JP2005239513A - Indium compound spintronics material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an indium compound spintronics material capable of simultaneously controlling magnetism and electric conductivity. <P>SOLUTION: This indium compound spintronics material is produced by doping at least one element selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb into indium oxide, and is composed such that the point symmetry of unit cells has the lattice translation structure of scandium oxide type crystal structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention provides transition metal elements M (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) or rare earth elements R (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy). , Ho, Er, Tm, Yb) and the like are related to an indium compound spintronic material in which indium oxide is doped with indium oxide and the point symmetry of a unit cell has a lattice translation structure of a scandium oxide type crystal structure.
The indium compound spintronic material of the present invention is required to have both of these characteristics because it has magnetism in addition to the translucency, conductivity, and stability of In ₂ O ₃ that has been put to practical use as a transparent electrode. It is suitable for use in a device.

  Conventionally, in the field of semiconductors constituting the main part of electronics, charge and spin of electrons have been recognized as being independent, and charge transfer has been used for function development.

  On the other hand, in recent years, a device that synergistically uses an electron charge and a spin function, that is, a spintronic device has been proposed.

With the aim of developing new spintronic devices, research on colored spintronic materials centering on compound semiconductors with a relatively small band gap, such as GaAsMn, has become active (for example, Non-patent Documents 1 to Non-Patent Documents). Reference 3).
Examples of research on spintronic materials based on wide gaps with excellent visible light transmission include TiO ₂ (see, for example, Non-Patent Document 4), ZnO (see, for example, Non-Patent Document 5 and Non-Patent Document 6), GaN (For example, see Non-Patent Document 7 and Non-Patent Document 8).

T. Hayashi, M. tanaka, and T. Nishunaga, journal of Applied Physics 81, (1997), p. 4865 H. Ohno, H. Munekata, T. Penney, S. von Molnar, and L. L. Chang, Physical Review Letter 68, (1992), p. 2664 F. matukura, H. Ohno, A. Shen, and Y. sugawara, Physical Review B 57, (1998), p. 2037 Y, matumoto, M. Murakami, T. shono, T. Hasegawa, T. Fukumura, M. Kawasaki, P. Ahmet, T. Chikyow, S. Koshihara, and h.koinuma, Science 291, (2001), p. 854 K. Sato and H. katayama-Yosida, Japan Journal of Applied Physics 39, (2000), p.555 Y.M.Cho, W.K.Choo, H.Kim, D.Kim and Y.Ihm, Applied Physics Letter 80, (2002), p.3358 K. Sato, H. katayama-Yosida, Japan Journal of Applied Physics 40, (2001), p.485 M. Sato, H. Tanida, K. Kato, T. Sasaki, Y. Yamamoto, S. Shimizu and H. Hori, Japan Journal of Applied Physics 41, (2002), p. 4513

However, since the above-described materials such as TiO ₂ and ZnO are wide gap oxides whose electrical conductivity is relatively difficult to control, even if spintronic materials based on them can be developed, There is a problem that it is not always easy to simultaneously control magnetism and electrical conductivity.
For this reason, it is considered difficult to make maximum use of the synergistic function of electron charge and spin in these wide gap oxides.

  In order to solve the above-mentioned problems, the present invention provides an indium compound spintronic material capable of simultaneously controlling magnetism and electrical conductivity.

In response to the problems described above, the present inventors have developed indium oxide, which has been put into practical use as a transparent electrode material, as a novel spintronic material that can control the charge and spin functions of electrons synergistically and freely. (In ₂ O ₃ ) as a base, and Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, that is, 3d transition metal element M, or Ce, Pr, Nd, Pm, Sm, Eu , Gd, Tb, Dy, Ho, Er, Tm, Yb, that is, doping with one or more elements selected from the rare earth elements R was considered.
These 3d transition metal element M and rare earth element R have magnetism when the element becomes an ion. Therefore, in order to simplify the explanation, these elements will be hereinafter referred to as “magnetic elements”.

  The indium oxide may be doped with one or more kinds of magnetic elements, and may be either the 3d transition metal element M or the rare earth element R, or may be doped with both the 3d transition metal element M and the rare earth element R. Good.

In the present invention, indium oxide is doped with a magnetic element, whereby in addition to translucency, conductivity, and stability of indium oxide (In ₂ O ₃ ), it is possible to impart magnetism.
By controlling the doping amount of the magnetic element, it is possible to control magnetism and electric conductivity, and it is also possible to control optical properties.
Thereby, a spintronic material capable of simultaneously controlling magnetism and electrical conductivity can be configured.
It is expected that the characteristics of the spintronic material can be switched or modulated by light irradiation or magnetic field application.

  Further, when the magnetic element doped in indium oxide is 30% or more of the whole (total of indium and magnetic element) in atomic%, that is, the composition ratio of the doped magnetic element and indium is 3: 7 or more, The interaction between the 3d orbitals of the transition metal element M or the 4f orbit of the rare earth element R is connected to the entire indium compound, and a long-range interaction is generated. As a result, the indium compound exhibits ferromagnetism.

On the other hand, when the magnetic element doped in indium oxide is less than 30% of the total (total of indium and magnetic element) in atomic%, that is, when the composition ratio of the doped magnetic element and indium is less than 3: 7, The above-mentioned interaction does not lead to the entire indium compound, but shows an independent behavior for a part, that is, for each cluster. Thereby, the cluster glass phenomenon by the spin cluster formed with the ion of the doped element will express.
Utilizing this cluster glass phenomenon for the characteristics of spintronic devices is also conceivable.

Further, in addition to the above magnetic elements, tin Sn can be doped.
Thus, when indium oxide is doped with tin Sn in addition to a magnetic element, Sn ⁴⁺ ions can act as a dopant for supplying electrons, and can have high electrical conductivity.
At this time, if the amount of Sn ⁴⁺ ion dopant, which is a dopant for supplying electrons, is controlled, the electrical conductivity can be controlled relatively easily.
Furthermore, a magnetic interaction (RKKY interaction) between localized moments of d electrons or f electrons occurs through conduction electrons (s electrons) based on high electrical conductivity of Sn doped in indium oxide. It is expected that a transition to ferromagnetism will occur.

In the present invention, the method for doping an element into indium oxide is not particularly limited, and various conventionally known methods can be used.
For example, a method of ion-implanting an element to be doped into indium oxide, a method of simultaneously depositing and growing an indium raw material and a raw material of the element to be doped, a method of synthesizing a mixture of an indium compound and a compound of the element to be doped, etc. Can be considered.

According to the present invention described above, the optical properties, electrical properties, and magnetic properties can be easily controlled, and the possibility that the function of the spintronic material can be switched or modulated by light irradiation, magnetic field application, or the like is further increased.
And according to the necessity of a device, electrical conductivity and magnetism can be selected.
Therefore, it is expected that spintronic materials are widely applied to MRAM, transparent spin FET, spin-polarized point electron source, and the like.
According to the present invention, excellent effects as described above are expected.

  Hereinafter, the features of the present invention will be described in more detail with specific embodiments.

(A. Method for synthesizing indium compound)
Here, the method of mixing and synthesizing the indium compound and the compound of the magnetic element to be doped will be described.
A case where an aqueous chloride solution is used as the compound of the indium compound and the magnetic element will be described.

First, indium chloride aqueous solution, magnetic element (the transition metal element M or a rare earth element R) and aqueous chloride solution, composition formula _{(In 1-x M x)} 2 O 3 or _{(In 1-x R x)} 2 O _3. Mix so that the desired x value (0 <x <1.0) is obtained.
The mixture is then stirred at room temperature for 24 hours and further dried.
Thereafter, it is fired at 900 ° C. for 1 hour in oxygen.
Thereby, an indium compound doped with a magnetic element can be synthesized.

(B. Characteristic measurement and measurement equipment of synthesized sample)
Various characteristics shown below were measured for the synthesized samples. In addition, the measurement equipment used is also shown.
1. Measurement of X-ray diffraction pattern: An X-ray diffractometer GeigerFlex2013 manufactured by Rigaku Corporation was used.
2. Measurement of light absorption spectrum: A diffuse reflectance spectrum was measured by using an integrating sphere in combination with a visible ultraviolet spectrophotometer (JASCO V-550) manufactured by JASCO Corporation.
3. Model cluster electronic structure calculation using DV-Xα method: electronic state density (DOS) of (In ₁₃ O ₄₂ ) ^45- cluster corresponding to undoped indium oxide In ₂ O ₃ and 8b of (In ₂ O ₃ ) The electronic density of states (DOS) of the (XIn ₁₂ O ₄₂ ) ^46- cluster in which the In ³⁺ ions at the site and the 24d site were substituted with X ³⁺ ions (X is a magnetic element) was calculated.
4). Measurement of magnetic properties: Superconducting quantum interference element susceptibility meter Quantum Design MPMS 5s was used.

(C. Result of measurement of characteristics of synthesized sample)
As a result of measuring the above-mentioned various characteristics of the indium compound sample synthesized by the above-described method, the following results were obtained in common for various samples having different x values of the composition, that is, the doping amount of the magnetic element. It was.

First, in the X-ray diffraction pattern, only a diffraction peak attributable to the crystal structure of indium oxide In ₂ O ₃ was observed, and no heterogeneous phase was detected.
Next, in the light absorption spectrum, it was confirmed that when the magnetic element was doped, new light absorption that was not present in undoped (undoped) indium oxide In ₂ O ₃ was observed.

In the model cluster electronic structure calculation using the DV-Xα method, from the result of calculating the electronic state density (DOS) of the (In ₁₃ O ₄₂ ) ^{45 -cluster} corresponding to the undoped indium oxide In ₂ O ₃ , It was confirmed that the valence band of (In ₂ O ₃ ) consists of 2p orbits of oxygen O, and the conduction band consists of 5s orbitals of indium In.
Then, _(In 2 _{O 3)} 8b site and 24d respectively ^{X 3+} ions ^{In 3+} ions site (X is a magnetic element; 3d transition metal element M or a rare earth element R) was substituted with _{(XIn 12} O ^{42) 46-} As a result of calculating the electronic density of states (DOS) of the cluster, when In ³⁺ ions are replaced with X ³⁺ ions, DOS originating from 3d orbitals of transition metal element M or 4f orbits of rare earth element R is formed in the band gap. It was confirmed that
Since this DOS corresponds well with the diffuse reflection spectrum observed in the indium oxide doped with the magnetic element, the new light absorption is due to the 3d orbital of the transition metal element M substituted with the In ³⁺ ion or the rare earth element R. It was confirmed that this was due to the transition of electrons related to the 4f orbit. Further, the electron spin DOS of the transition metal element M in the 3d orbital or the rare earth element R in the 4f orbit has an asymmetric shape, specifically, only one spin below the Fermi level, and has strong magnetic properties. It was confirmed that interaction could be expected.

Moreover, from the result of measuring the magnetic characteristics, it was confirmed that when magnetic element X is doped, a magnetic interaction appears in indium oxide In ₂ O ₃ which is a non-magnetic material.
Therefore, it can be seen that magnetism is imparted by doping indium oxide with a magnetic element.

  By the way, as described above, the indium compound spintronic material of the present invention in which a magnetic element is doped in indium oxide is expected to have a wide range of applications such as MRAM, spin FET, and spin-polarized point electron source.

  When used in an MRAM (magnetic memory), for example, an indium compound spintronic material of the present invention is used for a recording layer for storing information, and a magnetic layer (magnetization pinned layer) having a fixed magnetization direction is used. It is conceivable to configure the MRAM by providing it as a reference layer serving as a storage standard.

  When used in a spin FET, it is conceivable to use the indium compound spintronic material of the present invention for the channel portion. It is also conceivable that the substrate material is indium oxide, and a magnetic element is ion-implanted into a portion that becomes a channel of the FET.

  Next, specific examples of the present invention will be described.

(Example 1)
[Synthesis of (In _1-x Fe _x ) ₂ O ₃ ]
First, an InCl ₃ aqueous solution and an FeCl ₃ aqueous solution were mixed so that x = 0.075 in the composition formula (In _1-x Fe _x ) ₂ O ₃ .
Subsequently, the mixed aqueous solution was stirred at room temperature for 24 hours and dried.
Then, it baked at 900 degreeC in oxygen for 1 hour, the powder was obtained, and it was set as the sample of Example 1.

(Comparative Example 1)
Further, as a comparative control, a compound in which x = 0 in the above composition formula, that is, In ₂ O ₃ , was used in the same manner as in Example 1 (an InCl ₃ aqueous solution was stirred at room temperature for 24 hours and dried, then 900 ° C. in oxygen). To obtain a powder). This was used as a sample of Comparative Example 1.

[Measurement of various characteristics]
About the obtained sample of Example 1, the various characteristics mentioned above were measured as follows. Moreover, about the sample of the comparative example 1, the measurement of the X-ray-diffraction pattern and the measurement of the light absorption spectrum were performed.
1. Measurement of X-ray diffraction pattern: The X-ray diffraction pattern was measured using an X-ray diffractometer GeigerFlex2013 manufactured by Rigaku Corporation.
2. Measurement of light absorption spectrum: A diffuse reflectance spectrum was measured by using an integrating sphere in combination with a visible ultraviolet spectrophotometer (JASCO V-550) manufactured by JASCO Corporation.
3. Model cluster electronic structure calculation using DV-Xα method: electronic state density (DOS) of (In ₁₃ O ₄₂ ) ^45- cluster corresponding to undoped indium oxide In ₂ O ₃ , and (In ₂ O ₃ ) Electronic density of states (DOS) of (XIn ₁₂ O ₄₂ ) ^46- cluster in which In ³⁺ ions at 8b site and 24d site were substituted with X ³⁺ ions (X is a magnetic element) was calculated.
4). Measurement of magnetic properties: The following magnetic properties were measured using a Quantum Design MPMS 5s superconducting quantum interference device susceptibility meter.
(1) Measurement of DC magnetic susceptibility temperature dependence: Field-cooled (FC) where the applied magnetic field is 100G, the magnetic field is applied above the superconducting transition temperature and cooled to the superconducting state, and the magnetic field is not applied Then, the temperature dependence of the DC magnetic susceptibility was measured by two methods of zero-field-cooled (ZFC) in which a magnetic field was applied after cooling to a superconducting transition temperature or lower.
(2) Measurement of temperature / frequency dependency of AC magnetic susceptibility: The temperature dependency of AC magnetic susceptibility was measured by changing the frequency to 3 Hz, 10 Hz, 30 Hz, 100 Hz, 300 Hz, and 1000 Hz.
(3) Measurement of temperature / frequency dependence of nonlinear magnetic susceptibility: The frequency dependence was changed to 3 Hz, 10 Hz, 30 Hz, 100 Hz, 300 Hz, and 1000 Hz, and the temperature dependence of the nonlinear magnetic susceptibility was measured.

  First, with respect to the powders of the samples of Example 1 and Comparative Example 1, the generation phase was identified and the lattice constant was determined from the measurement result of the X-ray diffraction pattern. The X-ray diffraction patterns of the obtained samples are shown in FIG.

From FIG. 1, in any sample, only a diffraction peak that can be attributed to the crystal structure of indium oxide In ₂ O ₃ was observed, and no heterogeneous phase was detected.
In the sample of Example 1 (x = 0.075) doped with Fe, the lattice constant was 10.088Å. The lattice constant of the undoped sample of Comparative Example 1 (x = 0) was 10.118 mm, and the lattice constant decreased when Fe was doped.
That is, it is considered that the lattice point In ³⁺ (0.94Å) is replaced with Fe ³⁺ (low spin: 0.69Å, high spin: 0.79Å).

Next, the light absorption spectrum of each sample of Example 1 and Comparative Example 1 is shown in FIG.
From FIG. 2, light absorption was observed at about 2.3 eV in the sample of Example 1 doped with Fe (x = 0.075). This is light absorption that is not observed in the sample of Comparative Example 1 (x = 0).

As described above, from the results of the model cluster electronic structure calculation using the DV-Xα method, the electronic state density (DOS) of (In ₁₃ O ₄₂ ) ^45- cluster corresponding to the undoped indium oxide In ₂ O ₃ ), The valence band of indium oxide In ₂ O ₃ is composed of 2p orbits of oxygen O, and the conduction band is formed of 5s orbitals of indium In.

Next, the electronic density of states (DOS) of the (FeIn ₁₂ O ₄₂ ) ^46- cluster in which the In ³⁺ ions at the 8b site and the 24d site of the indium oxide In ₂ O ₃ are respectively replaced with Fe ³⁺ ions is shown in FIG. 3A and FIG. Shown in 3B. FIG. 3A shows the electronic state density (DOS) when the 8b site of indium oxide is replaced with Fe ³⁺ ions, and FIG. 3B shows the electronic state density (DOS) when the 24d site of indium oxide is replaced with Fe ³⁺ ions. ).
From FIG. 3A and FIG. 3B, it was confirmed that DOS originating from the Fe3d orbital was formed in the band gap when In ³⁺ ions were replaced with Fe ³⁺ ions at any site. This DOS corresponds well with the diffuse reflection spectrum confirmed with Fe-doped indium oxide, and the above-mentioned light absorption of about 2.3 eV is related to the 3d orbit of Fe ³⁺ ions substituting In ³⁺ ions. This is thought to be due to electron transition.

Next, FIG. 4A and FIG. 4B show the spin DOS of 3d electrons of Fe when the In ³⁺ ions at the 8b site and the 24d site of the indium oxide In ₂ O ₃ are respectively replaced with Fe ³⁺ ions. FIG. 4A shows spin DOS when the 8b site of indium oxide is substituted with Fe ³⁺ ions, and FIG. 4B shows spin DOS when the 24d site of indium oxide is substituted with Fe ³⁺ ions.
From FIG. 4A and FIG. 4B, the spin DOS of Fe 3d electrons is asymmetrical, and only one spin (up spin in FIG. 4A, down spin in FIG. 4B) is below Fermi level. It can be seen that the expression of can be expected.

Next, the measurement result of the temperature dependence of the DC magnetic susceptibility for the sample of Example 1 is shown in FIG. In FIG. 5, an enlarged view of the vicinity of 265K to 280K in the figure is shown as an inset.
From the inset of FIG. 5, it can be seen that at about 270 K, a difference starts to occur in the magnetic susceptibility of Field-cooled (FC) and Zero-field-cooled (ZFC).
5 shows that the DC susceptibility of FC increases as the temperature decreases, and the DC susceptibility of ZFC decreases gradually away from the DC susceptibility of FC.
The behavior of the magnetic susceptibility of FC and ZFC is considered to be due to the appearance of cluster glass by forming clusters.
Also, cusps (points) were observed at 30K in both the magnetic susceptibility of FC and ZFC.

Next, the measurement result of the temperature / frequency dependence of the AC magnetic susceptibility for the sample of Example 1 is shown in FIG.
From FIG. 6, the maximum points of magnetic susceptibility were observed at about 270K and about 30K.
In particular, the maximum point (temperature) of about 270 K shifted to the high temperature side as the measurement frequency increased.
ΔTp estimated from this shift amount is about 0.02, and this value suggests the possibility of the spin (cluster) glass phenomenon.

Next, the temperature / frequency dependence of the nonlinear magnetic susceptibility for the sample of Example 1 is shown in FIG.
From FIG. 7, a cusp (point) was observed at about 270 K, and it was observed to show a divergent behavior.
From this, it is considered that frustration exists between the spin clusters formed by Fe substituted with In in the lattice of indium oxide In ₂ O ₃ , and the cluster glass phenomenon appears.
Therefore, it can be said that the indium oxide-based spintronic material was successfully synthesized.
It can be seen that with the nonlinear magnetic susceptibility, the cusp temperature hardly shifts even when the measurement frequency is changed.

  The present invention is not limited to the above-described embodiments and examples, and various other configurations can be taken without departing from the gist of the present invention.

The indium compound spintronic material of the present invention has been proposed in the past as a possibility of simultaneously controlling optical, electrical, and magnetic properties and switching or modulating the function of the material by light irradiation or magnetic field application. It is bigger than the spintronics material.
Therefore, the indium compound spintronic material of the present invention is expected to have a wide range of applications such as MRAM, transparent spin FET material, and spin-polarized point electron source.

It is a figure which puts in order and shows the X-ray-diffraction pattern of each sample of Example 1 and Comparative Example 1 of this invention. It is a figure which puts in order and shows the light absorption spectrum of each sample of Example 1 and Comparative Example 1 of the present invention. It is a figure which shows the electronic state density (DOS) of the cluster which substituted the indium ion of 8b site and 24d site of A and B indium oxide with Fe3 ⁺ ion, respectively. A, B It is a figure which shows the spin DOS of the 3d electron of Fe when the indium ion of 8b site and 24d site of indium oxide is each substituted by Fe3 ⁺ ion. It is a figure which shows the measurement result of the temperature dependence of the direct current magnetic susceptibility of the sample of Example 1 of this invention. It is a figure which shows the measurement result of the frequency and temperature dependence of the alternating current magnetic susceptibility of the sample of Example 1 of this invention. It is a figure which shows the measurement result of the frequency and temperature dependence of the nonlinear magnetic susceptibility of the sample of Example 1 of this invention.

Claims (4)

Indium oxide
One or more selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb The element is doped,
An indium compound spintronic material characterized in that the point symmetry of the unit cell has a lattice translational structure of a scandium oxide type crystal structure.   A spin cluster formed by ions of a doped element having a composition ratio of the doped element and indium of less than 3: 7, having a property of causing a spin glass transition, and below the transition temperature of the spin glass transition. The indium compound spintronic material according to claim 1, wherein the indium compound spintronic material has a property of causing a cluster glass phenomenon.   2. The indium compound according to claim 1, wherein the composition ratio of the doped element and indium is 3: 7 or more and exhibits ferromagnetism due to a long-range interaction between the doped elements. Spintronic materials.   The indium compound spintronic material according to claim 1, wherein Sn is doped in addition to the doped element.

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