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Nuclear magnetic resonance studies of 161Dy and 163Dy in dysprosium iron garnet
Volume 35A, number 1
PHYSICS
s t r a y light and the 0.1 volt of p l a s m a light a r e negligible c o m p a r e d with the s c a t t e r i n g signal of about 1 volt. At 7° the s t r a y light of 1 volt is l a r g e r but s t i l l much l e s s than the 10 volt of the s c a t t e r i n g signal. In d i s c h a r g e A (1.7 × 109 n e u trons) at time t = 0, 7o and 90 ° s c a t t e r i n g s i g n a l s a r e s i m u l t a n e o u s l y detected. In d i s c h a r g e B (1.3 × 109 n e u t r o n s ) at t = 40 nsec 7° s c a t t e r i n g only is observed. Difficulties were e n c o u n t e r e d with hard X r a y s produced d u r i n g the p l a s m a collapse. It was n e c e s s a r y to shield p h o t o m u l t i p l i e r s with lead v e r y carefully. Also in many d i s c h a r g e s no 7° s c a t t e r i n g can be recorded. This s e e m s to be m o r e f r e q u e n t when the l a s e r is t r i g g e r e d late in the n e u t r o n pulse. It might be due to the f o r m a t i o n of the p l a s m a f i l a m e n t outside the obs e r v e d volume. To a s c e r t a i n that the 7° s i g n a l s were not caused by incident l a s e r light deflected by r a d i a l d e n s i t y g r a d i e n t s [4] we checked the wavelength b r o a d e n i n g of the signal. This has b e e n done with a F a b r y - P ~ r o t i n t e r f e r o m e t e r of 8 A f r e e s p e c t r a l r a n g e and c e n t r a l wavelength a d j u s t a b l e by
LE TTE
RS
3 May 1971
p r e s s u r e v a r i a t i o n . The 8 A r a n g e is analysed by 12oPhOtomultipliers [5] e v e r y o n e c o v e r i n g 0.65 A. The i n s t r u m e n t a l width of the F a b r y P 4 r o t is 1 A. Thus the 0.3.~ wide l a s e r s p e c t r u m extends over t h r e e channels. The 7° s i g n a l s c o v e r i n g m o r e than 7 channels s c a t t e r i n g has b e e n c l e a r l y observed. F r o m a very roufih e v a luation the half-width a p p e a r s to be 2.5 A and m o r e in different d i s c h a r g e s . The next step u n d e r way is a c a r e f u l c a l i b r a tion of the different c h a n n e l s so that the s p e c t r u m p r o f i l e s can be m e a s u r e d and the ion t e m p e r a t u r e deduced.
References [1] J. P. Baoonnet, G. Cesari, A. Coudeville and 5. P. Watteau, Phys. Letters 29A (1969) 19. [2] J. P. Baeonnet, G. Cesari, A. Coudeville and J.. P. Watteau, Ninth Intern. Conf. on Phenomena in ionized gases Bucharest (Rumania, 1969) p. 643. [3] E. E. Salpeter, Physical Review 120 (1960) 1528. [4] J. P. Baconnet, G. Cesari, A. Coudeville and J. P. Watteau, Onde Electrique 51, fasc. i (1971). [5] J. G. Hirschberg, C. Breton and R. Chabbal, 3rd Symposium on Engineering problems Munich (1964).
* ***
NUCLEAR MAGNETIC RESONANCE STUDIES OF 161Dy AND 163Dy IN DYSPROSIUM IRON GARNET R. L. S T R E E V E R and P. J. C A P L A N Institute~or Exploratory Research, US Army Electronics Command, Fort Monmouth, New Jersey, USA
Received 26March 1971
161Dy and 163Dy NMR have been studied at 4.2°K in polycrystalline DyIG powder with zero applied dc magnetic fields using the spin-echo technique.
NMR studies of rare earth nuclei in the rare earth iron garnets are of interest because they provide detailed information concerning the electric and magnetic hyperfine interactions at the rare earth sites. In the present note we report on NMR studies of 161Dy and 163Dy in DyIG. The spectrum obtained in the range between 400 MHz and 1400 MHz by plotting spin-echo amplitudes as a function of frequency is shown in fig. 1. Since the signals were observed at high rf power levels, they must arise from nuclei in domains, the situation being similar to that in E r I a [1].
F r o m MSssbauer studies of 160Dy Cohen [2] h a s obtained hyperfine fields and quadrupole i n t e r a c t i o n s for the two types of s i t e s , A and B, which a r i s e when the Fe m a g n e t i z a t i o n is a l o n g the easy, 111, d i r e c t i o n . Since both 161Dy and 163Dy have s p i n s }, we expect the NMR of e a c h isotope to exhibit two q u a d r u p o l e - s p l i t 5 - l i n e p a t t e r n s . The i n t e r p r e t a t i o n of fig. 1 is f u r t h e r aided by the fact that the m o m e n t r a t i o s ( 1 6 3 ~ / I 6 1 ~ ) = 1.4 + 1 ~ and ( 1 6 3 Q / 1 6 1 Q ) = 1.06 ± 1% a r e known [3]. L i n e s a r i s i n g f r o m s i t e s A and B a r e i n d i c a t e d in fig. 1 where the u n p r i m e d l i n e s a r i s e f r o m
Volume 35A, number 1
z
PHYSICS LETTERS
'~,B'
B
LU n-
400
lJ
B'
3 May 1971
B' B'
am
500
600
Jk 700
800
9CX
FREQUENCY
1000
I I O0
1200
1.300
1400
MHz
Fig. 1. NMR spectrum of DyIG. Unprimed lines arise from 161Dy and primed lines from 163Dy (see text). 161Dy and the p r i m e d l i n e s f r o m 163Dy. In addition to the o b s e r v e d l i n e s we expect l i n e s at about 158 MHz, 370 MHz and 1700 MHz. The line at 158 MHz would probably be too weak to o b s e r v e , the line at 370 MHz was not o b s e r v e d p r o b a b l y due to r e d u c e d r e c e i v e r s e n s i t i v i t y b e low 400 MHz, while the line at 1700 MHz is beyond the p r e s e n t r a n g e of our equipment. F r o m the c e n t e r s of t ~ e l f i v e - l i n e p a t t e r n s (at 758 and 648 MHz for IbIDy and at 1060 and 906 MHz for 163Dy) we can deduce the hyperfine fields at sites A and B to be about 5.45 and 4.66 × 106 Oe (taking for ~ of 161Dy a value of 0.455 nm [4]). These values are in good agreement with values of about 5.4 + 0.3 and 4.4 ± 0.3 x 106 Oe obtained from the 160Dy studies [2] at 20OK (taking the magnetic moment of the 2+ state of 160Dy to be 0.74 nm). If one assumes an approximate proportionality between hyperfine fields and ionic moments, as has been done by Cohen, these fields would correspond to moments at the A and B sites of about 8.4 ~B and 7.2 ~B, in good agreement with recent neutron diffraction studies [5]. Adjacent lines of the 5-line patterns will be split by an amount A = (~0)[ (e2 Qq/h)]. We find *****
A to be about 303 MHz and 139 MHz for the A and B s i t e s of the 161 isotope with c o r r e s p o n d i n g v a l u e s about 7% higher for the 163 isotope. These v a l u e s c o m p a r e with values of 300 ± 75 MHz and 37 + 37 MHz that one would calculate f r o m the 160Dy studies taking for Q of 161Dy a value of 2.6 + 0.3 b [6] and for Q of the 2+ state of 160Dy a value of about - 2.0 b [2]. The d i s a g r e e m e n t for site B may be due in p a r t to the different t e m p e r a t u r e s at which the two studies were c a r r i e d out. Any detailed a n a l y s i s of the q n a d r u pole i n t e r a c t i o n data would r e q u i r e c o n s i d e r i n g c o n t r i b u t i o n s to the field g r a d i e n t s f r o m both the r a r e e a r t h ion and the e x t e r n a l c h a r g e s .
References [1] R. L. Streever and P.J. Caplan, Phys. Letters 33A (1970) 413. [2] R.L.Cohen, Phys. Rev. 137A (1965) 1809. [3] S.Kobayashi, N.Sano and J.Itoh, J. Phys. Soc. Japan 21 (1966) 1456. [4] G.J. Bowden, D. St. P. Bunburyand J. M.Williams, Proc. Phys. Soc. (London) 91 (1967) 612. [5] F. Tcheou, E.F. Bertaut and H. Fuess, Solid State Commun. 8 (1970) 1751. [6] S.Ofer, M.Rakavy, E. Segal and B.Khurgin, Phys. Rev. 138A (1965) 241.
PHYSICS
s t r a y light and the 0.1 volt of p l a s m a light a r e negligible c o m p a r e d with the s c a t t e r i n g signal of about 1 volt. At 7° the s t r a y light of 1 volt is l a r g e r but s t i l l much l e s s than the 10 volt of the s c a t t e r i n g signal. In d i s c h a r g e A (1.7 × 109 n e u trons) at time t = 0, 7o and 90 ° s c a t t e r i n g s i g n a l s a r e s i m u l t a n e o u s l y detected. In d i s c h a r g e B (1.3 × 109 n e u t r o n s ) at t = 40 nsec 7° s c a t t e r i n g only is observed. Difficulties were e n c o u n t e r e d with hard X r a y s produced d u r i n g the p l a s m a collapse. It was n e c e s s a r y to shield p h o t o m u l t i p l i e r s with lead v e r y carefully. Also in many d i s c h a r g e s no 7° s c a t t e r i n g can be recorded. This s e e m s to be m o r e f r e q u e n t when the l a s e r is t r i g g e r e d late in the n e u t r o n pulse. It might be due to the f o r m a t i o n of the p l a s m a f i l a m e n t outside the obs e r v e d volume. To a s c e r t a i n that the 7° s i g n a l s were not caused by incident l a s e r light deflected by r a d i a l d e n s i t y g r a d i e n t s [4] we checked the wavelength b r o a d e n i n g of the signal. This has b e e n done with a F a b r y - P ~ r o t i n t e r f e r o m e t e r of 8 A f r e e s p e c t r a l r a n g e and c e n t r a l wavelength a d j u s t a b l e by
LE TTE
RS
3 May 1971
p r e s s u r e v a r i a t i o n . The 8 A r a n g e is analysed by 12oPhOtomultipliers [5] e v e r y o n e c o v e r i n g 0.65 A. The i n s t r u m e n t a l width of the F a b r y P 4 r o t is 1 A. Thus the 0.3.~ wide l a s e r s p e c t r u m extends over t h r e e channels. The 7° s i g n a l s c o v e r i n g m o r e than 7 channels s c a t t e r i n g has b e e n c l e a r l y observed. F r o m a very roufih e v a luation the half-width a p p e a r s to be 2.5 A and m o r e in different d i s c h a r g e s . The next step u n d e r way is a c a r e f u l c a l i b r a tion of the different c h a n n e l s so that the s p e c t r u m p r o f i l e s can be m e a s u r e d and the ion t e m p e r a t u r e deduced.
References [1] J. P. Baoonnet, G. Cesari, A. Coudeville and 5. P. Watteau, Phys. Letters 29A (1969) 19. [2] J. P. Baeonnet, G. Cesari, A. Coudeville and J.. P. Watteau, Ninth Intern. Conf. on Phenomena in ionized gases Bucharest (Rumania, 1969) p. 643. [3] E. E. Salpeter, Physical Review 120 (1960) 1528. [4] J. P. Baconnet, G. Cesari, A. Coudeville and J. P. Watteau, Onde Electrique 51, fasc. i (1971). [5] J. G. Hirschberg, C. Breton and R. Chabbal, 3rd Symposium on Engineering problems Munich (1964).
* ***
NUCLEAR MAGNETIC RESONANCE STUDIES OF 161Dy AND 163Dy IN DYSPROSIUM IRON GARNET R. L. S T R E E V E R and P. J. C A P L A N Institute~or Exploratory Research, US Army Electronics Command, Fort Monmouth, New Jersey, USA
Received 26March 1971
161Dy and 163Dy NMR have been studied at 4.2°K in polycrystalline DyIG powder with zero applied dc magnetic fields using the spin-echo technique.
NMR studies of rare earth nuclei in the rare earth iron garnets are of interest because they provide detailed information concerning the electric and magnetic hyperfine interactions at the rare earth sites. In the present note we report on NMR studies of 161Dy and 163Dy in DyIG. The spectrum obtained in the range between 400 MHz and 1400 MHz by plotting spin-echo amplitudes as a function of frequency is shown in fig. 1. Since the signals were observed at high rf power levels, they must arise from nuclei in domains, the situation being similar to that in E r I a [1].
F r o m MSssbauer studies of 160Dy Cohen [2] h a s obtained hyperfine fields and quadrupole i n t e r a c t i o n s for the two types of s i t e s , A and B, which a r i s e when the Fe m a g n e t i z a t i o n is a l o n g the easy, 111, d i r e c t i o n . Since both 161Dy and 163Dy have s p i n s }, we expect the NMR of e a c h isotope to exhibit two q u a d r u p o l e - s p l i t 5 - l i n e p a t t e r n s . The i n t e r p r e t a t i o n of fig. 1 is f u r t h e r aided by the fact that the m o m e n t r a t i o s ( 1 6 3 ~ / I 6 1 ~ ) = 1.4 + 1 ~ and ( 1 6 3 Q / 1 6 1 Q ) = 1.06 ± 1% a r e known [3]. L i n e s a r i s i n g f r o m s i t e s A and B a r e i n d i c a t e d in fig. 1 where the u n p r i m e d l i n e s a r i s e f r o m
Volume 35A, number 1
z
PHYSICS LETTERS
'~,B'
B
LU n-
400
lJ
B'
3 May 1971
B' B'
am
500
600
Jk 700
800
9CX
FREQUENCY
1000
I I O0
1200
1.300
1400
MHz
Fig. 1. NMR spectrum of DyIG. Unprimed lines arise from 161Dy and primed lines from 163Dy (see text). 161Dy and the p r i m e d l i n e s f r o m 163Dy. In addition to the o b s e r v e d l i n e s we expect l i n e s at about 158 MHz, 370 MHz and 1700 MHz. The line at 158 MHz would probably be too weak to o b s e r v e , the line at 370 MHz was not o b s e r v e d p r o b a b l y due to r e d u c e d r e c e i v e r s e n s i t i v i t y b e low 400 MHz, while the line at 1700 MHz is beyond the p r e s e n t r a n g e of our equipment. F r o m the c e n t e r s of t ~ e l f i v e - l i n e p a t t e r n s (at 758 and 648 MHz for IbIDy and at 1060 and 906 MHz for 163Dy) we can deduce the hyperfine fields at sites A and B to be about 5.45 and 4.66 × 106 Oe (taking for ~ of 161Dy a value of 0.455 nm [4]). These values are in good agreement with values of about 5.4 + 0.3 and 4.4 ± 0.3 x 106 Oe obtained from the 160Dy studies [2] at 20OK (taking the magnetic moment of the 2+ state of 160Dy to be 0.74 nm). If one assumes an approximate proportionality between hyperfine fields and ionic moments, as has been done by Cohen, these fields would correspond to moments at the A and B sites of about 8.4 ~B and 7.2 ~B, in good agreement with recent neutron diffraction studies [5]. Adjacent lines of the 5-line patterns will be split by an amount A = (~0)[ (e2 Qq/h)]. We find *****
A to be about 303 MHz and 139 MHz for the A and B s i t e s of the 161 isotope with c o r r e s p o n d i n g v a l u e s about 7% higher for the 163 isotope. These v a l u e s c o m p a r e with values of 300 ± 75 MHz and 37 + 37 MHz that one would calculate f r o m the 160Dy studies taking for Q of 161Dy a value of 2.6 + 0.3 b [6] and for Q of the 2+ state of 160Dy a value of about - 2.0 b [2]. The d i s a g r e e m e n t for site B may be due in p a r t to the different t e m p e r a t u r e s at which the two studies were c a r r i e d out. Any detailed a n a l y s i s of the q n a d r u pole i n t e r a c t i o n data would r e q u i r e c o n s i d e r i n g c o n t r i b u t i o n s to the field g r a d i e n t s f r o m both the r a r e e a r t h ion and the e x t e r n a l c h a r g e s .
References [1] R. L. Streever and P.J. Caplan, Phys. Letters 33A (1970) 413. [2] R.L.Cohen, Phys. Rev. 137A (1965) 1809. [3] S.Kobayashi, N.Sano and J.Itoh, J. Phys. Soc. Japan 21 (1966) 1456. [4] G.J. Bowden, D. St. P. Bunburyand J. M.Williams, Proc. Phys. Soc. (London) 91 (1967) 612. [5] F. Tcheou, E.F. Bertaut and H. Fuess, Solid State Commun. 8 (1970) 1751. [6] S.Ofer, M.Rakavy, E. Segal and B.Khurgin, Phys. Rev. 138A (1965) 241.