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MAGNETOOPTICAL PROPERTIES OF
ORTHOFERRITES AND GARNETS IN INFRARED
M. Chetkin, A. Shalygin, Yu. Scherbacov, A. Ahutkina, S. Medvedev, A.
Chervonenkis
To cite this version:
M. Chetkin, A. Shalygin, Yu. Scherbacov, A. Ahutkina, S. Medvedev, et al.. MAGNETOOPTI- CAL PROPERTIES OF ORTHOFERRITES AND GARNETS IN INFRARED. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-796-C1-797. �10.1051/jphyscol:19711280�. �jpa-00214117�
JOURNAL DE PHYSIQUE Colloque
C
1, supplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1-
796MAGNETOOPTICAL PROPERTIES OF ORTHOFERRITES AND GARNETS IN INFRARED
M. V. CHETKIN, A. N. SHALYGIN, Yu. I. SCHERBACOV, A. I. AHUTKINA,
Moscow State University
S . A. MEDVEDEV, A. Ya. CHERVONENKIS Moscow Energetical Institute, Moscow, U. S. S. R.
Rksumk.
-
Les propriktks magnkto-optiques de YFeO3, EuFe03, DyFeOs et DyIG sont ktudikes dans l'infra-rouge.Le terme non diagonal I e ; I du tenseur I e I et la birefringence des orthoferrites sont assez grands. Dans la direction de l'axe optique 1 la rotation Faraday de YFe03 est estimQ a partir de I e i I. La valeur calculke de cette rotation est 700 o/cm
& 1 = 1.15 y. Le rksultat expkrimental est en accord avec cette estimation. La rotation Faraday du DyIG est isotrope entre 80 et 293 OK et le facteur g du Dy3+ est egal
a
la valeur pour I'ion libre. On utilise l'equation du mouvernent du moment magnktique avec un facteur g anisotrope pour interprbter la rotation Faraday a 25 OK.Abstract. - Magnetooptical properties of the YFeO3, EuFeO3, DyFeOs and DyIG were investjgated-in infrared.
The nondiagonal components 1 ei [ of tensor I e 1 are large enough. Faraday Rotation (F. R.) along optrcal axls of YFe03 was estimated from the value I &i I. The calculated value of this rotation is equal to 700 o/cm at 1 = 1.15 p. The expe- rimental value is - 600 o/cm. The F. R. in DyIG is isotropic at 80-293 OK and g-factor Dy3+ equals its free ions value.
The equation of motion of the magnetic moment with anisotropic g-factor is used for interpretation F. R. at 25 OK.
Orthoferrites, like ferrite garnets, have a transpa- rency window in the infrared [I]. The transparency of the orthoferrites has been used for observing the domain structure [ l , 21. The polar Kerr effect of ortho- ferrites in the visible was investigated in [3, 41. Using the transparency of the single crystals, we have inves- tigated magnetooptical properties of orthoferrites YFeO,, EuFeO, and DyFeO, 151. The single crystals orthoferrites were grown by means of the technique of zone melting with optical heating [6]. Figure 1 gives ratio 2 6/1,(1) in YFe0, plate 102 p thickness cut in the { 001 ) plane. Here 2 6 is the change in intensity of radiation I passing through the system when the current in the electromagnet is switched. The electrical field of the incident radiation coincides with the axis
<
100>.
The analyser was rotated by 450 from<
100>.
For all thicknesses of the specimen the quantities 2 611, are the same for the same value of wavelength.
In birefringent crystals the Faraday rotation can only occur along the optical axis [7]. In the directions which do not coincide with the optic axis the angle
x
= 612 I, which defines the orientation of the major axis of the ellipse with respect to direction of polari- sation of the incident light, can be written in the following form [8].G33 E;'' 2 ,:dAn
tg 2
x
= - 2 k sin A = --- sin ---An 1 (1)
where An-birefringence,
Birefringence of YFeO, is large comparable with birefringence of the CaCO,
.
The inset figure I shows
I
E , ( of YFeO,, obtained with the help of (1). The values of1
E , ( are largeFIG. 1. - Relative change in the intensity of the radiation
2 611 passing through the YFe03 of thickness 102 p when the current in the electromagnet is switched as function of the
wavelength.
enough, as in visible [3, 41. The orthoferrites crystallize in an orthorombically distorted perovskite structure belonging to the two-axis crystals. The optical axis of YFeO, lies in the ( 100 ) plane and makes with the axis
<
001>
the angle of 400. That is very conve- nient to receive large F. R. The value of F. R. may be estimated fromI
el ] and the angle between the optical axis and<
001>.
For example, F. R. is equal to 700 O/cm a t 1 = 1.15 p. The experimental value is is the nondiagonal component of the dielectric - 600 O1cm. This F. is higher than in mG. In constant tensor, EO is the diagonal component, d i s the direction that coincide with the optical axis, thickness of the plate, 1 is the wavelength. From thethe value is small; = 0.40 and at 2 = l.15 {(period )> of the changing
x
we getand 0.63 fi respectively. Curves similar to those of An = (3.6
+
0.3) at A = 1.15 p, figure 1 were obtained for other orthoferrites. Birefrin- An = (3.5 f 0.3) at 1 = 1.8 p , gence of the orthoferrites is proportional to its ortho- An = (2.9 f 0.3) l o e 2 at ;1 = 6 p. rombical distortions. For example, in EuFeO, atArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711280
MAGNETOOPTICAL PROPERTIES OF ORTHOFERRITES AND GARNETS IN INFRARED C 1 - 797 ,I= 1.15 p An = (2.2
+
0.2) andx
= 0.60. The d F %curves ~ ( 1 ) in the vicinity of the absorption bands have some peculiarities [9].
In papers [lo] was found the frequency independent
Faraday effect a,, which exists due to the magnetic 'O0 - permeability in the optical frequence. I t was shown
that the F. R. in DyIG at 80-293 OK is isotropic [ l l ] and the values
+(A)
may be written in the form[lo-121 : 50 -
Here the first member is a,,.; g,,, gR, I,,, IR are the g-factor and the magnetizations of Fe3 and ~y~ +,
JE
= n . The g-factor of Dy3+ ion obtained from the value a,, equals its free ion value. The result of the -50investigation of the F. R. of oriented DyIG single crystals a t 25 OK in magnetic field H = 12 kOe is repre- sented in figure 2. From these results and (2) we
obtains : - y o 0
a;:11> = 180 f 10 O / C ~ ; FIG. 2. - The Faraday Rotation IXF (A) in oriented single crystals DyIG at 25 OK in magnetic field H = 12 kOe. (* - u p
<
110>
;@;:lo > = 120 f 10 O / C ~ ; - U F < l o o > ; X - M l ? < I 1 1
>).
Along the
<
110>
direction was found the birefrin- gence 113, 141 which varies from An = 1 .I x at 1 = 3.5 p up to An = 0.95 x a tA
= 6.6 p. In this case the value a,,<
110>
was calculated using (1).From the values a, and (2), using the magnetization data [I 51, may be determined gR
<
1 1 1>
= 1.55+
0.1,gR
<
100>
= 1.8+
0.1, gR<
110>
= 1.4+
0.1. - To obtain these values a,, the values cos ai = 1, J2/3,J1/3
were introduced in (2) for the<
11 1>, <
110>
and
<
100>
directions respectively. It is not excluded that anisotropic a& is due to the difference of values of cos a, from those mentioned above. In this case it must vanish in the high magnetic fields.The interpretation a,, at 80-293 OK mentioned above is based on using the Landau-Lifshitz equations with isotropic g-factor. At low temperature one must take into account that local symmetry of rare-earth
ions is not cubic. In this case we must employ the equations of motion of magnetic moment with aniso- tropic g-factor. Using the Vlasov's and Yshmuhame- tov's equations [16] and taking account of the six non-equivalent positions of the rare-earth ions in the unit cell, one obtains
along over all directions of the crystal. In (3) the g,
,,
gz2, g3, are the principal values of g-tensor. When gll = g22 = g33 = g~7 thengR = gJ. Ifg1l f g22 # g33, g, # g, and this is observed on the experiment for<
11 1>
direction.Allowance for non-colinear sublattices [17] within the Wolf's model [IS] doesn't lead to anisotropic a,, under condition of the equal magnetic moments of the rare-earth ions in unequivalent positions.
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