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Kazin P.E., et al. Nanosystems: Phys. Chem. Math., 2024,15 (1), 80-97.
http://nanojournal.ifmo.ru
Original article
DOI 10.17586/2220-8054-2024-15-1-80-97
Single-domain particles of manganese-for-iron substituted M-type barium hexaferrite: synthesis, crystal structure, and magnetic properties
Pavel E. Kazin1, Anastasia E. Sleptsova2, Alexander V. Vasiliev1, Artem A. Eliseev1, Robert E. Dinnebier2, Sebastian Bette2
1 Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia 2Max Planck Institute for Solid State Research, Stuttgart, Germany
Corresponding author: Pavel E. Kazin, [email protected]
PACS 75.47.Lx; 61.90.+d
Abstract Single-phase barium hexaferrite powders with crystallite sizes in a single-domain region and with the general composition BaFe i2-xMnxOi9, where x — 0, 2, 4, 6, were synthesized applying a citric sol-gel auto-combustion technique with final annealing temperatures of 900 - 1200 °C. The crystal structures were refined, and the magnetic properties were studied. The observed variations in atomic positions with the Mn-for-Fe substitution revealed presence of Mn in three oxidation state +2, +3, and +4, with a preference of Mn2+ to the tetrahedral 4f1 site and Mn4+ to the octahedral 2a and 12k sites. With the Mn-doping, the samples' magnetization decreased, while coercivity increased and reached 8.4 kOe for x — 6. The rise of the annealing temperature resulted in a slight growth of magnetization with a general tendency of the coercivity to decrease. A Curie temperature decreased with the Mn-doping remaining above room temperature for the maximal doping.
Keywords magnetic materials, ferrites, crystal structure, magnetization, coercivity
Acknowledgements The reported study was funded by RFBR, project number 21-53-12002.
For citation Kazin P.E., Sleptsova A.E., Vasiliev A.V., Eliseev A.A., Dinnebier R.E., Bette S. Single-domain particles of manganese-for-iron substituted M-type barium hexaferrite: synthesis, crystal structure, and magnetic properties. Nanosystems: Phys. Chem. Math., 2024,15 (1), 80-97.
1. Introduction
M-type hexaferrites are widely used to produce permanent magnets due to their excellent chemical and thermal stability and due to the low production costs, despite their moderate magnetic parameters such as magnetic energy and coercivity [1]. Besides that, there are very good prospectives for their application in ultra-high frequency devices functioning up to THz frequencies as well as in medium for high-density magnetic recording [2,3]. Variation in the chemical composition of hexaferrite has proven to be an excellent instrument to adjust and optimize the material magnetic properties [4,5]. This way, e.g., a giant coercivity and a sub-terahertz resonance have been achieved for an Al-Ca co-doped strontium hexaferrite [6,7]. However, in many cases the results of the hexaferrite doping are hard to predict because of the complex crystal structure in which the dopant atoms may prefer different crystallographic sites. In particular, partial substitution of Fe3+ by Mn3+ in MFei2Oi9 (M = Ba, Sr) resulted not only in the non-uniform site occupancies but also in the variation of the dopant atom oxidation state [8-11]. Using neutron diffraction, it was shown that in BaFei2-xMnx O19, Mn preferred 2a, 4f1, 12k, and to a less extent 4f2 sites, whereas it was not found in 4e site [9]. The authors observed that the (Fe,Mn)-O distance in the tetrahedral 4f1 site tended to increase with the Mn-doping suggesting that Fe3+ was replaced by Mn2+ cations. Because of the limited accuracy of the crystal structure parameters determination, the authors did not observe distinct regularities in other (Fe,Mn)-O distances and offered only a tentative picture of the Mn ions distribution in different oxidation states in the crystal structure. The magnetic properties of such deep Mn-substituted hexaferrites were studied only for coarsely grained samples prepared by a standard ceramic technology. Whereas maximum coercivity values may be obtained for single-domain particles which possess sizes in nanometer and submicron regions. Possibly smaller particles, with the size in a nanometer scale, are especially attractive candidates for high-density magnetic recording [3]. For a small Mn-for-Fe substitution the study of submicron particles revealed certain enhancement in coercivity [12,13]. Since an above-room-temperature ferrimagnetic order remains even in highly Fe-for-Mn substituted compounds, it looks useful to extend the study to deep Mn-doped hexaferrite samples representing ensembles of singledomain particles. In the present paper, we consider the synthesis of such BaFe12-xMnxO19 samples and investigate in detail their crystal structure and magnetic properties.
© Kazin P.E., Sleptsova A.E., Vasiliev A.V., Eliseev A.A., Dinnebier R.E., Bette S., 2024
2. Experimental
2.1. Samples preparation
The preparation method was similar to that described in [14]. The starting compounds, chemically grade BaCO3, Fe(NO3)3 • 9H2O, and Mn(NO3)2 • 4H2O, were taken in stoichiometric quantities corresponding to nominal compositions BaFe12-xMnxO19, where x = 0, 2, 4, 6. BaCO3 was dissolved in an excess of 5 % nitric acid using magnetic stirring. Nitrates of iron and manganese were dissolved in the obtained solution. Solid citric acid was added to the solution in a stoichiometric quantity corresponding to 3 mol of acid per 1 mol of all metal cations, and the solution pH was adjusted to 7 by adding dropwise a 25 % ammonia solution. The resulting solution was slowly evaporated on a heated sand bath to a viscous state with consequent initiation of a self-propagating exothermal reaction. The obtained highly porous product was heated in a furnace in air for 2 hours to a certain annealing temperature Tan, dwelled for 2 hours at this temperature, and quenched in air. The annealing temperatures were 900, 1000, 1100, and 1200 °C.
2.2. Samples characterization
High-precision X-ray powder diffraction (XRD) was conducted on a STOE STADI/P powder diffractometer in the Debay-Scherer geometry using MoKa1 radiation in the 20 range 2 - 110° with the 20 step of 0.015°. The crystal structure was refined in the space group P63/mmc using the Jana 2006 computer program [15]. The reflection's profile parameters, unit cell parameters, positional and isotropic atomic displacement parameters were refined. Occupancies of Fe and Mn were fixed assuming a uniform distribution of the elements at 3d metal atom sites admitting full occupancies of the sites. Crystallite sizes (diameter d and thickness h of platelike particles in ab plain and c direction, respectively) were estimated by fitting a full XRD pattern profile taking into account broadening of the XRD reflections caused by instrumental parameters, crystallite sizes, and effects of crystal strain. Because of correlations between the crystallite size parameters and the strain parameters, only smaller size h is reliably estimated with a large uncertainty though. To suppress the correlations, the strain parameters were assumed to be negligibly small and were set to zero. This allowed us to estimate both d and h. The latter parameter after this procedure was reduced by 20 - 30 %. The parameters obtained this way may be regarded as lower boundary values for average crystallite sizes. These values have to approach real crystallite dimensions for crystals without defects. The parameters were estimated for the samples annealed at temperatures up to 1100 °C. For Tan = 1200 °C, the lines broadening due to a crystal size was too small to be reliably determined.
Measurements of magnetization were performed on an original Faraday Balance magnetometer at the room temperature in the field range -17 - +17 kOe. A powder sample was fixed with glue on a small piece of paper to prevent rotation of the particles in magnetic field.
Measurements of the Curie temperatures were carried out using a Perkin-Elmer Pyris Diamond TG/DTA with a permanent Fe-Nd-B magnet fixed outside the sample chamber. A transition from paramagnetic to ferrimagnetic state was registered by monitoring an effective weight of the sample on the sample cooling with a rate of 10 Kmin-1.
Scanning electron microscopy observations were performed on a Carl Zeiss Leo Supra VP50 electron microscope.
3. Results and discussion
3.1. Crystal structure features and morphology
As evidenced from the XRD analysis all the samples comprise pure hexaferrite phases with a hexagonal crystallo-graphic symmetry. According to the scanning electron microscopy, samples annealed at 900 °C consist of grains looking like thick plates with a typical diameter of 100 - 200 nm and thickness of 50 - 100 nm (Fig. A1, Appendix). With the increasing of the annealing temperature, the grains grow reaching a diameter of 300 - 400 nm and thickness of 100 -200 nm for Tan = 1100 °C. For Tan = 1200 °C, a further and considerable increase in the grain size takes place. The crystallites become more anisotropic in shape and represent rounded plates with an average diameter of 0.7 micron in the undoped sample and 1-2 microns in the doped samples. The XRD peaks profile analysis provides values for the crystallites diameter and thickness (Table 1) corresponding well to the SEM results. This implies that the observed grains are single crystals. They have to be perfect enough since the line broadening connected to crystal defects and strains was considered as a negligible one in the XRD analysis. In general, undoped samples contain somewhat thicker platelike particles than Mn-doped ones. For the lowest annealing temperature, Mn-doped samples have slightly finer grains. With the Tan increase, a stronger growth of grains takes place in Mn-doped samples, and the most pronounced effect is observed in the sample with the maximum Mn content.
The critical diameter dc for a BaFe12O19 grain to represent a single magnetic domain is of 0.8 micron [4]. The Mn-doping usually leads to reduction of saturation magnetization Ms [8,9], and dc is expected to grow with the doping since it is inversely proportional to Ms2. Therefore, we regard that all the samples obtained represent ensembles of mostly monodomain grains. It especially concerns the samples annealed at lower temperatures.
The XRD patterns of all the samples are shown in Figs. A2-A17. The major results of the crystal structure refinement are collected in Table A1. Complete lists of atomic parameters are presented in Tables A2 and A3 for two limiting compositions, BaFe12O19 and BaFe6Mn6O19, for the samples annealed at 1200 °C. The dependencies of the crystal cell
Table 1. Crystallite diameter d (nm) and thickness h (nm) estimated from the full-profile XRD powder pattern analysis for BaFe12-xMnxO19. Standard deviation values are presented in parentheses.
T — T an 900 0 C T— Tan — 1000 0 C T— Tan — 1100 0 C
x d h d h d h
0 184(4) 77(1) 244(5) 130(2) 282(6) 175(4)
2 177(4) 63(1) 244(6) 106(2) 263(6) 107(2)
4 144(2) 69(1) 226(6) 76(1) 285(7) 104(2)
6 152(3) 63(1) 280(9) 78(1) 399(17) 131(3)
parameters on the Mn doping level and the annealing temperature are depicted in Fig. 1. The atomic radii of Fe3+ and Mn3+ are practically equal and amount to 0.645 A for coordination number 6 [16]. One could expect a negligible influence of the Mn doping, but it is not the case. The cell parameters distinctly depend on x. There is also a detectable, but smaller variation of the cell parameters with the annealing temperature. On going from x = 0 to x = 6, almost independently from Tan, a increases by 0.2 %, c drops by 0.3 %, so that c/a decreases by 0.5 %. As a result, cell volume V grows only slightly, by 0.2 %. The data correspond well to those obtained earlier for coarsely grained hexaferrites with similar composition [8].
(a)
(b)
(c)
(d)
Fig. 1. The dependence of crystal cell parameters on Mn content x in the BaFe12-xMnxO19 samples annealed at temperatures of 900 (circles), 1000 (crosses), 1100 (triangles), and 1200 °C (squares): (a) parameter a (A), (b) parameter c (A), (c) parameters' ratio a/c, (d) unit cell volume V (A3).
Despite the observed small variation of the cell parameters and the volume, some of interatomic distances change much stronger with the doping. It should be noted that by the X-ray diffraction it is virtually impossible to distinguish Mn from Fe, therefore, we did not determine the distribution of Mn and Fe between the transition metal (M) sites. However, the changes in certain M-O distances may indicate that Mn substitute Fe at the corresponding sites acquiring an oxidation state different from +3.
The crystal structure of barium hexaferrite may be considered as a distorted close packing of oxygen atoms forming a five layers' set with a thickness of c/2. The set includes S-block with a spinel structure and R-block containing Ba atoms. 1st oxygen layer includes Ba atoms replacing oxygen atoms and in addition Fe2 atoms at a split 2b site (resulting in a half-filled 4e site, M2). Fe2 shifts from the center of trigonal bipyramid of oxygen atoms along z and acquires tetrahedral coordination. Fe4 atoms (4f2 site, M4) are found between 1st and 2nd as well as between 5th and 1st oxygen layers in an octahedral coordination. Fe5 atoms (12k site, M5) are found between 2nd and 3rd as well as between 4th and 5th oxygen layers in an octahedral coordination. Fe1 (2a site, M1) and Fe3 (4fi site, M3) atoms are found between 3rd and 4th oxygen layers in octahedral and tetrahedral coordination, respectively.
The changes in the interatomic distances are more pronounced for the samples, annealed at a maximum temperature of 1200 0C. Hence, we will analyze such distances for these samples. The dependence of average M-O distances on the Mn content is shown in Fig. 2. The strongest change takes place for the tetrahedral 4f1 site: d(M3-O) linearly grows from 1.887 to 1.980 A (by ca. 5 %) on increasing x from 0 to 6. For the M1 atom, found in the same layer, the corresponding distance, just in opposite, decreases from 2.014 to 1.977 A (by ca. 2 %). A smaller decrease, from 2.032 to 2.008 A (by ca. 1.2%), is observed for d(M5-O). Distances d(M2-O) and d(M4-O) are not appreciably affected by the Mn doping. Taking into account equal radii (R) of Mn3+ and Fe3+ and admitting that Mn cannot occupy the same site as Mn2+ and Mn4+ (due to very large difference in their sizes) we may estimate content of Mn2+ and Mn4+ for every site. For a tetrahedral coordination, R(Fe3+) = 0.49 A and R(Mn2+) = 0.66 A [15]. Then the change of d(M3-O) corresponds to 55(5) % of Mn2+ at 4f1 site in BaFe6Mn6O19. For an octahedral coordination, R(Fe3+) = 0.645 A and R(Mn4+) = 0.53 A [16]. That corresponds to 32(7) % of Mn4+ at 2a site and 21(6) % of Mn4+ at 12k site. Due to comparable quantities of Mn4+ and Mn2+ ions found in the structure the average oxidation state of Mn approaches +3.
2.04
—i-1-1-1-1-1-1-1-1-1-1-1-10 1 2 3 4 5 6
Fig. 2. The dependence of average distances d(M-O) between 3d metal atom M (Fe, Mn) and oxygen atoms of the coordination sphere on Mn content x in the BaFe12-xMnxO19 samples annealed at 1200 0C: Ml (2a) - circles, M2 (4e) - crosses, M3 (4fi) - triangles, M4 (4f2) - squares, M5 (12k) -diamonds.
Occupancies of the M sites by Mn were estimated earlier for BaFe12-xMnxO19 ceramics using neutron powder diffraction [9]. For BaFe6Mn6O19 they corresponded to 0.73, 0.73, 0.27, and 0.54 for Ml, M3, M4, and M5 sites, respectively. No Mn was found at M2 site. We expect that a similar distribution of Mn ions takes place in our finely-grained samples. While the direct determination of Mn occupancies is not possible, the observed atomic displacement parameters Ueq of M sites reflect such occupancies (see Tables A2 and A3). In BaFe12O19, Ueq values for all 3d metal sites are close, while in BaFe6Mn6O19, Ueq correlates with the reported site occupancies, growing with the increase of the Mn occupancy. Combining the data [9] and our results we may suggest that (i) at 4f1 site, major part of Mn is in oxidation state +2, (ii) at 2a site, approximately half of Mn is in oxidation state +4, (iii) at 12k site, from one third to half of Mn is present as Mn4+, and (iv) at 4f2 site, Mn is mostly in oxidation state +3. It is interesting that, while d(M2-O) does not vary with the Mn content (which is in accordance with the reported absence of Mn at 4e site [9]), the distances to apical oxygen (Ol) and to those (O3) at the trigonal base of the distorted tetrahedron vary strongly. d(M2-O1) decreases from 2.138 to 2.072 A and d(M2-O3) increases from 1.847 to 1.867 A on going from BaFe12O19 to BaFe6Mn6O19. Most
probably, the observed changes are determined by a local structure distortion due to Mn incorporation in other M sites. Fe3+ at the M2 site provides the major magnetic anisotropy [17]. Our modelling of the Fe3+ electronic structure using the CONDON program [18] shows that such lengthening of d(Fe2-O3) reduces the axial magnetic anisotropy.
Apparently, strong variations in interatomic distances on the Mn doping compensate each other so that the change in the crystal cell parameters and volume becomes approximately one order of magnitude smaller. Such a compensation phenomenon is convenient to discuss considering variation in weighted average distances (along z axis) between the oxygen atomic layers, which we denote as h(n,m) = Az/c, where n and m are the numbers of oxygen layers (see Tables A2 and A3 for reference). Due to the crystal symmetry h(5,1) = h(1, 2) and h(4, 5) = h(2,3). In the undoped BaFeisOi9 sample, h(1,2) = 0.10047, h(2,3) = 0.09687, h(3,4) = 0.10532. In the maximally doped BaFe6Mn6O19 sample, h(1, 2) = 0.09993, h(2,3) = 0.09499, h(3,4) = 0.11016. Thus, h(3,4) reveals an increase with the biggest absolute value, apparently, due to a large quantity of Mn2+ at 4f1 site, which effect is not fully compensated by Mn4+ at 2a site. h(2,3) decreases moderately and h(1, 2) diminishes only slightly in consistence with the estimated Mn4+ occupancies. The changes in the interlayer distances for 5 consecutive oxygen layers are listed as follows: -0.5, -1.9, 4.8, -1.9, -0.5 %. This compensates the alteration of the crystal cell parameter c. Situated between the 3rd and 4th oxygen layers, the M3 (4f1) coordination tetrahedron expands both, in the c direction and in the ab plain, while the Ml (2a) coordination octahedron, expanding in the c direction, shrinks in the ab plain. As a result, the cell parameter a increases only slightly. The observed small multidirectional deformation of the hexaferrite crystal lattice was commonly attributed to the Jahn-Teller effect of Mn3+ [8,9]. In contrast to this, our study suggests that the stronger distortions affecting the net values of a and c are connected to simultaneous presence of non-Jahn-Teller Mn2+ and Mn4+ ions, rather than to the Jahn-Teller distortion of the Mn3+ polyhedron.
Fig. 3. The dependence of difference Ad(M-O) between average distances d(M-O) in BaFe6Mn6O19 and BaFe12O19 on samples annealing temperature Tan: Ml (2a) - circles, M3 (4f1) - triangles, M5 (12k) - diamonds.
Another interesting issue is possible dependence of Mn4+ and Mn2+ content on the sample annealing temperature and thus on the hexaferrite grain size. In Fig. 3, the differences Ad(M-O) between average distances d(M-O) in BaFe6Mn6O19 and BaFe12O19 are shown for the samples annealed at different temperatures. In general, Ad(Ml-O), Ad(M3-O), and Ad(M5-O) values are non-zero for the whole annealing temperature range, designating presence of Mn4+ and Mn2+ in all the samples. Determined with a better accuracy, Ad(M3-O) and Ad(M5-O) tend to decrease with decreasing Tan and drop by ca. 20 % on the Tan changing from 1200 to 900 0C. This implies that the degree of the Mn3+ disproportionation to Mn2+ and Mn4+ in the hexaferrite structure slightly decreases with lowering the sample annealing temperature and hence the grain size.
3.2. Magnetic properties
The dependence of the Curie temperature on the Mn content in the samples annealed at different temperatures is shown in Fig. 4. TC depends strongly on x and very little on Tan. TC decreases with increasing the Mn content almost linearly, approximately 48 K per 1 Mn in the formula unit. Undoped samples show identical TC of 737 K for all the annealing temperatures. In Mn-doped samples TC decreases by 7 K with increasing Tan from 900 to 1200 0C. This suggests that on the atomic scale, the changes in the undoped compound are negligible, whereas in the doped compounds, certain variations in the crystal structure may take place. Such variations may be connected to the disproportionation character of Mn3+: the suggested above increase of the Mn3+ disproportionation degree with the elevating annealing
Fig. 4. The dependence of Curie temperature TC on Mn content x in the BaFe12-xMnxO19 samples annealed at temperatures of 900 (circles), 1000 (crosses), 1100 (triangles), and 1200 0C (squares).
temperature may cause decrease of TC. This is reasonable since the arising Mn4+ ions in octahedral sites cannot efficiently take part in the antiferromagnetic exchange interaction because of the absence of electrons on the eg orbitals.
Magnetization and coercivity of the samples depend both, on the compound composition and the annealing temperature. To visualize better the latter dependence, in Fig. 5, magnetization and coercivity are displayed as a function of Tan. We analyze the magnetization of samples M taken at the highest applied field of 17 kOe. As the magnetization curves approach to saturation, this magnetization value is assumed to be close to saturation magnetization. The magnetization considerably decreases with increasing the Mn content in the compound. This agrees well with the fact that Mn3+ and Mn4+, possessing lower magnetic moments than Fe3+, occupy mostly sites of the major spin sublattice. In the undoped compound, M tends to increase with increasing Tan. This may be related to healing the crystal structure defects. In the Mn-doped samples the effect is smaller, and in BaFe6Mn6O19, the magnetization is nearly the same for all Tan. Possibly, the expected growth of magnetization is suppressed by the overlapped magnetization decrease owing to increase of the Mn3+ disproportionation degree.
(a)
(b)
Fig. 5. The dependence of magnetization M under a field of 17 kOe (a) and coercivity Hc (b) on samples' annealing temperature Tan in BaFe12-xMnxO19, where x = 0 (circles), 2 (crosses), 4 (triangles), 6 (squares).
Coercivities of the samples are high and, in most cases, exceed 5 kOe, which conforms with predominantly singledomain nature of the grains (crystallites). Coercivity of the undoped compound is nearly constant (^ 5.3 kOe) for lower Tan, decreasing to 4.8 kOe only for Tan = 1200 0C. The latter may be related to growth of the grains so that the size of some of them exceeds a monodomain critical size. The compound with a low Mn content x = 2 shows somewhat increased coercivity of 5.8 kOe for Tan = 900 0C, which decreases to 3.9 kOe for Tan = 1200 0C. Probably, due to a larger grain size for Tan = 1200 0 C and still substantial Ms, a higher fraction of grains is found in a multidomain
state. For the compounds with higher Mn content, the coercivity exhibits a maximum vs. Tan. The highest coercivity of 8.4 kOe is achieved for BaFe6Mn6O19 annealed at 1100 0C. An analysis of interatomic distances sheds some light on the observed increase of Hc. The distance Fe2-O3 becomes shorter with increasing Tan, changing from 1.902 to 1.867 A. And in accordance with the mentioned above theoretical calculations, such distance shortening should lead to a substantial raise of easy-axis magnetic anisotropy. The distance shortening may be in turn explained by rearrangement of other atoms because of increase of the Mn3+ disproportionation degree. A small drop of coercivity for Tan = 1200 0C may be related to an enlargement of the crystallite size.
4. Conclusions
Pure phase manganese for iron substituted barium hexaferrite samples BaFe12-xMnxO19 (x = 0, 2, 4, 6) were prepared by a sol-gel citrate method in the form of powders with crystallite sizes from tens of nanometers to about a micron, which ensured single domain nature of the compound grains. The variation in the grain size was achieved by the precursor annealing at temperatures 900 - 1200 0C. Detailed analysis of the crystal structure using powder X-ray diffraction data reveals small variations in the crystal cell parameters with the Mn substitution and the sample annealing temperature, and along with this, demonstrates an order of magnitude larger changes in interatomic distances. It is shown that Mn3+ replacing Fe3+ partially disproportionates to larger Mn2+ ions occupying tetrahedral 4f1 sites and smaller Mn4+ ions, occupying 2a and to a less extent 12k sites. The degree of disproportionation slightly grows with increasing the annealing temperature. The Curie temperature decreases almost linearly with x from 737 to 448 K and, for Mn doped samples, drops other several degrees with increasing the annealing temperature in accordance with the change in the relative content of Mn2+ and Mn4+. The magnetization decreases with x, while coercivity tends to increase, reaching 8.4 kOe for the sample with x = 6 annealed at 1100 0C. To our knowledge, the obtained maximum value of coercivity is one of the highest among Mn doped hexaferrites conceding only to a coercivity of 9.7 kOe registered in a submicron-grained SrFe12-xMnxO19 prepared by a mechano-chemical route [19].
Appendix
Table A1. Crystal cell parameters a and c, R-factors, and average M-O distances d (M = Fe, Mn) in BaFe12-xMnxO19, where x = 0, 2, 4, 6 (samples 1, 2 ,3,4, respectively), annealed at 900, 1000, 1100, 1200 0C (samples' second symbol a, b, c, d, respectively). Values of a, c, and d are in A.
Sample a (A) c (A) Rwp, Rall d(M1-O) d(M2-O) d(M3-O) d(M4-O) d(M5-O)
1a 5.8950(1) 23.2182(3) 0.031,0.019 2.013(5) 1.914(9) 1.887(6) 2.023(6) 2.032(4)
1b 5.8949(1) 23.2135(2) 0.029, 0.019 2.020(5) 1.916(7) 1.883(5) 2.020(5) 2.032(3)
1c 5.8941(1) 23.2067(2) 0.036, 0.015 2.008(4) 1.920(6) 1.888(4) 2.020(4) 2.031(3)
1d 5.8951(1) 23.2106(2) 0.038, 0.017 2.014(4) 1.920(6) 1.887(4) 2.020(4) 2.032(3)
2a 5.8965(1) 23.1981(3) 0.031,0.016 2.016(5) 1.921(8) 1.913(6) 2.016(6) 2.024(3)
2b 5.8972(1) 23.1985(3) 0.028, 0.023 2.008(5) 1.909(9) 1.914(6) 2.025(6) 2.024(4)
2c 5.8965(1) 23.1929(2) 0.035, 0.015 2.003(4) 1.922(6) 1.914(4) 2.015(4) 2.027(3)
2d 5.8987(1) 23.1978(2) 0.039, 0.016 2.004(4) 1.922(6) 1.920(4) 2.013(4) 2.025(3)
3a 5.9006(1) 23.1746(3) 0.028, 0.016 2.010(5) 1.928(7) 1.936(5) 2.014(5) 2.018(4)
3b 5.9009(1) 23.1720(3) 0.028, 0.022 2.011(5) 1.941(8) 1.939(6) 2.009(6) 2.016(4)
3c 5.9020(1) 23.1707(2) 0.030, 0.018 2.002(5) 1.919(7) 1.945(5) 2.015(5) 2.019(3)
3d 5.9025(1) 23.1743(2) 0.042, 0.016 1.996(4) 1.915(6) 1.953(4) 2.018(4) 2.014(3)
4a 5.9065(1) 23.1439(3) 0.027, 0.017 1.992(5) 1.950(7) 1.961(5) 2.003(6) 2.014(4)
4b 5.9066(1) 23.1420(3) 0.028, 0.021 1.983(5) 1.935(8) 1.967(6) 2.007(6) 2.015(4)
4c 5.9078(1) 23.1426(3) 0.029, 0.028 1.985(5) 1.921(8) 1.981(6) 2.016(6) 2.009(4)
4d 5.9091(1) 23.1494(2) 0.042, 0.023 1.977(4) 1.918(6) 1.980(4) 2.020(4) 2.008(3)
Table A2. Atomic parameters in the crystal structure of BaFe^Oig annealed at 1200 °C
Atom Occupancy x/a y/a z/c Uiso (A2 )
Ba 1 2/3 1/3 1/4 0.0065(2)
Fe1 1 0 0 0 0.0048(4)
Fe2 0.5 0 0 0.25869(14) 0.0039(6)
Fe3 1 1/3 2/3 0.02733(6) 0.0045(3)
Fe4 1 1/3 2/3 0.19032(5) 0.0047(3)
Fe5 1 0.16853(9) 0.33706(19) 0.89168(3) 0.0048(2)
O1 1 0 0 0.1492(2) 0.0063(4)
O2 1 2/3 1/3 0.0540(2) 0.0063(4)
O3 1 0.1799(5) 0.3597(11) 1/4 0.0063(4)
O4 1 0.1575(4) 0.3150(8) 0.05221(12) 0.0063(4)
O5 1 0.5002(4) 0.0003(8) 0.14964(13) 0.0063(4)
Table A3. Atomic parameters in the crystal structure of BaFe6Mn6O19 annealed at 1200 0C
Atom Occupancy x/a y/a z/c Uiso (A2 )
Ba 1 2/3 1/3 1/4 0.0093(2)
M1 1 0 0 0 0.0095(5)
M2 0.5 0 0 0.25908(14) 0.0022(7)
M3 1 1/3 2/3 0.02768(7) 0.0103(3)
M4 1 1/3 2/3 0.19062(6) 0.0069(3)
M5 1 0.16737(11) 0.3347(2) 0.89196(3) 0.0082(2)
O1 1 0 0 0.1514(3) 0.0154(5)
O2 1 2/3 1/3 0.0587(2) 0.0154(5)
O3 1 0.1813(6) 0.3626(12) 1/4 0.0154(5)
O4 1 0.1499(4) 0.2998(8) 0.05387(14) 0.0154(5)
O5 1 0.5012(4) 0.0023(9) 0.14962(16) 0.0154(5)
I
L
x = 0, Tan = 900 °C
x = 0, Tan = 1100 0C
x = 0, Tan = 1200 °C
x = 2, Tan = 900 0C
x = 2, Tan = 1100 0C
x = 2, Tan = 1200 0C
x = 4, Tan = 900 °C
x = 4, Tan = 1100 0C
x = 4, Tan = 1200 0C
x = 6, Tan = 900 °C
x = 6, Tan = 1100 0C
x = 6, Tan = 1200 0C
Fig. A1. Scanning electron microscopy images of BaFe12-xMnxO19 samples annealed at Ta
Fig. A2. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 0, Tan = 900 °C
Fig. A4. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 0, Tan = 1100 °C
Fig. A6. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 2, Tan = 900 °C
Fig. A8. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFe12-xMnxO19, x = 2, Tan = 1100 °C
Fig. A10. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 4, Tan = 900 °C
Fig. A12. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 4, Tan = 1100 °C
Fig. A14. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFe12-xMnxO19, x = 6, Tan = 900 °C
Fig. A16. Observed (crosses), calculated (line), and difference (line underneath) XRD patterns of
BaFei2-xMnxOi9, x = 6, Tan = 1100 °C
References
[1] Buschow K.H.J., de Boer F.R. Physics of Magnetism and Magnetic Materials, Kluwer Academic/Plenum Publishers, New York, 2003, 182 p.
[2] Harris V.G., Geiler A., Chen Y., Yoon S. D., Wu M., Yang A., Chen Z., He P., Parimi P. V., Zuo X., Patton C.E., Abe M., Acher O., Vittoria C. Recent advances in processing and applications of microwave ferrites. J. Magn. Magn. Mater., 2009, 321, P. 2035-2047.
[3] Shimizu O., Oyanagi M., Morooka A., Mori M., Kurihashi Y., Tada T., Suzuki H., Harasawa T. Development of advanced barium ferrite tape media. J. Magn. Magn. Mater., 2016, 400, P. 365-369.
[4] Pullar R.C. Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics. Prog. Mater. Sci., 2012, 57, P. 11911334.
[5] Banihashemi V., Ghazi M.E., Izadifard M., Dinnebier R.E. A study of Ca-doped hexaferrite Sr;L-xCaxFe12O1g (x = 0.0, 0.05, 0.1, 0.15, and 0.2) synthesized by sol-gel combustion method. Phys. Scr., 2020, 95, 095807.
[6] Trusov L.A., Gorbachev E.A., Lebedev V.A., Sleptsova A.E., Roslyakov I.V., Kozlyakova E.S., Vasiliev A.V., Dinnebier R.E., Jansen M., Kazin P.E. Ca-Al double-substituted strontium hexaferrites with giant coercivity. Chem. Commun., 2018, 54, P. 479-482.
[7] Gorbachev E.A., Trusov L.A., Sleptsova A.E., Kozlyakova E.S., Alyabyeva L.N., Yegiyan S.R., Prokhorov A.S., Lebedev V.A., Roslyakov I.V., Vasiliev A.V., Kazin P.E. Hexaferrite materials displaying ultra-high coercivity and sub-terahertz ferromagnetic resonance frequencies. Mater. Today, 2020, 32, P. 13-18.
[8] Obradors X., Collomb A., Pernet M., Jourbert J.C. Structural and magnetic properties of BaFe12-xMnxO19 hexagonal ferrites. J. Magn. Magn Mater., 1984, 44, P. 118-128.
[9] Collomb A., Obradors X., Isalgue A., Fruchart D. Neutron diffraction study of the crystallographic and magnetic structures of the BaFe12-xMnxO19 M-type hexagonal ferrites. J. Magn. Magn Mater., 1987, 69, P. 317-324.
[10] Thang P.D., Ho T.A., Dang N.T., Lee B.W., Phan T.L., Manh T.V., Kim D.H., Yang D.S. Mn-doped (Ba,Y)Fe12O1g hexaferrites: Crystal structure and oxidation states of Mn and Fe. Current Applied Physics, 2020, 20, P. 1263-1267.
[11] Okube M., Yoshizaki J., Toyoda T., Sasaki S. Cation distribution and magnetic structure of M-type BaTiMnFe1oO1g examined by synchrotron X-ray and neutron studies. J. Appl. Cryst., 2016, 49, P. 1433-1442.
[12] AdeelaN., Khan U., Iqbal M., RiazS., Ali H., MaazK., NaseemS. Magnetic and dielectric investigations of Mn-doped Ba hexaferrite nanoparticles by hydrothermal approach. J. Electronic Materials, 2016, 45, P. 5853-5859.
[13] Kim M., Lee H., Kim J. Magnetic properties of Mn substituted strontium ferrite powders synthesized by the molten salt method. AIP Advances, 2020, 10, 015325.
[14] Trusov L.A., Gorbachev E.A., Lebedev V.A., Sleptsova A.E., Roslyakov I.V., Kozlyakova E.S., Vasiliev A.V., Dinnebier R.E., Jansen M., Kazin P.E. Ca-Al double-substituted strontium hexaferrites with giant coercivity. Chem. Commun., 2018, 54, P. 479-482.
[15] Petrícek V., Dusek M., Palatinus L. Crystallographic Computing System JANA2006: General features. Z. Kristallogr.-Cryst. Mater., 2014, 229, P. 345-352.
[16] Shannon R.D. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr. A, 1976, 32, P. 751-767.
[17] Xu Y., Yang G.-L., Chu D.-P., Zhai H.-R. Theory of the single ion magnetocrystalline anisotropy of 3d ions. Phys. Stat. Sol. B, 1990, 157, P. 685-693.
[18] Schilder H., Lueken H. Computerized magnetic studies on d, f, d-d, f-f, and d-S; f-S systems under varying ligand and magnetic fields. J. Magn. Magn. Mater., 2004, 281, P. 17-26.
[19] Tenorio-Gonzalez F.N., Bolarin-Miro A.M., Sanchez-De Jesús F., Vera-Serna P., Menendez-Gonzalez N., Sanchez-Marcos J. Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite. J. Alloys Compd., 2017, 695, P. 2083-2090.
Submitted 29 December 2023; revised 2 January 2024; accepted 3 January 2024
Information about the authors:
Pavel E. Kazin - Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia; ORCID 0000-0002-1415-2190; [email protected]
Anastasia E. Sleptsova - Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany; ORCID 0000-0002-4788-2624; [email protected]
Alexander V Vasiliev - Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia; ORCID /0000-0003-4108-9040; [email protected]
Artem A. Eliseev - Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia; ORCID 0000-0002-3644-9673; [email protected]
Robert E. Dinnebier - Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany; ORCID 0000-0003-2778-2113; [email protected]
Sebastian Bette - Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany; ORCID 0000-0003-3575-0517; [email protected]
