a singlet, and multi-step recording will not be realized. In a multi-stage system linked by a ferromagnetic coupler, the linked molecule is considered to be one molecule, and at least one or more alkyl chains should be introduced to it.

That is, the π-conjugated organic molecule having at least one alkyl group bonded, which is used in the organic magnetic film of the present invention, may be represented by XYZ (1). In the formula, X and Z are each one of the above Chemical Formulas 1 to 4, and R in them is
A group in which one of ^{1 to} R ¹³ is lost, or

[Chemical 5] (In the formula, R ¹⁴ or R ¹⁵ represents an alkyl group or a hydrogen atom.) (Provided that at least one, preferably one, or one each of X and Z is present in the XYZ molecule). It has a linear alkyl group having 8 to 20 carbon atoms.). Y is called a coupler and has one of the following structures

[Chemical 6]

[Chemical 7]

[Chemical 8] And has a bond with X and Z at the portion marked with *. ). When R ^{1 to} R ¹⁵ are not linear alkyl groups having 8 to 20 carbon atoms, these are alkyl groups having 2 or less carbon atoms or hydrogen atoms. If the alkyl group has 3 or more carbon atoms, formation of a two-dimensional self-assembly of π-conjugated organic molecules may be hindered.

As an example of the π-conjugated organic molecule represented by the above formula (1), the following structural formula

[Chemical 9]

[Chemical 10]

[Chemical 11] (Wherein, Et represents an ethyl ^group, at least ^one, at least one of ^{R 18} and ^{R 1 9,} at least one of a linear alkyl group having 8 to 20 carbon atoms of ^{R 20} and ^{R 21} of ^{R 16} and ^{R 17} ).

A striped two-dimensional self-assembly of (high) spin-active molecules is formed on the surface of the substrate by dropping a solution of the (high) spin-active molecules chemically modified as described above onto a substrate such as a graphite substrate. Let it form. The spin active site of the π-conjugated organic molecule incorporating the sequence control site is
Form a striped pattern. After confirming this pattern with a scanning tunneling microscope, the spin active part is subjected to one-electron oxidation with a probe to generate delocalized cation radicals.
The generated cation radicals are fixed by forming anions and salts of the electrolyte added to the solution. When a π-conjugated organic molecule represented by the above formula (1) connected by a coupler is used, when a first oxidation potential is applied, first a monocation radical and a dication radical are selectively generated at a second oxidation potential. . In the dication radical, a ferromagnetic interaction works between two unpaired electrons due to spin correlation in a cross-conjugated system. The self-assembly in which information was written by electrochemical oxidation is read out by a magnetic force microscope. With a magnetic force microscope, the part that was not oxidized (magnetically inactive), the part that was subjected to one-electron oxidation, and the part where the ground triplet dication radical was generated by two-electron oxidation were
Each can be observed separately.

[0015]

EXAMPLES The present invention will be illustrated below with reference to Examples.
It is not intended to limit the light.Example 1 N, N, N ', N'-tetraoctadecyl-1,4-benzenediami
Was synthesized according to the following formula.

[Chemical 12] 215 mg (1.98 mmol) p-phenylenediamine and 6.15 g
(21.7 mmol) stearic acid to 100 with a reflux condenser
Place in a mL 3-neck flask and heat until the stearic acid is completely dissolved. Add 740 mg (19.7 mmol) sodium borohydride little by little, and add a small amount of diglyme when stirring becomes impossible (total volume 21 mL). After refluxing overnight, the obtained brown solid was suspended in 100 mL of toluene and filtered, and the filtrate was subjected to alumina column chromatography (solvent:
95 mg of a pale yellow solid, N, N,
N ', N'-tetraoctadecyl-1,4-benzenediamine was obtained.

Next, about 5 mg of N, N, N ', N'-tetraoctadecyl-1,4-benzenediamine thus obtained was added, 2 ml of phenyloctane was added, and ultrasonication was carried out, followed by filtration. And prepare a saturated solution. This solution was dropped onto the cleaved highly oriented sintered graphite to cover the surface, thereby forming a self-assembled monolayer.

[0017]Example 2 In this example, N, N′-bis [4
-(N "-ethyl-N'-octadecylamino) phenyl] -1,
3-Benzenediamine was synthesized. (1) First, p-N-stearyl bromoaniline was prepared according to the following formula.
Was synthesized.

[Chemical 13] p-Bromoaniline (1) 1.90 g (11.0 mmol) and 12.4 g (4
(3.5 mmol) stearic acid is put in a flask and heated until the stearic acid is dissolved. While heating, 2.53 g (66.8 mmol) of sodium borohydride are added in portions over 4 hours. At this time, a small amount of anhydrous tetrahydrofuran is added at any time so that the stirring can be performed smoothly (total volume 45 mL). Reflux overnight, add methanol to the reaction mixture and heat, then add 350 mL toluene, crush white solid well and filter. The filtrate was concentrated to 100 mL and purified with an alumina column (eluent: toluene) to obtain 2.18 g of a white powder as a crude product. The yield was 47%.

(2) Next, N-ethyl-N-stearyl-4-bromoaniline was synthesized according to the following formula.

[Chemical 14] pN-stearyl bromoaniline 207 mg (0.50 mmol) 5
Suspend in mL acetic acid and add 5 mL anhydrous THF to completely dissolve the reaction solution. 742 mg (19.6 mmol) NaBH ₄ is added in portions over 40 minutes, stirred for a further 30 minutes and then concentrated.
Unreacted NaBH ₄ is treated with a small amount of water and extracted with hexane. The organic layer is washed with water and saturated brine and dried over potassium hydroxide. The desiccant was filtered off, concentrated and dried under reduced pressure to give 211 mg of a pale yellow powder as a crude product 3. The yield was 95%.

(3) Next, Nt-butoxycarbonyl-N-
Stearyl-4-bromoaniline was synthesized according to the following formula.

[Chemical 15] pN-stearyl bromoaniline 1.07 g (2.83 mmol),
168 mg (1.38 mmol) 4-dimethylaminopyridine (DMA
P) in 5 mL of THF and 1.4 mL (6.09 mmol) of anhydrous t-
Butyl carbonic acid (BOC) ₂ O was added, the atmosphere was replaced with nitrogen, and the mixture was refluxed for 12 hours. Concentrate, dry under reduced pressure, purify by silica gel column, and
675 mg of the white solid 4 into which the C protecting group was introduced was obtained. Yield is 5
It was 1%.

(4) Next, N, N'-bis [4- (N ''-ethyl)
-N'-octadecylamino) phenyl] -1,3-benzenediamine was synthesized according to the following formula.

[Chemical 16] m-phenylenediamine 109.3 mg and N-ethyl-N-octadecyl-4-bromoaniline 541.9 mg, BINAP 49 mg, Pd
21.6 mg of ₂ (pdc) _{3 was} placed in a flask and 5 ml of toluene was added.
And stir. Sodium-t-butoxide 256 mg
Is added and the reaction is continued at 100 ° C. for 12 hours. After the solvent was distilled off, inorganic substances were removed by silica gel column chromatography, and then purification was performed using gel filtration chromatography. The yield was 30%.

(5) Next, about 5 mg of N, N'-bis [4- (N "-ethyl-N'-octadecylamino) phenyl] -1,3-benzenediamine thus obtained was taken. , Phenyloctane (2 ml) were added, and the mixture was sonicated and filtered,
Prepare a saturated solution. This solution was dropped onto the cleaved highly oriented sintered graphite to cover the surface, thereby forming a self-assembled monolayer. The substrate coated with the organic magnetic film obtained in this way was scanned with a scanning tunneling microscope (ST
The surface image was measured by M, DI Co., Nano Scope IIIa (tunnel current: 500 pA, bias voltage: -1.3).
V). The measurement was performed by a submerged method with the substrate covered with a saturated solution. A tunneling microscope image of the two-dimensional integrated film formed on the substrate is shown in FIG. Two parallel bands with a width of 1.2 nm and a width of 1.6 nm were observed. As shown in the schematic diagram in Fig. 3, the band with a width of 1.2 nm is due to two phenylenediamine moieties linked by metaphenylene groups,
The 1.6 nm band is thought to be due to the octadecyl group part. That is, it can be seen that the para-phenylenediamine moiety in which the meta-phenylene group forming the band is linked is isolated from the same moiety of other molecules for each molecule and arranged so that they can be independently oxidized and reduced.

Further, this N, N'-bis [4- (N ''-ethyl-
A solution of N'-octadecylamino) phenyl] -1,3-benzenediamine was prepared by using tetrahydrofuran as a solvent, and was subjected to two-electron oxidation by adding excess iodine, and an electron spin resonance spectrum (ESR device manufactured by JEOL) was measured. As a result, it was confirmed that it was a ground triplet biradical with zero-field splitting parameters (D = 3.94 × 10 ^-3 cm ^-1 , E = 0 cm ^-1 ) in a rigid solvent at low temperature.

[0023]

According to the conventional magnetic recording medium, a magnetic field is applied to the magnetic fine particles coated on the substrate to magnetize the particles in a specific direction. The magnetic zone of current magnetic disks is on the order of microns, depending on the size of the magnetic particles and magnetic head. However, when the organic magnetic film of the present invention is used as a magnetic recording medium, since the spin active zone is constructed by two-dimensional integration of π-conjugated organic molecules, the width of the zone is in the order of nanometers, and the length is compared. Then, it corresponds to downsizing of three digits and area of 5 to 6 digits. In principle, the organic magnetic film of the present invention can realize a recording medium having a density as high as about 10 ⁵ times that of a conventional magnetic recording medium. At present, the recording density is rather dependent on the spatial resolution (5 nm) of voltage application of the scanning tunneling microscope at the time of writing, and the detection resolution (about 100 nm) of the magnetic force microscope at the time of reading. It is considered that the recording density will be greatly improved and the theoretical limit will be approached with the progress of these measuring means in the future.

An example of utilizing the organic magnetic film of the present invention as a molecular-level magnetic recording medium is shown in FIG. By using the probe of a scanning tunneling microscope, an oxidation potential is applied to a predetermined position to locally generate an open shell molecule (cation radical) that bears an unpaired electron spin, thereby writing necessary information [ Record]. The locally oxidized portion written as information by the probe is read by a scanning magnetic force microscope. It is also possible to use a scanning tunneling microscope for reading. The potential required for this reading is much smaller than the potential used for writing [reading]. When it is desired to erase information, a reducing potential is applied to the writing position with a probe to convert the open shell molecule into a neutral species, thereby restoring the original state [erasing]. When a spin-active molecule serving as a recording medium is a high-spin active molecule in which a plurality of donor sites are cross-conjugated and linked, a ferromagnetic interaction is induced between a plurality of electron spins generated by oxidation. Generates high spin species. Since the oxidation number of the high spin active molecule can be controlled stepwise by the oxidation potential, it is possible to give "depth" to the magnetic information.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which two π-conjugated organic molecules are connected by a ferromagnetic coupler and appear as a difference in spin state between non-oxidized species, one-electron oxidized species and two-electron oxidized species.

FIG. 2 shows N, N′-bis [4- (N ″ -ethyl-N ″ -octadecylamino) phenyl] -1,3-benzene arranged on a highly oriented pyrolytic graphite substrate of Example 2. It is a figure which shows the scanning tunneling microscope photograph (STM) of diamine.

FIG. 3 shows the generation of high spin species of N, N′-bis [4- (N ″ -ethyl-N ″ -octadecylamino) phenyl] -1,3-benzenediamine and the molecular arrangement of STM images. It is a figure.

FIG. 4 is a diagram showing an example of use as a magnetic recording medium.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07D 333/18 C07D 333/18 339/06 339/06 F term (reference) 4C023 NA07 4C069 AC07 BA03 BB34 5D006 BA08 BA11 CB01 CB07 DA03 EA01 FA09 5E049 CC05 DB01 DB16

Claims (7)

[Claims] 1. An organic magnetic film comprising a π-conjugated organic molecule having at least one alkyl group bonded, wherein
An organic magnetic film self-assembled on a highly oriented substrate so that the conjugated organic molecules are electrochemically oxidized independently of other π-conjugated organic molecules. 2. A magnetic response can be exhibited by converting the π-conjugated organic molecule into an ion radical type magnetic species having a doublet or triplet electronic state by electrochemical oxidation. The organic magnetic film according to claim 1. 3. The organic magnetic film according to claim 1, wherein the highly oriented substrate is highly oriented pyrolytic graphite. 4. The organic magnetic film according to claim 1, wherein the alkyl group is linear and has 8 to 20 carbon atoms. 5. The π-conjugated organic molecule is one of the following:
molecule [Chemical 1] [Chemical 2] [Chemical 3] [Chemical 4] (In the formula, R¹~ R^FourAt least one of which has 8 to 2 carbon atoms
0 straight chain alkyl group, R ⁵Or R⁶At least one of
A straight-chain alkyl group having 8 to 20 carbon atoms, R⁷Is a hydrogen atom,
Methyl group or ethyl group, R⁸Or R⁹At least one of
Is a linear alkyl group having 8 to 20 carbon atoms, R¹⁰~ R^Thirteen
At least one of which is a linear alkyl group having 8 to 20 carbon atoms
And n and m each represent an integer of 3 to 6. )so
The organic magnetic film according to any one of claims 1 to 4. 6. The π-conjugated organic molecule has the general formula (1):   XYZ (1) (In the formula, X and Z are respectively [Chemical 1] [Chemical 2] [Chemical 3] [Chemical 4] (In the formula, R¹~ R^FourAt least one of which has 8 to 2 carbon atoms
0 straight chain alkyl group, R ⁵Or R⁶At least one of
A straight-chain alkyl group having 8 to 20 carbon atoms, R⁷Is a hydrogen atom,
Methyl group or ethyl group, R⁸Or R⁹At least one of
Is a linear alkyl group having 8 to 20 carbon atoms, R¹⁰~ R^Thirteen
At least one of which is a linear alkyl group having 8 to 20 carbon atoms
And n and m each represent an integer of 3 to 6. )of
Either of them, R in it¹~ R^ThirteenOne of the lost
The broken group, or [Chemical 5] (In the formula, R¹⁴Or R¹⁵Is an alkyl group or hydrogen atom
Represent ) (Provided that at least in the XYZ molecule)
Has one straight-chain alkyl group having 8 to 20 carbon atoms
It ), Y is one of the following structures [Chemical 6] [Chemical 7] [Chemical 8] And has a bond with X and Z at the portion marked with *. )
The organic magnetic film according to any one of claims 1 to 3. 7. A magnetic recording medium comprising a substrate coated with the organic magnetic film according to claim 1. Description: