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EPR measurements on single crystals of -NiSO4 · 6H2O
Volume 44A, number 1
PHYSICS LETTERS
7 May 1973
E P R M E A S U R E M E N T S ON S I N G L E C R Y S T A L S O F
-NiSO 4 • 6 H 2 0
W.M. PONTUSCHKA, A. PICCINI, C.J.A. QUADROS and S. ISOTANI Instituto de Ffsica da Universidade de S~o Paulo,* Departamento de Fisica dos Materials e Mec3nica, S. Paulo, S.P., Brasil, C.P. 20516 Received 12 March 1973 EPR measurements on sinlge crystals of a - NiSO4 • 6 H 2 0 were carried out at room temperature. From the results were deduced the spin Hamiltonian parameters D = 4.85 ± 0.09 cm -1 and E = 0.06 ± 0.01 cm -1 and the direction cosines of the crystalline field.
The EPR measurements on single crystals of aNiSO4 • 6H20 were carried out at room temperature using a homodyne spectrometer, of the reflection type, which operates in the X band with a frequency near 9 GHz/s. We observed one line whose width ranged from 1 to 2 kG and whose position was between 9.4 and 14 kG. From our results it was possible to calculate the spin Hamiltonian parameters, D = 4.85 + 0.09 cm -1 andE = 0.06 + 0.01 cm -1, assumingg = 2.25 [1 ]. Furthermore, it was possible to evaluate the directions of the crystalline field coordinates of the i-th Ni++ion (i = 1, 2, 3, 4) of the unitary cell in terms of direction cosines with respect to the crystallographic axes (a, b, c), where c is parallel to the tetragonal axis: X1234 - (~
x/2/2; ~ x/~-/2;
0
)
Y1234=(~ 0.534; +--
- 0.656)
21234 - - ( ~ 0.464; + 0 . 4 6 4 ;
~ 0.755)
The orientations assumed to carry out the measurements done in this paper are based on the structure of a - NiSO 4 • 6H20 determined by Bevers and Lipson [2]. The crystals were grown by evaporation in neutral saturated solution at 35°C. We observed the variation in the position of the line as a function of the orientation of the crystal, rotating about the principal axes. In the figure are plotted the * Supported by BNDE, CNPq and FAPESP, (Brasil).
H (kG) -x l XXX
THEORETICAL EXPERIMENTAL
X
5:
. . . . . . k. . . . . . . . . HIIx
0 Hlly
50
HIIx (degrees)
Fig. 1. Comparison of experimental and theoretical positions of the EPR line observed in single crystals of c~ - NiSO4 • 6 H 2 0 as a function of the angle of rotation about the Z axis.
positions of the EPR line observed during the rotation of the crystal about the Z-axis of the crystalline field. The results are in good agreement with theoretical calculations using our parameters. At lower temperatures, down to -180°C, there appears a structure consisting of 2 to 4 lines superposed on the EPR line observed. The calculations using the spin Hamiltonian parameters obtained by us, were verified by comparison with the results of an EPR measurement of ct -NiSO 4 • 6H20 reported by Hou and Bloembergen [3]. They used a spectrometer operating in 30 GHz/s, at 77°K, with the applied field parallel to the crystallographic c axis, and obtained a EPR line at 6.5 +- 0.4 kG. Our prevision under these conditions is 6.4 kG. On the other hand our values for the spin Hamiltonian parameters can be compared with some results of spin Hamiltonian parameters of ¢~- NiSO4 • 6H20 determined by means of other methods. So, we can mention the following results: 57
PHYSICS LETTERS
V o l u m e 44A, n u m b e r 1
7 May 1973
R.A. Fisher and E.W. Hornung
[1]
D = 4 . 7 4 l -+ 0.001 cm l k," =0.01 ±0.06 cm 1
(specific heat)
7 ' < 4.2~K
J.W. Stout and W.B. Hardley
[4]
D=4.76 E =0.28
-+0.07 -+0.07
cm - l cm 1
(specific heat)
r "< 20°K
T. Watanabe
[5]
D = 4.5
± 0.3
cm -1
(magnetic susceptibility)
l,g 20 K
± (1.3
cm
(magnetic susceptibility)
l < 4.2" K
t:'~0
N.F. de Oliveira
[6]
D = 4.0
t
k :~ ()
W e are i n d e p t e d t o Mr. K . W a t a r i f o r e l a b o r a t i o n o f a c o m p u t e r p r o g r a m u s e d in t h i s w o r k .
References
[ t ] R.A. Fisher and E.W. Hornung, Journal of Chem. Phys. 48 (1968) 4284.
58
[2] C.A. Beevers and H. Lipson, Z. Krist 83 (1932) 123. [3] S.L. Hou and N. Bloembergen, Phys. Rev. 138 ( 1965 ) A1218. [4] J.W. Stout and W.B. Hadley, Journal of Chem. Phys. 4iJ (1964) 55. [5] T. Watanabe, Journal of Phys. Soc. Japan 17 (1962) 1856. [6] N.F. de Oliveira Jr. - Estudo das propriedades magn&icas de u m ]'on de nlquel sujeiro a um campo cristalino oct,'iedrico, tese de D o u t o r a m e n t o (1966 ).
PHYSICS LETTERS
7 May 1973
E P R M E A S U R E M E N T S ON S I N G L E C R Y S T A L S O F
-NiSO 4 • 6 H 2 0
W.M. PONTUSCHKA, A. PICCINI, C.J.A. QUADROS and S. ISOTANI Instituto de Ffsica da Universidade de S~o Paulo,* Departamento de Fisica dos Materials e Mec3nica, S. Paulo, S.P., Brasil, C.P. 20516 Received 12 March 1973 EPR measurements on sinlge crystals of a - NiSO4 • 6 H 2 0 were carried out at room temperature. From the results were deduced the spin Hamiltonian parameters D = 4.85 ± 0.09 cm -1 and E = 0.06 ± 0.01 cm -1 and the direction cosines of the crystalline field.
The EPR measurements on single crystals of aNiSO4 • 6H20 were carried out at room temperature using a homodyne spectrometer, of the reflection type, which operates in the X band with a frequency near 9 GHz/s. We observed one line whose width ranged from 1 to 2 kG and whose position was between 9.4 and 14 kG. From our results it was possible to calculate the spin Hamiltonian parameters, D = 4.85 + 0.09 cm -1 andE = 0.06 + 0.01 cm -1, assumingg = 2.25 [1 ]. Furthermore, it was possible to evaluate the directions of the crystalline field coordinates of the i-th Ni++ion (i = 1, 2, 3, 4) of the unitary cell in terms of direction cosines with respect to the crystallographic axes (a, b, c), where c is parallel to the tetragonal axis: X1234 - (~
x/2/2; ~ x/~-/2;
0
)
Y1234=(~ 0.534; +--
- 0.656)
21234 - - ( ~ 0.464; + 0 . 4 6 4 ;
~ 0.755)
The orientations assumed to carry out the measurements done in this paper are based on the structure of a - NiSO 4 • 6H20 determined by Bevers and Lipson [2]. The crystals were grown by evaporation in neutral saturated solution at 35°C. We observed the variation in the position of the line as a function of the orientation of the crystal, rotating about the principal axes. In the figure are plotted the * Supported by BNDE, CNPq and FAPESP, (Brasil).
H (kG) -x l XXX
THEORETICAL EXPERIMENTAL
X
5:
. . . . . . k. . . . . . . . . HIIx
0 Hlly
50
HIIx (degrees)
Fig. 1. Comparison of experimental and theoretical positions of the EPR line observed in single crystals of c~ - NiSO4 • 6 H 2 0 as a function of the angle of rotation about the Z axis.
positions of the EPR line observed during the rotation of the crystal about the Z-axis of the crystalline field. The results are in good agreement with theoretical calculations using our parameters. At lower temperatures, down to -180°C, there appears a structure consisting of 2 to 4 lines superposed on the EPR line observed. The calculations using the spin Hamiltonian parameters obtained by us, were verified by comparison with the results of an EPR measurement of ct -NiSO 4 • 6H20 reported by Hou and Bloembergen [3]. They used a spectrometer operating in 30 GHz/s, at 77°K, with the applied field parallel to the crystallographic c axis, and obtained a EPR line at 6.5 +- 0.4 kG. Our prevision under these conditions is 6.4 kG. On the other hand our values for the spin Hamiltonian parameters can be compared with some results of spin Hamiltonian parameters of ¢~- NiSO4 • 6H20 determined by means of other methods. So, we can mention the following results: 57
PHYSICS LETTERS
V o l u m e 44A, n u m b e r 1
7 May 1973
R.A. Fisher and E.W. Hornung
[1]
D = 4 . 7 4 l -+ 0.001 cm l k," =0.01 ±0.06 cm 1
(specific heat)
7 ' < 4.2~K
J.W. Stout and W.B. Hardley
[4]
D=4.76 E =0.28
-+0.07 -+0.07
cm - l cm 1
(specific heat)
r "< 20°K
T. Watanabe
[5]
D = 4.5
± 0.3
cm -1
(magnetic susceptibility)
l,g 20 K
± (1.3
cm
(magnetic susceptibility)
l < 4.2" K
t:'~0
N.F. de Oliveira
[6]
D = 4.0
t
k :~ ()
W e are i n d e p t e d t o Mr. K . W a t a r i f o r e l a b o r a t i o n o f a c o m p u t e r p r o g r a m u s e d in t h i s w o r k .
References
[ t ] R.A. Fisher and E.W. Hornung, Journal of Chem. Phys. 48 (1968) 4284.
58
[2] C.A. Beevers and H. Lipson, Z. Krist 83 (1932) 123. [3] S.L. Hou and N. Bloembergen, Phys. Rev. 138 ( 1965 ) A1218. [4] J.W. Stout and W.B. Hadley, Journal of Chem. Phys. 4iJ (1964) 55. [5] T. Watanabe, Journal of Phys. Soc. Japan 17 (1962) 1856. [6] N.F. de Oliveira Jr. - Estudo das propriedades magn&icas de u m ]'on de nlquel sujeiro a um campo cristalino oct,'iedrico, tese de D o u t o r a m e n t o (1966 ).