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Paramagnetic dispersion at radiofrequencies in a few gadolinium salts
Physica
X, no 8
October
1943
PARAMAGNETIC DISPERSION AT RADIOFREQUENCIES IN A FEW GADOLINIUM SALTS by L. J. F. B R O E R and C. J. G O R T E R Communication from the Zeeman-laboratorium of the University of Amsterdam
Summary
Paramagnetic dispersion of the hydrated sulphate, oxalate and acetate of gadolinium was studied between liquid air temperatures and room temperature. A negative result was obtained on gadolinium oxide and on hydrated dysprosiuha sulphate.
§ 1. Introduction. The phenomenon of paramagnetic dispersion at the temperatures of liquid air has up till now exclusively been studied in salts belonging to the iron-group. It was found that paramagnetic dispersion at relatively low fields and frequencies could only be observed in compounds to which C u r i e's law applies very well 1). This can be understood from C a s i m i r and D u P r C s theory 2) as in those compounds the specific heat of the spin system (b/T 2) is small. As, apart from the gadolinium ion, which has a basic S-state, the rare earth ions in crystals are subject to large internal S t a r k-effects 3), it had to be expected that among the rare earth ions merely the gadolinium ion gives rise to paramagnetic dispersion in relatively low fields. I n f a c t D e H a a s and D u P r ~ * ) s u c ceeded in observing paramagnetic dispersion in gadolinium sulphate octahydrate at liquid helium temperatures in frequencies of about 102. In the present research we performed experiments on hydrated dysprosium sulphate, gadolinium oxide, hydrated gadolinium oxalate, hydrated gadolinium sulphate and hydrated gadolinium acetate. § 2. Experiments and results. The salts were prepared from oxides obtained front Dr. W. F r a n k e, Frankfurt a. Main. The gadolinium oxide was indicated to be 99% pure and to contain less than 1% Sm; the dysprosium oxide contained some Ho and Tb. - -
621
- -
622
L.J.F. B R O E R A N D C. J. G O R T E R
The method of the measurements will be described in detail in another paper 9). The result on the dysprosium salt and the gadolinium oxide and also on the oxalate at 290°K were negative. t.00
0.t
0.2
0.5
t.0
2.0
~Ox
~6
Fig. 1. Paramagnetic dispersion in hydrated gadolinium sulphate at 77.4°K.
~/X'o "I,00
o.8o 0.61
\
OA4
7"--9oOK 0.20
x H= 3200 ® H=2400
o H= 1600 • H= 8 0 0
0
I
0."/
0.2
0.5
1.0
2.0
5..Ox t06"-~---~
Fig, 2. Paramagnetic dispersion in hydrated gadolinium sulphate at 90.2°K.
The positive results are given in the figures 1, .., 10, where the high frequency susceptibility divided by the static susceptibility in
PARAMAGNETIC DISPERSION'AT RADIOFREQUENCIES
623
different parallel fields//c is given as a funct*ion of the f r e q u e n c y v. The curves are drawn according to C a s i m i r and D u P r ~ ' s formulae: X' --
XoF
1 + p ~ + z o (1 - - F )
(1)
CH 2 F
--
b +
(2)
CH 2 '
t.00
080
060
0.40 "T=290OK x H = 3200 0.20 -- ® H , , 2 4 0 0 -
o H= f600 • H', 800 0.2
0.5
t.0
20
5.0
fO.OX 106 V
Fig. 3..Paramagnetic dispersion in hydrated gadolinium sulphate at 290°K.
tOO
0.20 _
®
H=2(O0
o H = ~1600 ,0
• N=
--
.x.~,~
_x_ x-
800
o.~ o.'2 o.s ~.o 2.0 s:o x ,--~--or-y Fig. 4. Paramagnetic dispersion irJ hydrated gadotinium oxalate at 77.4°K.
624
L . J . F . BROER AND C. J. GORTER
t.00
w
060
0.40
"0-.-.--
O--
•-o...-_____L
x H = 3200 0.2~ - ® H = 2 4 0 0 o H=1600 • H= 800 0 t 0.t 0.2
0.5
t.0
2.0
5..OX 106
Fig. 5. Paramagnetic dispersion in hydrated gadolinium oxalate at 90.2°K.
1.00 I I I I
O.8O
0.60 0.4O
I T=
~95° K x H=3200 e H= 2400 "
0.20
o H= ¢600
0
•
a2
H = 800
0.5
¢.0
2.0
5.0x 106 V
Fig. 6. Paramagnetic dispersion in hydrated gadolinium oxalate at 195°K.
T h e values of p a n d of F m a y be f o u n d in the T a b l e s I, I I a n d I I I . The b/c-values are 3.9 × 106, 1.8 × l06 a n d 8.7 × 106 (oerstedt) 2 for Gd2(S04) 3 . 8H20, Gd2(C204)3.10H20 and Gd(C2H302) a . 4 H 2 0 respectively.
625
PARAMAGNETIC DISPERSION AT RADIOFREQUENCIES
~.00
0.80
0.60 X'
0.40 T= 770 K × H=3200 ® H = 2400 o H= 1600
0.20
0.2
0.5
"1.0
20
5.0
1oo Io V
Fig. 7. P a r a m a g n e t i c dispersion in h y d r a t e d gadolinium acetate at 77.4°K.
"1.00
0.80
o-.
0.60
040
T=9OOK x H=3200 ® H=2400 o H"-f600
0.26 0
0.2
0.5
1.0
2.0
5.0
10.0 x 106 Y
Fig. 8. P a r a m a g n e t i c dispersion in h y d r a t e d gadolinium acetate at 90.2°K.
§ 3. Discussion. It was in agreement with our expectation that no dispersion could be observed in the dysprosium salt. Though the deviations from C u r i e's law are rather small in this salt, the splitting by internal electric fields of the basic 6H1s/2-1evel certainly gives rise to a b/C-value which is much larger than the values of H~2 we Physica X
40
626
L.J.F. B R O E R A N D C. J. G O R T E R
1.00
0.00 •
O - -
•
0.60
0.40 0.20_
0
T= 195°K x H=3200 ® H=2400 o H=1600 I t.0 2.0
. 5,0 X "!06
Fig. 9. Paramagnetic dispersion in hydrated gadolinium acetate at 195°K.
/X'o ~.00 086
0.66
0.40 T= 2 9 0 ° K x H = 3200 ® H=2400 o H= f600
0 2.0 5.0 10.0 x 106 ~-Fig. 10. Paramagnetic dispersion in hydrated gadolinium acetate at 290°K.
h a d at o u r disposal. Also in Gd:Oa the strong interaction b e t w e e n the rare e a r t h ions will give rise to a high b/C-value. I n b o t h cases however we c a n n o t exclude t h a t also a low value of p has to be b l a m e d for the n e g a t i v e result. I n general the results c o n s t i t u t e a c o n f i r m a t i o n of C a s i m i r
PARAMAGNETIC
DISPERSION
627
AT RADIOFREQUENCIES
and D u P r ~'s formulae, t h o u g h at the higher t e m p e r a t u r e s these formulae are r a t h e r accepted t h a n tested. TABLE
Hc
10 e p 77.4 ° K
800 1600 2400 3200
I
l0 s p 90.2 ° K
10 a p 290 ° K
1.7 s
2.1
0.50
0.136
2.1 2.5 2.8
2.5 2.8 s 3.15
0.55 0.69 0.79
0.40 0.59 s 0.73
F
F - a n d p - v a l u e s of Gd~ ( S O 4 ) s . 8 H = O
TABLE
He
II
10 e p 77.4 ° K
10 6 p 90.2 ° K
10 6 p 195 ° K
1.7 s 2.0 2.7 2.9 s
1.8 2.0 2.7 2.9 s
0.31 0.45 0.69 0.85
800 1600 ' 2400 3200
F
0.25 0.59 0.76 ~ 0.85
F - a n d p - v a l u e s o f G d 2 (C,O6)a • 10 H 2 0
TABLE
He 1600 2400 3200
III
10 6 p
10 e O
10' p
10 e p
77.4 ° K
90.2 ° K
195" K
290 ° K
0.67 0.71 0.77
0.41 0.46 0.53
0.27 0.28 0.29
0.11 0.12 0.14 s
F - a n d p - v a l u e s of G d ( C : H 3 0 , h
F 0.23 0.40 0.54
• 4 H20
The b/C-value found for gadolinium sulphate (3.9 x 106) is in r a t h e r good agreement with the values derived b y D e H a a s and D u P r ~ 4) from their dispersion measurements (3.0 x 106). The agreement with the results of the direct determinations of the specific heat (b/T2) is even considerably better. G i a u q u e and M a c D o u g a 1 l's measurements s) lead to b/C = 3.8 x 106 and V a n D i j k and A u e r ' s m e a s u r e m e n t s T ) t o b / C - ~ 3 . 7 x 106. The b/C-values do not show inverse parallelism with the molecular volumes, which are about 125,140 and 200 per ion for the sulphate, the oxalate and the acetate respectively. This suggests t h a t the specific heat of the spinsystem is not due to interaction between
628
PARAMAGNETIC D I S P E R S I O N AT R A D I O F R E Q U E N C I E S
the gadolinium ions, but to interaction of those ions with their diamagnetic surroundings. The results on the p-values are rather complex. In previous researches on salts of the iron-group i) it was found that for the same ion the 0-values are generally smaller when the b/C-values are larger. This would lead us to expect that Pacaau < P~,zpha~ < ?o~al~u,but a comparison of Table I and II shows that while the ?-values at liquid air temperatures are about the same in the sulphate and in the oxalate, at room temperature ?o~t~t,is at least 20 times smaller than p , , ~ u - In fact the dependence on temperature of the 0-value of the gadolinium oxalate as well as of the sulphate is very anomalous. While in the acetate the variation of lies between T -1 and T -2 (like in the case of the Mn-salts 1)) in the oxalate p is practically independent Of T at liquid air temperatures and varies at least as T -8 between solid carbon dioxide temperatures and room temperature. .In the sulphate Ovaries rather slowly between 90°K and 290°K, but has an inverse dependence on T between 77 ° and 90°K. This again demonstrates that the present theory describing the lattice vibration with the aid of one single D e b ij e-temperature s) which leads to an expected variation with T between T -7 and T -2 is much to simple to account for the dependence of p on T in the different compounds. We are indebted to Mr. J. L. V e r s t e r, phys. cand., for his assistance in some of the measurements. Received July 3rd, 1943.
REFERENCES 1) P. T e u n i s s e n , a n d C . J. G o r t e r , Physica, 7, 33, 1940. P. T e u n i s s e n , Thesis, Groningen 1939. 2) H . B . G . C a s i m i r a n d F . K. D u P r ~ , Physica, 5,507, 1938. 3) W.G. P e n n e y and R. S c h l a p p , Phys. Rev., 40, 637, 1932. 4) W . J . d e H a a s and F. K. D u P r ~ , Physica, 6,705, 1939. 5) D.C. S c h e r i n g and L . J . F . B r o e r . . 6) W . F . G i a u q u e a n d D . P. M a c D o u g a l l , J. Am. chem. Soc.,57, 1175, 1935. M . H . H e b b and E. M. P u r c e l 1, J. chem. Phys., 5, 338, 1937. 7) H. v a n D i j k and W. U. A u e r , Physica, 9, 785, 1942. 8) R. K r o n i g , Phy3ica, 6,33, 1939.
X, no 8
October
1943
PARAMAGNETIC DISPERSION AT RADIOFREQUENCIES IN A FEW GADOLINIUM SALTS by L. J. F. B R O E R and C. J. G O R T E R Communication from the Zeeman-laboratorium of the University of Amsterdam
Summary
Paramagnetic dispersion of the hydrated sulphate, oxalate and acetate of gadolinium was studied between liquid air temperatures and room temperature. A negative result was obtained on gadolinium oxide and on hydrated dysprosiuha sulphate.
§ 1. Introduction. The phenomenon of paramagnetic dispersion at the temperatures of liquid air has up till now exclusively been studied in salts belonging to the iron-group. It was found that paramagnetic dispersion at relatively low fields and frequencies could only be observed in compounds to which C u r i e's law applies very well 1). This can be understood from C a s i m i r and D u P r C s theory 2) as in those compounds the specific heat of the spin system (b/T 2) is small. As, apart from the gadolinium ion, which has a basic S-state, the rare earth ions in crystals are subject to large internal S t a r k-effects 3), it had to be expected that among the rare earth ions merely the gadolinium ion gives rise to paramagnetic dispersion in relatively low fields. I n f a c t D e H a a s and D u P r ~ * ) s u c ceeded in observing paramagnetic dispersion in gadolinium sulphate octahydrate at liquid helium temperatures in frequencies of about 102. In the present research we performed experiments on hydrated dysprosium sulphate, gadolinium oxide, hydrated gadolinium oxalate, hydrated gadolinium sulphate and hydrated gadolinium acetate. § 2. Experiments and results. The salts were prepared from oxides obtained front Dr. W. F r a n k e, Frankfurt a. Main. The gadolinium oxide was indicated to be 99% pure and to contain less than 1% Sm; the dysprosium oxide contained some Ho and Tb. - -
621
- -
622
L.J.F. B R O E R A N D C. J. G O R T E R
The method of the measurements will be described in detail in another paper 9). The result on the dysprosium salt and the gadolinium oxide and also on the oxalate at 290°K were negative. t.00
0.t
0.2
0.5
t.0
2.0
~Ox
~6
Fig. 1. Paramagnetic dispersion in hydrated gadolinium sulphate at 77.4°K.
~/X'o "I,00
o.8o 0.61
\
OA4
7"--9oOK 0.20
x H= 3200 ® H=2400
o H= 1600 • H= 8 0 0
0
I
0."/
0.2
0.5
1.0
2.0
5..Ox t06"-~---~
Fig, 2. Paramagnetic dispersion in hydrated gadolinium sulphate at 90.2°K.
The positive results are given in the figures 1, .., 10, where the high frequency susceptibility divided by the static susceptibility in
PARAMAGNETIC DISPERSION'AT RADIOFREQUENCIES
623
different parallel fields//c is given as a funct*ion of the f r e q u e n c y v. The curves are drawn according to C a s i m i r and D u P r ~ ' s formulae: X' --
XoF
1 + p ~ + z o (1 - - F )
(1)
CH 2 F
--
b +
(2)
CH 2 '
t.00
080
060
0.40 "T=290OK x H = 3200 0.20 -- ® H , , 2 4 0 0 -
o H= f600 • H', 800 0.2
0.5
t.0
20
5.0
fO.OX 106 V
Fig. 3..Paramagnetic dispersion in hydrated gadolinium sulphate at 290°K.
tOO
0.20 _
®
H=2(O0
o H = ~1600 ,0
• N=
--
.x.~,~
_x_ x-
800
o.~ o.'2 o.s ~.o 2.0 s:o x ,--~--or-y Fig. 4. Paramagnetic dispersion irJ hydrated gadotinium oxalate at 77.4°K.
624
L . J . F . BROER AND C. J. GORTER
t.00
w
060
0.40
"0-.-.--
O--
•-o...-_____L
x H = 3200 0.2~ - ® H = 2 4 0 0 o H=1600 • H= 800 0 t 0.t 0.2
0.5
t.0
2.0
5..OX 106
Fig. 5. Paramagnetic dispersion in hydrated gadolinium oxalate at 90.2°K.
1.00 I I I I
O.8O
0.60 0.4O
I T=
~95° K x H=3200 e H= 2400 "
0.20
o H= ¢600
0
•
a2
H = 800
0.5
¢.0
2.0
5.0x 106 V
Fig. 6. Paramagnetic dispersion in hydrated gadolinium oxalate at 195°K.
T h e values of p a n d of F m a y be f o u n d in the T a b l e s I, I I a n d I I I . The b/c-values are 3.9 × 106, 1.8 × l06 a n d 8.7 × 106 (oerstedt) 2 for Gd2(S04) 3 . 8H20, Gd2(C204)3.10H20 and Gd(C2H302) a . 4 H 2 0 respectively.
625
PARAMAGNETIC DISPERSION AT RADIOFREQUENCIES
~.00
0.80
0.60 X'
0.40 T= 770 K × H=3200 ® H = 2400 o H= 1600
0.20
0.2
0.5
"1.0
20
5.0
1oo Io V
Fig. 7. P a r a m a g n e t i c dispersion in h y d r a t e d gadolinium acetate at 77.4°K.
"1.00
0.80
o-.
0.60
040
T=9OOK x H=3200 ® H=2400 o H"-f600
0.26 0
0.2
0.5
1.0
2.0
5.0
10.0 x 106 Y
Fig. 8. P a r a m a g n e t i c dispersion in h y d r a t e d gadolinium acetate at 90.2°K.
§ 3. Discussion. It was in agreement with our expectation that no dispersion could be observed in the dysprosium salt. Though the deviations from C u r i e's law are rather small in this salt, the splitting by internal electric fields of the basic 6H1s/2-1evel certainly gives rise to a b/C-value which is much larger than the values of H~2 we Physica X
40
626
L.J.F. B R O E R A N D C. J. G O R T E R
1.00
0.00 •
O - -
•
0.60
0.40 0.20_
0
T= 195°K x H=3200 ® H=2400 o H=1600 I t.0 2.0
. 5,0 X "!06
Fig. 9. Paramagnetic dispersion in hydrated gadolinium acetate at 195°K.
/X'o ~.00 086
0.66
0.40 T= 2 9 0 ° K x H = 3200 ® H=2400 o H= f600
0 2.0 5.0 10.0 x 106 ~-Fig. 10. Paramagnetic dispersion in hydrated gadolinium acetate at 290°K.
h a d at o u r disposal. Also in Gd:Oa the strong interaction b e t w e e n the rare e a r t h ions will give rise to a high b/C-value. I n b o t h cases however we c a n n o t exclude t h a t also a low value of p has to be b l a m e d for the n e g a t i v e result. I n general the results c o n s t i t u t e a c o n f i r m a t i o n of C a s i m i r
PARAMAGNETIC
DISPERSION
627
AT RADIOFREQUENCIES
and D u P r ~'s formulae, t h o u g h at the higher t e m p e r a t u r e s these formulae are r a t h e r accepted t h a n tested. TABLE
Hc
10 e p 77.4 ° K
800 1600 2400 3200
I
l0 s p 90.2 ° K
10 a p 290 ° K
1.7 s
2.1
0.50
0.136
2.1 2.5 2.8
2.5 2.8 s 3.15
0.55 0.69 0.79
0.40 0.59 s 0.73
F
F - a n d p - v a l u e s of Gd~ ( S O 4 ) s . 8 H = O
TABLE
He
II
10 e p 77.4 ° K
10 6 p 90.2 ° K
10 6 p 195 ° K
1.7 s 2.0 2.7 2.9 s
1.8 2.0 2.7 2.9 s
0.31 0.45 0.69 0.85
800 1600 ' 2400 3200
F
0.25 0.59 0.76 ~ 0.85
F - a n d p - v a l u e s o f G d 2 (C,O6)a • 10 H 2 0
TABLE
He 1600 2400 3200
III
10 6 p
10 e O
10' p
10 e p
77.4 ° K
90.2 ° K
195" K
290 ° K
0.67 0.71 0.77
0.41 0.46 0.53
0.27 0.28 0.29
0.11 0.12 0.14 s
F - a n d p - v a l u e s of G d ( C : H 3 0 , h
F 0.23 0.40 0.54
• 4 H20
The b/C-value found for gadolinium sulphate (3.9 x 106) is in r a t h e r good agreement with the values derived b y D e H a a s and D u P r ~ 4) from their dispersion measurements (3.0 x 106). The agreement with the results of the direct determinations of the specific heat (b/T2) is even considerably better. G i a u q u e and M a c D o u g a 1 l's measurements s) lead to b/C = 3.8 x 106 and V a n D i j k and A u e r ' s m e a s u r e m e n t s T ) t o b / C - ~ 3 . 7 x 106. The b/C-values do not show inverse parallelism with the molecular volumes, which are about 125,140 and 200 per ion for the sulphate, the oxalate and the acetate respectively. This suggests t h a t the specific heat of the spinsystem is not due to interaction between
628
PARAMAGNETIC D I S P E R S I O N AT R A D I O F R E Q U E N C I E S
the gadolinium ions, but to interaction of those ions with their diamagnetic surroundings. The results on the p-values are rather complex. In previous researches on salts of the iron-group i) it was found that for the same ion the 0-values are generally smaller when the b/C-values are larger. This would lead us to expect that Pacaau < P~,zpha~ < ?o~al~u,but a comparison of Table I and II shows that while the ?-values at liquid air temperatures are about the same in the sulphate and in the oxalate, at room temperature ?o~t~t,is at least 20 times smaller than p , , ~ u - In fact the dependence on temperature of the 0-value of the gadolinium oxalate as well as of the sulphate is very anomalous. While in the acetate the variation of lies between T -1 and T -2 (like in the case of the Mn-salts 1)) in the oxalate p is practically independent Of T at liquid air temperatures and varies at least as T -8 between solid carbon dioxide temperatures and room temperature. .In the sulphate Ovaries rather slowly between 90°K and 290°K, but has an inverse dependence on T between 77 ° and 90°K. This again demonstrates that the present theory describing the lattice vibration with the aid of one single D e b ij e-temperature s) which leads to an expected variation with T between T -7 and T -2 is much to simple to account for the dependence of p on T in the different compounds. We are indebted to Mr. J. L. V e r s t e r, phys. cand., for his assistance in some of the measurements. Received July 3rd, 1943.
REFERENCES 1) P. T e u n i s s e n , a n d C . J. G o r t e r , Physica, 7, 33, 1940. P. T e u n i s s e n , Thesis, Groningen 1939. 2) H . B . G . C a s i m i r a n d F . K. D u P r ~ , Physica, 5,507, 1938. 3) W.G. P e n n e y and R. S c h l a p p , Phys. Rev., 40, 637, 1932. 4) W . J . d e H a a s and F. K. D u P r ~ , Physica, 6,705, 1939. 5) D.C. S c h e r i n g and L . J . F . B r o e r . . 6) W . F . G i a u q u e a n d D . P. M a c D o u g a l l , J. Am. chem. Soc.,57, 1175, 1935. M . H . H e b b and E. M. P u r c e l 1, J. chem. Phys., 5, 338, 1937. 7) H. v a n D i j k and W. U. A u e r , Physica, 9, 785, 1942. 8) R. K r o n i g , Phy3ica, 6,33, 1939.