- Email: [email protected]
Faraday rotation in KCl-KBr and KBr-KI single mixed crystals in high magnetic fields
Volume
28A, number
FARADAY
11
ROTATION
PHYSICS
IN IN
KCl-KBr HIGH
LETTERS
AND
10 March 1969
KBr-KI
MAGNETIC
SINGLE
MIXED
CRYSTALS
FIELDS
E. tiTYsA~0 Wihuri Physical Laboratory, University of Turku, Turku, Finland and Department of Physics, Tampere Technical University, Tampere, Finland
and R. LAIHO Wihuri
Physical
Labmatory,
University
Received
of Turku,
10 February
Turku,
Finland
1969
The Faraday rotation of some mixed crystals of alkali halides was found to be a sensitive function of the composition, showing a saturation effect. of the electronic polarization.
In alkali halides the Coulomb forces are in balance for both types of ions. This results in the well known additivity rule of the total polarizability. Roberts [l] has pointed out that, in many less symmetrical crystals, unbalanced forces cause a saturation effect between the electric field strength and the dipole moment. The values of the polarizability derived from the observed dielectric constants are smaller than the theoretical values, indicating a saturation effects. Mixed crystals of alkali halides are interesting with regard to local anisotropy. A saturation effect is expected to be found in some magnetooptical effects. The optical Faraday rotation is related to the electronic polarizability through the energy derivative of the refractive index and through the Zeeman splitting of the electronic energy levels. The values of the Faraday rotation in pure alkali halides are well known [2]. In the present work, we extended Faraday rotation measurements to some KCl-KBr and KBr-KI single mixed crystals. The new measuring method is described elsewhere [3]. The measurements were carried out in pulsed 200 kOe magnetic fields at room temperature. At a fixed photon energy of 2.1 eV, the Verdet coefficient V versus the KBr concentration in KCl-KBr and in KBr-KI shows a nonlinear behaviour, as illustrated in fig. 1. In mixed crystals, which contain fifty percent of KBr, the greatest anisotropy can be expected in the local field, 734
0
50 KBr
in
KBr-KI
and nonlinear
100 KBr
in
50 KBr-KCI
0 (mole%1
Fig. 1. The Verdet coefficient of Kerr-KI and KBr-KC1
mixed crystals versus the KBr concentration.
and here we find the greatest deviation from the values of the Verdet coefficient obtained by linear interpolation. In the case of KBr-KI, there are only a few experimental points in the curve in fig. 1, because of the large solubility gap. Because the Verdet coefficients of the mixed crystals are sensitive to compostion, the Faraday rotation measurements can be used in the determination of the composition, especially in the case of heavier mixed crystals. 1. S. Roberts, Phys. Rev. 76 (1949) 1251. 2. S. Ramaseshan, Proc. Indian Acad. Sci. 28 (1948) 360. 3. E. Mtiintysalo and R. Laiho, Ann. Univ. Turkuensis AI, No. 122 (1968).
28A, number
FARADAY
11
ROTATION
PHYSICS
IN IN
KCl-KBr HIGH
LETTERS
AND
10 March 1969
KBr-KI
MAGNETIC
SINGLE
MIXED
CRYSTALS
FIELDS
E. tiTYsA~0 Wihuri Physical Laboratory, University of Turku, Turku, Finland and Department of Physics, Tampere Technical University, Tampere, Finland
and R. LAIHO Wihuri
Physical
Labmatory,
University
Received
of Turku,
10 February
Turku,
Finland
1969
The Faraday rotation of some mixed crystals of alkali halides was found to be a sensitive function of the composition, showing a saturation effect. of the electronic polarization.
In alkali halides the Coulomb forces are in balance for both types of ions. This results in the well known additivity rule of the total polarizability. Roberts [l] has pointed out that, in many less symmetrical crystals, unbalanced forces cause a saturation effect between the electric field strength and the dipole moment. The values of the polarizability derived from the observed dielectric constants are smaller than the theoretical values, indicating a saturation effects. Mixed crystals of alkali halides are interesting with regard to local anisotropy. A saturation effect is expected to be found in some magnetooptical effects. The optical Faraday rotation is related to the electronic polarizability through the energy derivative of the refractive index and through the Zeeman splitting of the electronic energy levels. The values of the Faraday rotation in pure alkali halides are well known [2]. In the present work, we extended Faraday rotation measurements to some KCl-KBr and KBr-KI single mixed crystals. The new measuring method is described elsewhere [3]. The measurements were carried out in pulsed 200 kOe magnetic fields at room temperature. At a fixed photon energy of 2.1 eV, the Verdet coefficient V versus the KBr concentration in KCl-KBr and in KBr-KI shows a nonlinear behaviour, as illustrated in fig. 1. In mixed crystals, which contain fifty percent of KBr, the greatest anisotropy can be expected in the local field, 734
0
50 KBr
in
KBr-KI
and nonlinear
100 KBr
in
50 KBr-KCI
0 (mole%1
Fig. 1. The Verdet coefficient of Kerr-KI and KBr-KC1
mixed crystals versus the KBr concentration.
and here we find the greatest deviation from the values of the Verdet coefficient obtained by linear interpolation. In the case of KBr-KI, there are only a few experimental points in the curve in fig. 1, because of the large solubility gap. Because the Verdet coefficients of the mixed crystals are sensitive to compostion, the Faraday rotation measurements can be used in the determination of the composition, especially in the case of heavier mixed crystals. 1. S. Roberts, Phys. Rev. 76 (1949) 1251. 2. S. Ramaseshan, Proc. Indian Acad. Sci. 28 (1948) 360. 3. E. Mtiintysalo and R. Laiho, Ann. Univ. Turkuensis AI, No. 122 (1968).