E P R S P E C T R U M O F G A D O L I N I U M I N H Y D R A T E D P R A S E O D Y M I U M N I T R A T E

BY G. B. SINGI-I AND PtrrcI-IA VENKATESWARLU, F.A.Sc. (Department of Physics, Indian Institute of Technology, Kanpur, India)

Rer December 9, 1966

ABSTRACT

The paramagnetie resonance speetrum of Gd s+ in Pr (NO0z.6H~O single crystals, is studied at room temperature. A seven line spectrum for H/[Z as well as for H/[X eorresponding to AM = +_ 1 transitions is observed along with a number of low field transitions (&M>/2). The spin-Hamiltonian analyses is presented.

INTRODUCTION

P~C~~,ITLY we have studied the paramagnetic resonance ~ of Gd a+ doped in SmCln.6H20 single erystals. Earlier Weger and Low 2 have reported the results on Gd s+ doped LaC13.TH~O and Johnston, Wong and Stafsudd s on Gd s+ doped Lao (SO4)a.9HzO single crystals. We felt that ir would be interesting to extend the study to some of the other hydrated salts. The present paper deals with the paramagnetic resonance of Gd 3+ doped Pr (NO3)8.6H~O single crystals.

THEORY

The resonance field equations for H/[Z corresponding to AM-----4-1 are given in the earlier paper z along with the transformations of bn m needed to get the resonance ¡ equations for H//X. By making use of the earlier literature~,~, 6 it can be shown that the resonance ¡ equations for H//Z corresponding to the observed low field transitions (AM >/2) are as follows:

1 5 -- ~ - * - - ~: g/3H

1[ { 60 ._99_0 _~}] =~ hv+6b~. ~ ~ I + F 1

3 3 ~ - " - 2: gBH

1 [ {1' 42 120 ~.] ----- ~ hv + E _ 25F~ 1 ~ - ~ } j ,

361

362 G. B. SINGH AND PUTCHA VENKATESWARLU

1 5 2 ---+-- ] : gflH

1 [h• + 6b2 ~ 22b,~ + E {1 270F = ~ -- 9F 2

1 7 2 ~ - - 2 : gflH

1 = -~ [ hv + 12b~ ~ -- 2b4 ~ + 6b8 ~

+ E 1 + F 1 - - 5 F 1 F '

60 }] 1 - - F '

where

5 3 ~--+--~: gfiH

-- 1 [hv -- 4b~. ~ + lOb4 ~ + 14b6 ~

+ E 1 - - 5 F 1 - - F 1 +3-F �9

�9 90 5 5 l [ h v E { 1 - - ~ = } ] , ~.-+ -- 2: g B H = 3

3 7 : g/3H ~ ~-->-- 2

1 [hv + lOb2 ~ + lOb4 ~ - - 8bn ~ = 5

210 F 60

7 7 l [ h v E { 1

b o (b2)~ F - - g ~ , E - - 1 8 g / 3 H .

EPR Spectrum of Gadolinium in Hydrated Praseodymium Nitrate 363

EXPERIMENTAL RESULTS AND DISCUSSIONS

The experimental procedure and method of growing Gd a+ doped Pr (NO3)~ .6HzO single crystals are the same as reported in the earlier paper. ~ Pr (NOz)a .6H20"is a triclini6 crystal for which n6 crystallographic structure seems to be available. The EPR of Gd 3+ doped in this crystal shows a seven line spectrum for H//Z as well as for H/ /X corresponding to the ~ M = 4- 1 transitions. The spectra obtained are given in Figs. 1 and 2, respectively.

~mr ~ n~/2 ~r191 l l 2 ~ | l g - f / l * - ~ [ 2 -;~ff2~ - .,~!2 - 5 t 2 ~ - 7 / 9

570.06 1560.6G 2468.1G ~575-?G 4504,2G 5289,�91 6400.5G

Fic. 1. EPR spectrum of Gd a+ in single crystals of Pr (NO3)3.6H~O at H[/Z direction.

1065"46 177"6"96 2.546-96 :53~4"5G 4165,9G

t t 505.9.9 6 6023"9G

FIG. 2. EPR spectrum of Gd 8+ in single crystals of Pr (NO~)a.6HzO at H//X direction.

The peak to peak derivative width of A M = + 1 transitions is about 14-17 gauss which is much less than that reported earlier in the case of Gd z+ doped SmCla.6H20 single crystals. Apart from the A M = 4-1 transitions a number of low field transitions are also observed in the present case. These varied in position and intensity as the magnetic field is rotated with respect to the Z-axis. A careful study of these fines is made for H//Z direction and the observed transitions are shown in Fig. 3 along with A M = 4- 1 transitions. The parameters of the spin-Hamiltonian have been obtained in the manner described in the earlier paper 1 and are given in Table I, where the para- meters obtained earlier 1 in the case of Gd 8+ doped SmC13.6H20 are also included for the sake of comparison. The absolute sign of b~. ~ could not be

364 G . B . SINGH AND PUTCHA VENKATESWARLU

determined in the prescnt exper iment since the measurements made here are at r o o m tempera ture . We assumed b ~ to be posit ive and found the relative

signs o f the different b parameters .

8 7 0 - 0 0

FIG. 3.

H

1 5 6 0 . 6 6 2",468-t G 3375-7~ 4 3 0 4 - 2 G 5 2 8 9 . 8 G 6 4 0 0 . 6 G

Low field transitions ( A M > 2) of Gd a+ in single crystals ofPr (NO,)a.6H=O along with seven A M --- 4- 1 transitions at HI/Z direction.

TAnI~ I

The spin-Hamiltonian parameters o f Gd 8+ doped Pr(NOz)a.6H~O and SrnCIs . 6H~O single crystals

Gd •+ doped Pr (NOa)a. 6HaO G d ~- doped SmCI3.6H~O

gJl . . . . 1"993+_'002 1-990+_ "002

g~ . . . . 1 "987 +_ "002 1 "990 +- "002

b, o . . . . 488.5 ((3) 667.7 ((3)

b~ ~ . . . . 1.6 - -12 .0

be ~ . . . . 0.11 - -0 .87

bz ~ . . . . . --377.5 - -426.3

b~ --b~ ~ . . 11.2 48.64

bee--b~+be 2 .. 5"83 --11-39

EP R Spectrum of Gadolinium in Hydrated Praseodymium Nitrate 365

The resonance fields corresponding to ZkM ----- zk 1 transifions for HI/Z, calculated using the parameters listed in Table I, are given in Table II along with the observed resonance fields for H/]Z in the case of Gd 8+ doped Pr(NOs)3.6H20 single crystals. The corresponding observed values for H]/X are also included in Table II. The relafive separafions between the four doublets pertaining to the zero-¡ energy levels, are calculated and are given in Table III along with the relative separations reported eaflier 1 in the case of Gd 3+ doped SmC13.6H20 single crystals.

TABLB II

Observed and calculated A M = 4-1 transitions of Gd 3+ in Pr(NOa)3.6H~O single crystals

Transition H parallel to the Z-axis H parallel to the X-axis

Observed Calculated Observed

5/2-+ 7/2 570.0 (G) 563.8 ((3) 6023.9 (G)

312-+ 5/2 1560.6 1544.3 5059.9

112-+ 3/2 2468.1 2470.3 4165.9

--1/2-+ 1/2 3375.7 3379.8 3334.8

--3/2-+--1/2 4304.2 4305.0 2546.9

--5/2-+--3/2 5289.8 5291.1 1776.9

--7/2-+--512 6400.8 6401.0 1065.4

DPPH marker .. 3385.8 ~G) ..

Ir may be noted here that Drumheller 6 has reported earlier low field transitions up to A M = 4- 1 in the case ofBaF2 : Gd ~+ and Low and ShaltieF reported transitions up to A M = 4- 5 in case of ThO2 : Gd ~-. An attempt is made to identify the low ¡ transitions in the present experiments by compa¡ the observed transitions with the theoreticaUy expected positions. The resonance fields corresponding to these lines are Iisted in Table IV along with the assigned transitions and the theoreticaUy expected resonance fields. The assignments are to be taken as tentative as these are involving very large values of AM. These assignments, if correct, indicate the presente of a large amotmt of mixing of the different states at low field values.

366 G. B. SmGH AND PUTCHA VENKATESWARLU

TABLE III

Relative separations between the zero-field energy levels of Gd 3+ doped Pr (NOa)a. 61-120 and SmCla. 6HzO

Gd 3+ doped Pr (NOz)3.6H20 Gd .s+ doped SmCh. 6I-IaO kmc. kmc.

+_7[2+--+_+ 5[2 7.74 1 0 " 0

_+ 5[2+- ~ _ 3/2 4.93 7.1

__. 312~-+ _ 1[2 6 "01 7.4

TABLE IV

Low field transitions of Gd 3+ doped'Pr (NOa)a.61120

Relative intensity Transition (measured Observed

to within 20%) Expected

--1[2 -- 5[2 5 3026 (G) 3036 (G)

3 [ 2 - 3[2 16 728 719+__7

1/2 -- 5[2 5 1777 1753

(-- 1/2 -- 7/2) + 5 2937 2985

(5/2 -- 3/2) + 16 350 416+_3

5/2 -- 5/2 10 753 748

3[2 -- 7[2 9 1669 1668

(7[2 -- 7/2) + 24 530 491

Unassigned* 15 1861 ..

+ The transitions indicated in parentheses show larger deviations between observed and calcu- lated values than others. They are therefole to be taken as doubtful assignments.

* The origin of this line is not well understood. It might be due to some impurity.

There are two isotopes of Gd 3+ (155, 157) that have a nuclear spin 3[2 with relative abundance 14.7 and 15.7 per cent, respectively. The Gd 156, Gd 15s, Gd 16~ and others which total about 70% will have no hyperfine inter- action while Gd 155 and Gd 157 wiU have. The absence of the hyperfine structure

EPR Spectrum of Gadolinium in Hydrated Praseodymium Nitrate 367

in the present expe¡ could be explained probably due to the large width of the lines. It may be noted that the hyperfine structure 6-8 reported so far for Gd 3+ is either in the case of samples enriched s with Gd 155, xs• or in the cases where the transitions are sufficiently narrow 7, 9-al for the hyperfine structure to be dearly visible.

The presence of ordy one set of spectrum corresponding to A M -t- 1 transitions in the case of Gd ~- doped Pr (NOa)a. 6H~O shows that gadolinium ion occupies only one kind of observable site in Pr (NO3)a.6H20. The fact that the zero-field splitting (4-7/2 <--> 4- 1/2) is approximately 18.68 kmc. in the case of Gd z+ doped Pr (NO3)3.6H~O as against 24-5 kmc. in the case of Gd a+ doped SmCI3.6H20 indicates that the crystalline electric field experi- enced by Gd ~+ ion due to the ligands is much weaker in the case o f Pr (NO3)3.6HzO than in the case of SmCI3.6HzO.

ACKNOWLEDGEMENT

Thanks are due to the Council of Scientific and Industrial Research for financial help.

REFERENCES

I. Singh, G. B. and Putcha Venkateswarlu

2. Weger, M. and Low, W.

3. Johnston, D. R., Wong, E. Y. and Stafsudd, O .M.

4. Jones, D. A., Baker, J. M. and Pope, D. F. D.

5. Baker, J. M., Bleaney, B. and Hayes, W.

6. John E. Drumheller ..

7. Low, W. and Shaltiel, D . . .

8. Low, W. ..

9. Hutton, D. R. and Troup, G.J.

10. Hempstead, C. F. and Bowers, K. D.

11.

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