- Email: [email protected]
Effects of Gd substitution on the structural and magnetic properties of strontium hexaferrites
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 316 (2007) 170–173 www.elsevier.com/locate/jmmm
Effects of Gd substitution on the structural and magnetic properties of strontium hexaferrites G. Litsardakisa,, I. Manolakisa, C. Serletisb, K.G. Efthimiadisb a
Department of Electrical & Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece b Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece Available online 27 February 2007
Abstract The effect of Gd substitution in M-type strontium hexaferrites has been examined in two series of samples, ðSr1x Gdx ÞO 5:25 Fe2 O3 and Sr1x Gdx Fe12x Cox O19 , both prepared by the ceramic method, where x ¼ 020:40. The samples have been characterized by XRD, VSM and SEM-EDAX techniques. All substituted samples present primarily the hexaferrite structure. Sample ðSr0:95 Gdx0:05 ÞO 5:25 Fe2 O3 is single phase. Formation of impurity phases is affected by stoichiometry and presence of Co. In Sr–Gd samples, coercivity showed a maximum value of 305 kA/m (3.8 kOe) for x ¼ 0:20, while remanence and saturation magnetization did not decrease. Coercivity and magnetization in the Sr–Gd–Co series decreased steadily with substitution degree. r 2007 Elsevier B.V. All rights reserved. PACS: 75.50.Ww Keywords: M-type hexaferrites; Magnetic properties; Permanent magnets; Rare-earth substitution
1. Introduction M-type hexagonal ferrites had and still have a prominent position in the permanent magnet market, due to their unique combination of acceptable magnetic performance and low cost. Improvement of the magnetic properties has been attempted extensively, mainly by various substitutions. Recently, a new perspective emerged from a series of successful La–Co [1–4] and La-only [5] substitutions, which resulted in an important increase in coercivity, without a simultaneous drop in remanence. The increased anisotropy field was suggested as the reason for this advanced performance. These studies triggered the interest in the area of rare-earth substitution in M-type hexaferrites and many researchers attempted to replace La, as substituting element for Ba or Sr, with other rare-earth elements, e.g. Sm [6,7], Nd [8,9] or Pr [10]. An improvement of the magnetic behavior was generally observed, which was attributed mainly to microstructural changes in relation to Corresponding author. Tel.: +30 2310 996384; fax: +30 2310 996302.
E-mail address: [email protected] (G. Litsardakis). 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2007.02.046
the impurity phases that occur, rather than to an increase of magnetocrystalline anisotropy. It was concluded that the rare earth ions do not enter exclusively as substitutes, but also form impurity phases. The investigation of possible replacement of La with Gd is the goal of our recent studies. It was shown [11] that Gd has a positive effect on the coercivity of Ba–Gd–Co ferrites ðBa1x Gdx Fe12x Cox O19 Þ, presenting a maximum value at substitution degree of x ¼ 0:1. On the other hand, the magnetization exhibited a decrease with increasing Gd content and a number of secondary Gd phases were detected. This behavior focused our interest on the study of Gd substitution in Sr hexaferrites, in order to examine the analogy of results in Ba and Sr hexaferrites, which had been noted for La- and La–Co substitution [2]. The present report concerns Gd-only substitution in a non-stoichiometric Sr surplus series (noted as Sr–Gd series), aiming to reduce the presence of hematite ðFe2 O3 Þ and to study in more detail the way Gd influences the magnetic properties of the material. In addition, it also includes the characterization of a Sr–Gd–Co series, to compare to previous Ba–Gd–Co results [11].
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
2. Experimental procedure
G: Gd3Fe5O12
3. Results All substituted samples present the M-structure as their main phase. Phase formation is affected by stoichiometry (Fig. 1 and Table 1)and in the Sr–Gd–Co series by the presence of Co as well. Formation of single phase substituted material has been achieved only for ðSr0:95 Gdx0:05 ÞO 5:25Fe2 O3 ðx ¼ 0:05Þ. In this Sr–Gd series, small traces ðo2%Þ of GdFeO3 were detected for samples x ¼ 0:1 0:2. For xX0:2 Fe2 O3 is also formed, while for x ¼ 0:25 Gd3 Fe5 O12 appears. From the phase analysis (Table 1), one can calculate the percentage of Gd present in GdFeO3 and Gd3 Fe5 O12 , which ranges from 10% to 33%. In the Sr–Gd–Co series, hematite is present as secondary phase, in percentages up to 9% w/w for x ¼ 0:4, while traces ðo1%Þ of Gd3 Fe5 O12 and CoFe2 O4 were also detected in all substituted samples. It seems that in both cases Gd only partially enters the M-lattice, forming simultaneously secondary Gd phases. However, there is no significant variation of T c with the substitution degree, for both series. Regarding the magnetic properties, it is remarkable that coercivity in Sr–Gd samples displays a constant rise up to a maximum value of 305 kA/m (3.8 kOe), for x ¼ 0:20 (Fig. 3), which is higher than the typical value for SrFe12 O19 (279 kA/m [2]), while remanence and saturation magnetization do not decrease up to that Gd concentration ðx ¼ 0:2Þ and remain constant at about 40 and 65 Am2 =kg, respectively (Fig. 2). The results for this series appear to be analogous to La–Co and La-only substitution, which
H: Fe3O3O: GdFeO3
O
↓ G
H
G G
↓
↓ ↓ ↓
SrGd0.25
O
G
↓H ↓ ↓
GH
H
G
↓
↓
O ↓H
H H
G
↓ ↓
↓ ↓
↓
O
SrGd0.2
↓
SrGd0.15
Intensity (a.u.)
Two series of samples were produced by the classic ceramic route. A series of Gd-only substituted, Sr-surplus ð½Srþ2 =½Feþ3 ¼ 1=10:5Þ hexaferrites, according to the formula ðSr1x Gdx ÞO 5:25 Fe2 O3 , x ¼ 0, 0.05, 0.10, 0.15, 0.20, 0.25, and a series of Gd–Co substituted stoichiometric 1 Sr hexaferrites ð½Srþ2 =½Feþ3 ¼ 12 Þ, according to the formula Sr1x Gdx Fe12x Cox O19 , x ¼ 0, 0.1, 0.2, 0.3, 0.4. The starting materials (Fe2 O3 , SrCO3 , Co3 O4 and Gd2 O3 powders of analytical grade) were mixed and calcined for 1 h at 900 C in air. Milling was performed in a stainless steel ball mill for 24 h. The samples were isotropically pressed into pellets and fired for 2 h at 1200 C in air. X-ray patterns were obtained by a powder diffractometer, using Fe Ka radiation and analyzed with the Rietveld method. Magnetization and coercivity measurements (hysteresis loops) were carried out on compacted, non-aligned powder samples, using a vibrating sample magnetometer with maximum attainable field of 1.8 T at room temperature. Curie temperature ðT c Þ values were obtained from thermomagnetic measurements in a field of 30 mT. Grain size and microstructure were observed by a JEOL JSM 5900 LV scanning electron microscope, equipped with an INCA x-sight detector (Oxford Instruments) for EDX microanalysis.
171
SrGd0.1
SrGd0.05
1 0 7
1 0 1 2 0 3
20
0 0 6
1 10 001 81 2
30
40
1 1 4
SrO.. 5.25Fe2O3 2 0 2 221 3 1 0 000 1 5 018 6
50
2 0 6
1 0 11
2 0 9
60
2 2 2 1 30 1 2 0 3 700112 0 0 100 04 1 14 12 0 14 8
70
1 0 152 0 13
80
2 0 14
90
2theta Fe Kα (degrees) Fig. 1. X-ray diffractograms of ðSr1x Gdx ÞO 5:25 Fe2 O3 .
however concerns single-phase compounds. The choice of a Sr-surplus formula without Co addition resulted in limited presence of secondary phases, as it is shown in Fig. 1. Similarly, only at very low Gd content a single phase compound is formed, but the positive influence of the secondary phase on the magnetic properties is quite obvious, with constant values of magnetization and increasing coercivity up to x ¼ 0:2. It is interesting to note that, despite the increase of the GdFeO3 and hematite percentage with x, the specific magnetization and remanence do not decrease. This might be an indication of an intrinsic effect of Gd. For x ¼ 0:25, the formation of Gd3 Fe5 O12 and the increased amount of Fe2 O3 is probably responsible for the decline of the magnetic properties. In contrast, coercivity and magnetization in the Sr–Gd–Co series decrease steadily with substitution degree (Figs. 2, 3). The variation of coercivity is different from that of Ba–Gd–Co ferrites [11], where a positive effect (maximum for x ¼ 0:1) has been observed. The effect on the magnetization is the same in both Sr/Ba–Gd–Co series (decrease with x), fact that can be correlated to the presence in both cases of various Fe, Gd and Co-impurities. The microstructural observation by SEM showed hexagonal-like grains of about 122 mm, with similar features for both series. In the Sr–Gd series, sintering is influenced by Gd substitution and the presence of secondary phases, as extended grain growth and sintering was observed for samples x ¼ 020:10 (Fig. 4), while for samples x ¼ 0:1520:2 the grain size is kept under 1 mm
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
172
Table 1 Crystal phases identified from X-ray diffractograms: SrFe12 O19 (M); Fe2 O3 ðHÞ; GdFeO3 ðOÞ; Gd3 Fe5 O12 ðGÞ x
Phases in SrGd series
Gd % present in O+G impurities
H 0 0.05 0.1 0.15 0.2 0.25
O
G
Single phase M Single phase M 0:42 0:12 1:3 0:14 1:8 0:15 0:77 0:14
— — 2:16 0:52 3:63 0:57
— — — 0:55 0:06
10 32 33 18
Specific magnetization (Am2/kg)
100 SrGdCo σ at 1.8 T SrGdCo σ R 80
SrGd σ at 1.8T SrGdCo σR
60
40
20 0.0
0.1
0.2
0.3
0.4
Substitution degree, x Fig. 2. Specific magnetization values of the two series.
Fig. 4. SEM image of the SrO 5:25 Fe2 O3 ðx ¼ 0Þ sample.
350 Coercivity, Hc (kA/m)
300 250 200 150 100
SrGdCo SrGd
50 0 0.0
0.1
0.2
0.3
0.4
Substitution degre, x Fig. 3. Coercivity values of the two series. Fig. 5. SEM image of the ðSr0:80 Gd0:20 ÞO 5:25 Fe2 O3 ðx ¼ 0Þ sample.
(Fig. 5). It seems that Gd acts as a grain growth inhibitor, drastically above a certain concentration, thereby achieving higher coercivity values for samples x ¼ 0:1520:2. This can be appointed as an extrinsic effect of Gd on the microstructure of the Gd-only materials, directly affecting coercivity. A grain growth inhibition effect is not observed in the case of the Sr–Gd–Co samples, probably due to the presence of Co and of additional secondary phases, which are responsible for the decrease of the magnetic properties values with x.
These results demonstrate the potential of the use of Gd in substituted hexaferrites. Finally, it is expected that a softer preparation method of Gd substituted hexaferrites, such as chemical coprecipitation, may yield single phase compounds at even higher substitution degrees than x ¼ 0:05 and allow a thorough investigation of possible intrinsic effects and structural or magnetic changes, associated to the presence of Gd in the M-lattice.
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
Acknowledgments This work is part of the project ‘‘New magnetic rareearth substituted hexaferrites’’, funded by the Hellenic Ministry of National Education and the EU—Operational Program for Education and Initial Vocational Training— Action ‘‘Pythagoras II’’. References [1] Y. Ogata, Y. Kubota, T. Takami, M. Tokunaga, T. Shinohara, IEEE Trans. Magn. 35 (5) (1999) 3334. [2] F. Kools, A. Morel, P. Tenaud, M. Rossignol, O. Isnard, R. Grossinger, J.M. Le Breton, J. Teillet, Proceedings of the International Conference on Ferrites ICF8, Kyoto, Japan 2000, p. 437.
173
[3] F. Kools, A. Morel, R. Grossinger, J.M. Le Breton, P. Tenaud, J. Magn. Magn. Mater. 242–245 (2002) 1270. [4] R. Grossinger, C. Tellez Blanco, M. Kupferling, M. Muller, G. Wiesinger, Physica B 327 (2003) 202. [5] H. Yamamoto, IEEE Trans. Magn. 26 (3) (1990) 1144. [6] L. Lechevallier, J.M. Le Breton, J.F. Wang, I.R. Harris, J. Magn. Magn. Mater. 269 (2004) 192. [7] J.F. Wang, C.B. Ponton, I.R. Harris, J. Magn. Magn. Mater. 298 (2006) 122. [8] H. Mocuta, L. Lechevallier, J.M. Le Breton, J.F. Wang, I.R. Harris, J. Alloy Compd. 364 (2004) 48. [9] H. Yamamoto, M. Isono, T. Kobayashi, J. Magn. Magn. Mater. 295 (2005) 51. [10] J.F. Wang, C.B. Ponton, I.R. Harris, J. Alloy Compd. 403 (2005) 104. [11] G. Litsardakis, I. Manolakis, K. Efthimiadis, J. Alloy. Compd. 427 (2007) 194.
Journal of Magnetism and Magnetic Materials 316 (2007) 170–173 www.elsevier.com/locate/jmmm
Effects of Gd substitution on the structural and magnetic properties of strontium hexaferrites G. Litsardakisa,, I. Manolakisa, C. Serletisb, K.G. Efthimiadisb a
Department of Electrical & Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece b Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece Available online 27 February 2007
Abstract The effect of Gd substitution in M-type strontium hexaferrites has been examined in two series of samples, ðSr1x Gdx ÞO 5:25 Fe2 O3 and Sr1x Gdx Fe12x Cox O19 , both prepared by the ceramic method, where x ¼ 020:40. The samples have been characterized by XRD, VSM and SEM-EDAX techniques. All substituted samples present primarily the hexaferrite structure. Sample ðSr0:95 Gdx0:05 ÞO 5:25 Fe2 O3 is single phase. Formation of impurity phases is affected by stoichiometry and presence of Co. In Sr–Gd samples, coercivity showed a maximum value of 305 kA/m (3.8 kOe) for x ¼ 0:20, while remanence and saturation magnetization did not decrease. Coercivity and magnetization in the Sr–Gd–Co series decreased steadily with substitution degree. r 2007 Elsevier B.V. All rights reserved. PACS: 75.50.Ww Keywords: M-type hexaferrites; Magnetic properties; Permanent magnets; Rare-earth substitution
1. Introduction M-type hexagonal ferrites had and still have a prominent position in the permanent magnet market, due to their unique combination of acceptable magnetic performance and low cost. Improvement of the magnetic properties has been attempted extensively, mainly by various substitutions. Recently, a new perspective emerged from a series of successful La–Co [1–4] and La-only [5] substitutions, which resulted in an important increase in coercivity, without a simultaneous drop in remanence. The increased anisotropy field was suggested as the reason for this advanced performance. These studies triggered the interest in the area of rare-earth substitution in M-type hexaferrites and many researchers attempted to replace La, as substituting element for Ba or Sr, with other rare-earth elements, e.g. Sm [6,7], Nd [8,9] or Pr [10]. An improvement of the magnetic behavior was generally observed, which was attributed mainly to microstructural changes in relation to Corresponding author. Tel.: +30 2310 996384; fax: +30 2310 996302.
E-mail address: [email protected] (G. Litsardakis). 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2007.02.046
the impurity phases that occur, rather than to an increase of magnetocrystalline anisotropy. It was concluded that the rare earth ions do not enter exclusively as substitutes, but also form impurity phases. The investigation of possible replacement of La with Gd is the goal of our recent studies. It was shown [11] that Gd has a positive effect on the coercivity of Ba–Gd–Co ferrites ðBa1x Gdx Fe12x Cox O19 Þ, presenting a maximum value at substitution degree of x ¼ 0:1. On the other hand, the magnetization exhibited a decrease with increasing Gd content and a number of secondary Gd phases were detected. This behavior focused our interest on the study of Gd substitution in Sr hexaferrites, in order to examine the analogy of results in Ba and Sr hexaferrites, which had been noted for La- and La–Co substitution [2]. The present report concerns Gd-only substitution in a non-stoichiometric Sr surplus series (noted as Sr–Gd series), aiming to reduce the presence of hematite ðFe2 O3 Þ and to study in more detail the way Gd influences the magnetic properties of the material. In addition, it also includes the characterization of a Sr–Gd–Co series, to compare to previous Ba–Gd–Co results [11].
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
2. Experimental procedure
G: Gd3Fe5O12
3. Results All substituted samples present the M-structure as their main phase. Phase formation is affected by stoichiometry (Fig. 1 and Table 1)and in the Sr–Gd–Co series by the presence of Co as well. Formation of single phase substituted material has been achieved only for ðSr0:95 Gdx0:05 ÞO 5:25Fe2 O3 ðx ¼ 0:05Þ. In this Sr–Gd series, small traces ðo2%Þ of GdFeO3 were detected for samples x ¼ 0:1 0:2. For xX0:2 Fe2 O3 is also formed, while for x ¼ 0:25 Gd3 Fe5 O12 appears. From the phase analysis (Table 1), one can calculate the percentage of Gd present in GdFeO3 and Gd3 Fe5 O12 , which ranges from 10% to 33%. In the Sr–Gd–Co series, hematite is present as secondary phase, in percentages up to 9% w/w for x ¼ 0:4, while traces ðo1%Þ of Gd3 Fe5 O12 and CoFe2 O4 were also detected in all substituted samples. It seems that in both cases Gd only partially enters the M-lattice, forming simultaneously secondary Gd phases. However, there is no significant variation of T c with the substitution degree, for both series. Regarding the magnetic properties, it is remarkable that coercivity in Sr–Gd samples displays a constant rise up to a maximum value of 305 kA/m (3.8 kOe), for x ¼ 0:20 (Fig. 3), which is higher than the typical value for SrFe12 O19 (279 kA/m [2]), while remanence and saturation magnetization do not decrease up to that Gd concentration ðx ¼ 0:2Þ and remain constant at about 40 and 65 Am2 =kg, respectively (Fig. 2). The results for this series appear to be analogous to La–Co and La-only substitution, which
H: Fe3O3O: GdFeO3
O
↓ G
H
G G
↓
↓ ↓ ↓
SrGd0.25
O
G
↓H ↓ ↓
GH
H
G
↓
↓
O ↓H
H H
G
↓ ↓
↓ ↓
↓
O
SrGd0.2
↓
SrGd0.15
Intensity (a.u.)
Two series of samples were produced by the classic ceramic route. A series of Gd-only substituted, Sr-surplus ð½Srþ2 =½Feþ3 ¼ 1=10:5Þ hexaferrites, according to the formula ðSr1x Gdx ÞO 5:25 Fe2 O3 , x ¼ 0, 0.05, 0.10, 0.15, 0.20, 0.25, and a series of Gd–Co substituted stoichiometric 1 Sr hexaferrites ð½Srþ2 =½Feþ3 ¼ 12 Þ, according to the formula Sr1x Gdx Fe12x Cox O19 , x ¼ 0, 0.1, 0.2, 0.3, 0.4. The starting materials (Fe2 O3 , SrCO3 , Co3 O4 and Gd2 O3 powders of analytical grade) were mixed and calcined for 1 h at 900 C in air. Milling was performed in a stainless steel ball mill for 24 h. The samples were isotropically pressed into pellets and fired for 2 h at 1200 C in air. X-ray patterns were obtained by a powder diffractometer, using Fe Ka radiation and analyzed with the Rietveld method. Magnetization and coercivity measurements (hysteresis loops) were carried out on compacted, non-aligned powder samples, using a vibrating sample magnetometer with maximum attainable field of 1.8 T at room temperature. Curie temperature ðT c Þ values were obtained from thermomagnetic measurements in a field of 30 mT. Grain size and microstructure were observed by a JEOL JSM 5900 LV scanning electron microscope, equipped with an INCA x-sight detector (Oxford Instruments) for EDX microanalysis.
171
SrGd0.1
SrGd0.05
1 0 7
1 0 1 2 0 3
20
0 0 6
1 10 001 81 2
30
40
1 1 4
SrO.. 5.25Fe2O3 2 0 2 221 3 1 0 000 1 5 018 6
50
2 0 6
1 0 11
2 0 9
60
2 2 2 1 30 1 2 0 3 700112 0 0 100 04 1 14 12 0 14 8
70
1 0 152 0 13
80
2 0 14
90
2theta Fe Kα (degrees) Fig. 1. X-ray diffractograms of ðSr1x Gdx ÞO 5:25 Fe2 O3 .
however concerns single-phase compounds. The choice of a Sr-surplus formula without Co addition resulted in limited presence of secondary phases, as it is shown in Fig. 1. Similarly, only at very low Gd content a single phase compound is formed, but the positive influence of the secondary phase on the magnetic properties is quite obvious, with constant values of magnetization and increasing coercivity up to x ¼ 0:2. It is interesting to note that, despite the increase of the GdFeO3 and hematite percentage with x, the specific magnetization and remanence do not decrease. This might be an indication of an intrinsic effect of Gd. For x ¼ 0:25, the formation of Gd3 Fe5 O12 and the increased amount of Fe2 O3 is probably responsible for the decline of the magnetic properties. In contrast, coercivity and magnetization in the Sr–Gd–Co series decrease steadily with substitution degree (Figs. 2, 3). The variation of coercivity is different from that of Ba–Gd–Co ferrites [11], where a positive effect (maximum for x ¼ 0:1) has been observed. The effect on the magnetization is the same in both Sr/Ba–Gd–Co series (decrease with x), fact that can be correlated to the presence in both cases of various Fe, Gd and Co-impurities. The microstructural observation by SEM showed hexagonal-like grains of about 122 mm, with similar features for both series. In the Sr–Gd series, sintering is influenced by Gd substitution and the presence of secondary phases, as extended grain growth and sintering was observed for samples x ¼ 020:10 (Fig. 4), while for samples x ¼ 0:1520:2 the grain size is kept under 1 mm
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
172
Table 1 Crystal phases identified from X-ray diffractograms: SrFe12 O19 (M); Fe2 O3 ðHÞ; GdFeO3 ðOÞ; Gd3 Fe5 O12 ðGÞ x
Phases in SrGd series
Gd % present in O+G impurities
H 0 0.05 0.1 0.15 0.2 0.25
O
G
Single phase M Single phase M 0:42 0:12 1:3 0:14 1:8 0:15 0:77 0:14
— — 2:16 0:52 3:63 0:57
— — — 0:55 0:06
10 32 33 18
Specific magnetization (Am2/kg)
100 SrGdCo σ at 1.8 T SrGdCo σ R 80
SrGd σ at 1.8T SrGdCo σR
60
40
20 0.0
0.1
0.2
0.3
0.4
Substitution degree, x Fig. 2. Specific magnetization values of the two series.
Fig. 4. SEM image of the SrO 5:25 Fe2 O3 ðx ¼ 0Þ sample.
350 Coercivity, Hc (kA/m)
300 250 200 150 100
SrGdCo SrGd
50 0 0.0
0.1
0.2
0.3
0.4
Substitution degre, x Fig. 3. Coercivity values of the two series. Fig. 5. SEM image of the ðSr0:80 Gd0:20 ÞO 5:25 Fe2 O3 ðx ¼ 0Þ sample.
(Fig. 5). It seems that Gd acts as a grain growth inhibitor, drastically above a certain concentration, thereby achieving higher coercivity values for samples x ¼ 0:1520:2. This can be appointed as an extrinsic effect of Gd on the microstructure of the Gd-only materials, directly affecting coercivity. A grain growth inhibition effect is not observed in the case of the Sr–Gd–Co samples, probably due to the presence of Co and of additional secondary phases, which are responsible for the decrease of the magnetic properties values with x.
These results demonstrate the potential of the use of Gd in substituted hexaferrites. Finally, it is expected that a softer preparation method of Gd substituted hexaferrites, such as chemical coprecipitation, may yield single phase compounds at even higher substitution degrees than x ¼ 0:05 and allow a thorough investigation of possible intrinsic effects and structural or magnetic changes, associated to the presence of Gd in the M-lattice.
ARTICLE IN PRESS G. Litsardakis et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 170–173
Acknowledgments This work is part of the project ‘‘New magnetic rareearth substituted hexaferrites’’, funded by the Hellenic Ministry of National Education and the EU—Operational Program for Education and Initial Vocational Training— Action ‘‘Pythagoras II’’. References [1] Y. Ogata, Y. Kubota, T. Takami, M. Tokunaga, T. Shinohara, IEEE Trans. Magn. 35 (5) (1999) 3334. [2] F. Kools, A. Morel, P. Tenaud, M. Rossignol, O. Isnard, R. Grossinger, J.M. Le Breton, J. Teillet, Proceedings of the International Conference on Ferrites ICF8, Kyoto, Japan 2000, p. 437.
173
[3] F. Kools, A. Morel, R. Grossinger, J.M. Le Breton, P. Tenaud, J. Magn. Magn. Mater. 242–245 (2002) 1270. [4] R. Grossinger, C. Tellez Blanco, M. Kupferling, M. Muller, G. Wiesinger, Physica B 327 (2003) 202. [5] H. Yamamoto, IEEE Trans. Magn. 26 (3) (1990) 1144. [6] L. Lechevallier, J.M. Le Breton, J.F. Wang, I.R. Harris, J. Magn. Magn. Mater. 269 (2004) 192. [7] J.F. Wang, C.B. Ponton, I.R. Harris, J. Magn. Magn. Mater. 298 (2006) 122. [8] H. Mocuta, L. Lechevallier, J.M. Le Breton, J.F. Wang, I.R. Harris, J. Alloy Compd. 364 (2004) 48. [9] H. Yamamoto, M. Isono, T. Kobayashi, J. Magn. Magn. Mater. 295 (2005) 51. [10] J.F. Wang, C.B. Ponton, I.R. Harris, J. Alloy Compd. 403 (2005) 104. [11] G. Litsardakis, I. Manolakis, K. Efthimiadis, J. Alloy. Compd. 427 (2007) 194.