Method of obtaining calcium-doped lanthanum manganite. RU patent 2505485.

FIELD: chemistry.

SUBSTANCE: calcium-doped lanthanum manganite is obtained by reaction from lanthanum, manganese and calcium oxides by their grinding, first annealing in air at 1350±50°C, cooling to room temperature, re-grinding and pressing obtained material in tablets, its re-annealing in air at 1350±50°C, further annealing in oxygen and cooling to room temperature, with obtaining samples with composition La_1-xCa_xMn_1-zO₃, in which selected calcium concentration is 0.05<x<0.22, selected manganese concentration is 0<z≤0.05, first annealing in air is carried out for 12 hours, second re-annealing in air is carried out for 4 hours, annealing in oxygen is carried out at T=650±20°C for 50 hours, and further cooling to room temperature is carried out in air at rate not lower than 10°C/min.

EFFECT: material is simple in manufacturing and comparatively cheap, has high magnet-resistance in broad area of temperatures 5-300 K and especially high values of magnet-resistance at nitrogen and helium temperatures.

5 dwg, 3 tbl

The invention relates to the development of ways to obtain new compounds with high values of magnetoresistance and can be used in the chemical industry and microelectronics.

Currently, for the manufacture of magnetic resistors, devices, non-destructive testing, displacement sensors, alarms, devices for measuring DC and AC magnetic field, electric current, magnetic recording devices and reliable information storage, etc. require materials with high values of magnetoresistance in a wide range of temperatures and magnetic fields.

Magnetoresistance is the change in the electrical resistance ρ of the material under the application of magnetic field H and is determined by the expression:

It shows the percentage change of the resistivity at a given value of the magnetic field.

Known methods for producing europium chalcogenides (EuO, EuS, EuSe, EuTe) with face-centered cubic lattice [3. Metfessel, Demattis, Magnetic semiconductors, M.: Mir, 1972, 405 S., English translation], which are semiconductors above the Curie temperature (T_C=10-70) and undergo the effect of giant magnetoresistance (GMR) in the transition from the paramagnetic to the ferromagnetic state. These with the organisations receive from oxides and metals of the respective elements by annealing at 1000-1300°C in sealed vials. The resistivity of them decreases in a magnetic field up to 10⁸%. The GMR effect is caused by the dependence of the band structure from the magnetization of the sample and decrease the activation energy DE of electrical resistivity ρ~exp(ΔE/kT) in a magnetic field.

The disadvantage of these methods is that obtained by using these methods, substances pass into the metallic state below T_Cand the implementation of the MS effect, resulting in a narrow temperature interval near T_C.

Also known is a method of obtaining oxide compounds lanthanum manganites of the type La_1-xA_xMnO₃in which trivalent ion La⁺³substituted divalent ion (acceptor), where A=CA, Sr, Ba, and other alkali metals; 0.2<x≤0.4, which is close to T_C≈150-350 To feel the effect of colossal magnetoresistance (CMR) [Nagaev AL lanthanum Manganites and other magnetic semiconductors with giant magnetoresistance // Phys. - 1996. - C, No. 8. S-859]. These substances are derived from oxides of the parent compounds by annealing at 1200-1380°C in air. Then the powders thoroughly fray, again annealed at 1390°C in air, pressed into tablets at room temperature and annealed in oxygen at 600°C and a pressure of 200 atmospheres or oxygen flow at 1300°C [.Schiffer et al. Low Temperature Magnetoresistance and the Magnetic Phase Diagram of La_1-xCa_xMnO₃, Phys. Rev.Let., v.75, p.3336-3339 (1995)]

The disadvantage of this method is that the resulting substances implementation effect CCM occurs in a narrow temperature range, because when the concentration of acceptors x above the threshold flow (x_then=0.17-0.22, depending on the type of acceptor) connection switching in ferromagnetic metallic state with low MS values below T_C=200-240 K. the Resistivity in the lanthanum manganite doped with calcium, decreases by about 5 times in a magnetic field of 4 T near T_C≈230 K, below this temperature the resistivity at H≥0.2 TL from the magnetic field is almost independent [.Schiffer et al. Low Temperatire Magnetoresistance and the Magnetic Phase Diagram of La_1-xCa_xMnO₃, Phys.Rev. Let., v.75, p.3336-3339 (1995)]. The highest MS values observed near T_Cwhen the concentration of acceptors near-threshold leakage, x≈x_thenabove which the sample is transferred into the metallic state. Doped calcium manganite lanthanum La_1-xCa_xMnO₃enters a conductive state when x≥0.22 [.Okuda et al., Low-temperature properties of La_1-xCa_xMnO₃single crystals: Comparison with La_1-xSr_xMnO₃, Phys.Rev B, 61, 8009-8015(2000)].

Thus, to achieve high value MS manganites is necessary that the concentration of acceptors was close to threshold leakage, but the sample is not passed in conducting the status.

The closest to the technical nature of the claimed invention is a method of producing lanthanum manganite doped with calcium, the reaction of the oxides of lanthanum, calcium and manganese, [J.Alonso and other Mn+4 cation localization in La-rich La_1-xCa_xMnO_ymanganites, Phys.Rev. 62, 11328 (2000)], which as of lanthanum manganite doped with calcium, get (La_1-xCa_x)_wMn_zO₃with x=0.05-0.25, w=z=0.99-0.96, oxides is subjected to processing including grinding and annealing in air at T=1350±50°C, re-grinding and pressing of the material obtained in tablets, followed by annealing in air at T=1350±50°C and quenching to room temperature. Annealing at T=1350±50°C for 24 hours in a stream of oxygen and cooling it to room temperature at a rate of 2°C/min, While the total amount of time spent on the annealing of the material in air and oxygen at temperatures up to T=1350±50°C, is more than 130 hours.

In this method of producing lanthanum manganite doped with calcium, an increase in the concentration of acceptors, determined by the concentration of Mn⁺⁴above the threshold flow x_then=0.22, is achieved due to vacancies, La and Mn. In (La_1-xCa_x)_wMn_zO₃formed Mn⁺⁴with concentration x_Mn+4=3-3_w+xw+3(1-z). The sample does not pass into the metal sosteniendola of this method are the low values of MS, since the resistivity is reduced approximately 10 times near T_C≈200 K and decreases to less than 2 times in a magnetic field of 9 T at lower temperatures. Vacancies in the La sublattice increase the carrier concentration close to the threshold leakage, but does not lead to an increase in MC. Jahn-teller splitting of the energy of Mn⁺³near ion Sa is less than the splitting energy of Mn⁺³near vacancies ion La and energetically advantageous for the occurrence of Mn⁺⁴near ion Sa [J.Alonso et al., Mn+4 cation localization in La-rich La_1-xCa_xMnO_ymanganites, Phys.Rev. 62, 11328 (2000)]. As a consequence, additional media due to vacancies lanthanum localized in the tail of the valence band, their state from the magnetic field is not affected and, accordingly, does not change the resistivity in a magnetic field.

The basis of the invention is increasing the magnetoresistance of manganite doped with calcium, with high values in a wide range of temperatures, particularly when nitrogen and helium temperatures, at the expense of achieving non-metallic States of the sample at a concentration of carriers close to the threshold flow.

The problem is solved in that in the method of producing lanthanum manganite doped with calcium, the reaction of the oxides of lanthanum, manganese and calcium, including chafing, the first annealing them in air at 150±50°C, cooling to room temperature, re-grinding and pressing of the material obtained in tablets, re-annealing it in air at 1350±50°C and subsequent annealing in oxygen and cooled to room temperature, according to the invention as lanthanum manganite doped with calcium, get La_1-xCa_xMn_1-zO₃in which the concentration of calcium pick 0.05<x<0.22, the concentration of manganese select 0<z≤0.95, the first annealing in air is carried out in 12 hours, repeated the second annealing (tablets) in the air should be performed within 4 hours annealing in oxygen is carried out at T=650±20°C for 50 hours and subsequent cooling to room temperature is performed on the air at a speed of not less than 10°C/min

The choice of the concentration of calcium 0.05<x<0.22 in La_1-xCa_xMn_zO₃provides a non-metallic nature of the electrical connection in the whole temperature interval.

The concentration of manganese choose less than stoichiometry to 5%, 0<z≤0.95, which provides an increase in the concentration of acceptors, they don't put the connection in the metallic state. When the concentration of Mn is higher stoichiometry than 5% of the sample becomes unstable and decays with time.

The choice of the concentration of ions in lanthanum sublattice equal stoichiometry, reduces the number of carriers due to the lack of Vaca is Sciez ion La and eliminates the transfer of the sample into a state with low MS values.

Annealing La_1-xCa_xMnO_yoxygen is carried out to increase the concentration of carriers. Annealing La_1-xCa_xMnO_yoxygen at high temperatures increases the concentration of oxygen above the stoichiometric value to y=3+δ, with δ≤0,16 depending on x. The excess oxygen creates in La_1-xCa_xMnO_3+δcation vacancies La, CA, Mn and additional charge carriers localized on Iona Mn⁺³forming Mn⁺⁴with concentration x_Mn+4=x+2δ. In the most immediate way of [J.Alonso, etc. of Mn⁺⁴cation localization in La-rich La_1-xCa_xMnO_ymanganites, Phys.Rev.B 62, 11328 (2000)] increasing the concentration of carriers by annealing in oxygen is not achieved, because after annealing in oxygen at 1300±50°With the sample cooled to room temperature with a speed of less than 2 K/min At such a cooling rate, the oxygen concentration in the sample becomes equal to the stoichiometric, δ=0 [.Dabrowski et al. Oxygen Content and Structures of La_1-xCa_xMnO_3+δas a Function of Synthesis Conditions, J. of Sol. State Chem., 146, 448(1999)].

In the present method, the temperature of annealing in oxygen is reduced to 650±20°C and the cooling rate is chosen not less than 10°C/min to avoid depletion of the sample with oxygen during cooling. The diffusion rate of oxygen in manganites at 900°C is equal to V_{the WPPT}≈0.4 μm/hour.[R. Shiozaki et al. Effect of oxygen annealing on the electrical properties of La_1-x xMnO_3+δsingle crystals around the compositional metal-insulator transition, Phys.Rev. B, v.63, 184419(2001)]. The diffusion rate of oxygen in La_1-xCa_xMnO₃decreases with decreasing temperature and diffusion virtually absent (V_{the WPPT}≈0) at temperatures below 500°C [.Dabrowski et al. Oxygen Content and Structures of La_1-xCa_xMnO_3+δas a Function of Synthesis Conditions, J. of Sol. State Chem., 146, 448(1999)]. In the inventive method, the diffusion rate of oxygen at 650±20°C, it becomes significantly less V_{the WPPT}≈0.4 μm/h at 900°C, and cooling rate 10°C/min for¹/₄hours achieved the status of V_{the WPPT}≈0 (T=500°C) and the oxygen content practical: does not change during the cooling process in polycrystals with grain size of 3-4 microns. The cooling rate 10°C/min is achieved by simply removing the sample from the furnace and cooled at room temperature. Decrease annealing temperature in 2 times and the exception hardening simplifies and reduces the cost of production technology.

The technical result is achieved in that in a method of producing doped calcium manganite lanthanum reaction of the oxides of lanthanum, calcium and manganese, including annealing them in air and subsequent annealing in oxygen atmosphere, it is new that the concentration of the divalent metal is calcium choosing smaller or close to the threshold flow, the concentration of lanthanum wybir is t equal stoichiometry, the concentration of manganese choose less than stoichiometry to 5%, annealed in oxygen atmosphere at 650±20°C for ~2 days. When the cooling speed of not less than 10°C/min provides high values of magnetoresistance in a wide range of temperatures, particularly when nitrogen and helium temperatures, at the expense of achieving non-metallic States of the sample at a concentration of carriers close to the threshold flow.

Figure 1 shows the temperature dependence of the electrical resistance of lanthanum manganites doped with calcium, in a magnetic field H=0-9 T, obtained by the claimed method. Insert figure 1 shows the temperature dependence of the activation energy of La_0.95Ca_0.05Mn_0,97O_3+δ(1) and La_0.85Ca_0.15Mn_0.97O_3+δ(2) when N=0.

Figure 2 shows the temperature dependence of the magnetoresistance lanthanum manganites doped with calcium, obtained by the claimed method in a magnetic field H=1-9 T.

Figure 3 shows the temperature dependence of the cluster size La_0.90CA_0.10Mn_0.97O_3+δwhen N=0 and 9 T.

Figure 4 shows the dependence of magnetization on the magnetic field strength at 2 To samples known and inventive ways.

Figure 5 shows the temperature dependence of the relative sizes of the clusters in the fields 1-9 T samples, the scientists of the inventive method, where R_KL(T, N) and R_KL(T,H=0) - the sizes of clusters at a given temperature T and magnetic field H and H=0, respectively.

The proposed method is as follows. Take the initial mixture of oxide compounds from the condition that the weight of La, Mn and CA oxides was equal to the weight of La, Mn and CA in the sample of La_1-xCa_xMn_zO₃. Table 1 shows an example of obtaining samples of the composition of La_1-xCa_xMn_zO₃(x=0.05, 0.10 and 0.15, z=0.97 and 0.95) from the source of oxides of La₂O₃, Mn₃O₄and Cao.

The synthesis is carried out in 3 stages.

1). Carefully grind the powder source composition in an agate mortar to a fine powder and spend the first annealing at 1350±50°C for 12 hours in air. As a result of synthesis get loose powdery mass.

2). Carefully grind the powdered mass in an agate mortar until a fine powder to achieve homogeneity of the substance. The resulting powder using a special mold is pressed the pill (disk) with a diameter of 10 mm and a thickness of about 2 mm with subsequent annealing in air at 1350±50°C for 4 hours. As a result of synthesis get tablets in the form of dense ingots.

3). Annealed tablets in the form of dense ingots at T=650±20°C in oxygen for 50 hours. Remove the samples from the oven and cool them at room temperature in air with a speed of not less than 10°C/min to the Desired duration of annealing in oxygen was determined by the increase in weight of the samples after annealing: after 50 hours of annealing, the sample weight remained practically unchanged, indicating full saturation of the sample with oxygen under specified conditions.

Chilled samples cut diamond circle on the bars with dimensions of ≈5×2×1 mm³for magnetic and electric measurements. Measurement of the electrical resistance of a 4-contact method for installing PPMS in a magnetic field up to 9 T, in the temperature range 5-400 K. For electrical measurements the contact of the metal indium is applied by ultrasonic soldering iron: current contacts at the ends of the bar, and potential contacts on the wide surface of the bar at a distance of 2-3 mm

Magnetic measurements were performed on the magnetometer MPMS-5XL SQUID and install PPMS in a magnetic field up to 9 T in the temperature range 5 are 300 K. the Curie Temperature determined from the temperature dependence of the magnetic permeability at a frequency of 1 kHz.

The concentration of Mn⁺⁴was determined by the method of oxidation-reduction titration with used the eat as reducing salt Mora.

X-ray diffraction and x-ray studies were made on the x-ray apparatus DRONE 2.0 on the radiation Cr kα.

Table 2 presents the crystal structure, parameters and the volume of the lattice, the Curie temperature T_Cthe studied samples and the concentration of ions of Mn⁺⁴.

Table 2 shows that at room temperature stoichiometric (z=1) and Mn vacancies(z=0.97) samples of La_1-xCa_xMn_zO₃with x=0.05, δ≈0, we have orthorhombic O'-phase with C/a<√2, the samples with x=0.10, 0.15, δ≈0 have a structure close to quasichemical and≈b≈C. Vacancies Mn slightly reduce the volume of the unit cell, without changing the crystal structure.

Annealed in oxygen samples of La_1-xCa_xMn_0.97O_3+δwith x=0.05 and x=0.10 at room temperature have a rhombohedral structure (R-phase). The samples with x=0.15 and δ≈0 are two-phase: they are containing is mainly About'-orthorhombic phase and less than 10% - rhombohedral phase. Annealing in oxygen reduces the volume of the unit cell V 2.6, 1.8, and 0.8% for samples with x=0.05, 0.10 and 0.15, respectively. This decrease is consistent with the change in the share of ion Mn⁺³having a large (0.645 A) ionic radius than that of Mn⁺⁴(0.530). After annealing in oxygen concentration of Mn⁺⁴increased by 28=9.3, 7.4 and 3.4% in the samples with x=0.05, 0.10 and 0.15, respectively. The deficit to 3% of Mn decreases T_Cfor samples with x=0.05-0.10 and δ=0, for x=0.15 and δ≈0 T_Csignificantly reduced compared with the stoichiometric with z=0. In these samples the detected common lanthanum manganites change the values of MS near-temperature magnetic transitions.

Annealing of the samples of La_1-xCa_xMn_0,97O₃at 650±20°C and 1 ATM of oxygen for 50 hours leads to changes in their magnetic properties (table I): T_Creduced by 35-75 To, the sample becomes ferromagnetic with close values of T_C≈85-92 K. Annealing in oxygen increases the excess oxygen 8 and the ratio of Mn⁴/Mn⁺³above the threshold flow. However, the samples do not transition into the metallic state, they are semiconductors with high sensitivity to the magnetic field, the electrical resistance change of more than 10⁴in the field of 9 T, and the magnetoresistance over a million % at low temperatures.

the temperature dependence of electrical resistivity (figure 1) depend on the concentration of CA, are semiconducting in nature and are temperature-dependent activation energy ΔΕ (box figure 1). The proximity of the carrier concentration to the threshold flow indicates the maximum resistivity at H=0 in the sample of La_0.90CA_0.10Mn_0.97O₃+8 at T≈80 K≈T_C.

From figure 2 it is seen that MS in the sample of La_0.90CA_0.10Mn_0.97O_3+δincreases with decreasing temperature and reaches values of more than 1 million % in a magnetic field of 9 T at liquid helium temperature. In samples of La_0.95CA_0.05Mn_0.97About_3+δand La_0.85CA_0.15Mn_0.97About_3+δon authors plants could not be determined MS at T<50 K. In appearance according to MS(T) can be expected values MS>>10^6%.

The proposed method is based on physical phenomena inherent in the manganites, and explained in a model of phase separation [Alagai. Lanthanum manganites and other magnetic semiconductors with giant magnetoresistance // Phys. - 1996. - So 166, No. 8. S-858; Musican, Cigugur, Inhomogeneous charge state and phase separation in manganites // Phys 171, 577(2001)]. The original connection LaMnO₃is antiferromagnetic semiconductor and magnetoresistive properties is not. The substitution of trivalent La⁺³in La_1-xA_xMnO₃on the divalent ion A=CA, Sr, a (acceptor) causes a current carrier. Jonas La⁺³located in the center of the cube of 8 ions of Mn⁺³. Carriers in doped manganites are not free. They captured the nearest ion Mn⁺³forming Mn⁺⁴. Since all 8 of ions of Mn⁺³inner circle equivalent to an acceptor, the electron is smeared between them, which creates around the carrier charge polaron - (unit cell cluster) size 2R_pol≈√3a≈0.7 nm, where a=0.4 nm is the lattice parameter. The electron is in a potential well of the Coulomb blockade

where e is the electron charge, ε'_p- the dielectric constant of the lattice. When the values of ε'_p=12 and 2R_pol=0.7 nm is the value of E_C≈150 MeV≈1.8·10³To, (1 MeV=11.6 K) is many times greater than room temperature. Because of these conditions, the electron is localized, and the conductivity is caused by tunneling (jumps) media between polarons has a semiconductor character and is described by the expression:

where χ~1/a tunneling parameter, ρ₀≈10³Ohm·cm - weakly temperature-dependent value. The 1st term in (3) is associated with overcoming the energy of the Coulomb blockade, the 2nd term in (2) determines the overlap of the wave functions of the clusters and increases when s→0. The concentration of polarons (clusters) and the distance between them is determined by what centrala acceptors. Polarons are isolated from each other at a distance s=r_KL-KL-2R_KLwhere R_KL-KL=a(x)^-1/3- the distance between the polarons. For example, s=0.052 nm at x=0.15.

In the known method [EL the Nagaev. Lanthanum manganites and other magnetic semiconductors with giant magnetoresistance // Phys. - 1996. - C, No. 8. S-858], due to the double exchange interaction between Mn ions₊₃-On^-2-Mn⁺⁴in La_1-xA_xMnO₃when 0.2<x≤0.4 ferromagnetic state occurs with T_C=150-250 K. In the region of T_Cwhen the temperature decreases because of the gain in exchange energy is the rapid consolidation of polarons in larger associations (clusters). When the concentration of acceptors x=0.2-0.4 polarons (clusters) touch each other, forming one large cluster with s→0, E_C=0. Tunneling spectroscopy in La_2/3CA_1/3MnO₃shows the transformation of the small (about 1 nm) clusters in giant (>100 nm) ferromagnetic conductive clusters near T_C[.Fath et al., Spatially Inhomogeneous Metal-Insulator Transition in doped Manganites, Science 285, 1540 (1999)]. If you increase the size of the polaron resistivity decreases because of the reduction of E_Cin (3). Consequently, in the narrow interval of temperature decrease is a huge reduction in the electrical resistivity and the transition of the sample from a dielectric state into metal is economical. The sample becomes bad a metal with a low MS values.

In connection La_1-xCa_xMn_1-zO_3+δobtained by the claimed method, the concentration of Mn⁺⁴x_Mn+4exceeded (see table 1) the percolation threshold x_then=0.22. Note that samples with N=0 is not moving in the metallic state in the entire investigated temperature region 5 are 300 K (figure 1). This is due to the fact that the size of the clusters increases with decreasing temperature, but not as rapidly as in the known method.

Cluster sizes D_klincrease (figure 3) is approximately 1.5 times when the temperature decreases from room temperature up to T≈125 T_Withsamples. The sizes of clusters estimated by measurements of super-paramagnetic properties of the method proposed in [NI Solin. The law of conductivity Efros-Shklovskii and localized States in kabalarian lanthanum manganites. JETP letters, v.91, no. 12, s-749(2010)]. This method allows to determine the size of the clusters to T≈125 K≈1.5 T_With. Change cluster sizes depending on the temperature can be approximately estimated from the activation energy, is shown in the insert of figure 1, using the expression (2). The value of E_Withdecreases by about 1.5-1.7 times, while lowering the temperature to T_Within agreement with the corresponding increase in the size of the clusters (see (2) and 3). From reducing E Withfrom 150 to 30 MeV (box 1) and (2) you can roughly estimate that the cluster size is increased to ≈5-6 nm at T=50 K. In semiconductor physics the activation energy is expressed in electron-volts, which corresponds to 1 eV≈11600 K. (Physical encyclopedic dictionary edited Amerkhanov, str, Moscow, "Soviet encyclopedia", 1983). Then E_With=30 MeV corresponds to 350 K, i.e. the temperature (energy) of the Coulomb blockade is always considerably higher than the temperature of the sample, which provides a non-metallic behavior of the electrical resistance.

In La_1-xCa_xMn_zO₃there current carriers (Mn⁺⁴with concentration x_Mn+4=x+3(1-z), i.e. ion Sa creates 1 ion Mn⁺⁴and each vacancy Mn creates 3 ion Mn⁺⁴. These ions Mn⁺⁴different influence on the magnetic state and accordingly the temperature of the transition to the conducting (metallic) state. Ferromagnetism in manganites due to the double exchange mechanism of manganese ions through oxygen ion: Mn⁺³-O^-2-Mn⁺⁴. Ions of Mn⁺⁴arising from the substitution of La⁺³CA⁺²in La_1-xCa_xMnO₃when x≥0.22, turn the sample below T_Cin the ferromagnetic metallic state. Although the deficiency of Mn in La_1-xCa_xMn_1-zO₃is a source of additional ions Mn^{+4 he does not gain double exchange. According to the results of our research (see table 2) T_Cis not increased, and decreased with increasing concentration of CA. The sample does not come in the metallic state, as the removal of manganese ion destroys the link in the chain of jump of the electron Mn+3-On-2-Mn+4and, apparently, promotes the appearance of additional clusters. These ions Mn+4we believe, localized in a cluster near the vacancy Mn, and the increase in the concentration of Mn+4reduces energy double exchange, as vacancies Mn increase the distance of the jump of the electron in the chain of Mn+3-On-2-Mn+4. As a consequence, T_Cweakly decreases with increasing the concentration of CA (see table 2). As our research shows, these samples do not have a high magnetoresistive properties.}

Annealing in oxygen creates an excess of oxygen in La_1-xCa_xMn_zO_3+δ, cation vacancies, La, CA, Mn and additional charge carriers localized on Iona Mn⁺³forming Mn⁺⁴with concentration x_Mn+4=x+3(1-z)+2δ, and increases the carrier concentration above the threshold flow. Apparently, they are localized near vacancies, forming clusters. This is evidenced by the results of measurements of the magnetization. The magnetization of the sample obtained by the claimed method, the por is low fields (H≈0) is approximately 2 times less than the magnetization of the sample, obtained in a known manner, and increases with increasing magnetic field strength (figure 4) to the values of the magnetization of the sample obtained in a known manner. This means that in the prepared by the claimed method the sample about half of the magnetic moments localized in clusters and in a magnetic field, they line up along the magnetic field direction, increasing the size of the magnetic clusters (figure 5), which, in turn, leads to high values of MS. The majority of carriers localized in clusters and are excluded from the exchange interaction. The sample is low-alloy connection with disseminated in clusters. Because of this increased distance of the jump of the electron in the chain of Mn⁺³-O^-2-Mn⁺⁴reduced energy double exchange. T_Creduced by 35-75 K for x=0.05-0.15. The samples with x=0.05-0.15 become a ferromagnet with close values of T_C≈85-92 (see table 2).

The magnetoresistance due to the increasing size of the polaron (clusters) in a magnetic field and are determined mainly by the 1st term in (3). Clusters in the manganites are strongly linked with the magnetic matrix, they are in the so-called modulated canted antiferromagnetic structure. The clusters are not free, are strongly linked with the magnetic matrix and oriented in a certain way Rel is relative to the crystallographic axes. For example, in La_0.90Ca_0.10MnO₃the magnetic moments of the clusters is directed perpendicular to the axis of antiferromagnetism. [R. Kober-Lehouelleur et al., Magnetic ground state of low-doped manganites probed by spin dynamics in a magnetic field, Phys. Rev B, 70, 144409 (2004)]. The cluster sizes increase due to establishment of the neighboring cluster ions MP matrix and ions MP cluster along the direction of the magnetic field, increasing the magnetization of the sample (figure 4). In manganites, the cluster sizes can increase tenfold in a magnetic field, which leads to a decrease in the energy of the Coulomb blockade E_Within (2) and the relation E_C/k_InT in (3). Due to the exponential dependence of electrical resistivity (3) the size of the clusters, it can be reduced in the hundreds of thousands of times. However, close to Those in the known method, the temperature facilitates the integration of clusters in large. Due to this change cluster size, respectively, and the electrical resistivity in a magnetic field is not that big. For example, if the cluster size with decreasing temperature increases from 1 nm to 50 nm, at T=50 K the ratio of E_C/k_BT≈1 when N=0, even when the increase in the magnetic field of the cluster size to infinity (EC=0), the maximum value of MS is small: MS=ρ(H=0)/ρ(H)=exp[E_C(N=0)/k_BT]/exp[E_C(N)/k_BT]≈ exp(1)≈2-3. In the present method, as shown by the estimates is use, change the size of the cluster when the temperature drops almost 10 times smaller (see box in figure 1 and figure 3). As a consequence, the achieved conditions for obtaining high values of MS.

The temperature dependence of the relative sizes of the clusters in the fields 1-9 samples obtained by the claimed method, where R_kl(T,N) and R_kl(T,H=0) - the sizes of clusters at a given temperature T and magnetic field H and H=0, respectively, is shown in figure 5. As can be seen (figure 5), the size of the clusters increased with increasing magnetic field strength from ten percent at room temperature up to several hundred percent at low temperatures. Due to the exponential dependence of the electrical resistance (3) from the cluster size magnetoresistance reaches values of more than 10⁵-10⁶% at low temperatures (figure 2). Field and temperature dependence of cluster size are well described in the model of phase separation in metal drops a small radius in the dielectric paramagnetic and antiferromagnetic matrix [Musican, Cigugur, Inhomogeneous charge state and phase separation in manganites, Phys 171, 577 (2001)].

From table 3 it can be seen that the inventive method allows to obtain higher values of MS in a wide range of temperatures with less energy consumption set is controlled by the duration of heating at high temperatures in an hour. Other costs associated with obtaining samples (weighing, grinding, extrusion and the like), it is assumed approximately equal.

The practical value of the proposed method is that this method allows to obtain compounds with significantly higher (up to 10²-10³time) values of magnetoresistance, especially when nitrogen and helium temperatures, in comparison with the known and the most intimate of ways. Another aspect of the compounds, obtained by the claimed method, is monotonic growth of their MS from magnetic fields up to 9 Tesla. This opens up the possibility to use the proposed method in the manufacture of a more wide-range (up to 9 T and more) magnetoresistive sensors magnetic field sensors in a strong constant and pulsed magnetic fields.

These results provide good prospects for the use of the proposed method for creating materials for magnetoresistive sensors in cryogenic and space magnetometry.

Thus, the use of the claimed invention will:

- to develop the elements of microelectronics based on the effect of CCM in a wide range of operating temperatures from 5 to 300 K;

- get up to 10³times more sensitive to the magnetic field than previously known, the elements of microelectronics;

- reduce for the rata, compared with the known method for the production of materials with CCM by reducing the duration of annealing in air, exceptions hardening and reduce the temperature of annealing in oxygen.

The method of producing lanthanum manganite doped with calcium, the reaction of the oxides of lanthanum, manganese and calcium, including chafing, the first annealing in air at 1350±50°C, cooling to room temperature, re-grinding and pressing of the material obtained in tablets, re-annealing it in air at 1350±50°C and subsequent annealing in oxygen and cooled to room temperature, characterized in that as lanthanum manganite doped with calcium, get La_1-xCa_xMn_1-zO₃in which the concentration of calcium pick 0.05<x<0.22, the concentration of manganese select 0<z≤0.05, the first annealing in air is carried out in 12 hours, repeated a second annealing in air should be performed within 4 hours annealing in oxygen is carried out at T=650±20°C for 50 hours and subsequent cooling to room temperature is performed on the air at a speed of not less than 10°C/min