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ON THE HYPERFINE MAGNETIC FIELDS OF THE
TWO SITES IN SPINEL FERRITES
N. Eissa, A. Bahgat
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplbment au no 12, Tome 37, Dkcembve 1976, page C6-575
ON THE HYPERFINE MAGNETIC FIELDS OF THE
TWO SITES IN SPINEL FERRITES
N. A. EISSA and A. A. BAHGAT
Mossbauer Effect Lab., Faculty of Science, Al-Azhar University, Cairo, Egypt.
R6sum6. - Les champs magnetiques hyperfins agissant aux noyaux de 57Fe dans les sites des sous-reseaux A et B d'une spinelle NiFez01 apparaissent comme dependent fortement I'un de l'autre suivant la relation :
ou Cest une constante valant 0,ll.
Abstract. - The hyperfine magnetic fields experienced by the 57Fe nuclei in the A and B sublat-
tices cf NiFe20.i were fund to be strongly dependent on each other according to the relation
where the constant C = 0.1 1.
1 . Introduction.
-
The Mossbauer effect (ME) technique has been used to determine the temperature dependence of the hyperfine magnetic field at iron nuclei in ferrimagnetic materials, such as NiFe20, [l-31. It was observed in this ferrite that there are two different six lines Zeeman patterns corresponding to the hyperfine magnetic fields acting on the 5 7 ~ e nuclei in the tetrahedral (A), and octahedral (B) sites of the ferrite. The six line hyperfine patterns attributed to each site are well resolved in a large temperature range. This leads to the possibility of the accurate determination of the corresponding internal magnetic field of each site. Morel [I] studied NiFe204 by the ME and found that there exists a strong positive B-B interaction between Ni ions and Fe ions in the B site. Van Loef [4] compiled the published data about the HMF of ferrites measured by ME and found that these data follow the one-third power law,
where T is the absolute temperature of the sample,
Tn
its N6el temperature. He determined the value of the constants /3 and D for the two sites of the ferrite which are listed in table I.Although many authors [l-51 studied NiFe204 by the ME, until now no simple relation exists which relates the experimentally measured data of the HMF of both sites of the ferrite to each other. So, in the present work it was decided to drive such an empirical formula.
Measured parameters for NiFe204 Parameter
-
h(4.2) kOe h(O) H at T/Tn = 0.5 at T/Tn = 0.75 D D Tn6)
Ref. - [51 present [21 present [21 present 141 present 141 present 111 present2. Experimental.
-
The ferrite sample (NiFe204) was prepared by the usual ceramic method [6]. The X-ray diffraction measurement of the sample shows that it has only a single phase of spinel structure. ME spectra were measured at various temperatuzs (78<
T<
900 K) with temperature fluctuations of about 1 K. The ME spectrometer was of the constant acceleration type, coupled to a Tt256 multichannel analyser. The source was 57Co in a Cr matrix, and the absorber contained 0.5 mg 57Fe/cm2.3. Results and discussion.
-
The ME spectra of the ferrite measured at different temperatures are foundC6-576 N. A. EISSA AND A. A. BAHGAT to contain two resolved six llnes Zeeman patterns up to
about 600 K. At higher temperatures the two patterns overlapped. Extrapolation to zero Kelvin and zero HMF, gives the data listed in Table I. Figure 1 shows the temperature dependence of the reduced HMF,
FIG. 1. -Relation between Log reduced HMF and Log reduced temperature.
which was analyzed according to the one-third power law in the temperature range TITn 2 0.4. This gives the tabulated values of
p
and D, and shows the applicabi- lity of this law to our data, figure 2.In order to derive the required empirical relation, the reduced HMF HB/HA was plotted against the reduced temperature TIT,, where HB = [h(T)/h(O)], and HA = [h(T)/h(O)],. The data were least square
FIG. 2. - Variation of the HMF of both A and B sites of the ferrite with TITn.
FIG. 3. - Relation between HRIHA VS. TITn.
fitted and a straight line was obtained, figure 3. This
could be represented by,
where C is a constant, and equals 0.1 1. Relation (2) defines the dependence of the HMF of both sites on each other. It was possible to apply it to resolve even the superimposed peaks which exist in the high tempe- rature range with sufficient accuracy.
References
[I] MOREL, J. P., J. Phys. Chem. Solids 28 (1967) 629. [5] CHAPPERT, J., FRANKEL, R. B., Phys. Rev. Lett. 19 (1967) [2] VAN LOEF, J. J., Physiea 32 (1966) 2102. 570.
