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Submitted on 1 Jan 1971
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MAGNETOSTRICTION OF YTTERBIUM ORTHOFERRITE
A. Clark, H. Belson
To cite this version:
A. Clark, H. Belson. MAGNETOSTRICTION OF YTTERBIUM ORTHOFERRITE. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-490-C1-491. �10.1051/jphyscol:19711161�. �jpa-00213982�
JOURNAL DE PHYSIQUE Colloque C l , supplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - 490
MAGNETO STRICTION OF YTTERBIUM ORTHOFERRITE
A. E. CLARK and H. S. BELSON
U. S. Naval Ordnance Laboratory White Oak, Silver Spring, Maryland 20910
Rksumk. - La magnktostriction de monocristaux de YbFeO3 a ktk mesur6e dans des champs magnktiques allant jusqu'a 105 kOe. A la tempkrature ambiante, la variation relative de longueur dans les directions cristallographiques
a, b ou c est infkrieure 8- 0,2 X 10-6 B 35 kOe et 1,5 X 10-6 2t 105 kOe.
A 4,7 OK, a cause de la contribution de l'ion Yb3+, la magnktostriction parallkle 8- l'axe a est grande et du type 5 un ion, essentiellement.
Des mesures d'aimantation, faites dans le m2me domaine de tempkrature et avec les mEmes valeurs de champ magn6- tique, montrent que l'aimantation est trks fortement anisotrope avec une saturation de type paramagnktique du sous- rkseau des terres rares parallele B la direction a.
Abstract. - Magnetostriction measurements have been made on single crystals of YbFeOs in fields up to 105 kOe.
At room temperature, the fractional changes in length along the crystallographic a, b and c directions are less than 0.2 X 10-6 at 35 kOe and 1.5 X 10-6 at 105 kOe. At 4.7 O K , because of the Yb3+ contribution, the magnetostriction parallel to a is large and predominantly single-ion like.
Magnetization measurements made over the same temperature and field ranges reveal a huge anisotropic magneti- zation with paramagnetic saturation of the rare earth sublattice parallel to a.
Magnetization measurements on polycrystals of the rare earth orthoferrites (RFeO,) by Forestier [l] and Pauthenet [2] and on single crystals of YbFeO, by Bozorth [3] Treves [4] and Belov [5] have revealed a
(( weak D, or parasitic )), ferromagnetism which can be described at low fields by : o = oo + xH, where o0 is the spontaneous magnetization and X is the para- magnetic susceptibility. Some high field magnetization measurements were reported by Belov [5] at room temperature, but no high field magnetostriction studies are known. I t is the purpose of this paper to report our high field magnetostriction studies on YbFeO, from room temperature to 4.7 OK and to present complete magnetization measurements over the same temperature range.
Magnetization. - I n order to understand the ma- gnetostriction, even qualitatively, a knowledge of the magnetization is necessary. We have measured the magnetization of YbFeO, along the a, b, and c ortho- rhombic axes in fields up t o 150 kOe [6] at tempera- tures between 4.5 OK and 300 OK. The crystals were flux-grown by J. R. Cunnigham of our laboratory.
Magnetization curves for H parallel to the c axis are given in figure 1. Above 8.9 OK, the spontaneous magnetization increases with decreasing temperature in an unusual way. The Treves [4] relationship :
a,, = .91 B(T) [l + 158/T] ,
where B(T) denotes the temperature dependence of the Fe sublattices, does not hold below 100 OK. Instead c,, rises too slowly with decreasing temperature. This can be accounted for by a depopulation of a higher energy level in the rare earth manifold or by a decrease in angle between the nearly antiferromagnetic iron sublattices. In agreement with Bozorth [3] the sponta- neous magnetization parallel to c decreases with decreasing temperature below 8.9 OK, suggesting a rotation of the easy axis away from the c direction.
The fields required to pull the magnetization back into the c axis a t temperatures of 4.5 OK and 6.0 OK are shown in figure 1.
The magnetization parallel to a is entirely different (Fig. 2). Along a the susceptibility increases rapidly with decreasing temperature following a simple Curie law with n, g J ~ ( ~ + 1) = 4.8 pb. This is close t o the full rare earth free ion value of 4.5 p,, in striking contrast to the effective moment parallel to c. In addition, the approach to paramagnetic saturation can clearly be seen at high fields below 13 OK. At this
H H [hoe)
FIG. 1. -Magnetization of YbFe03 parallel to c. FIG. 2. - Magnetization of YbFeO3 parallel to a and b.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711161
MAGNETOSTRICTION OF YTTERBIUM ORTHOFERRITE C 1 - 491
temperature, although the spontaneous magnetization is parallel to c, the magnetization at 100 kOe parallel to a is four times larger than that parallel to c. Thus, similar to the Fe spins, the rare earth moments find it easier to lie along a. At 4.5 OK, a a, vs 1/H plot yields a total saturation moment of 3.1 p,.
The b direction is magnetically hard for both the rare earth and iron sublattices.
Magnetostriction. - Our magnetostriction measu- rements were made in continuous fields up to 105 kOe [6] using special low magnetoresistance strain gages manufactured by Kyowa Electronics Co. In Table I
Room Temperature Magnetostriction C)
H
(kOe)IZ& l a c l$b @a abc l e c (X1O6) - - - - - -
35 0 0 0 0 -0.3 -0.2
105 0.5 - 0.5 - 1.0 - 0.3 - 2.5 0
(a) The experimental uncertainty at 35 kOe is & 0.2 X 10-6 ; at 105 kOe it is f 1.5 X 10-6.
we show six magnetostriction coefficients at room temperature in fields of 35 kOe and 105 kOe. All coefficients are very small. A,,,,, represents the change in length along the m direction with the applied field and magnetization along n. We use the symbol, A:,,,
to identify the measurements in which the applied field is not parallel to the magnetization (n represents only the field direction).
Only a small fraction of the total magnetization ever appears along the b axis (Fig. 2), thus all b magneto- striction coefficients remain small as the temperature is decreased. At 5 OK, A&,, A& and are negative with magnitudes less than 0.3 X 1 0 - 6 / ~ (kOe).
A positive field dependent strain appears along the .c direction as the temperature is lowered (Fig. 3).
Above 7.7 OK the magnetostriction is proportional to H 2 . Between 7.7 OK and 90 OK, the magnetostriction rises too rapidly to be accounted for by a simple 1- or 2-ion interaction of the rare earth ions. The 100 kOe magnetization increases by only 75 % over this temperature range, compared to the six-fold increase in magnetostriction. The break in the 4.7 OK magnetization curve at 40 kOe (Fig. 1) is clearly reflected in the magnetostriction, A,,, at the same temperature.
Another large positive coefficient is A,,. This is expected because of the huge field induced paramagne- tism parallel to a. At high temperatures, the magneto- striction is proportional to H 2 . At 4.8 OK, it is almost linear. The evolution from the H2 dependence to the low temperature behavior can be accounted for by the Refer '[l] FORESTIER (H.) and GUIOT-GUILLAIN (G.), C. R.
Acad. Sci. Paris, 1950, 230, 1844.
{2] PAUTHENET (R.) and BLUM (l?.), C. R. Acad. Sci.
Paris, 1954, 239, 33.
91 BOZORTH (R.), KRAMER (V.) and REMEIKA (J.), Phys.
Rev. Letters, 1958, 1 , 3.
FIG 3. - ,Lcc VS magnetic field.
increase of magnetization along a, assuming it to be essentially due to the rare earths. Figure 2 shows that the knee of the 4.50K magnetization curve occurs near 50 kOe. Above this field there is only a slow approach to saturation. Assuming that the major contribution to the magnetostriction is due to a single- ion mechanism and that the temperature and field dependences of the iron sublattice magnetization are negligible, we find the magnetostriction given by the dotted line in figure 4. The agreement between the
FIG. 4. - Aaa and l a c VS magnetic field
observed and calculated values of A,,, in both shape and magnitude, is good. We conclude that the rare earth ions make the dominent contribution to the magnetization and magnetostriction parallel to a, and that their magnetoelastic interaction is primarily single-ion like.
ences
[4] TREVES (D.), J. Appl. Phys., 1965, 36, 1033.
[5] BELOV (K.), KADOMTSEVA (A.) and LEVITIN (R.), Soviet Physics, JETP, 1965, 20, 291.
[6] The fields were obtained at the U. S. Naval Research Lab.
