INFLUENCE OF THE Zn2+ AND Cd2+ ION CONTENTS UPON THE NATURAL SPIN RESONANCE FREQUENCY IN Ni-Zn AND Ni-Cd FERRITES

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INFLUENCE OF THE Zn2+ AND Cd2+ ION

CONTENTS UPON THE NATURAL SPIN

RESONANCE FREQUENCY IN Ni-Zn AND Ni-Cd

FERRITES

J. Gieraltowski

To cite this version:

JOURNAL DE PHYSIQUE Collogue CI, supplement au n° 4, Tome 38, Avril 1977, page Cl-57

INFLUENCE OF THE Zn

AND Cd

ION CONTENTS UPON

THE NATURAL SPIN RESONANCE FREQUENCY

IN Ni-Zn AND Ni-Cd FERRITES

J. GIERALTOWSKI (*)

Equipe de Recherche Materiaux Magnetiques du C. N . R. S. 92190 Meudon-Bellevue, France

Résumé. —- L'influence de la concentration en ions Zn2+ et Cd2+ sur la résonance naturelle de

spin a été étudiée dans des ferrites de Ni-Zn et de Ni-Cd.

Des expériences antérieures faites par d'autres auteurs avaient montré que la substitution d'ions Zn2+ aux ions Ni2+ conduisait à un changement du champ total d'anisotropie effective donc de la

fréquence de la résonance naturelle des spins.

Dans le présent travail les mesures de cette fréquence ont été effectuées en utilisant une ligne co-axiale spécialement adaptée aux mesures de perméabilité complexe.

On a calculé, à partir des valeurs mesurées de la fréquence de résonance, les valeurs de l'énergie d'anisotropie totale K en utilisant la formule de Snoek. On compare ces valeurs pour les deux séries de ferrites étudiées.

Abstract. — The influence of the Zn2+ and Cd2+ ion contents upon the natural spin resonance

in Ni-Zn and Ni-Cd ferrites has been investigated.

Previous experiments by other authors have shown that substituting Zn2+ ions for Ni2+ ions

leads to a change of the total effective anisotropy field and consequently of the natural spin reso-nance frequency fi.

ft measurements have been carried out by using a coaxial line specially adapted to measure the

complex permeability.

From the/r values measured the total anisotropy energy values ^Thave been calculated by using the Snoek formula and have been compared for the two series of Ni-Zn and Ni-Cd ferrites which have been investigated.

1. Introduction. — The fact that the spin resonance frequency value has been found to be the same for a series of samples with different grain sizes and diffe-rent porosities has permitted to consider that it is the composition only which determines the total aniso-tropy. The first result in this domain has been esta-blished on N i F e204 and Ni-Zn ferrites [1, 2]. On the

other hand results from many authors have shown that substituting, in the Ni1_xZnJCFe204 compositions,

Zn2 + ions for N i2 + leads to a change of the natural

spin resonance frequency. This fact has been related by Globus [3] to the Z n2 + ion concentration in the

tetra-hedral sites, since the Zn2 + ion radius is larger than

the F e3 + ion radius. So the degree of concentration

of Zn2 + ions determines the frequency of the natural

spin resonance. Some results about the expansion anomaly have recently shown that Cd2 + ions, when

they replaced the Fe3 + ions, seem to play a similar role

as the Z n2 + ions [4]. It has been of interest to see

what is the influence of Cd2 + ions upon the frequency

of the naturf.l spin resonance for Ni-Cd ferrites and to compare with Ni-Zn ferrites.

Both the Ni-Zn and Ni-Cd samples have been cho-sen according to their ionic structure quality, checked

(*) Permanent address : Magnetic Materials Research Labo-ratory Polfer, ul. Dzielna 60, Warszawa, Poland.

by chemical and X-ray analyzis and by measurements of the initial permeability thermal spectrum [4].

2. Results. — We have measured the complex permeability frequency spectra of both the series Ni1_;cZnJCFe204withx = 0 to 0.7 and Nij _JCd^Fe204

with x — 0.1 to 0.3. Measurements have been perform-ed by using a coaxial line which has been specially prepared for complex permeability and permitivity measurements in the frequency range 0.1 to 2.5 GHz. The toroid shaped samples have been precisely machin-ed to the size of the 50 ohm coaxial line.

The natural spin resonance frequency determination has been done by analyzing the magnetic loss curves as a function of frequency. In some cases we had great difficulties in determining those frequencies, because, for polydomain samples, the spin resonance is superim-posed upon the domain wall dispersion and appears as a very weak phenomenon ; such a fact has imposed to perform very accurate measurements.

Figure 1 shows magnetic loss spectra for Ni-Zn ferrites. The resonance character of such curves can be easily seen. On the same figure the complex permeabi-lity spectrum of a N i F e204 monodomain sample is

also plotted, which shows a clear resonance peak with no perturbation due to the domain wall losses. The spin resonance frequency value for this sample is

C1-58 J. GIERALTOWSKI

NI Fe20,, monodomaln

0 , 1''

0.2 b.5 I " " I " " 1.0 2.0 " " I 1

f ( GHz 1

FIG. 1.

-

tions.

in agreement with the results obtained on some other multidomain samples of the same composition and with the results of Globus in 1962 [I, 21.

Figure 2 shows the same type of curves in the case of Ni-Cd ferrites. To make the comparison easier the

Re. 2.

-

same NiFe20, monodomain sample curve is also plotted on the picture.

From figures 1 and 2 we can see that the way of variation of the spin natural frequencies as a function of Zn2+ and Cd2+ non magnetic ion concentrations (in the tetrahedral sites) are the same for both Ni-Zn and Ni-Cd ferrites : the spin resonance frequency decreases with the increase of the non magnetic ion concentration.

Figure 3 shows such a variation of the resonance frequency as a function of concentrations. In addition

0 0.2 0.4 0.6 0.8

x -

FIG. 3. - Natural spin resonance frequency versus Zn2f and Cd2+ ion concentrations.

we can see that for Ni-Zn ferrites the resonance fre- quency values are systematically a little higher than those for Ni-Cd ferrites.

Using the Snoek formula [5] and some other well known relations :

Xrot = (P' ₄

-

-

MS

TC 3 He,,

where w = pulsation of the natural spin resonance

y = gyromagnetic coefficient He,, = total anisotropy field

K = total energy of the anisotropy Ms = saturation magnetization

Zn2+ AND Cd2+ ION CONTENTS UPON THE NATURAL SPIN RESONANCE FREQUENCY C1-59 measurements f r o m i, from p'- I of monodomann sample

FIG. 4. - Total anisotropy Kversus Zn2+ and CdZ+ ion concen-

trations.

We can notice here a very good agreement between the results obtained from the spin resonance frequency measurements and those found on the monodomain sample.

The rotational permeability values for both types of ferrites have been also calculated and are reported figure 5. The initial permeability value of the mono- domain sample of Ni-Zn ferrite is indicated by a star. 3. Discussion. - Despite the fact that Cd2+ ions are larger than Zn2+ ions, it seems that only the concentration of non magnetic ions (which substitute for Fe3' ions) influences strongly the natural spin resonance frequency value. That confirms a similar result obtained by Globus, Pascard and Cagan [4] :

from their investigations it appears that the fundamen- tal role for the Curie temperature change is the ion concentration, the role of the ion size appearing to be secondary. In our present case, since the measurements have been made at room temperature, it is obvious that the temperature gap between room temperature value and the Curie temperature value determines the

Ni1_XCdxFe20,

+

FIG. 5. - Initial rotational permeability versus Zn2+ and Cd2+

ion concentrations.

value of the observed resonance frequency ; the ani- sotropies of the samples are indeed function of this gap, so the spin resonance frequency is lower when the concentration is higher.

But it seems that in the case of Ni-Cd ferrites the influence of the anisotropy upon the Curie tempera- ure variations is weaker than in the case of Ni-Zn, ferrites ; we find for the same Zn2' and Cd2+ ion concentrations almost the same frequency value despite the much larger variation of T, in the case of

Cd than in the case of Zn.

References

[I] GLOBUS, A., C . R. Hebd. Sdan. Acad. Sci. 255 (1962) 1709. [4] GLOBUS, A., PASCARD. H., CAGAN, V., J. Physique Colloq.

[2] GLOBUS, A., Thesis, Paris 1963. 38 (1977) C1.