JP2812915B2 - Grain-free manganese oxide-based crystal and magnetoresistive element using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel grain-free manganese oxide crystal having a perovskite structure, a method for producing the same, and a magnetoresistive element comprising the same.

[0002]

BACKGROUND OF THE INVENTION Since the discovery of high-temperature superconductivity in copper oxides, the spin-charge coupling kinetics of transition metal oxides has regained attention, and perovskites exhibiting a negative giant magnetoresistance phenomenon in connection therewith. Research on manganese oxide-based materials has started.

[0003] Then, La-Ca-Mn-based oxide LaAlO ₃ substrate so far, La-Pb-Mn-based oxide, a thin film such as La-Ba-Mn based oxide is epitaxially grown have been proposed ["Science (Sci
ence), Vol. 264, pp. 413, "Physical Rev Letters (Physical Rev)
view Letters ", Vol. 71, p. 2331," Physical Review Bee (Physical)
Review B) ", Vol. 63, p. 1990].

On the other hand, some crystalline ceramics mainly composed of a manganese oxide having a perovskite structure are known, and all of them are obtained as an aggregate of a large number of crystals partitioned by a large number of grain boundaries. And a single crystal was not obtained.

[0005] Then, the present inventors have found that a Pr-Ca-Mn-based oxide having a perovskite structure and exhibiting a large magnetic resistance near the magnetic phase transition temperature, ie, near the transition temperature between the ferromagnetic phase and the antiferromagnetic phase. And Pr-Sr-Mn-based oxides without grain boundaries (Japanese Patent Application No. 6-271566).
A grain-boundary crystal of an a-Sr-Mn-based oxide (Japanese Patent Application No. Hei 6
271567) and the like. However, in order to use these materials as a magnetoresistive element, a grain-boundary crystal having better magnetoresistive characteristics and hysteresis characteristics is required according to the purpose of use.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a grain-boundary crystal having improved magnetoresistance and hysteresis characteristics as compared with the grain-bound crystal known so far. It is a thing.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to develop a novel grain-boundary crystal having a magnetic phase transition temperature different from that of a conventional grain-boundary crystal. As a result of the superposition, the previously proposed Pr—Sr—Mn-based oxide or La
The present inventors have found that substituting a part of Pr or La of the -Sr-Mn-based oxide with Nd can improve the magnetoresistance and hysteresis characteristics thereof, and have accomplished the present invention based on this finding.

Namely, the present invention has the general formula _{(Nd 1-x M x)} 1-y Sr y MnO 3 ... (I) ( where M in the formula is La or Pr, x and y are in the following ranges 0.2 ≦ x ≦ 0.8, 0.4 ≦ y ≦ 0.
An object of the present invention is to provide a grain-free manganese oxide-based crystal having a perovskite structure having a composition represented by 6).

According to the present invention, Nd, Sr and M
n and La or Pr in the form of an oxide or a compound capable of being converted to an oxide by heating, and having an atomic ratio Sr / Mn of 0.4 to
0.6, atomic ratio (Nd + M) / Mn (where M is the same as above) 0.6 to 0.4, atomic ratio (Nd + M + Sr) /
By mixing and sintering at a ratio of Mn of 1 and an atomic ratio of Nd / M of １ ／ to 4/1, the crystal of the sintered body is grown from a molten state by a floating zone method. A grain-free manganese oxide-based crystal having a perovskite structure having a composition represented by the formula can be produced.

According to the present invention, there is also provided a memory switching type magnetoresistive element comprising a grain-free manganese oxide-based crystal having a perovskite structure having a composition represented by the general formula (I).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the general formula (I), M is La or Pr. When M is La, x is particularly preferably 0.6 or less. When M is Pr, x is 0.2
Good magnetic properties are exhibited over the entire range of ０．８0.8. In order to produce a grain-boundary manganese oxide-based crystal having a perovskite structure having a composition represented by the general formula (I) according to the method of the present invention, an oxide of Nd, Sr, Mn, La, or Pr or heat Are mixed in a predetermined ratio to prepare a raw material mixture. The oxide used at this time is, for example, Nd ₂ O ₃ , Pr ₂ O ₃ ,
La ₂ O ₃ , SrO, Mn ₃ O _{4 and the} like. Examples of the compound which can be converted to an oxide by heating include Nd.
₂ (CO ₃ ) ₃ , Pr ₂ (CO ₃ ) ₃ , La ₂ (CO ₃ ) ₃ , M
carbonates such as nCO ₃ and SrCO ₃ , and Nd (HCO ₃ )
₃ , Pr (HCO ₃ ) ₃ , La (HCO ₃ ) ₃ , Sr (HC
Bicarbonates such as O ₃ ) ₂ and Mn (HCO ₃ ) ₂ . Each of these raw materials is used in powder form,
The atomic ratio of Sr to Mn is 0.4 to 0.6, the total atomic ratio of Nd and M to Mn is 0.6 to 0.4, and the total atomic ratio of Nd, M and Sr to Mn is 1. Mixed in proportions. This mixture includes methanol, ethanol,
It is preferred to use wet mixing with a volatile organic solvent such as acetone.

Next, this raw material mixture is placed in air at 100
After sintering at a temperature in the range of 0 to 1400 ° C., the obtained sintered body is finely pulverized. After the sintering and pulverization processes are repeated twice or more to homogenize the composition, the obtained powder is formed into a block shape, for example, a column shape by a conventional forming method, for example, press forming, and further formed into a 1100 to 1100 in air. 150
Sinter at a temperature in the range of 0 ° C. In this molding, a binder such as polyvinyl alcohol can be used. Next, the obtained sintered body is grown from a molten state in an oxygen atmosphere using a floating zone method. As the atmosphere in the floating zone method, pure oxygen may be used, or a mixed gas of oxygen and an inert gas such as argon or air may be used. An appropriate growth rate at this time is about 5 to 15 mm / h.

The thus obtained non-grain-bound manganese oxide-based crystal is analyzed by X-ray diffraction, electron beam microanalysis, ICP mass spectrometry and titration analysis to confirm the values of x and y. be able to.

In the grain-boundary manganese oxide-based crystal of the present invention, the electric resistance and the magnetization change sharply with a change in temperature, and the magnetic resistance depends on the magnetic field. Is shown. For example, it has an excellent magnetic field characteristic that causes a resistance change of 6 digits or more around the temperature of liquid nitrogen (77 K).

Further, since the change in resistance shows hysteresis as a function of the magnitude of temperature-induced or magnetic field-induced magnetization, this change can be used as a structure memory and a resistance switch memory or a magnetic memory associated therewith. The novel grain-free manganese oxide-based crystal of the present invention exhibits a larger hysteresis than conventional ones, and is therefore advantageous in use.

[0016]

Next, the present invention will be described in more detail by way of examples.

[0017] Example 1 Mn ₃ O ₄ powder 100 parts by weight, Nd ₂ O ₃ 88.9 parts by weight, were mixed Pr ₂ O ₃ 29.0 parts by weight SrCO ₃ 104 parts by weight of each powder, ethanol 50 parts by weight were added, and the mixture was stirred in an agate mortar for 30 minutes. Next, this mixture was calcined in air at 1050 ° C. for 24 hours, and then the calcined product was pulverized into fine powder, and 50 parts by weight of ethanol was added and mixed again.

The resulting powder mixture was formed into a cylindrical rod having a diameter of 5 mm and a length of about 80 mm by a ² ton / cm ² hydraulic press, and was fired and heated at 1350 ° C. for 48 hours in air. Next, the rod thus obtained was melted using a floating zone furnace equipped with two halogen incandescent lamps and a semi-ellipsoidal focusing mirror to grow crystals. At this time, the raw material rod and the seed rod move in opposite directions at a relative speed of 30r.
The crystal was grown at a speed of about 5 mm / h in a 100% oxygen flow while rotating at pm.

Next, the central part of the crystal thus obtained was cut, crushed to a powder, and subjected to powder X-ray diffraction analysis and
When CP mass spectrometry was performed, (Nd _0.75 Pr _0.25 )
A grain-free manganese oxide-based crystal having a composition of _0.5 Sr _0.5 MnO ₃ was obtained, and it was confirmed that there was no other impurity phase.

This crystal has a ₀ = 5.4375 ° and b ₀ =
It was an orthorhombic system (space group Pnma) having 7.6357 ° and c ₀ = 5.4802 °. FIG. 1 is a graph showing the temperature dependence of the magnetization of this.

[0021] Example 2 Mn ₃ O ₄ powder 100 parts by weight, Nd ₂ O ₃ 59.9 parts by weight, were mixed Pr ₅ O ₃ 58.1 parts by weight SrCO ₃ 104 parts by weight of each powder preparation (Nd _0.5 Pr _0.5 ) _{0.5 in the same} manner as in Example 1 using the raw material mixture thus obtained.
A grain-free manganese oxide-based crystal having a composition of Sr _0.5 MnO ₃ was produced.

This crystal has a ₀ = 5.4386Å, b ₀
= 7.6405 ° and c ₀ = 5.4809 ° (having an orthorhombic system (space group Pnma)). FIG. 2 is a graph showing the temperature dependence of the magnetization of the sample, and FIG. 3 is a graph showing the temperature dependence of the electric resistance under different magnetic fields.

[0023] EXAMPLE 3 Mn ₃ O ₄ powder 100 parts by weight, Nd ₂ O ₃ 94.8 parts by weight, La ₂ O ₃ 23.0 parts by weight SrCO ₃ 104.
In the same manner as in Example 1, (Nd _0.8 La _0.2 )
A grain-boundary manganese oxide-based crystal having a composition of _0.5 Sr _0.5 MnO ₃ was produced.

This crystal has a ₀ = 5.432Å and b ₀ =
It was an orthorhombic system (space group Pnma) with 7.642 ° and c ₀ = 5.478 °. FIG. 4 is a graph showing the temperature dependence of the magnetization of this substance, FIG. 5 is a graph showing the temperature dependence of the electric resistance of the substance under different magnetic fields, and FIG. 6 is a phase diagram showing the electronic state of the substance.

[0025]

The novel grain-free manganese oxide-based crystal of the present invention has excellent magnetoresistance and hysteresis characteristics and is suitable as a memory switching element or a magnetic recording head element.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between temperature and magnetization of a crystal obtained in Example 1.

FIG. 2 is a graph showing a relationship between temperature and magnetization of a crystal obtained in Example 2.

FIG. 3 is a graph showing the relationship between temperature and electric resistance of the crystal obtained in Example 2 under different magnetic fields.

FIG. 4 is a graph showing the relationship between the temperature and the magnetization of the crystal obtained in Example 3.

FIG. 5 is a graph showing the relationship between temperature and electric resistance of the crystal obtained in Example 3 under different magnetic fields.

FIG. 6 is a phase diagram showing the electronic state of the crystal obtained in Example 3.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideki Kuwahara 1-1-4 Higashi, Tsukuba, Ibaraki Pref. Atom Technology Research Center within the Research Institute for Industrial Technology (72) Yoshiki Tokura 1-1-4 Higashi, Tsukuba, Ibaraki Atom technology research body in the Research Institute for Industrial Technology (72) Inventor Yasuhide Tomioka 1-1-4 Higashi Tsukuba, Ibaraki Prefecture Atom technology research body in the Research Institute for Industrial Technology (72) Inventor Atsushi Asamitsu 1 1-4 Atom technology research institute for industrial technology fusion research institute (72) Inventor Hiroshi Moritomo 1-1-4 Higashi Tsukuba, Ibaraki Pref. Atom technology research institute for industrial technology fusion research institute (58) Field surveyed (Int.Cl . ^6, DB name) C30B 1/00 - 35/00 C01G 1/00 - 57/00 H01L 43/08 - 43/10

Claims (3)

(57) [Claims] M according to claim 1 of the general formula _{(Nd 1-x M x)} 1-y Sr y MnO 3 ( in the formula is La or Pr, x and y are numbers in the following range .0.2 ≦ x ≦ 0.8, 0.4 ≦ y ≦ 0.
A grain-boundary manganese oxide-based crystal having a perovskite structure having a composition represented by 6). 2. Nd, Sr and Mn and La or Pr in the form of an oxide or a compound capable of being converted to an oxide by heating, in the form of an atomic ratio Sr / Mn of 0.4 to 0.6 and an atomic ratio ( N
d + M) / Mn (M is La or Pr) 0.6 to
0.4, the atomic ratio (Nd + M + Sr) / Mn is 1, and the atomic ratio Nd / M is mixed at a ratio of 0.25 to 4 and sintered.
Then the general formula _{(Nd 1-x M x)} 1-y Sr y MnO 3 ( having the same meaning as the M in the formula above, wherein the crystal is grown by a floating zone method of this sintered body from the molten state , X and y are numbers in the following range: 0.25 ≦ x ≦ 0.6, 0.4 ≦ y ≦
A method for producing a grain-free manganese oxide-based crystal having a perovskite structure having a composition represented by 0.6). M of 3. A general formula _{(Nd 1-x M x)} 1-y Sr y MnO 3 ( in the formula is La or Pr, x and y are numbers in the following range .0.2 ≦ x ≦ 0.6, 0.4 ≦ y ≦ 0.
A memory switching type magnetoresistive element comprising a grain-boundary manganese oxide-based crystal having a perovskite structure having a composition represented by 6).