Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite

Accepted Manuscript Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite F.N. Tenorio-González, A.M. Bolarín-Miró, F. Sánchez-De Jesús, P. Vera-Serna, N. Menéndez-González, J. Sánchez-Marcos PII:

S0925-8388(16)33505-8

DOI:

10.1016/j.jallcom.2016.11.047

Reference:

JALCOM 39542

To appear in:

Journal of Alloys and Compounds

Received Date: 9 August 2016 Revised Date:

18 October 2016

Accepted Date: 3 November 2016

Please cite this article as: F.N. Tenorio-González, A.M. Bolarín-Miró, F. Sánchez-De Jesús, P. VeraSerna, N. Menéndez-González, J. Sánchez-Marcos, Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite, Journal of Alloys and Compounds (2016), doi: 10.1016/ j.jallcom.2016.11.047. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Crystal structure and magnetic properties of high Mn-doped strontium hexaferrite

1

Área Académica de Ciencias de la Tierra y Materiales, Universidad Autónoma del Estado de Hidalgo Mineral de la Reforma, Hidalgo, 42184, México, Tel. +527717172000 ext. 2280

División de Ingenierías, Universidad Politécnica de Tecámac, Estado de México, 55740, México. 3

Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, Madrid, 28049, España.

SC

2

RI PT

F. N. Tenorio-González1,2, A. M. Bolarín-Miró1, F. Sánchez-De Jesús1,*, P. Vera-Serna2, N. Menéndez-González 3, J. Sánchez-Marcos3

e-mail: [email protected]

M AN U

Abstract

We present a study on the effect of the substitution of Fe+3 by Mn+3 on the structural and magnetic properties of strontium hexaferrite, SrFe12-xMnxO19 (0 ≤ x ≤ 5), which is synthesized by assisted highenergy ball milling. A mechanism of substitution is proposed. Fe2O3, SrCO3 and Mn2O3 powders were mixed in a stoichiometric ratio, milled for 5 h and annealed at 950°C for 2 h. The X-ray

TE D

diffraction patterns confirm the formation of a hexaferrite structure with small amounts of Fe2O3 as a second phase for low doping levels of Mn3+ and reveal a modification of the lattice parameters as the rate of Mn3+ substitution increases. The magnetic properties demonstrate an important reduction of the magnetic saturation and a significant increase in the coercivity field with cation substitution. The

AC C

avoiding the 2b site.

EP

Mössbauer results confirm that the Mn3+ ions preferentially occupy the 2a and 12k sites while

Keywords: High-energy ball milling, Mn-doped Sr-hexaferrite, Mössbauer spectroscopy, SrFe12xMnxO19,

High coercivity 1

ACCEPTED MANUSCRIPT

1. Introduction Hexagonal M-type SrFe12O19 (SrM) ferrites have attracted significant attention for their use in permanent magnetic motors, magnetic recording media and other fields due to their superior

RI PT

magnetic properties, high corrosion resistance, high chemical stability, low-cost production and nontoxicity [1–3].

This M-type ferrite consists of smaller units: a cubic S block with a spinel-type structure and a

SC

hexagonal R block that contains the Sr ions. According to the Wyckoff positions, this structure has 2 Sr2+ ions in the 2d site and 38 O2- ions in the 4e, 4f, 6h, 12k1 and 12k2 sites (the 12k1 and 12k2 sites

M AN U

have different atomic coordinates) [4]. Additionally, the structure has 24 Fe3+ magnetic ions per unit cell, which are distributed among five different crystallographic sites: three octahedral 12k, 2a and 4f2 sites, one tetrahedral 4f1 site and one trigonal bi-pyramidal 2b site. The 12k, 2a, and 2b sites have parallel spins, while the 4f1 and 4f2 sites also have parallel spins between them but anti-parallel spins

TE D

with the other sites. The magnetic structure is a collinear ferrimagnetic structure with a net moment per formula unit of only 20 µ B at 4.2 K and a large magnetocrystalline anisotropy constant (K≈3x106 erg/cm3) [2,5–6].

EP

The substitution of Fe3+ or Sr2+ sites is an effective way to modify the magnetic properties of

AC C

strontium hexaferrites [7-9]. Strontium hexaferrite is an excellent material for Fe doping because its structure allows for the replacement of all the Fe3+ ions by other trivalent ions without any trace of secondary phases [10], therefore allowing for widespread variations in the magnetic behavior depending on the doping concentration, the type of cation used as the dopant, and the doping method [7]. The Mn-doped M-type ferrite is a potentially useful material, as Mn is a transition metal that can present different valences and is similar to Fe, therefore, it can replace this ion. To the best of our knowledge, the Mn-doped M-type ferrite has been only used in low substitution levels (<0.5) because 2

ACCEPTED MANUSCRIPT

some studies have shown that high substitution levels destroy the Gorter collinear magnetic structure and significantly reduce the saturation magnetization [10–12]. Silva et al. [11] synthesized SrFe12xMnxO19

(x = 0 and 0.1) using a proteic sol–gel process; they observed a reduction in the

RI PT

magnetization saturation and remanence and a considerable reduction in the coercivity field. A similar study was reported by Sharma et al. [12], who obtained BaFe12-xMnxO19 (x = 0 and 0.5) using high-energy ball milling for 30 h and subsequent annealing at 1050 ºC; their results indicate that the

SC

magnetization decreases as the Mn fraction increases due to the reduction of the average magnetic

M AN U

moment of the lattice.

Undoped and doped strontium hexaferrites can be synthesized by several processes. The conventional and earliest process involves the calcination and sintering of a mixture of oxides or carbonates in a furnace at 1300 ºC [13]. This process produces large particle sizes and consumes a significant amount of energy [3]. Nanostructured hexaferrites can be produced using wet chemical methods, such as the

TE D

sol-gel [14], hydrothermal [15] and coprecipitation [16] processes, among others [17]. One method is mechanosynthesis; typically, this method promotes the formation of ferrites by the mechanical activation of strontium carbonate and iron oxide [1, 18]. Compared to the traditional method (the

EP

solid state reaction), the mechanochemical method has been shown to achieve high coercivity and

AC C

magnetic saturation in these materials [3, 19], and it is versatile and economical. Although there is a significant number of interesting studies on doped strontium hexaferrites, there is a lack of information regarding situations in which high levels (≥1) of the doping element are introduced into the hexagonal structure, and the effects of high-level doping are not well-known, aside from the expected effect due to the occupied interstitial site, which is particularly prominent when mechanosynthesis is used as the synthesis method and Mn3+ is used as the dopant. Therefore, in this study, Mn-doped strontium hexagonal ferrites were produced by high-energy ball milling of 3

ACCEPTED MANUSCRIPT

oxide and carbonate powders followed by annealing. The effect of different amounts of Mn+3 on the crystal structure and the magnetic properties of strontium hexaferrites was systematically investigated. Moreover, a proposal for the mechanism of the substitution of Fe+3 by Mn+3 is

RI PT

described, which can be applied to other similar systems.

SC

2. Materials and Methods

Fe2O3 (Sigma Aldrich, 99% purity), SrCO3 (Sigma Aldrich, 99.9% purity) and Mn2O3 (Sigma

M AN U

Aldrich, 99.9% purity) powders were used as the precursor materials. These powders were mixed in a stoichiometric ratio according to the following equation:

SrCO3 + (6 - x/2) Fe2O3 + x/2Mn2O3→ SrFe12-xMnxO19 + CO2

eq. 1

A total of 5 g of the starting mixtures was loaded with steel balls of 1.27 cm in diameter into a

TE D

hardened steel cylindrical vial (50 cm3) and milled for 5 hours. The ball–to-powder weight ratio was 10:1, and all experiments were performed in air at room temperature. Afterward, the milled powders,

EP

also referred to as the as-milled powders, with different compositions (x), were annealed in a tube furnace at 950 °C for 2 h in an air atmosphere; the heating rate was 10 °C/min. These experimental

AC C

conditions were selected according to procedures used in previous studies [20]. The milled and annealed powders with different compositions (x) were characterized using X-ray diffraction (XRD) with a Rigaku D8 advance diffractometer with CuKα radiation. Patterns were collected in a 2θ interval of 20-80° with increments of 0.02 (2θ). Initial crystallographic data were obtained from the Crystallography Open Database (COD). Then, Rietveld refinements were performed on the X-ray diffraction patterns to obtain the cell parameters, crystallite sizes and microstrains of the powders

4

ACCEPTED MANUSCRIPT

[21]. Scanning electron microscopy (SEM) conducted with a JEOL-100-CX II was used to determine the morphology and qualitative particle size. Fourier transform infrared (FT-IR) spectroscopy measurements of the samples (annealed powders)

RI PT

were performed on a Nicolet FT-IR Magna 700 in the range of 450–1600 cm-1 with KBr pellets. Mössbauer spectroscopy was used to determine the Fe3+ coordination in the structure. The spectra were registered at room temperature in triangular mode using a conventional spectrometer with a 50-

SC

mCi 57Co (Rh) source. The spectral analyses were performed with a nonlinear adjustment using the NORMOS [22] program. The calibration energy was calculated with an α-Fe (6 µm) foil spectrum.

M AN U

Magnetization studies were carried out at room temperature using a vibrating sample magnetometer (VSM), Microsense EV7, with a maximum field of ±18 kOe.

TE D

3. Results and Discussion

Figure 1 shows the X-ray diffraction (XRD) patterns of stoichiometric mixtures of the precursors milled for 5 h to obtain SrFe12-xMnxO19 by varying x from 0 to 5, ∆x=1. The XRD pattern

EP

that corresponds to the x=0 (undoped strontium hexaferrite) composition shows peaks of the starting materials Fe2O3 (COD 1011267, R3cH) and SrCO3 (COD 1539128, Pmcn). For the x>3 samples, the

AC C

XRD patterns also show the reflections of the Mn2O3 (COD 1514103, Pbca) material. However, the samples with 0
ACCEPTED MANUSCRIPT

crystallite size (D) and the microstrain (µs) of the milled powders, which are obtained by the Rietveld refinement of the XRD patterns (Figure 1). The calculated crystallite sizes are from 10 to 40 nm, depending of the precursors, which indicates that the milled powder has a nanocrystalline size.

RI PT

Additionally, the particle size does not show a correlation with the Mn concentration. The microstrain does not change with the Mn doping level (x), and it remains nearly constant for each precursor. As was expected, the mechanical milling process does not provide enough energy to

SC

complete the reaction that corresponds to the formation of Mn-doped strontium hexaferrite (eq. 1), therefore, an annealing process is required to enable the completion of the reaction. Based on

M AN U

previous studies [1,19,20], an annealing treatment at 950°C for 2 h was conducted for all samples.

X-ray powder diffraction patterns for the different annealed hexaferrite compositions are shown in Figure 2. The main structure is associated with the strontium hexaferrite (SrFe12O19, COD: 1008855), with a space group P63/mmc (Table II). Nevertheless, a Rietveld analysis of the x=0

TE D

pattern shows a small percentage of Fe2O3, approximately 3.4 wt.%. This phenomenon was reported by Alamolhoda et al. [23] when strontium hexaferrite was obtained using sol-gel auto-combustion. They found that the hexagonal crystal structure is stable for a Fe/Sr molar ratio of 10, and the

EP

presence of strontium ions is more important than the presence of iron ions in the formation of

AC C

hexaferrite. Therefore, for a Fe/Sr molar ratio higher than 10, the lack of Sr2+ ions results in the formation of hematite, as was previously observed in the study. This small amount of Fe2O3 is reduced as the Mn concentration increases, and for x≥4, it is not detectable by XRD. Rietveld refinements also allow us to study the evolution of the cell parameters, crystallite size and microstrain with the manganese content (table II). These results confirm that nanocrystalline hexaferrite with a crystallite size of approximately 150 nm was obtained by assisted high-energy ball 6

ACCEPTED MANUSCRIPT

milling. In comparison with the “as-milled” powder (Table I), the microstrain of the annealed powder decreased remarkably due to the effect of thermal treatment on the relaxation of the structure. For the annealed powder, increasing the Mn3+ content promotes an increase in the microstrain induced by

RI PT

Mn3+ substitution. The a parameter, the hexaferrite plane, increases as the manganese concentration increases, whereas the c parameter decreases, which results in a flattening of the structure. The c/a evolution shows a linear tendency with the manganese concentration, and the cell volume remains

SC

nearly constant, as observed in Figure 3. These results confirm that manganese cations are inside the

M AN U

structure substituting iron cations.

To qualitatively determine the particle size and morphology of the annealed powders, representative SEM micrographs of the powders milled for 5 h and annealed at 950°C for different Mn doping levels (x=1, 3 and 5) are shown in Figure 4. As observed, for all the compositions, the powder is formed by aggregates of irregular and rounded particles with a size distribution from 250 to 600 nm.

TE D

Likewise, several sintering necks are observed between roughly spherical particles as a consequence of the diffusion process during the annealing treatment at 950°C. There are no considerable

EP

differences in the morphology as a result of the Mn doping level.

Although XRD does not show any signature of strontium carbonate, the samples were further

AC C

characterized using FT-IR spectroscopy in the range from 1600 to 450 cm-1, as observed in Figure 5. Generally, the SrCO3 shows a large band at 1474 cm-1 and a narrow band at 855 cm-1 [15], but the FT-IR spectra do not show any bands at these wavelengths. The total decomposition of SrCO3 occurred at 950 ºC, as observed by Sivakumar et al. [24].

Zhao et al. [25] reported that the M-type ferrite has 24 vibration modes for iron ions, as detected by infrared spectroscopy. In particular, the Fe3+ ions with parallel spins have 12 bands 7

ACCEPTED MANUSCRIPT

distributed along a range from 152 to 360 cm-1, the Fe3+ ions in the 4f2 site have 8 vibration modes observed within a 371 - 438 cm-1 range, and those in the 4f1 site have 4 vibration modes distributed in a range from 480 to 588 cm-1. The absorption bands observed in Figure 5 at 478, 550 and 595 cm-1

RI PT

correspond to the M-O vibration modes of SrFe12O19 [26]. The bands at approximately 478, 505 and 595 cm-1 have been assigned to the Fe-O bending vibration and the Fe-O stretching vibrations, respectively, (Fe3+ in the 4f2 site), while the band at 550 cm-1 corresponds to Sr-O bending vibration

SC

[27]. The Fe-O (Fe3+ in 4f2 site) peak intensities at 478 and 595 cm-1 remained constant for all doping levels, which indicates the low influence of Mn3+ ions in this position. The Sr-O band broadened as a

M AN U

result of Mn3+ doping because some oxygen atoms became more tightly bonded, as the presence of Sr-O-Fe and Sr-O-Mn bonds resulted in a small position disorder.

The hysteresis loops at 300 K for the doped and undoped strontium hexaferrite are presented in Figure 6. None of the curves show a magnetic saturation even at 18 kOe, and the magnetization

TE D

values decrease as the Mn content increases. To study the evolution of this decrease, the magnetic saturation values have been obtained after fitting the data to the well know law of approach to

EP

saturation magnetization [28]:

eq. 2

AC C

M(H)=MS(1-A/H-B/H2)+χH

where χH is associated with a possible high-field magnetic susceptibility, which may be neglected if the Curie temperature is high enough, as is the case in this study. The A constant represents the microstrain and inclusions, and normally, this value is zero at high fields; B is due to crystal anisotropy. The MS values obtained after the eq. 2 fits are shown in Figure 7. Because the hysteresis loops are carried out at 300 K, the values obtained are smaller than the 20 µB value expected at 0 K, with 8 sites up and 4 sites down with 5 µB in each group of sites, but the values are very similar to 8

ACCEPTED MANUSCRIPT

the value obtained at 300 K for the undoped material [29]. The evolution of MS with the Mn content is linear, and in fact, a linear fit indicates that the substitution of one iron cation by a manganese cation reduces the magnetization by 1.63 µB. The Fe3+ cation can be replaced by Mn3+ in any of the

RI PT

five sites, and one of these approaches, which produces the largest magnetization reduction, is when the Mn3+ cations are allocated in the 2a, 2b or 12k crystallographic sites. In this situation, the magnetization reduction expected for the substitution of one cation is the difference between the

SC

magnetic moments of the two cations, 5 µB for Fe3+ and 3.5 µB for Mn3+ [30]. Therefore, the expected slope for MS versus x should be 1.5 µB/Mn. By considering the experimental slope value and the

M AN U

theoretical one, it is possible to conclude that the Mn3+ cations prefer the 2a, 2b or 12k crystallographic sites. The small difference found between the slope values could be explained in terms of a magnetic interaction reduction or a super-exchange interaction reduction [10].

Usually the magnetic interparticle interaction is studied through the ratio between the remanence and

TE D

saturation magnetization (Mr/Ms). These values are representative of different types of intergrain group exchanges. For Mr/Ms < 0.5, the particles interact by magnetostatic interaction; Mr/Ms = 0.5

EP

indicates the presence of randomly oriented non-interacting particles that undergo coherent rotation, and 0.5 < Mr/Ms < 1 indicates the existence of exchange coupling particles [31]. In the studied case,

AC C

although both values decrease as the manganese concentration increases, the ratio (Mr/MS) is constant for all samples, as observed in table III. According to these criteria, the interaction of Mndoped strontium hexaferrite particles is through magnetostatic interactions, and the presence of Mn3+ does not change this interaction. The coercivity field (HC) value denotes the intensity of the magnetic field that is required to reduce the magnetization of a sample to zero after the sample has been magnetized. Generally, the value of 9

ACCEPTED MANUSCRIPT

Hc changes with variations in the stoichiometry, crystallinity and anisotropy. Additionally, the magnetic anisotropy depends on the magnetocrystalline, shape (related to the bulk geometry), and the induced magnetic and stress anisotropies. Changes in the coercivity field and induced magnetic

RI PT

anisotropy are presumably not related to shape anisotropy because all the samples had powders that were of the same size when the magnetic characterization was carried out and we did not apply any magnetic field during the annealing process.

SC

As shown in table III, the Hc obtained for the undoped sample, 5.5 kOe, is comparable with the

M AN U

previously published results [32,33]. The substitution of iron for each manganese ion increases the coercivity field to 9.7 kOe. Figure 7 depicts this behavior and shows a linear dependence with the Mn content. This increase could be attributed to the microstress induced by the iron substitution. The A parameter of eq. 2, table III, gives information about the microstrain, as previously mentioned. The evolution of this parameter is similar to the coercivity field, as observed in table III, and comparable

TE D

to the microstrain behavior obtained from the Rietveld refinements, as observed in table II. To extend the study and confirm these results, Mössbauer spectroscopy experiments were carried out.

EP

Figure 8 shows the Mössbauer spectra at room temperature for the SrFe12-xMnxO19 (0 ≤ x ≤ 5). The spectra of SrFe12-xMnxO19 (x ≤1) were fitted as a convolution of six sextets, which correspond to the

AC C

spectra of five iron crystallographic sites in the hexaferrite, three octahedral positions (12k, 4f2 and 2a), one tetrahedral position (4f1), and one trigonal bi-pyramidal position (2b); the other octahedral iron position corresponds to the hematite that was detected in the X-ray diffraction patterns. For x ≥ 2, the hematite was not observable by Mössbauer spectroscopy; therefore, only the five sextets that correspond to the hexaferrite were considered in the fit. We fixed equal full widths at half maximum (FWHM) and the intensity ratio of 3: 2: 1: 1: 2: 3 for the six Lorentzian lines in the refinement of 10

ACCEPTED MANUSCRIPT

each sextet except for the 12k position. When the substitution level increased due to the misfit induced in the lattice, a broadening of the linewidths was observed.

RI PT

Table IV shows the Mössbauer hyperfine parameters, where δ represents the isomer shift, ∆ is the quadrupole splitting, Bhf is the hyperfine magnetic field, and A is the relative area of each subspectrum. The isomer shift provides information regarding the valence state and chemical bonding and confirms the presence of Fe3+ ions in all the cases. The IS of the SrFe12O19 sample

SC

follows the sequence 4f1<2b<2a, 12k<4f2 , which is in agreement with previously reported results

M AN U

[34,35]. Table III shows the low influence of Mn3+ on the δ of the Fe3+ located in the octahedral position; however, the isomer shift of the Fe(4f1) increases as the Mn3+ content increases, which indicates a decrease in the s-electron density at the Fe nucleus. In contrast, the δ change of the Fe(2b) site indicates that the opposite effect occurs at this site.

TE D

It is well known that the nucleus is held in position by Coulomb forces and that the electric field at the nucleus is generated by thermal vibrations (non-stationary nuclei) [36]. Therefore, all nuclei should have the same quadrupole splitting value, but the non-spherical symmetric distribution of ions

EP

in the lattice adds a field gradient. As shown in table V, the most symmetric nuclei are those of Fe(2a) because this ion has six bonds with a similar distance (d0), while the least symmetric is that of

AC C

Fe(2b) because the nucleus of this ion is in a trigonal bi-pyramidal site with two Fe(2b)-O(4e) bonds and three Fe(2b)-O(6h) bonds, in good agreement with the quadrupole splitting values shown in Table IV. In all positions, the values of ∆ decrease as the substitution increases, which indicates that the distortions around the Fe3+ are lower as the a lattice increases, and the c decreases when the Mn3+ increases.

11

ACCEPTED MANUSCRIPT

On the other hand, the magnetic hyperfine field of the samples follows the sequence 2b,12k<4f1<2a<4f2, and it also decreases as the Mn content increases because the Mn3+ ions produce

RI PT

a minor magnetic hyperfine field on the Fe3+ ions due the smaller magnetic moment of Mn3+, 3.5 µ B. Figure 9 shows the Fe population in the hexaferrite structure, which has been calculated from the specific Mn concentration and the Mössbauer subspectrum area, assuming that the Lamb-Mössbauer factor is the same in all sites. The Mössbauer study suggests that the Mn3+ ions are preferentially

SC

located in the 2a sites, and they completely replace the Fe. If the Mn content increases, it replaces up

M AN U

to 3 atoms of Fe in the 12k position and finally occupies the 4f1 and 4f2 positions, but the dopant avoids the bipyramidal position, in agreement with previously reported results [11, 37]. These results confirm the behavior of the magnetic saturation moment as the Mn3+ content is modified.

TE D

4. Conclusions

Manganese-doped strontium hexaferrite (SrFe12-xMnxO19, 0≤x≤5) powders with crystallite sizes of approximately 150 nm have been successfully produced by high-energy ball milling for 5 h and

EP

annealing at 950 °C for 2 h. X-ray diffraction verified that only the hexagonal P63/mmc structure is

AC C

present, and the structure is retained for all doping levels (0≤x≤5) of the prepared powders. Although the lattice parameters show changes that indicate the presence of Mn inside the structure, the volume is not affected. FT-IR analysis confirms the absence of strontium carbonate and the disturbance of some Fe-O bands by the presence of the Mn-O bond. The saturation magnetization and the coercivity field obtained for the undoped sample are 77.6 emu/g and 5.5 kOe, respectively. Moreover, when the manganese doping level is increased, Ms and Mr reduce significantly, and conversely, Hc increases. The decrease of the saturation magnetization with the addition of Mn3+ is observed because Mn 12

ACCEPTED MANUSCRIPT

prefers the 2a and 12k sites, thereby decreasing the magnetization to 1.63 µB/Mn, as observed in the Mössbauer study. The significant increase in the coercivity field, up to 9.7 kOe for x=5, is related to the increase of the microstrain induced by Mn3+ substitution. The microstrain was determined not

RI PT

only by XRD but also by analysis of the hysteresis loops. The presence of Mn3+ as the doped ion primarily affects the magnetic anisotropy of the Sr-hexaferrite, which widens the range of potential

AC C

EP

TE D

M AN U

SC

applications of these hexaferrites due to their tunable magnetic properties.

13

ACCEPTED MANUSCRIPT

References [1]

P. Vera Serna, C. García Campos, F. Sánchez De Jesús, A.M. Bolarín Miró, J.A. Juanico

RI PT

Lorán, J. Longwell, Mechanosynthesis, Crystal Structure and Magnetic Characterization of Neodymium Orthoferrite, Mater. Res. 19 (2016) 389–393. doi:10.1590/1980-5373-MR-20150214.

A. Xia, C. Zuo, L. Chen, C. Jin, Y. Lv, Hexagonal SrFe12O19 ferrites: Hydrothermal synthesis and

their

sintering

properties,

J.

Magn.

Magn.

332

(2013)

186–191.

R.C. Pullar, Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite

ceramics,

Prog.

doi:10.1016/j.pmatsci.2012.04.001.

Mater.

Sci.

57

(2012)

1191–1334.

C.M. Fang, F. Kools, R. Metselaar, G. de With, R. a de Groot, Magnetic and electronic

TE D

[4]

Mater.

M AN U

doi:10.1016/j.jmmm.2012.12.035. [3]

SC

[2]

properties of strontium hexaferrite SrFe12O19 from first-principles calculations, J. Phys.

[5]

EP

Condens. Matter. 15 (2003) 6229. doi:10.1088/0953-8984/15/36/311. J. Park, Y.-K. Hong, S.-G. Kim, S. Kim, L.S.I. Liyanage, J. Lee, W. Lee, G.S. Abo, K.-H. Hur,

AC C

S.-Y. An, Maximum energy product at elevated temperatures for hexagonal strontium ferrite (SrFe12O19)

magnet,

J.

Magn.

Magn.

Mater.

355

(2014)

1–6.

doi:10.1016/j.jmmm.2013.11.032. [6]

F.N. Tenorio Gonzalez, A.M. Bolarín Miró, F. Sánchez De Jesús, C.A. Cortés Escobedo, S. Ammar, Mechanism and microstructural evolution of polyol mediated synthesis of nanostructured M-type SrFe12O19, J. Magn. Magn. Mater. 407 (2016) 188–194. 14

ACCEPTED MANUSCRIPT

doi:10.1016/j.jmmm.2016.01.068. [7]

J. Luo, Structural and magnetic properties of Nd-doped strontium ferrite nanoparticles, Mat.

[8]

RI PT

Letters 80 (2012) 162–164. doi:10.1016/j.matlet.2012.04.107. A. Baniasadi, A. Ghasemi, A. Nemati, M. Azami Ghadikolaei, E. Paimozd, Effect of Ti–Zn substitution on structural, magnetic and microwave absorption characteristics of strontium

[9]

SC

hexaferrite, J. Alloys Compd. 583 (2014) 325–328. doi:10.1016/j.jallcom.2013.08.188.

S. Shakoor, M.N. Ashiq, M.A. Malana, A. Mahmood, M.F. Warsi, M. Najam-ul-Haq, N.

M AN U

Karamat, Electrical, dielectric and magnetic characterization of Bi–Cr substituted M-type strontium hexaferrite nanomaterials, J. Magn. Magn. Mater. 362 (2014) 110–114. doi:10.1016/j.jmmm.2014.03.038. [10]

X. Obradors, A. Collomb, M. Pernet, J.C. Joubert, A. Isalgué, Structural and magnetic

TE D

properties of BaFe12-xMnxO19 hexagonal ferrites, J. Magn. Magn. Mater. 44 (1984) 118–128. doi:10.1016/0304-8853(84)90053-2.

W.M.S. Silva, N.S. Ferreira, J.M. Soares, R.B. da Silva, M.A. Macêdo, Investigation of

EP

[11]

structural and magnetic properties of nanocrystalline Mn-doped SrFe12O19 prepared by proteic process,

J.

Magn.

Magn.

Mater.

395

(2015)

263–270.

AC C

sol–gel

doi:10.1016/j.jmmm.2015.07.085. [12]

P. Sharma, R.A. Rocha, S.N. Medeiros, B. Hallouche, A. Paesano, Structural and magnetic studies on mechanosynthesized BaFe12−xMnxO19, J. Magn. Magn. Mater. 316 (2007) 29–33. doi:10.1016/j.jmmm.2007.03.207.

[13]

D. Seifert, J. Töpfer, M. Stadelbauer, R. Grössinger, J.-M. Le Breton, Rare-Earth-Substituted 15

ACCEPTED MANUSCRIPT

Sr1−xLnxFe12O19 Hexagonal Ferrites, J. Am. Ceram. Soc. 94 (2011) 2109–2118. doi:10.1111/j.1551-2916.2010.04363.x. T.M.H. Dang, V.D. Trinh, D.H. Bui, M.H. Phan, D.C. Huynh, Sol–gel hydrothermal synthesis

RI PT

[14]

of strontium hexaferrite nanoparticles and the relation between their crystal structure and high coercivity

properties,

Adv.

Nat.

Sci.

Nanosci.

Nanotechnol.

[15]

(2012)

025015.

SC

doi:10.1088/2043-6262/3/2/025015.

3

M. Jean, V. Nachbaur, J. Bran, J.-M. Le Breton, Synthesis and characterization of SrFe12O19

doi:10.1016/j.jallcom.2010.02.002. [16]

M AN U

powder obtained by hydrothermal process, J. Alloys Compd. 496 (2010) 306–312.

A. Ataie, S. Heshmati-Manesh, Synthesis of ultra-fine particles of strontium hexaferrite by a modified

co-precipitation

method,

J.

Eur.

Ceram.

Soc.

21

(2001)

1951–1955.

[17]

TE D

doi:10.1016/S0955-2219(01)00149-2.

J.R. Liu, R.Y. Hong, W.G. Feng, D. Badami, Y.Q. Wang, Large-scale production of strontium ferrite by molten-salt-assisted coprecipitation, Powder Technol. 262 (2014) 142–149.

J.H. Luo, Preparation of Strontium Ferrite Powders by Mechanochemical Process, Appl.

AC C

[18]

EP

doi:10.1016/j.powtec.2014.04.076.

Mech. Mater. 110-116 (2011) 1736–1740. doi:10.4028/www.scientific.net/AMM.110116.1736. [19]

A.M. Bolarín-Miró, F. Sánchez-De Jesús, C.A. Cortés-Escobedo, S. Díaz-De la Torre, R. Valenzuela, Synthesis of M-type SrFe12O19 by mechanosynthesis assisted by spark plasma sintering, J. Alloys Compd. 643 (2015) S226–S230. doi:10.1016/j.jallcom.2014.11.124. 16

ACCEPTED MANUSCRIPT

[20]

F. Sánchez-De Jesús, A.M. Bolarín-Miró, C.A. Cortés-Escobedo, R. Valenzuela, S. Ammar, Mechanosynthesis, crystal structure and magnetic characterization of M-type SrFe12O19,

[21]

RI PT

Ceram. Int. 40 (2014) 4033–4038. doi:10.1016/j.ceramint.2013.08.056. J. Rodríguez-Carvajal, Recent advances in magnetic structure determination by neutron powder diffraction, Phys. B Condens. Matter. 192 (1993) 55–69. doi:10.1016/0921-

[22]

SC

4526(93)90108-I.

R.A. Brand, Improving the validity of hyperfine field distributions from magnetic alloys, Nucl.

M AN U

Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 28 (1987) 398– 416. doi:10.1016/0168-583X(87)90182-0.

[23] S. Alamolhoda, S.A. Seyyed Ebrahimi, A. Badiei, Optimization of the Fe/Sr ratio in processing of ultrafine strontium hexaferrite powders by a sol-gel autocombustion method,

[24]

TE D

Phys. Met. Metallogr. 102 (2006) S71–S73. doi:10.1134/S0031918X06140183. M. Sivakumar, A. Gedanken, W. Zhong, Y.. Du, D. Bhattacharya, Y. Yeshurun, I. Felner, Nanophase formation of strontium hexaferrite fine powder by the sonochemical method using

W.-Y. Zhao, P. Wei, H.-B. Cheng, X.-F. Tang, Q.-J. Zhang, FTIR Spectra, Lattice Shrinkage,

AC C

[25]

EP

Fe(CO)5, J. Magn. Magn. Mater. 268 (2004) 95–104. doi:10.1016/S0304-8853(03)00479-7.

and Magnetic Properties of CoTi-Substituted M-Type Barium Hexaferrite Nanoparticles, J. Am. Ceram. Soc. 90 (2007) 2095–2103. doi:10.1111/j.1551-2916.2007.01690.x. [26]

A. Mali, A. Ataie, Structural characterization of nano-crystalline BaFe12O19 powders synthesized

by

sol–gel

combustion

route,

doi:10.1016/j.scriptamat.2005.06.037. 17

Scr.

Mater.

53

(2005)

1065–1070.

ACCEPTED MANUSCRIPT

[27] A. Thakur, R.R. Singh, P.B. Barman, Synthesis and characterizations of Nd3+ doped SrFe12O19 nanoparticles,

Mater.

Chem.

Phys.

141

(2013)

562–569.

[28]

RI PT

doi:10.1016/j.matchemphys.2013.05.063. W.F. Brown, Theory of the Approach to Magnetic Saturation, Phys. Rev. 58 (1940) 736–743. doi:10.1103/PhysRev.58.736.

B.T. Shirk, W.R. Buessem, Temperature Dependence of Ms and K1 of BaFe12O19 and

SC

[29]

SrFe12O19 Single Crystals, J. Appl. Phys. 40 (1969) 1294. doi:10.1063/1.1657636. E.F. Bertaut, M. Mercier, R. Pauthenet, R. Pauthenet, Ordre magnétique et propriétés

M AN U

[30]

magnétiques de MnYO3, J. Phys. 25 (1964) 550–557. doi:10.1051/jphys:01964002505055000. [31]

P.P. Goswami, H.A. Choudhury, S. Chakma, V.S. Moholkar, P.P. Goswami, H.A. Choudhury, S. Chakma, V.S. Moholkar, Sonochemical Synthesis of Cobalt Ferrite Nanoparticles, Int. J.

[32]

TE D

Chem. Eng. (2013) 1–6. doi:10.1155/2013/934234. H. Yamamoto, H. Kumehara, R. Takeuchi, H. Nishio, H. Nishio, Magnetic Properties of Sr-M

J.. Wang, C.. Ponton, R. Grössinger, I.. Harris, A study of La-substituted strontium hexaferrite by

hydrothermal

synthesis,

AC C

[33]

EP

Ferrite Fine Particles, Le J. Phys. IV. 07 (1997) C1–535–C1–536. doi:10.1051/jp4:19971219.

J.

Alloys

Compd.

369

(2004)

170–177.

doi:10.1016/j.jallcom.2003.09.097. [34]

B.J. Evans, F. Grandjean, A.P. Lilot, R.H. Vogel, A. Gérard, 57Fe hyperfine interaction parameters and selected magnetic properties of high purity MFe12O19 (M=Sr, Ba), J. Magn. Magn. Mater. 67 (1987) 123–129. doi:10.1016/0304-8853(87)90728-1.

18

ACCEPTED MANUSCRIPT

[35]

S. Katlakunta, S.S. Meena, S. Srinath, M. Bououdina, R. Sandhya, K. Praveena, Improved magnetic properties of Cr3+ doped SrFe12O19 synthesized via microwave hydrothermal route,

[36]

B. Fultz, B. Fultz, Mössbauer Spectrometry, in: Charact. Mater., John Wiley & Sons, Inc., Hoboken, NJ, USA, 2002. doi:10.1002/0471266965.com069.

SC

A. Collomb, X. Obradors, A. Isalgué, D. Fruchart, Neutron diffraction study of the crystallographic and magnetic structures of the BaFe12−xMnxO19 m-type hexagonal ferrites, J.

EP

TE D

M AN U

Magn. Magn. Mater. 69 (1987) 317–324. doi:10.1016/0304-8853(87)90259-9.

AC C

[37]

RI PT

Mater. Res. Bull. 63 (2015) 58–66. doi:10.1016/j.materresbull.2014.11.043.

19

ACCEPTED MANUSCRIPT

Tables and Figures

Table I. Rietveld refinement values of X-ray diffraction patterns of the milled powder for different

RI PT

values of x ( 0≤x ≤5).

Table II. Rietveld refinement values of X-ray diffraction patterns of the annealed powders (SrFe12different values of x ( 0≤x ≤5).

SC

xMnxO19) for

Table III: Coercivity field (Hc), calculated magnetic saturation (Ms), remanent magnetization (Mr),

M AN U

magnetization ratio (Mr/Ms), and constant of inclusions and microstress (A).

Table IV: The Mössbauer hyperfine parameters of the Mn-doped strontium hexaferrite obtained at room temperature.

TE D

Table V: Interatomic distances and chemical bonding of the undoped strontium hexaferrite. Figure 1: XRD pattern of a mixture of SrCO3, Fe2O3 and Mn2O3 milled for 5 h to obtain SrFe12-xMnxO19 with x varied from 0 to 5, ∆x=1.

EP

Figure 2: XRD pattern of SrFe12-xMnxO19, with x varied from 0 to 5, ∆x=1, after annealing at 950°C for 2

AC C

h. The Rietveld refinement of the undoped strontium hexaferrite is included (red line). Figure 3: Lattice parameters ratio, a/c, and the volume of SrFe12-xMnxO19 for different levels of Mndoping, x ( 0≤x ≤5).

Figure 4: SEM micrographs of the annealed powder of SrFe12-xMnxO19 for different levels of Mndoping, x ( 0≤x ≤5). Figure 5: FT-IR spectra of SrFe12-xMnxO19 for different levels of Mn-doping, x ( 0≤x ≤5). 20

ACCEPTED MANUSCRIPT

Figure 6: Magnetic hysteresis loops (M-H) of SrFe12-xMnxO19 ( 0≤x ≤5) at 300 K. Figure 7: MS and HC of SrFe12-xMnxO19 ( 0≤x ≤5), the red line is a linear fit and the dotted line is a visual

RI PT

line. Figure 8: Room temperature Mössbauer spectra of SrFe12-xMnxO19 ( 0≤x ≤5).

AC C

EP

TE D

M AN U

SC

Figure 9: Variation of the Fe population in the hexaferrite structure with the Mn content (x).

21

ACCEPTED MANUSCRIPT

Table I Mn doped level (x) x=0

x=1 µs

D (nm)

18.41

0.00265

Mn2O3

*

SrCO3

34.02

D (nm)

Fe2O3

x=2 µs

D (nm)

18.01

0.00284

*

*

0.00312

32.53

x=3

x=4

µs

D (nm)

µs

18.30

0.00319

18.28

0.00276

*

19.55

0.00291

11.10

0.00225

0.00452

34.07

0.00324

39.28

0.00338

M AN U TE D EP AC C

x=5 µs

D (nm)

µs

18.73

0.00282

22.66

0.00346

16.32

0.00389

14.61

0.00196

35.11

0.00340

32.12

0.00461

SC

D: crystallite size, µs: microstrain, *Beyond detection limit

D (nm)

RI PT

Phase

ACCEPTED MANUSCRIPT

Table II x

a (Å)

c (Å)

D (nm)

µs

SrFe12O19

0

5.8809(1)

23.0635(5)

167.93

0.00036

SrMnFe11O19

1

5.8812(2)

23.049(1)

144.29

0.00038

SrMn2Fe10O19

2

5.8832(2)

23.035(1)

153.90

SrMn3Fe9O19

3

5.8855(3)

23.022(1)

151.49

SrMn4Fe8O19

4

5.8857(3)

23.000(2)

142.43

SrMn5Fe8O19

5

5.8890(5)

22.994(2)

146.22

M AN U TE D EP AC C

0.00039 0.00040 0.00047 0.00052

SC

D: crystallite size, µs microstrain

RI PT

Material

ACCEPTED MANUSCRIPT

Table III Hc (kOe) 5.5(1) 5.7(1) 7.1(1) 8.0(1) 8.8(1) 9.7(1)

Mr (emu/g) 33.9(1) 31.3(1) 27.1(1) 23.3(1) 19.4(1) 15.0(1)

Mr/Ms 0.44(1) 0.44(1) 0.43(1) 0.43(1) 0.44(1) 0.42(1)

A (A/m) x103 4.45(5) 4.47(15) 5.25(7) 5.53(9) 5.85(13) 6.40(13)

AC C

EP

TE D

M AN U

SC

0 1 2 3 4 5

Ms (emu/g) 77.6(2) 71.4(5) 63.3(2) 54.1(2) 44.0(3) 34.8(2)

RI PT

Sample

ACCEPTED MANUSCRIPT

Table IV ∆ (mm/s)

A (%)

41.2 49.0 52.0 50.3 41.0 51.8 41.1 48.5 51.1 50.2 41.1 51.6 40.4 47.6 50.4 49.8 39.8 39.5 46.7 49.7 39.0 38.3 45.2 48.5 38.3 36.6 43.3 46.9 36.9

0.35 0.27 0.36 0.35 0.28 0.39 0.36 0.28 0.40 0.34 0.28 0.40 0.34 0.29 0.38 0.38 0.22 0.33 0.30 0.37 0.21 0.31 0.33 0.36 0.20 0.34 0.37 0.36 0.18

0.39 0.17 0.25 0.09 2.19 0.15 0.39 0.10 0.30 0.01 2.12 0.14 0.33 0.07 0.29 0.07 1.80 0.29 0.06 0.34 1.74 0.25 0.03 0.35 1.70 0.23 0.01 0.32 1.65

47 17 14 12 6 4 54 17 13 6 7 3 50 21 17 2 10 49 24 16 0 11 48 22 18 12 47 18 23 12

EP

AC C

RI PT

δ* (mm/s)

TE D

12k 4f1 4f2 SrFe12O19 2a 2b Fe2O3 12k 4f1 4f2 SrMnFe11O19 2a 2b Fe2O3 12k 4f1 SrMn2Fe10O19 4f2 2a 2b 12k 4f1 SrMn3Fe9O19 4f2 2a 2b 12k 4f1 SrMn4Fe8O19 4f2 2a 2b 12k 4f1 SrMn5Fe7O19 4f2 2a 2b * Relative to α-Fe

Bhf (T)

SC

Position

M AN U

Material

ACCEPTED MANUSCRIPT

Table V

RI PT

Quantity of bonds 6 2 3 1 3 3 3 1 1 2 2

AC C

EP

TE D

M AN U

Fe(2a)-O(12k1) Fe(2b)- O(4e) Fe(2b)- O(6h) Fe(4f1)- O(4f) Fe(4f1)- O(12k1) Fe(4f2)- O(6h) Fe(4f2)- O(12k2) Fe(12k)- O(4e) Fe(12k)- O(4f) Fe(12k)- O(12k1) Fe(12k)- O(12k2)

d0 (Å) 2.027 2.267 1.87 1.897 1.932 2.061 1.987 1.980 2.091 2.121 1.923

SC

Bond

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

x=1

b)

x=3

M AN U

SC

a)

RI PT

ACCEPTED MANUSCRIPT

c)

AC C

EP

TE D

x=5

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Highlights SrMnxFe12-xO19, were obtained by high energy ball milling and annealing at 950 °C.

•

A high concentration of Mn, up to x=5, has been obtained.

•

The substitution mechanism and effect of Mn3+ in Sr-hexaferrites are reported.

•

The Mn3+ ions occupy 2a and 12k sites confirmed by Mössbauer study.

•

The substitution of Fe3+ per Mn3+ increases the coercivity field up to 9.7 kOe.

AC C

EP

TE D

M AN U

SC

RI PT

•