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Site occupancy of Ga3+ in NiGaxFe2-xO4 ferrites
Journal
of Magnetism
and Magnetic
SITE OCCUPANCY C. QWNTANAR UNAM,
Materials
54-57
1339
(1986) 1339-1340
OF Ga3’ IN NiGa, Fe,_ ,O, FERRITES +, M. JIMkNEZ
*, V. FUENTES
Apdo. Postal 76
542, M&co.
*, S. ABURTO
* and R. VALENZUELA
+
DF, 04510 MPxico
Miissbauer spectra of the NiGa,Fe,_,O, system were obtained at 11 K and the ratio of line intensities were determined. Results show that a high concentration Ga 31 does not enter completely in A-sites. The lattice constant decreases linearly with the mean ionic tetrahedral radius. The Curie temperature decreases smoothly as I increases.
1. Introduction Current research [l-3] assumes that the Ga’+ ion prefers to occupy the tetrahedral (or A) sites. If we work on that hypothesis, the NiGa,Fe,_,O, ferrite system could be very convenient to study the magnetic interactions. The fact that the Fe’+ and Ni2+ ions that occupy B-sites in Ni ferrite remain in the same place in the new system, allows us a very convenient way to control the number of interactions Fe3+(A)-0-Fe3-(B) and Fe’+(A)-0-Ni’+(B). Besides, the charge distribution is not altered in the spine1 as a whole. Finally, since the sizes of Fe3’ and Ga3+ ions are quite similar [4] they alter only slightly the properties of these ferrites. We feel then that a detailed knowledge of the way in which Ga3+ and Fe3+ compete for the occupancy of A-sites is important.
2. Materials and methods We worked on samples already used and described in a previous work [5]. In these samples of NiGa,FeZxO,. x = 0.0, 0.25, 0.50, 0.75 and 1.0. The initial magnetic permeabilities and Curie temperatures were measured. X-ray diffraction measure* Facultad + Instituto
de Ciencias. de Investigaciones
ments ~ using an internal standard (ZnO) - gave us an accurate value of the lattice parameter. The Miissbauer spectra were obtained at 11 K using a closed cycle refrigeration system (Displex, model Cs-202 Air Products).
3. Results and discussion
It is seen in fig. 1, that the lattice creases linearly as the Ga concentration
constant a deincreases. This is easily understood if we recall that the Ga3+ is slightly smaller than Fe’+ both in the tetra and octahedral sites t41. Following the analysis of Globus [6], we can define a “ mean ionic radius on tetrahedral sites per molecule” as
With this definition. it is seen in fig. 2 (segment AB) that linear relationships exists between the lattice constant and the mean ionic radius of gallium in tetrahedral sites. The slopes of segments AB and BC are significantly different. At least in the case of small or medium concentrations, we may interpret these behaviours as follows: while in the Ni-Zn ferrite the Zn*+ ion kicks-out a I
en Materiales
8.50T
_c:: _:::::A> ;
-*
e
r-----0151
,
:
:
:
1
2
3
‘
:
I
:
x 618
I
..
8.30
..
a.25
:
: 9
Fig. 1. Lattice constant a versus Ga3+ concentration Our experimental values. + Maxwell data [3].
I 12
(x).
l
0304-8853/86/$03.50
8.35
0 Elsevier Science Publishers
I
0 L5
B
A
0 50
i
0 55
8
0.60
tet
Fig. 2. Lattice parameter versus mean ionic radius. i) BC corresponds to experimental data for Ni-Zn ferrite [8]. ii) AB represents our results (0) for Ni-Ga ferrite. iii) BD corresponds to data in BC corrected so that only the effect of Zn in A-sites remains.
B.V.
To see if the experimental data for NiLZn ferrite (fig. 2. segment BC) are compatible with this interprrtation. L\~Jcan correct these values in such a way as IO have only the effect of the A-sites. To acomplish this ue used the Maxwell [3] data for Ni- Al ferrite. and we got the segment BD. We see that a purely geometric interpretation fully accounts for the experimental data. The Miisshauer spectra are shown in fig. 3. and the table 1 presents the concentration values obtained. For the well trained eye. the mam result of these spectra is the warning that not all the Ga’ ’ entered Into A-sites as could be na’ivel? expected. Fortunately thi\ does not invalidate the main geometric argument presented earlier. On the contrary. this result has an interesting side effect: it allows US to understand some experimental results about the C’urie temperature \\. concentration. In fact. as shown in fig. 4. the high concentration points ( .I = 0.75 and .Y= 1.0) fall up and to the right of the usual theoretical curve obtained by molecular field theory [7]. Now. if we take into account the MCssbauer result\. these points should be displaced towards the left as shown in the same figure (+) closing the gap between our theoretical curve and experimental data. Fig. 1. Miiaduuer
spectra of NiGa,
Fe2
,(I,
taken at 1 I K
Fe” ion by entering the A-sites and then this Fe” replaces the Ni’+ in the B-sites, in the case of NiLGa ferrite the Cia“ enters the A-sites and the B-sites remain unaltered. We may say then that there are two factors changing the lattice parameter: on one hand the Zn’+ ions replacing the Fe3+ ions and on the other. these Fe ’ + ions replacing the Ni’ ’ ones. Then the overall effect is the sum of a decrease due to what happens in the B-sites and an increase due to what goes on at the A-sites.
KC‘. KomeiJn. Rcs. Rep. X (19.53) 304. J.B. Goodenough and L. Lorh. Ph\i. Re\. YX (1955)391. L.R. Maxwell and S.J. Pickart. Phys. Rev. 92 (1953) 391. R.1). Shannon and C‘.T. Prewitt. Acta C‘ryt. 825 (19hY) Y2S. M. Jirn&vx, C‘. Qulntannr. S. Ahurto. V Fucntra ,~ncl R. Valenrurla. Ad\. (‘eramic.\ (in pro\). A. Glohus. H. Paxad and V. Cagan. J. de Phys. 3X (1’277) (‘I-163. S. Aburto. M. Jim&xr. M.L. Marqulna and R. V,~len/wla. Proc. 3rd. Intern. Conf. on Ferrites, Kyoto. 19X0. ed. H Watanabe (Center for Academic Public:ition\. Jqun. IYXl )
p. 18X. L.K. Lcung. (1973) 19.
B.J. Evonr
and A.H.
Morrl\h,
Phvh. Kc\.
13 X
of Magnetism
and Magnetic
SITE OCCUPANCY C. QWNTANAR UNAM,
Materials
54-57
1339
(1986) 1339-1340
OF Ga3’ IN NiGa, Fe,_ ,O, FERRITES +, M. JIMkNEZ
*, V. FUENTES
Apdo. Postal 76
542, M&co.
*, S. ABURTO
* and R. VALENZUELA
+
DF, 04510 MPxico
Miissbauer spectra of the NiGa,Fe,_,O, system were obtained at 11 K and the ratio of line intensities were determined. Results show that a high concentration Ga 31 does not enter completely in A-sites. The lattice constant decreases linearly with the mean ionic tetrahedral radius. The Curie temperature decreases smoothly as I increases.
1. Introduction Current research [l-3] assumes that the Ga’+ ion prefers to occupy the tetrahedral (or A) sites. If we work on that hypothesis, the NiGa,Fe,_,O, ferrite system could be very convenient to study the magnetic interactions. The fact that the Fe’+ and Ni2+ ions that occupy B-sites in Ni ferrite remain in the same place in the new system, allows us a very convenient way to control the number of interactions Fe3+(A)-0-Fe3-(B) and Fe’+(A)-0-Ni’+(B). Besides, the charge distribution is not altered in the spine1 as a whole. Finally, since the sizes of Fe3’ and Ga3+ ions are quite similar [4] they alter only slightly the properties of these ferrites. We feel then that a detailed knowledge of the way in which Ga3+ and Fe3+ compete for the occupancy of A-sites is important.
2. Materials and methods We worked on samples already used and described in a previous work [5]. In these samples of NiGa,FeZxO,. x = 0.0, 0.25, 0.50, 0.75 and 1.0. The initial magnetic permeabilities and Curie temperatures were measured. X-ray diffraction measure* Facultad + Instituto
de Ciencias. de Investigaciones
ments ~ using an internal standard (ZnO) - gave us an accurate value of the lattice parameter. The Miissbauer spectra were obtained at 11 K using a closed cycle refrigeration system (Displex, model Cs-202 Air Products).
3. Results and discussion
It is seen in fig. 1, that the lattice creases linearly as the Ga concentration
constant a deincreases. This is easily understood if we recall that the Ga3+ is slightly smaller than Fe’+ both in the tetra and octahedral sites t41. Following the analysis of Globus [6], we can define a “ mean ionic radius on tetrahedral sites per molecule” as
With this definition. it is seen in fig. 2 (segment AB) that linear relationships exists between the lattice constant and the mean ionic radius of gallium in tetrahedral sites. The slopes of segments AB and BC are significantly different. At least in the case of small or medium concentrations, we may interpret these behaviours as follows: while in the Ni-Zn ferrite the Zn*+ ion kicks-out a I
en Materiales
8.50T
_c:: _:::::A> ;
-*
e
r-----0151
,
:
:
:
1
2
3
‘
:
I
:
x 618
I
..
8.30
..
a.25
:
: 9
Fig. 1. Lattice constant a versus Ga3+ concentration Our experimental values. + Maxwell data [3].
I 12
(x).
l
0304-8853/86/$03.50
8.35
0 Elsevier Science Publishers
I
0 L5
B
A
0 50
i
0 55
8
0.60
tet
Fig. 2. Lattice parameter versus mean ionic radius. i) BC corresponds to experimental data for Ni-Zn ferrite [8]. ii) AB represents our results (0) for Ni-Ga ferrite. iii) BD corresponds to data in BC corrected so that only the effect of Zn in A-sites remains.
B.V.
To see if the experimental data for NiLZn ferrite (fig. 2. segment BC) are compatible with this interprrtation. L\~Jcan correct these values in such a way as IO have only the effect of the A-sites. To acomplish this ue used the Maxwell [3] data for Ni- Al ferrite. and we got the segment BD. We see that a purely geometric interpretation fully accounts for the experimental data. The Miisshauer spectra are shown in fig. 3. and the table 1 presents the concentration values obtained. For the well trained eye. the mam result of these spectra is the warning that not all the Ga’ ’ entered Into A-sites as could be na’ivel? expected. Fortunately thi\ does not invalidate the main geometric argument presented earlier. On the contrary. this result has an interesting side effect: it allows US to understand some experimental results about the C’urie temperature \\. concentration. In fact. as shown in fig. 4. the high concentration points ( .I = 0.75 and .Y= 1.0) fall up and to the right of the usual theoretical curve obtained by molecular field theory [7]. Now. if we take into account the MCssbauer result\. these points should be displaced towards the left as shown in the same figure (+) closing the gap between our theoretical curve and experimental data. Fig. 1. Miiaduuer
spectra of NiGa,
Fe2
,(I,
taken at 1 I K
Fe” ion by entering the A-sites and then this Fe” replaces the Ni’+ in the B-sites, in the case of NiLGa ferrite the Cia“ enters the A-sites and the B-sites remain unaltered. We may say then that there are two factors changing the lattice parameter: on one hand the Zn’+ ions replacing the Fe3+ ions and on the other. these Fe ’ + ions replacing the Ni’ ’ ones. Then the overall effect is the sum of a decrease due to what happens in the B-sites and an increase due to what goes on at the A-sites.
KC‘. KomeiJn. Rcs. Rep. X (19.53) 304. J.B. Goodenough and L. Lorh. Ph\i. Re\. YX (1955)391. L.R. Maxwell and S.J. Pickart. Phys. Rev. 92 (1953) 391. R.1). Shannon and C‘.T. Prewitt. Acta C‘ryt. 825 (19hY) Y2S. M. Jirn&vx, C‘. Qulntannr. S. Ahurto. V Fucntra ,~ncl R. Valenrurla. Ad\. (‘eramic.\ (in pro\). A. Glohus. H. Paxad and V. Cagan. J. de Phys. 3X (1’277) (‘I-163. S. Aburto. M. Jim&xr. M.L. Marqulna and R. V,~len/wla. Proc. 3rd. Intern. Conf. on Ferrites, Kyoto. 19X0. ed. H Watanabe (Center for Academic Public:ition\. Jqun. IYXl )
p. 18X. L.K. Lcung. (1973) 19.
B.J. Evonr
and A.H.
Morrl\h,
Phvh. Kc\.
13 X