HAL Id: jpa-00214996
https://hal.archives-ouvertes.fr/jpa-00214996
Submitted on 1 Jan 1972
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
INFLUENCE OF SPONTANEOUS POLARIZATION ON THE EPR SPECTRA OF Cr3+ IONS IN TGFB
J. Stankowski, S. Waplak
To cite this version:
J. Stankowski, S. Waplak. INFLUENCE OF SPONTANEOUS POLARIZATION ON THE EPR SPECTRA OF Cr3+ IONS IN TGFB. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-177-C2- 178. �10.1051/jphyscol:1972260�. �jpa-00214996�
JOURNAL DE PHYSIQUE Colloque C2, suppliment au no 4, Tome 33, Avvil 1972, page C2-177
INFLUENCE OF SPONTANEOUS POLARIZATION ON THE EPR SPECTRA OF Cr3+ IONS IN TGFB
J. STANKOWSKI and S. WAPLAK
Laboratory of Radiospectroscopy, Institut of Physics, Polish Academy of Sciences, Poznan, Poland
RBsumC. - LC spectre EPR de I'ion Cr3+ du TGFB est etudie en fonction de la temperature au voisinage du point de Curie. Au-dessus du point de Curie, le champ cristallin agissant sur l'ion Cr3+
montre que la symLtrie est cubique tandis qu'au-dessous du point de Curie la polarisation spontanke perturbe le champ cristallin cubique et la symetrie devient rhombique.
Abstract. - The EPR spcctrum of Cr3+ ion in TGFB was examined versus temperaturenear the Curie point. Above the Curie point the crystal field acting on Cr3+ ion indicate the Cubic symmetry whereas below the Curie point the spontaneous polarization disturbs the Cubic crystal field and the symmetry becomes rhombic.
EPR investigation of TGFB : Cr3+ single crystal was performed with a microwave spectrometer JES-3 BX at 9.4 kMc/s. Spectrum observed in this frequency region is very simple because the zero-field splitting of the spin energy is small and EPR spectrum consisting three groups of lines. The central lines are associated to t h e 3 o 3 transitions and the two satellitar lines to the k 9 tt f Q. Figure 1 schows the angular
FIG. 1. - Angular dependence of the EPR spectrum of TGFB :
Cr3+ crystals, with general direction (( z )> as rotation axis perpendicular to B.
Chromium co-ordinates with two glycine molecules and two B e ~ z - groups. The closest octahedral neigh- bourhood of the Cr3+ ion is trigonal, with deformation in the 1111 1 direction.
The bounding forces within the complex are larger then the complex-crystal interactions, thus it can be treated as an isolated paramagnetic cluster. This suggestion is strongly supported by the EPR spectrum detected near the Curie point (Fig. 2). The spontaneous
dependence of the EPR spectrum when the crystal was rotated about the general direction (( z
*
of one of the two complexes I/ and II/ in the crystal. The crystal-field acting on chromium ion is rhombic here and the spin-hamiltonian parameters of Cr3+ in TGFB are [l] :FIG. 2. -Temperature dependence of EPR spectrum for B parallel to (< z )> direction.
polarization disturbs the cubic crystal field acting on the doped cluster and the synlmetry of EPR spectrum becomes rhombic. The spontaneous polarization
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972260
C2-178 J. STANKOWSKI AND S. WAPLAK
wanishes above the Curie point and the crystal field as paramagnetic ion is a sensitive probe of the internal again cubic symmetry ; EPR spectrum is isotropic. electric field associated with the spontaneous pola- Figure 3 shows the ten2perature dependence of the D rization.
parameter. In TGFB : Cr3+ similarly as in other The authors wishes to thank Dr. J. Stankowska for ferroelectrics of TGS type the D parameter is linearly making the crystals and for information on dielectric dependent on the spontaneous polarization. A doped properties.
FIG. 3. - Zero-field splitting D-parameter versus temperature.
References
