ON MAGNETIC STRUCTURE OF HIGHLY DILUTED IRON GARNETS

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ON MAGNETIC STRUCTURE OF HIGHLY DILUTED IRON GARNETS

A. Dodokin, I. Lyubutin

To cite this version:

A. Dodokin, I. Lyubutin. ON MAGNETIC STRUCTURE OF HIGHLY DILUTED IRON GARNETS.

Journal de Physique Colloques, 1979, 40 (C2), pp.C2-342-C2-342. �10.1051/jphyscol:19792121�. �jpa-

00218492�

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JOURNAL DE PHYSIQUE Colloque C2. .suppl&ment au n O 3. Tome 40. mars 1979, page C2-342

ON MAGNET1 C STRUCTURE O F HIGHLY D l L U T E D I R O N GARNETS

A.P. Dodokin, I.S. Lyubutin

I n s t i t u t e of CrystuZZograpky Academy of Sciences of the USSR, Moscow

RCsud.- On a mesurd le champ hyperfin au noyau de '19sn dans des grenats de fer diluCs. La va- Leur expsrimentale trouv6e pour la concentration critique est celle qui correspond 2 un complet ddsordre rnagndtique.

Abstract.-The value of the hyperfine magnetic field at Sn'I9 nuclei in diluted iron garnets is obtained. The experimental value of the field at the critical concentration x=xc was that which corresponds to the value associated with full magnetic disorder in the garnets.

Recently it was found by neutron diffraction method that the long range order disappears in iron- garnets Y ,-,Cax~e2-x~x] (Fe3)01 in the range of

1.2 < x < 1.8 at 4.2K /I/ (D is diamagnetic ion).

A percolation theory for tandon distribution bounds was used to explain this phenomenon. According to

this theory there is a certain critical concentration xc (for the garnets with octahedral substitu- tion xc=1.2). For x<xc the garnet consists of the ferrimagnetic clusters of different sizes and among them there is at least one infinite cluster. In this case a long range order may exist and ferrimagnetic phase transition is possible. For x%xC all ferrite clusters are finite.

We applied the Gssbauer effect (nuclei

~e~~ and sn119 ) to get the information about the microscopic picture of the magnetic ordering in the diluted ferrimagnets Y3-&a, pe,-,~n,J (Fe3)Oln.

OSxS2 at 4.2K. It was found that for all concentra- tions the hyperfine field at ~e~~ and snH9 nuclei are present. The resonance lines are noticeably broadened.

The hyperfine fields at iron nuclei in a- and d-sublattices are practically independent of the concentration x. The absence of definite chan- ges in ~Zssbauer ~e~~ spectra when passing from the ferrimagnetic state x<xc to the finite cluster state %,xc means that the iron ions spin fluctua- tions are very slow and each spin has a certain direction during a long time (T >> 10-'s). We point out that no long range order can exist in a system of finite clusters.

It was found that the hyperfine field at tin decreases rapidly with the concentration. When all magnetic moments in the garnet are oriented randomly then che hyperfine fields at tin nuclei

have a certain distribution function with the cor- responding average value of the field H _D

'".

^{We have}

solved the problem of determination for the average module value of the sum of n randomly oriented uni- ty vectors <kn> and have found the distribution functions pn. In the case of the garnets we found

as>=

2391105 2.28. Then using our experimental data, we have estimated the value of the average hyperfine field for the case of the complete disor-

Sn

der HdiGOrd. 76.8 kOe. It turned out that this value of the field corresponds to the critical concentration x = 1.2 on the experimental curve ~'"(x).

Any deviation from this value of the fields means that there is some correlation of the magnetic moments in the diluted system and that the short range order exists.

The investigation of the experimental hyperfine field distribution function can give the answer whether the completely magnetic disordered state in this kind of garnets and related systems exists.

References

/I/ Plakhtii, V.P.,Golosovskii, I.V., Kudryashov.

V.A., Parfenova, N.N., Srnirnov, O.P., Procee- dings of International Conference of Magnetism ICM-73, v.S.p.236.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792121