NEW Li-Ti-Zn FERRITES WITH NARROW FERRIMAGNETIC RESONANCE LINEWIDTH

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NEW Li-Ti-Zn FERRITES WITH NARROW

FERRIMAGNETIC RESONANCE LINEWIDTH

M. Konwicki, S. Makolagwa

To cite this version:

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JOURNAL DE PHYSIQUE Colloque C l , supplhent au no 4, Tome 38, Avril 1977, page C1 -271

NEW Li-Ti-Zn FERRITES WITH NARROW

FERRIMAGNETIC RESONANCE LINEWIDTH

M. KONWICKI and S. MAKOLAGWA

Polfer Research Laboratory, Ul. Dzielna 60, 01-029 Warszawa, Poland

Rbum6. - On presente des rtsultats cristallographiques, magnktiques et microondes sur le systeme L ~ o , s ~ I - z + ~ ) Z ~ Z T ~ ~ F ~ ~ . ~ - O , S ( X + ~ ~ ) O ~ avec 0 d X d 0,s et 0,7 d y d 1,3. Les materiaw de composition chimique correspondant a X > 0 et y > 0,9 ont des temperatures de Curie bien plus tlevks que celles prevues. Ces ferrites presentent un faible champ d'anisotropie et une largeur de raie de resonance ttroite. On peut obtenir des materiaux pour microondes ayant une aimantation de 200-500 G, une largeur de raie de 30-60 Oe et une temperature de Curie sufirieure A 140°C. Abstract. - Crystallographic, magnetic, and microwave data are reported of the

L ~ O . ~ ( I - ~ + ~ , Z ~ ~ T ~ ~ F ~ ~ . J - O . ~ ~ ~ + ~ ~ ) O ~ system for X ranging from 0 to 0.5 and y from 0.7 to 1.3.

The materials of chemical composition corresponding to X > 0 and y > 0.9 have the Curie temperature much higher than expected. The ferrites reveal a low magnetic anisotropy field and have a narrow ferrimagnetic resonance line. The microwave materials with the magnetization of 200-500 G, AH of 30-60 Oe and the Curie point higher than 140 OC can be obtained.

1. Introduction. - Recently, the ferrimagnetic Li-Ti-Zn system of chemical formula

was extensively examined within the region of y

<

0.9 and x 2 0 [l-41.

Some interesting microwave materials with rectan- gular hysteresis loop or narrow ferrimagnetic resonance linewidth AH were found [l]. In this region the

magnetization 4 nM, decreases with increasing Ti4+ ions content. The diamagnetic Ti4+ ions are expected to substitute the paramagnetic Fe3 + ions in the octahe- dral sites. The diamagnetic Zn2+ ions enter tetrahedral sites. Therefore for increasing X the magnetization

4 7tM, increases up to x z 0.4. For larger X values the

magnetization decreases because the spin arrangement becomes non collinear and forms a type of canting structure. The Curie temperature T, lowers with x

and y because the diamagnetic ions contribute to reduction of A-B interaction. For y = 0.9 and X = 0 the Curie temperature was found to be

-

180 OC [ l , 2, 31, and it lowers markedly with Zn2+ ions content. The investigations of the Li-Ti-Zn system were perform- ed in the range of 0

<

X

<

0.5 and 0.7

<

y

<

1.3.

It was found that some ferrites, with y > 0.9 and

x > 0, can have relatively high Curie point in spite of

high content of diamagnetic ions in the chemical compound. These ferrites have a narrow ferrimagnetic resonance linewidth AH. Hereunder some properties of the investigated ferrite are described.

2. Experimental procedure. - Li-Ti-Zn ferrites within the region of 0 G x

<

0.5 and 0.7 6 y G 1.3

were investigated. Some extra Mn (0.05 Mn ions/for-

mula unit) and Bi (0.003 Bi ions/formula unit) were added to all the ferrites to obtain samples with low dielectric losses and of a high density [l]. The samples were prepared from Li2C03, TiO,, Fe203, ZnO, MnC03 and Bi203, all of high purity, by using stan- dard ceramic procedure. The raw materials were mixed in a polyamide mill with steel balls in ethyl alcohol suspension. The prefired powders (860 OC/4 h)

were milled once again. The steel ball wear was correct- ed to obtain stoichiometric powders. With water used as a binder, the powder was pressed into disk shapes at a pressure of 1 ton/cm2.

The samples were sintered at 950-1 100 O C for

2-10 hours and cooled sIowly in a n oxygen atmos- phere. The X-ray analysis revealed a single spine1 phase. No traces of other phases were found in the microstructure of the sintered materials. The grains were large with numerous small pores trapped inside. According to the chemical analysis the samples did not contain Fe2+ ions. The bulk density of the specimens was not less than 98

%

of the theoretical value.

3. Crystallographic data.

-

The lattice constant a,, measured by X-rays for various samples versus the

x and y contents is shown in figure 1. For the zinc-fre ferrite (X = 0) the lattice constant increases with the ~ i content up to y ~ + z 1. For y > 1 the lattice constant is indepedent of ions content as it was found previoulsy [2].

For x > 0, a. seems to be almost independent of y

within the region examined. Only a slight minimum in

the vicinity of y = 1 might be noticed. Instead, the lattice constant increases significantly with Zn2+ ions content, caused by the large ionic radius

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C1 -272 M. KONWICKI A N D S. MAKOLAGWA

FIG. 1 . - Lattice constant vs X and j j in

Li0.5(1-~+~)Zn~Ti~Fe2.5-0.s(~+3/,04

( I . = 0.74 a ) of Z n 2 + ions. Two Zn2+ ions substitute

a couple of smaller ions Lil+ (r = 0.68 a ) and Fe3 * ( r = 0.64

A).

4. Magnetization. - The only source of magnetization of the ferrite are the paramagnetic ions. In the Li-Zn-Ti system only the Fe3.' ions can be considered. Their distribution between the sublattices was assumed as follows :

T o compare the calculation with the experimental results the magnetic moments were found by extrapo- lating to 0 K the CJ = f (T) curves taken for the

sintered specimens.

The measurements of a were accomplished using a magnetic balance at a magnetic field of 7 kOe within

the temperature range from liquid nitrogen (some of them from liquid helium) to T,.

The results of the extrapolation are shown in figure 2 (full lines). For y d 0.9 the calculated magnetic moments meet those obtained experimentally. For

y > 0.9 the experimental points lie over the theoretical

lines thus indicating an extra quantity of diamagnetic ions (Lil+ and/or Ti4+) in the tetrahedral sites. The difference between experimental and theoretical values of magnetization diminishes with the increase of Zn2+ content up to X w 0.4, at which value the experimental

points almost fit the theory. For X > 0.4 this difference

changes the sign. A decrease of the magnetic moments

for X > 0.4 can be attributed to the spin canting [4].

The room temperature magnetization increases with increasing the Zn2+ ions content up to X = 0.3 as it is shown in figure 3. For X > 0.3 the 4 xMs diminishes

with X . It ischiefly brought about by the decrease of the

magnetic moments at 0 K.

The M n 3 + ions, present as a small addition, are expected to be in trivalent state and substitute the Fe3+ ions in B sites.

The theoretical magnetic moment at 0 K was calculated assuming the collinear spin arrangement. The results of this calculation are shown in figure 2 (parallel dashed lines).

FIG. 3. - Room temperature magnetization vs X and y in

Lie. S ( ~ - ~ + Y ) Z ~ ~ T ~ Y F ~ Z . S - 0 . 5 ( ~ + . 3 ! ~ ) 0 4 .

FIG. 2. - Magnetic moment at 0 K vs X and y in

Lio. S ( I - Z + ~ , Z ~ Z T ~ ~ F ~ Z . 5-0. ~ ( ~ + 3 ? , ) 0 4 .

Dashed lines indicate the calculated values and the full lines present the extrapolated values.

The Ti4+ ions content lower the 4 nM, for all values of X . The ferrites investigated show some pecu-

liarity in the dependence of the Curie temperatures versus diamagnetic ions content (see Fig. 4). For zinc-free ferrites (X = 0) the Curie temperature decreases monotonically with increasing y as it was found previously [2, 3, 41. For the ferrites with X > 0

the Curie temperature decreases as y increases up to 0.9 but afterwards this increase becomes anomalous.

For y > 0.9, Tc has approximately the same value

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NEW Li-Ti-Zn FERRITES WITH NARROW FERRIMAGNETIC RESONANCE LINEWIDTH Cl-273

FIG. 4. - Curie temperature vs X and y in FIG. 5. - X-band ferrimagnetic resonance linewidth vs X and y

Lio. 5 ( 1 - ~ + ~ ) Z n ~ T i ~ F e z . 5-0.5(~+3$!)04. in Lio. s(l-z+y)ZnsTiUFez. 5 - 0 . 5 ( ~ + 3 ~ ) 0 4 .

the diamagnetic ions content ( ~ i ~ ' and z n 2 + ) does not diminish the Curie point. Tc remains higher than 100 OC up to y = 1.2.

For y > 1.2 or X > 0.4 the results become unreliable

because of the difficulties in determination of Tc from

o = f (T) curves. In this case the o = f(T) curves have a long tail, caused by some microinhomogeneities the materials. On the other hand no foreign phase was found by X-ray and microstructure analysis. Origin of the observed anomalous increase of T, is not clear yet.

We note that the o = f (T) curves are reproducible for slowly cooled specimens. The Mn and Bi ions addition do not affect the character of the pheno- menon.

5. Resonance properties.

-

As was reported previously, the Ti4+ and ZnZ+ ions lower the anisotropy of the Li ferrites. In [l], a significant decrease of AH was found for ~ i ~ ' ( ~ d 0.9) and Zn2+ substituted ferrites. In figure 5 we present the X-band ferrimagnetic resonance linewidth of the ferrites with the Ti4+ ions content up to y = 1.2. For zinc-free ferrites (X = 0) AH decreases with X and increases for large y

with a minimum of 200 Oe at y m 0.9. It seems that the minimum of AH points out the Ti4' ions content at which the decrease of magnetization prevails against the decrease of anisotropy. AHis drastically reduced by the introduction of ZnZf ions. For X = 0.2, 0.3 and 0.4 AH is small (AH

<

60 Oe) from about y = 0.8 to y = 1.1. The value of 30 Oe was found for unpolished spheres of the ferrite with X = 0.3 and y = 1.0 (T, w 160 OC). This suggests a low anisotropy field region for X > 0 and y > 0.8. We noted that even a

small amount of ZnZf ions (X = 0.1) can drastically diminish AH.

6. Conclusion. - The crystallographic, magnetic

and microwave properties of the

were investigated within the region of 0 G X G 0.5

and 0.7 G y G 1.3.

A region was found (X > 0, y > 0.9), where the Curie temperature does not decrease with the diamagnetic ions content.

The Curie temperature are much higher than expected.

It suggests that the A-B interaction increases with the diamagnetic ions content. It can be caused by the favourable ordering of the paramagnetic Fe3

"

ions in both sublattices. We note that the quenched specimens have significantly lower Curie temperature than those slowly cooled.

These ferrite reveals also a low magnetic anisotropy field. In consequence the ferrimagnetic resonance linewidth AH is markedly diminished. The region offers a series of ferrite materials with A H within 30-60 Oe, the room temperature magnetization within 200-500 G and the Curie temperature higher than 140 OC.

The materials are of low dielectric losses. They are competitive with the classical YAlIG materials.

Acknowledgment.

-

The authors wish to thank Mrs. K. Wojczynska for assistance in preparing the specimens and Mr. J. Masiulanis for X-ray measurements.

References

[l] BABA, P. D., ARGENTINA, G. M., COURTNEY, W. E., [3] SILVESTROWITCH, E. E., SOLODOUHINA, R. V., FERRITI, DIONNE, G. F., and TEMME, D. H., IEEE Tram. Magn. Nauk. Tech. Minsk, (1968) 405.

MAG-8 (1972) 83. [4] DIONNE, G. F., J. Appl. Phys. 45 (1974) 3621.