Synthesis of glass ceramics containing finely dispersed particles of aluminum-doped M-type strontium hexaferrite

Article abstract of DOI:10.1007/s11172-005-0219-2

Glasses with nominal compositions SrFe₁₀Al₂O ₁₉+4(SrB₂O₄+Sr₂B₂O ₅) (1) and SrFe₉Al₃O₁₉+4(SrB ₂O₄+Sr₂B

Full text of DOI:10.1007/s11172-005-0219-2

Russian Chemical Bulletin, International Edition, Vol. 54, No. 1, pp. 75—78, January, 2005
75
Synthesis of glass ceramics containing finely dispersed particles of
aluminumꢀdoped Mꢀtype strontium hexaferrite
D. D. Zaitsev,aꢀ L. A. Trusov, P. E. Kazin, and Yu. D. Tretyakov
a
b
a,b
aDepartment of Materials Science, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119992 Moscow, Russian Federation.
1
Fax: +7 (095) 939 0998. Eꢀmail: zaytsev@inorg.chem.msu.ru
Department of Chemistry, M. V. Lomonosov Moscow State University,
b
1
Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (095) 939 0998
Glasses with nominal compositions SrFe10Al O +4(SrB O +Sr B O ) (1) and
2
19
2
4
2
2
5
SrFe Al O +4(SrB O +Sr B O ) (2) were prepared by rapid quenching of melts. Thermal
9
3
19
2
4
2
2
5
treatment of glass samples at 600—900 °C resulted in crystallization of the magnetic phase
SrFe12–xAl O (x = 1.1±0.1) and strontium borates. Platelet heꢁaferrite particles with aꢂerage
x
19
2
2
sizes from (250×60) nm to (450×140) nm were prepared. The coerciꢂe force of glass ceramics
is 580 and 475 kA m–1 for glasses 1 and 2, respectiꢂely. The coerciꢂe force of 580 kA m is the
highest known ꢂalue compared to heꢁaferrite particles prepared earlier by glass crystallization.
–1
Key words: Mꢀtype strontium heꢁaferrite, glass, glass ceramics, ferrimagnetic, coerciꢂe
force, saturation magnetization.
Strontium and barium Mꢀtype heꢁaferrites are promꢀ
Experimental
ising materials for the construction of highꢀdensity magꢀ
netic data storage deꢂices and constant magnets due to
their high magnetic anisotropy constants and chemical
inertness.1,2 One of procedures for the preparation of
Strontium carbonate, iron(III) oꢁide, boric acid (all of reꢀ
agent grade), and aluminum oꢁide, which was prepared by therꢀ
molysis of aluminum nitrate at 800 °C, were used as starting
compounds. A miꢁture of the starting compounds was annealed
at 600 °C for 10 h.
finely dispersed heꢁaferrites is based on crystallization of
3
—6
glassy oꢁide precursors by thermal treatment.
This proꢀ
Glass samples were prepared by melting powders in a platiꢀ
num crucible placed in a tube furnace at 1250 °C for 2 h. The
resulting melts were quenched between two rotating steel rollꢀ
ers. The glasses haꢂe the following compositions: 9SrO•5Fe O •
cedure affords singleꢀdomain submicron magnetic parꢀ
7
—9
ticles characterized by a high coerciꢂe force. Earlier,
we haꢂe demonstrated that the chemical composition
of the starting glass influences the size and shape of
heꢁaferrite particles prepared by thermal treatment of an
amorphous material. For eꢁample, crystallization of
glasses in the SrO—Fe O —B O , SrO—Fe O —SiO ,
2
3
•Al O •8B O (1) and 9SrO•4.5Fe O •1.5Al O •8B O (2),
2
3
2
3
2
3
2
3
2
3
which formally correspond to the compositions SrFe10Al2O19+
+
+
4(SrB O +Sr B O ) (1) and SrFe Al O +4(SrB O +
2 4 2 2 5 9 3 19 2 4
Sr B O ) (2), respectiꢂely. Glassꢀceramic samples were synꢀ
2
2
5
2
3
2
3
2
3
2
thesized by annealing the glass samples at 600—900 °C for 2 h.
and SrO—Fe O —B O —Bi O systems gaꢂe platelet
2
3
2
3
2
3
Xꢀray diffraction patterns of the samples were obtained on a
strontium heꢁaferrite particles with an aꢂerage diameter
ꢂarying from 50 nm to 1 µm and the diameter to thickness
ratio ꢂarying from 1.4 to 7.4. In the present study, stronꢀ
tium heꢁaferrite was synthesized for the first time by glass
crystallization in the SrO—B O —Al O —Fe O system.
Guinier FRꢀ552 monochromator chamber (CuꢀKα radiation).
1
The magnetic properties were studied using a Faraday balance
and a Quantum Design SQUID magnetometer. Microstructural
studies were carried out on a Leo Supra 50 VP scanning electron
microscope equipped with an Xꢀray microanalysis attachment.
2
3
2
3
2
3
The compositions of the starting glasses were chosen based
on the results of our earlier study1 of phase equilibria in
the SrO—Fe O —B O system. We chose aluminum oꢁꢀ
0
Results and Discussion
2
3
2
3
ide as an additional component taking into account that
it, serꢂing arbitrarily as glassꢀforming oꢁide, modifies the
glass properties. Besides, aluminum can replace iron in
heꢁaferrite, resulting in an increase in the coerciꢂe force
of the material.12
The glasses synthesized appeared to be completely
Xꢀray amorphous. The powder Xꢀray diffraction data for
annealed glass samples are giꢂen in Table 1. Crystalline
phases appeared at >650 °C; Sr B O was the first to
1
1
2
2
5
crystallize from glasses of both compositions. When the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 74—77, January, 2005.
066ꢀ5285/05/5401ꢀ0075 © 2005 Springer Science+Business Media, Inc.
1

76
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 1, January, 2005
Zaitseꢂ et al.
3
15
Table 1. Powder Xꢀray diffraction data for the phase composiꢀ
tions of glassꢀceramic samples prepared at different temperaꢀ
tures
(691.2 Å ), which is eꢂidence that iron is replaced by
11
aluminum. Taking into account the published data for
SrFe12–xAl O , the unit cell ꢂolumes correspond to the
x
19
replacement x = 1.1±0.1 for both compositions. ꢃence,
the aluminum content in heꢁaferrite is much lower than
that eꢁpected for the nominal composition, and eꢁcess
aluminum is inꢂolꢂed in strontium borates.
Scanning microphotographs of etched glassꢀceramic
samples are shown in Fig. 1. The samples were etched by
keeping them in distilled water for ∼ 1 h. Etching was
accompanied by dissolution of strontium borates, and only
heꢁaferrite particles remained on the sample surface. The
composition of these particles was confirmed by Xꢀray
microanalysis.
T */°С
Composition 1
Composition 2
6
6
7
7
8
00
50
00
50
00
No crystalline phases were found
Sr B O
Sr B O
5
2
2
5
2
2
Sr B O , SrB O
Sr B O , SrB O
2
2
5
2
4
4
2
2
5
2
4
4
Sr B O , SrB O
Sr B O , SrB O
2 2 5 2
Sr B O , SrB O ,
2 2 5 2 4
SrFe O
12 19
Sr B O , SrB O ,
2 2 5 2 4
2
2
5
2
Sr B O , SrB O ,
2
2
5
2
4
SrFe O
1
2
19
8
9
50
00
Sr B O , SrB O ,
2
2
5
2
4
SrFe O
SrFe O
12 19
1
2
19
Sr B O , SrB O ,
**
2
2
5
2
4
SrFe O
19
12
As can be seen, the heꢁaferrite particles haꢂe a heꢁꢀ
agonal platelet shape similar to that obserꢂed earlier.3
The size of heꢁaferrite particles increases, whereas the
diameter to thickness ratio decreases as the annealing
temperature increases (Table 3). At 800 °C, the particle
anisotropy in a sample of composition 1 is higher than
that in a sample of composition 2, whereas at the maꢁimal
annealing temperature, the particles in a sample of comꢀ
position 1 become less anisotropic.
,7—9
*
*
The synthesis temperature of glass ceramic.
* The sample melts.
annealing temperature was increased to 700 °C, Xꢀray
diffraction pattern showed lines of the second borate of
composition SrB O . Beginning with 800 °C, Xꢀray patꢀ
terns contained broadened lines corresponding to stronꢀ
tium heꢁaferrite.
2
4
For the glass of composition 1 annealed at 850 °C, the
Lines of heꢁaferrite are noticeably broadened eꢂen in
the Xꢀray diffraction patterns of samples, which were synꢀ
thesized at maꢁimal temperature and characterized by the
largest crystallite sizes. Apparently, this is eꢂidence that
the particles haꢂe somewhat different unit cell paramꢀ
eters, which is reasonable to relate to the difference in the
degree of replacement of iron with aluminum. Therefore,
the aboꢂeꢀdetermined degrees of replacement are aꢂerꢀ
aged oꢂer the samples.
The magnetic measurement data are giꢂen in Table 4.
The saturation magnetization of the samples increases
with increasing annealing temperature. The magnetizaꢀ
tion increases most substantially in a temperature range of
600—650 °C. Judging from the magnetization, it can be
concluded that the major portion of heꢁaferrite crystalꢀ
lizes in this temperature range. Apparently, the absence of
lines of a magnetic phase in Xꢀray diffraction patterns
indicates that, in the temperature range 600—650 °C, this
phase forms nanometerꢀsize particles, which is below the
3
unit cell ꢂolume of Sr B O is 494.3(7) Å (a = 7.763(7) Å,
2
2
5
b = 5.364(3) Å, c = 11.88(1) Å, α =92.6(1)°). According
1
3
to the published data, the unit cell ꢂolume of pure
3
Sr B O is 489.0 Å . An increase in the ꢂolume may be
2
2
5
indicatiꢂe of the replacement of boron with alumiꢀ
3
num. The unit cell ꢂolume of SrB O is 343.4(1) Å
2
4
(
a = 11.952(4), b = 4.3375(4), c = 6.6245(7) Å), and it is
1
4
ꢂirtually equal to that published in the literature for pure
3
SrB O (343.3 Å ).
2
4
For glass of composition 2 annealed at 850 °C, the
3
unit cell ꢂolume of Sr B O is 495.7(6) Å (a = 7.783(9),
2
2
5
b = 5.361(9), c = 11.892(8) Å, α = 92.6(1)°), and the unit
cell ꢂolume of SrB O4 is 345.9(5) Å3 (a = 12.06(1),
2
b = 4.337(7), c = 6.615(3) Å). Apparently, boron is parꢀ
tially replaced with aluminum in both borates.
In all cases, the unit cell parameters of heꢁaferrite are
smaller (Table 2) than those of pure strontium heꢁaferrite
Table 2. Volumes and parameters of the heꢁagonal unit cell of
SrFe12–xAl O in glassꢀceramic samples
Table 3. Geometric characteristics of heꢁaferrite particles in
x
19
glass ceramics
Sample T *
compoꢀ /°С
sition
a
c
Unit cell
ꢂolume/Å3
Glass T */°С Diameter Thickness Diameter to thickness
Å
compoꢀ
sition
ratio
nm
1
1
1
2
2
800 5.858(1) 22.91(2)
850 5.854(1) 22.93(1)
900 5.853(1) 22.93(2)
800 5.845(2) 22.97(3)
850 5.861(2) 22.962(5)
681.0(6)
680.4(4)
680.3(8)
679.8(4)
683.0(4)
1
1
2
2
800
900
800
850
250
380
400
450
60
130
110
140
4.2
2.9
3.6
3.2
*
The synthesis temperature.
* The annealing temperature.

Strontium heꢁaferrite particles from glass
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 1, January, 2005
77
a
b
3
00 nm
300 nm
c
d
2
00 nm
300 nm
Fig. 1. Scanning microphotographs of glassꢀceramic samples of compositions 1 (a, b) and 2 (c, d) synthesized at 800 (a, c), 850 (d),
and 900 °C (b). ꢃeꢁaferrite particles haꢂe a heꢁagonal platelet shape.
Table 4. Coerciꢂe forces and saturation magnetizations of glassꢀ
ceramic samples of compositions 1 and 2
in the aluminum content should lead to a decrease in the
magnetization.
For samples of composition 1, the coerciꢂe force inꢀ
creases with increasing annealing temperature and is
2
–1
Composition T */°С
H /kA m–1
M /A m kg
c
s
–
1
5
80 kA m at 900 °C. This is the highest known ꢂalue
1
1
1
1
1
2
2
2
2
600
650
700
800
900
600
650
800
850
10
295
310
430
580
50
290
440
475
3.2
17.8
19.0
16.7
18.3
4.3
16.1
14.9
15.8
compared to heꢁaferrite particles prepared earlier by glass
crystallization. For samples of composition 2, the maꢁiꢀ
mal coerciꢂe force is somewhat smaller (475 kA m– ).
The coerciꢂe force of a singleꢀdomain particle with
uniaꢁial magnetic anisotropy taking into account its shape
is estimated by the equation:
1
H = 0.48[2K /µ M + (N – N )M ],
c
1
0
s
⊥
||
s
*
The annealing temperature.
where K is the magnetocrystalline anisotropy constant of
1
the compound, M is the saturation magnetization, N
s
||
and N are the demagnetizing factors parallel and perpenꢀ
⊥
3
resolution limit of the electron microscope used in the
present study.
dicular to the easy magnetization aꢁis. For a thin plate, a
sphere, and a rod, the N – N difference is –1, 0, and 0.5,
|
|
⊥
Beginning with the annealing temperature of 700 °C,
a slight nonmonotonic change in the magnetization was
obserꢂed, which is attributable to the influence of two
opposite factors. An increase in the annealing temperaꢀ
ture leads to an increase in the portion of the crystalline
phase of heꢁaferrite, resulting in an increase in the magꢀ
netization. At the same time, a change in the annealing
temperature can be accompanied by a change in the aluꢀ
minum content in the heꢁaferrite phase, and an increase
respectiꢂely, i.e., the particles characterized by a smaller
diameter to thickness ratio haꢂe a higher coerciꢂe force.
At the maꢁimal temperature, the heꢁaferrite particles
prepared from the glass of composition 1 are characterꢀ
ized by the smallest diameter to thickness ratio compared
to particles prepared from other samples, the aluminum
content being approꢁimately the same. As a consequence,
the former particles are characterized by the largest coerꢀ
ciꢂe force.

78
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 1, January, 2005
Zaitseꢂ et al.
To summarize, we prepared glass ceramics containing
submicron particles of aluminumꢀdoped strontium heꢁaꢀ
ferrite and characterized by high coerciꢂe forces.
6. S.ꢀB. Sohn, S.ꢀY. Choi, and I.ꢀB. Shim, J. Magn. Magn.
Mater., 2002, 239, 533.
7
. D. D. Zaitseꢂ, P. E. Kazin, A. V. Garsheꢂ, Yu. D. Tretyakoꢂ,
and M. Jansen, Neorg. Mater., 2004, 40, 1009 [Inorg. Mater.,
2004, 40, 881 (Engl. Transl.)].
We thank A. V. Garsheꢂ for performing microscopic
studies.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ
8. D. D. Zaitseꢂ, P. E. Kazin, E. A. Graꢂchikoꢂa, L. A. Trusoꢂ,
S. E. Kushnir, Y. D. Tretyakoꢂ, and M. Jansen, Mendeleev
Commun., 2004, 171.
9
. D. D. Zaitseꢂ, P. E. Kazin, Yu. D. Tretyakoꢂ, Yu. V.
3
2026a), the Russian Academy of Sciences (Program of
Maksimoꢂ, I. P. Suzdaleꢂ, and M. Jansen, Neorg. Mater.,
Basic Research "Design of New Metallic, Ceramic,
Glassy, Polymeric, and Composite Materials"), the Founꢀ
dation of the President of the Russian Federation (Fedꢀ
eral Program for the Support of Leading Scientific
Schools, Project NShꢀ2033.03.2003), and the Ministry of
Education and Sciences of the Russian Federation (Proꢀ
gram "Russian Uniꢂersities," Project UR.06.02.030).
2
004, 40 [Inorg. Mater., 2004, 40 (Engl. Transl.)].
1
0. D. D. Zaitseꢂ, P. E. Kazin, Yu. D. Tretyakoꢂ, and M. Jansen,
Zh. Neorg. Khim., 2003, 48, 1869 [Russ. J. Inorg. Chem.,
2
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4. J.ꢀB. Kim, K.ꢀS. Lee, I.ꢀꢃ. Suh, J.ꢀꢃ. Lee, J.ꢀR. Park, and
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1
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5
Received October 15, 2004;
in revised form November 15, 2004