ON MAGNETOSTRICTION OF GADOLINIUM IRON GARNETS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80T00246A009700050002-8
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 13
• Document Creation Date: December 22, 2016
• Document Release Date: August 4, 2009
• Sequence Number: 2
• Publication Date: February 25, 1960
• Content Type: REPORT

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K. P. BELOV AND A. V. PEDKO
ON MAGNETOSTRICTION OF GADOLINIUM IRON GARNETS
The temperature dependence of magnetostriction in the gadolinium ferrite
having structure of a garnet has been measured within the temperature range
from liquid nitrogen. up to the Curie point. Attemperatures above the compensation
point of sublattices. 6K the magnetostriction isotherms are of the same kind as
for ferromagnetics 0- i I and 1--L have opposide signs and the ~- vs. ff
curves exhibit saturation. In cooling below there is an effect of superposition
oflarge volume magnetostriction of paraprocess on the "ordinary" magnetostriction
which results in the distortion of the magnetostriction isotherms (%1// and /L
are of the same sign and without saturation). It is shown that the "ordinary"
magnetostriction is due to the interaction of Fe ions in sublattices a and d,
while the volume magnetostriction of the paraprocess is due to the interaction
of Gd3+ and Fe'"' ions.
1. In this report we should like to point out that peculiar magnetostrictive
properties of gadolinium iron garnets, which we found out in the temperature
range from the liquid nitrogen up to the Curie point.
The magnetic properties of these interesting substances are known to have
been studied by Pauthenet 11/, Gilleo and Geller. They have thrown light upon the
character of the interaction of the magnetic sublattices in iron garnets. Here
we intend to show that the investigation. of the magnetostriction in the gadolinium
iron ge.rnets.enables one to obtain the necessary data for finding out the details
of the interaction of the sublattices in this material.
2. To study magnetostriction we prepared by the ordinary ceramic technics
several samples of gadolinium ferrites. They were sufficiently large and had the
following contents:
3Gd203.5Fe2O3
3Gd203.0, 2Gd2O3 . ~+, 8Fe203
3Gd203.0,2Y203.1,8Fe203
It was desirable for us to know the influence of a small change of composition
on the magnetostriction.
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By X-ray analysis it was ascertained that all ferrites had the structure
of a garnet.
Fig. 1 shows the dependence of Cf an T . The values of the Curie
points 0 and the compensation points ? are close to the values observed
by Pauthenet /I/. The magnetisation isotherms above OK and below ?K are of
entirely different character. Fig. 2 presents the magnetic hysteresis loops
taken at the boiling, points of nitrogen and helium. Although hysteresis is
completed in relatively weak fields, there is no saturation of magnetisation
on fig. 2.
To show with certainly that here we deal with paraprocess and not with
the rotation of magnetisation in domains we measured the temperature dependence
of magnetostriction. The magnitude of magnetostriction in the gadolinium ferrite
is not large;we measured it with the aid of wire tensometers using photoelectric
amplifier (FEOU-15). It was found, that at the temperatures above the compensation
point (&K) the curves of longitudinal/ // and transversal _~-,_L magnetostriction
are of the same kind as for the ordinary ferromagnetics (fig-3); -1\11 and __L..
have opposite signs and there is saturation on the curves (.201C). Below the
compensation point ( BK ), at the liquid nitrogen temperature, for instance,
the shape of these curves changes sharply. In weak fields one can see the signs
of "ordinary" magnetostriction (opposite signs of /Al/ and _1. ), in stronger
fields however andll~have the same positive signs without any tendency to
saturation. It is clear that in the temperature range below B'K we have an effect
of superposition of large volume magnetostriction of paraprocess on the "ordinary"
magnetostriction.
Fig. 4, 5,6 show isotherms of longitudinal magnetostriction, taken for various
samples of gadolinium iron garnet with different contents. One can see that in
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-3-
the temperature region above QK the longitudinal striction is negative and
saturation takes place, when the temperature decreases below Gk , the influence
of magnetostriction of paraprocess increases and the sign of longitudinal magneto-
striction becomes, positive.
The valued 7 - the slope of the curve in strong fields may be taken as a 14
characteristic of magnetostriction of paraprocess. One can see on fig 7 that
with decreasing temperature the value increases. The increase of magneto-
atriction of ,paraprocess with the decrease of temperature is an unusual phenomenon
which has not been observed before in other ferromagnetics. We know that in
all ferromagnetics the paraprocess and the magnetostriction of the paraprocess
increase with increasing temperature, and the value d d reaches its maximum
4Jt
near the Curie point. In gadolinium ferrites the increase of d ? near the
A
Curie point also takes place but the value of H is small in comparison with
the value of Q below the compensation point 81(.
3. To understand the observed phenomenon, we shall proceed from Neel's
model for iron garnets. According to this model iron garnets have 3 magnetic
sublattices: c. d and a /3/. The sublattice c is formed by Gd 34- ions, while
the sublattices d and a are formed by Few ions. All three sublattices inter-
act antiferromagnetically, and according to the measured value of magnetic
momenta the resultant magnetisation of these sublattices can be presented in
the following way:
Gd3t Fe3+ Fe3+
Our experiments in magnetostriction make us suppose that there is something
like two ferromagnetic states in the gadolinium iron garnet. One of them is
ions take part in
determined by the interaction of sublattices d and a (Fe 3+-
this interaction), and the other is determined by the interaction of the sub-
lattice c with the sublattice d and a (the interaction of the Gd ions with
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3.,-
Fe ). Both these interactions originate magnetostrictions of different types.
The interaction d - a (we mean magnetic dipol coupling) results in "ordinary"
magnetostriction. One can ,provide an indirect proof of this fact by measuring
magnetostriction in the yttrium iron garnet (3Y203.5Fe203). If we substitute
nonmagnetic Y3+ ions for the Gd3 + ions in the sublattice c only the interaction
d - a will take place. The measurements of magnetostriction in the sample
3Y203.5Fe203 have shown that it belongs to the usual type.
The large volume magnetostriction.of the paraprocess at the temperature
3t 3t
below 191j , we attribute to the interaction of the Gd ions with the Fe ions,
in other words, this magnetostriction is due to the interaction of the sublattices
c and d - a. The exchange interaction of the Gd3 ions with the Fe3t ions is
small, which originates the large paraprocess. The greater are the atomic
magnetic moments and the smaller is exchange interaction, the greater is the
paraprocess. Under these conditions the external field will "disturb" the
magnetic spin moments inside the domains with greater ease. At the same time
the thermal motion will destroy the spontaneous magnetisation faster. It will
cause the broadening of spontaneous magnetisation curves in such materials (curve 1
on fig. 8), as it takes place in invar alloy Ni30 per cent Fe 70 per cent.
On the contrary in the case of sublattices a - d the interaction is strong and
the resultant magnetic moment is small, therefore the curve will be steeper
(curve 2 on fig. 8). Taking into consideration the character of the temperature
behavior of the curves, we can qualitatively explain the appearance of the
compensation point 9K in the gadolinium iron garnet. Subtracting graphically
the curve 2 from the curve 1, we shall have the curve 3 with the compensation
point (curve 3, fig. 8).
In this way the measuring of magnetostriction in the gadolinium iron
garned makes it ,possible to estimate qualitatively the character and the
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3t 3+
maguitude of the interaction of Gd and Fe ions and to understand the type
of the dependence of the spontaneous magnetisation upon the temperature in
iron garnets. Due to the large magnetostriction of paraprocess in the gadolinium
iron garnet below &K we are to expect greatinfluence of ,pressure on the magnitude
of spontaneous magnetisation. This means that the dependence of exchange inter-
action on the interatomic distances between the Gd3 and Fe3 ions is greater than
+
the same dependence between the Fe 3+ and Fe 3 ions.
4. The gadolinium iron garnets have some other peculiar..features in their
magnetic behaviour. Thus, for example, the coercive force greatly increases
when temperature approaches 9 , and reaches its maximum at 9K . At first
we explained the existence of this maximum 14 c.- in a very simple way. We assumed
that some structural itihomogenities in polycristalline ferrites manifests them-
selves in the vicinity of &7 . Due to this inhomogenit we can consider our
sample near &K consisting of a weak magnetic medium and stronger ferromagnetic
areas with slightly different compensation points. This causes the appearance of
monodomain structure, the processes of remagnetisation are hindered, and P L
increases. Our further measurements of temperature dependence of Ac- showed,
however, that actually more complex maxima (double maxima - fig. 9) are to be
found in the neighborhood of GM,( in most cases. Both maxima are situated
close to each other, but on the opposite sides of 01< . So far we cannot
offer an exhaustive interpretation of the observed phenomenon. It is possible
that the two above mentioned ferromagnetic states (the interaction of the ions
Gd3+ - Feat and Fe3 - Fe 3) are responsible for the appearance of the double
The physics Faculti of the Moscow
State University.
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LITERATURE
1. B. Panthenet Compt. Rend. 24+2 , 1859 (1956): 243, 1737 (1956).
2. S. Geller and M. Gilleo Acts, Cryst. 10, 3, 239 (1957).
3. L. Neel Con}pt. Rend. 239, 8 (195+)
1i. K. P. Belov "Elasticity, Heat and Electric Phenomena in Ferromagnetics,
Moscow, ed. 2 (1957).
28.10.1959
(Belov, K. P.)
(Pedko, A. V.)
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The Explanatory Texts to the Diagrams
Fig. The dependence of the spontaneous magnetisation on temperature
in gadolinium iron garnets: 1. 3Gd203.5Fe203; 2. 3 Gd203.0,2Gd203.4,
8Fe203; 3. 3Gd203.0.2Y203;4,8Fe203
Fig. 2. Hysteresis loops of the gadolinium iron garnet at low temperatures.
Fig. 3. Transversal and longitudinal magnetostriction for the ferrite
3Gd2o3.0,2Gd203.4,8Fe203 at the room temperature and the liquid
nitrogen temperature.
Fig. 4. Isotherms of the longitudinal magnetostriction of tie ferrite
3Gd2o3.o,2Gd203.4, 8Fe203 above the compensation point.
Fig. 5. Isotherms of the longitudinal magnetostriction of the ferrite
3Gd2o3.0,2Gd203.4, 8Fe203 below and above the compensation point.
Fig. 6. Isotherms similar to those in fig. 5., only for the ferrite
3Gd203.5Fe203.
Fig. 7. The dependence of the value = on temperatures for:
li H
1. 3Gd203.5Fe203.
2. 3Gd203.0,2Gd203.4, 8Fe203.
3. 3Gd203.0,2Y203.4,8Fe203.
Fig. 8. To the explanation of the temperature dependence of the spontaneous
magnetisation of the gadolinium iron garnet.
Fig. 9. The temperature dependence of the coercive force in the ferrite
3Gd203.0,2Gd203.4,8Fe203.
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