Solid solutions of BiFeO3– SmCoO3were synthesized by a solid-state method. Peculiarities of the  influence of isovalent substitution of Bi 3+ and Fe 3+ ions in BiFeO3by Sm 3+ , Co 3+ ions on the crystal  structure and magnetic properties of Bi1–xSmxFe1–xCoxO3solid solutions are found. It is shown that the  substitution 3-25% of the Bi 3+ , Fe 3+ ions in BiFe0O3by Sm 3+ , Co 3+ ions results in the gradual destruction of the antiferromagnetic and conception of ferromagnetic ordering. In this case replacing up to  10% of Sm 3+ and Co 3+ ions in SmCoO3by Bi 3+ and Fe 3+ ions leads to the stabilization of Co 3+ ions in a  diamagnetic state

Bashkirov, L. A.

Galyas, A. I.

Lobanovski, L. S.

Petrov, G. S.

Trukhanov, S. V.

Zatsiupa, A. A.

Solid solutions of BiFeO3– SmCoO3were synthesized by a solid-state method. Peculiarities of the influence of isovalent substitution of Bi 3+ and Fe 3+ ions in BiFeO3by Sm 3+ , Co 3+ ions on the crystal structure and magnetic properties of Bi1–xSmxFe1–xCoxO3solid solutions are found. It is shown that the substitution 3-25% of the Bi 3+ , Fe 3+ ions in BiFe0O3by Sm 3+ , Co 3+ ions results in the gradual destruction of the antiferromagnetic and conception of ferromagnetic ordering. In this case replacing up to 10% of Sm 3+ and Co 3+ ions in SmCoO3by Bi 3+ and Fe 3+ ions leads to the stabilization of Co 3+ ions in a diamagnetic state

Belarusian State Technological University

Chemistry and Technology of Inorganic Materials and Substances 31  УДК 537.6224 A. A. Zatsiupa, PhD (Chemistry), assistant lecturer (BSTU); L. A. Bashkirov, D.Sc. (Chemistry),  professor (BSTU); G. S. Petrov, PhD (Chemistry), assistant professor (BSTU); L. S. Lobanovski,  PhD (Physics and Mathematics), senior researcher (Scientific and Practical Materials Centre  of Belarus NAS); S. V. Trukhanov, PhD (Physics and Mathematics), senior researcher  (Scientific and Practical Materials Centre of Belarus NAS); A. I. Galyas, PhD (Physics  and Mathematics), senior researcher (Scientific and Practical Materials Centre of Belarus NAS) MAGNETIC PROPERTIES OF SOLID SOLUTIONS OF BiFeO3 – SmCoO3 SYSTEM  Solid solutions of BiFeO3 – SmCoO3 were synthesized by a solid-state method. Peculiarities of the influence of isovalent substitution of Bi3+ and Fe3+ ions in BiFeO3 by Sm3+, Co3+ ions on the crystal structure and magnetic properties of Bi1–xSmxFe1–xCoxO3 solid solutions are found. It is shown that the substitution 3-25% of the Bi3+, Fe3+ ions in BiFe0O3 by Sm3+, Co3+ ions results in the gradual destruc-tion of the antiferromagnetic and conception of ferromagnetic ordering. In this case replacing up to 10% of Sm3+ and Co3+ ions in SmCoO3 by Bi3+ and Fe3+ ions leads to the stabilization of Co3+ ions in a diamagnetic state.  thIntroduction. BiFeO3compound belongs to ferroelectromagnetics (multiferroics), i.e. sub-stances with simultaneous electric dipolar and magnetic spin ordering. Communication between magnetic and electric subsystems in ferroelectro-magnetics manifesting itself as magnetoelectric effects, affords ground for controlling magnetic properties of a material by means of the electric field and, on the contrary, for carrying out modula-tion of electric polarization by means of the mag-netic field. All this helps consider  multiferroics as possible materials for creating essentially new de-vices in information and energy saving technolo-gies, magnetic memory devices and spin electron-ics, magnetic field sensors, etc. [1–3]. Bismuth ferrite BiFeO3 is the only material showing both ferroelectric and antiferromagnetic ordering (with a weak ferromagnetic contribution) at room temperature, which offers exciting possi-bilities for its practical application. However, the existence of spatially-modulated cycloid-type spin structure in BiFeO3 (every iron ion is surrounded with six iron ions with noncollinear antiferromag-netic spin ordering) the modulation period of which is incommensurate with the crystal lattice period, results in almost full suppression of a magnetoelectric effect in volume samples of BiFeO3. Application of large magnetic fields (not less than 20 T), substitution of Bi3+ ions by ions of rare-earth elements or Fe3+ ions by ions of oth-er metals promotes transition to proportional fer-romagnetic ordering. The present paper deals with the study of the magnetic properties of Bi1–xSmxFe1–xCoxO3 solid solutions generated as a result of simultaneous isovalent substitution of Bi3+ ions by Sm3+ ions in BiFeO3 and equivalent amount of Fe3+ ions by Co3+ ions. Experimental technique. The synthesis of polycrystalline samples of the Bi1–xSmxFe1–xCoxO3 solid solutions (0 ≤ x ≤ 1.0) was carried out by sol-id-state method from Bi2O3, Fe2O3, Sm2O3 and Co3O4. Powders of the starting compounds taken in set molar ratios were mixed and ground for 30 minutes in a planetary mill with the addition of ethanol. The received batch with ethanol in it was pressed under pressure of 50–75 MPa to produce tablets 25 mm in diameter and 5–7 mm high which then were fired in the air at 800°C for 8 hours. Af-ter preliminary firing the tablets were crushed, ground and pressed to produce bars 30 mm long with the cross-section of 5x5 mm2. Conditions of synthesizing samples of the system in the air de-pended on the composition and varied greatly: T = 850–1250°C, lasting from 30 minutes to 8 hours. The more bismuth ions were substituted by rare-earth element ions, the higher the synthesis temperature was. X-ray diffractograms were received on the D8 ADVANCE diffractometer with the use of CuKα-radiation. The crystal structure parameters were determined by means of the X-ray diffraction tabu-lar RTP processor and data of the card catalogue of the International Center for Diffraction Data (ICDD JCPDS). Research workers of the Scientific and Practi-cal Materials Centre of the NAS of Belarus meas-ured specific magnetization (σsp) of the samples obtained at 7 and 300 K in the fields of up to 14 T and their specific magnetic susceptibility (χsp) in the  magnetic field of 0.86 T at  the temperatures ranging from 7 to 300 K by the vibration method, using the universal high-field measuring system (Cryogenic Ltd, London) and  Faraday method,  the range of temperatures being 77–950 K.  Results and discussion. From the data obtained by the X-ray phase analysis of samples of the (1 – x)ВiFеО3 – x SmCoO3 system (Fig. 1) it follows that in the system involved solid solutions with per-ovskite structure, based on both ВiFеО3 and  SmCoO3, are generated though some of them con-tain impurity phases of Bi25FeO39, CoFe2O4 ferrites. 32 ISSN 1683-0377. Proceedings of BSTU. 2013. No. 3. Chemistry and Technology of Inorganic Substances   20 30 40 50 60 70 80****109876543212град   Fig. 1. X-ray diffractograms of Bi1–xSmxFe1–xCoxO3 samples when x values are different: 1 – 0; 2 – 0.03; 3 – 0.05; 4 – 0.1; 5 – 0.25; 6 – 0.5;  7 – 0.75; 8 – 0.9; 9 – 0.95; 10 – 1.0; * – phase Bi25FeO39; □ - CoFe2O4  The crystalline structure of ВiFеО3 was characterized by a rhombohedrally distorted cell of perovskite with the following parame-ters: a = 3.963 Å and α = 89°44' which is co-herent with literary data [4]. With the increase in the degree of substitution of x of Fe3+ ions by Co3+ ions and of Bi3+ ions by Sm3+ ions up to 0.1 there is a gradual approach to concentration transition from the rhombohedrally distorted cell of perovskite of ВiFеО3 to the orthorhom-bically distorted structure of perovskite which Bi1–xSmxFe1–xCoxO3 solid solutions with 0.1 ≤ x ≤ 1.0 possess (Fig. 1). Dependences of specific magnetization (σsp), measured by Faraday method in the magnetic field of 0.86 T for the Bi1–xSmxFe1–xCoxO3 solid solu-tions are given in Fig. 2. Fig. 2 shows that the increase of  x substitution degree in diamagnetic ions of Bi3+ by paramagnetic ions of Sm3+ and of paramagnetic ions of Fe3+ by Co3+ ions which at temperatures below 300 K are in the diamagnetic low-spin (LS) state, and at higher temperatures - in paramagnetic intermediate (IS) or high-spin (HS) states, results in gradual rise of specific magnetization. For example, at 300 K σsp for the Bi1–xSmxFe1–xCoxO3 sample when x = 0.03 is equal to 0.63 Gs · cm3/g, and for the samples when x = 0.05; 0.10; 0.25 it is equal to 1.49; 3.97; 14.34 Gs · cm3/g respectively. In this case, marked increase in specific magnetization of Bi1–xSmxFe1–xCoxO3 samples with x increasing from 0.03 to 0.25 can be explained by the presence of ferromagnetic phase of CoFe2O4 ferrite  in samples where x = 0.1 and 0.25. The increase of σsp in growth of a degree of substitution of x can be also a consequence of structural distortion when intro-ducing samarium ions with a smaller ionic radius (rSm3+ = 0.97 Å) [5], than in bismuth ions (rBi3+ = 1.20 Å) [5] which promotes the destruction of spiral spatially-modulated structure of ВiFеО3 and emergence of weak ferromagnetism. For ex-ample, such destruction of the spatially-modulated structure with the formation of solid solutions of Bi1–xSmxFe1–xCoxO3 when Bi3+ ions were substitut-ed by Sm3+ ions was reported in papers [6, 7].                       Fig. 2. Dependences of specific magnetization (σsp)  on temperature T for Bi1–xSmxFe1–xCoxO3 samples  when x values are different: 1 – 0.03; 2 – 0.05; 3 – 0.1; 4 – 0.25; 5 – 0.5; 6 – 0.75;  7 – 0.9; 8 – 0.95; 9 – 1.0    It should be noted that the type of curves of temperature dependences σsp for Bi1–xSmxFe1–xCoxO3 solid solutions (0.03 ≤ x ≤ 0.5) (fig. 2, a) is indicative of the presence in the samples of the ferromagnetic phase for which Curie temperature (Tc) changes slightly. So, for solid solutions with x = 0.03; 0.05; 0.10; 0.25 Tc is equal to 789; 778; 767; 739 K respectively. However, on roentgeno-grams of the samples with 10 and 25% degree of substitution there is an X-ray peak of the most in-tensive reflex of CoFe2O4 ferrite (2Θ = 35.43º, d = 2.53144 Å) for which Curie temperature and specific saturation magnetization (σsp) at 0 K are equal to 793 K and 90 Gs · cm3/g respectively [8]. It greatly hinders the interpretation of magnetic properties of the solid solutions under considera-tion. However, the weight of evidence suggests that ferromagnetism of the samples is caused not only by the presence of the ferromagnetic phase, CoFe2O4, but also by weak ferromagnetism of the main phase, since on roentgenograms of the sam-10 9 8 7 6 5   2 1   20        30         40        50       60         70        802, degree 0      200   400    600   800   1000 16128403142sp, Gs  сm3/g T, К    sp, Gs  сm3/g sp, Gs  сm3/g 0.240.160.080      200   400    600   800   1000T, К 67895 0 200 400 600 800 1000 T, К 1.20.80.40Chemistry and Technology of Inorganic Materials and Substances 33  ples with x = 0.03; 0.05 CoFe2O4 impurity is ab-sent, but temperature dependences of specific magnetization of the samples (Fig. 2, a) show the presence of a ferromagnetic phase in them. On temperature dependences of magnetization for the Bi1–xSmxFe1–xCoxO3 samples with the de-gree of substitution x = 0.03 and 0.05 and no CoFe2O4 impurity, as well as with x = 0.1 and 0.25 and impurity of the ferromagnetic phase, CoFe2O4 there were various anomalies observed to show that substitution of 25% of Bi3+, Fe3+ions by those of Sm3+, Co3+ in BiFeO3 did not result in complete collapse of antiferromagnetic ordering of magnetic moments of Fe3+ ions in the basic BiFeO3 compound. Temperature dependences of specific magneti-zation for SmCoO3 and the Bi1–xSmxFe1–xCoxO3 solid solution with х = 0.95 (Fig. 2, b, Curves 8, 9) show that, indeed, spin transition of Co3+ ions from diamagnetic LS to paramagnetic IS and/or HS state in SmCoO3 occurs over the temperature range of 300–650 K (with the increase of temperature, σsp does not decrease as it should be in the  paramag-netic but increases) and in the solid solution with x = 0.95 spin transition is observed over the tem-perature range of 400–800 K. Dependence of σsp on T for the Bi1–xSmxFe1–xCoxO3 sample with x = 0.9 (Fig. 2, b, Curve 7) already has no region of increasing σsp when temperature rises. Therefore, in the solid solution involved spin transition of Co3+ ions over the temperature range of 77–1000 K is not observed and Co3+ ions are in the diamagnet-ic low-spin state at up to 1000 K. Field dependences of specific magnetization for the Bi1–xSmxFe1–xCoxO3 samples (x = 0; 0.03; 0.05; 0.1) measured at temperatures of 7 and 300 K, are given in Fig. 3. It is established that in small magnetic fields (H < 2–5 T), both at the temperature of 7 K and at 300 K, the growth of specific magnetization of cobaltite-ferrites Bi1–xSmxFe1–xCoxO3 in which 0.03 ≤ x ≤ 0.25 when the magnetic field increases is not linear. However, with further increase in the field up to 14 T linear dependence of σsp on H is observed: σsp = σo + χH,  where σo – the value of spontaneous magnetization obtained on extrapolation of an area of linear de-pendence of σsp on H up to H = 0; χH – magnetiza-tion due to a paraprocess.   Fig. 3. Dependences of specific magnetization (σsp)  on magnetic field intensity (H) at temperatures of 7 K (a) and 300 K (b) for Bi1–xSmxFe1--xCoxO3 samples when the degree of x substitution is: 1 – 0; 2 – 0.03; 3 – 0.05; 4 – 0.1  At the temperature of 300K demagnetization curves for the cobaltite-ferrites involved show absence of remaining magnetization (σr) and co-ercive force (Hc) which are observed on the field dependences of  σsp at the  temperature of 7 K (see the table). It demonstrates the existence of  ferromagnetic phase both in samples of Bi1–xSmxFe1–xCoxO3 with x = 0.03; 0.05where there is no impurity of cobaltite-ferrites, CoFe2O4 and in samples with x = 0.1; 0.25 in which this ferro-magnetic phase exists. Pay attention that in [9] the results of  nickel magnetization study are given at temperatures which are slightly higher than the Curie ferromag-netic temperature, in a so-called transitional area. It is shown that transition from ferromagnetic state into paramagnetic one occurs gradually, and in the transitional area of temperatures both states coex-ist. As the temperature moves off from the Curie temperature, field dependence gradually changes from the curves with nonlinear dependence in weak and linear dependence in strong magnetic fields in which magnetization increases due to a paraprocess, to uniform linear dependence both in small and large fields. Table Values of spontaneous specific magnetization (σo) and specific magnetization in the magnetic field of 14 T (σ14), specific residual magnetization (σr) and coercive force (Hc) at 7 and 300 K for Bi1–xSmxFe1–xCoxO3  Composition x 7 K 300 K σ0, Gs · cm3/g σ14, Gs · cm3/gσr, Gs · cm3/g Нс, kOe σ0, Gs · cm3/g σ14, Gs · cm3/g 0.03 0.6 1.9 0.5 2.0 0.6 1.90.05 1.5 2.8 1.0 2.0 1.6 2.60.1 4.5 6.3 2.5 2.0 4.0 5.00.25 17.2 20.6 11.9 2.0 15.3 16.40.5 1.5 4.0 0.7 3.0 0.4 1.7–26420sp, Gs  сm3/g sp, Gs  сm3/g –2–4  2  4  6  8  10 12 14Н, Т Н, Т43214321   2  4  6  8 10 12 14–2–4–2642034 ISSN 1683-0377. Proceedings of BSTU. 2013. No. 3. Chemistry and Technology of Inorganic Substances  The obtained field and temperature depend-ences of specific magnetization for solid solutions of the Bi1–xSmxFe1–xCoxO3 system also show that partial substitution of Bi3+, Fe3+ ions in antiferro-magnetic bismuth ferrite BiFeO3 by ions of Sm3+, Co3+ results in gradual destruction of antiferro-magnetic ordering and in generation of ferromag-netic ordering, and there is an area which is transi-tional for the degree of x substitution in which both states of magnetic ordering coexist.   Fig. 4. Dependences of specific magnetization (σsp)  on magnetic field intensity (H) at temperatures of 7 K (a) and 300 K (b) for Bi1–xSmxFe1–xCoxO3 samples  with the degree of x substitution: 1 – 0.75; 2 – 0.9; 3 – 0.95; 4 – 1.0  In the Bi1–xSmxFe1–xCoxO3 solid solutions with 0.75 ≤ x ≤ 1.0 there is no magnetic ordering of paramagnetic ions, and over the temperature range of 5–1000 K they are paramagnetic (Fig. 2, b). However, linear dependence σsp on H at up to 14 T is observed at T = 300 K (Fig. 4, b), while at 7 K it is absent (fig. 4, a). Conclusion. Solid solutions of the (1 – x)BiFeO3 – x SmCoO3 system were synthesized by solid-state method. It has been established that in the system concerned solid solutions of Bi1–xSmxFe1–xCoxO3, cobaltite-ferrites with the struc-ture of both rhombohedrally distorted perovskite (0 ≤ x ≤ 0.05) and orthorhombically distorted one (0.1 ≤ x ≤ 1.0) are formed. The results of the re-search show that substitution of  3 – 25% of Bi3+, Fe3+ in BiFeO3 by Sm3+, Co3+ ions leads to gradual destruction of antiferromagnetic ordering and to generation of ferromagnetic ordering, and that there is a transitional by degree of x substitution area in which both states of magnetic ordering co-exist. It is established that substitution of 10% of Sm3+ and Co3+ in SmCoO3 by ions of Bi3+ and Fe3+ promotes the stabilization of Co3+ ions in a dia-magnetic state, which causes gradual temperature offset of Co3+ diamagnetic ions spin transition into the paramagnetic state: from 300 K for SmCoO3 to 1000 K for Bi0.1Sm0.9Fe0.1Co0.9O3 solid solution. The work has been performed within the task 1.02 of the GPNI "Functional and Engineering Industry Materials and Technologies, Modern Na-nomaterials and Nanotechnologies. References 1. Пятаков, А. П. Магнитоэлектрические материалы и мультиферроики / А. П. Пятаков, А. К. Звездин // Успехи физических наук. – 2012. – Т. 182, № 6. – С. 593–620.  2. Catalan, G. Physics and Applications of Bis-muth Ferrite / G. Catalan, J. F. Scott // Advanced Materials. – 2009. – Vol. 21. – P. 2463–2485. 3. Khikhlovskyi, V. V. The renaissance of mul-tiferroics: bismuth ferrite (BiFeO3) − a candidate multiferroic material in nanoscience / V. V. Khi-khlovskyi [Electronic resource]. – 2010. – Mode of access: http://www.rug.nl/zernike/education/ top-masternanoscience/NS190Khikhlovskyi.pdf. – Date of access: 22.03.2012. 4. Макоед, И. И. Получение и физические свойства мультиферроиков: монография / И. И. Макоед. – Брест: БрГУ, 2009. – 181 с. 5. Шаскольская, М. П. Кристаллография / М. П. Шаскольская. − М.: Высш. шк., 1976. – 391 с. 6. Effect of Sm substitution on ferroelectric and magnetic properties of BiFeO3 / V. A. Khom-chenko [et al.] // Scripta Materialia. – 2010. – Vol. 62. – P. 238−241. 7. Mansour, A.-H. X-ray diffraction and mag-netization studies of BiFeO3 multiferroic com-pounds substituted by Sm3+, Gd3+, Ca2+ / A.-H. Mansour // Cryst. Res. Technol. – 2010. – Vol. 45, № 1. – P. 89−93. 8. Смит, Я. Ферриты / Я. Смит, Х. Вейн. – М.: Изд-во иностранной литературы, 1962. – 504 с. 9. Белов, К. П. Магнитные превращения / К. П. Белов. – М.: Государственное издательство физико-математической литературы, 1959. – 259 с. Received 20.02.2013 а b0    4     8    12   16 Н, Т sp, Gs  сm3/g sp, Gs  сm3/g 0     4     8    12    16Н, Т12341,2 0,8 0,4 0,0 6 4 2 0 

Magnetic properties of solid solutions of BiFeO3– SmCoO3 system

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Magnetic properties of solid solutions of BiFeO3– SmCoO3 system

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