Magnetic properties of the single crystalline Dy3Ni studied by magnetization measurement and 161Dy Mössbauer spectroscopy

Journal of Magnetism and Magnetic Materials 170 (1997) 201 210

ELSEVIER

~ i leurnal of magnetism and magnetic 4d~ materials

Magnetic properties of the single crystalline Dy3Ni studied by magnetization measurement and 61Dy M6ssbauer spectroscopy Hideya Onodera a'*, Hisao Kobayashi b, Hiroshi Yamauchi a, Masayoshi Ohashi a, Yasuo Yamaguchi" ~'lnstitute for Materials Research. Tohoku University, Sendai 980-77, Japan b Department of Physics, Tohoku University, Sendai 980- 77, Japan

Received 13 September 1996: received in revised form 5 November 1996

Abstract Magnetic properties of Dy3Ni have been investigated by means of magnetization measurement and 161Dy M6ssbauer spectroscopy on the single-crystalline and powdered samples, respectively. Dy3Ni is a noncollinear antiferromagnet below TN = 52 K. There occur two antiferromagnetic order order transitions at Ttl = 22 K and T,z = 34 K. The effective paramagnetic moment /~eff is 11.7 laB/Dy whose large value is presumably attributable to the paramagnetic moment on the Ni atom. The metamagnetic transitions occur around 45, 78 and 51 kOe at 4.2 K along the a-, b- and c-axis, respectively. The M6ssbauer spectroscopy has shown that the Dy 3+ ions are in strong crystal fields of A ° ~ 800 K/a~ and have the full moment of 10 gB. There is no evidence for the Ni moment to participate in the magnetic ordering below TN down to 4.2 K. PACS: 75.25; 75.30.c; 76.80 Keywords." Dy3Ni; Magnetization; M6ssbauer spectroscopy; Magnetic transition; Magnetic moment

!. Introduction T h e intermetallic D y 3 N i c o m p o u n d crystallizes in the o r t h o r h o m b i c F e 3 C - t y p e s t r u c t u r e with the space g r o u p of P n m a . T h e D y a t o m s o c c u p y the 4c a n d 8d sites, a n d c o n s t r u c t two t r i g o n a l prisms in

* Corresponding author. Tel.: + 81-22-215-2037; fax: + 8122-2 ! 5-2036; e-mail: [email protected].

a unit cell. T h e N i a t o m o c c u p y i n g the 4c site is l o c a t e d at the center of the D y prism. T a l i k has r e p o r t e d t h a t D y 3 N i is an a n t i f e r r o m a g n e t at the N6el t e m p a r a t u r e TN = 40 K, a n d there occurs a m a g n e t i c o r d e r - o r d e r t r a n s i t i o n at 20 K [1]. The effective p a r a m a g n e t i c moment/Leff is 11.24 laB/Dy, which is larger t h a n the t h e o r e t i c a l value of 10.63 gB, a n d then it was suggested t h a t the Ni a t o m carries a p a r a m a g n e t i c m o m e n t . F u r t h e r more, T a l i k a n d M y d l a r z have f o u n d o u t that Y3Ni

0304-8853,,'97,/$17.00 ,~ 1997 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 0 0 8 - 5

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H. Onodera et aL / Journal of Magnetism and Magnetic Materials 170 (1997) 201-210

Table 1 Magnetic properties of Dy3Ni

TN(K) T,2 (K) T,1 (K) 0p (K) ~t/eff (~a/Dy)

H~ (kOe) at 4.2 K tiDy (lIB) at 4.2 K

Present work

Talik [1]"

F6ron et al. [4]

42

35

(a) (b)

52 34 22 1.2 - 17.9

20 35

29

(c) (a)

16.5 11.7

11.24

10.6

(b) (c) (a) (b) (c) (Magn.) (M6ss.)

11.8 11.6 48 (up), 43 (down) 78 48 (up), 43 (down) 9.9 10.0

~The magnetic susceptibility was measured in the applied field parallel to the [4 1 (3] direction of single crystal.

shows a metamagnetic transition under an applied field around 10 T at 4.2 K while the compound shows no magnetic order down to 4.2 K [2]. They suggested the existence of spin fluctuations on Ni to be responsible for the properties mentioned above. In the present work, the magnetic properties of Dy3Ni (Table 1) are investigated by means of magnetometric experiments on a single-crystalline sample, and ~61Dy M6ssbauer spectroscopy on a powder sample in order to obtain additional and precise information, focussing our interest especially on the behavior of Ni moment.

2. Experimental

Purities of Dy and Ni in sample preparation were 99.9%. The compound was synthesized by a conventional argon-arc technique. For ensuring homogeneity, the ingot was turned over and remelted several times. The powdered sample was obtained after annealing at 900°C for a week in a tantalum foil which was sealed in an evacuated quartz tube. X-ray diffraction measurements on the powdered samples were carried out using Fe-K~ radiation. The diffraction patterns exhibit only the lines characteristic of Fe3C-type structure. It was confirmed that the sample was a single-phase corn-

pound, since no indication of secondary phase was found after annealing. Single crystals were grown by the Czochralski method using a triarc furnace. The single-crystalline sample for magnetometric measurements was shaped into a sphere with diameter of about 2 ram. The magnetization was measured as functions of temperature and magnetic field using magnetometers with sample-extraction and vibratingsample methods. The temperature-dependence of magnetization was measured in the range 2-300 K. The magnetic fields below 10kOe were used to observe the magnetic transitions and the paramagnetic susceptibility, and up to 230 kOe to measure magnetization processes. The high magnetic fields were produced using a water-cooled Bitter-type magnet at the High Field Laboratory for Superconducting Materials (HFLSM) in Tohoku University. A M6ssbauer absorber was prepared from the powdered sample with a thickness of about 150mg/cm z. The 161Dy M6ssbauer effect was measured by an ordinary transmission-type spectrometer with the constant acceleration driving mode. A standard 161Tb source which was made by neutron irradiation of GdF3 containing 16°Gd enriched up to 97.86% at the Japan Material Testing Reactor (JMTR) was kept at room temperature. The M6ssbauer T-rays were detected with a

H. Onoderaet al. / Journalof Magnetismand MagneticMaterials 170 (1997) 201 210 proportional counter of Kr C O 2 mixture gas of 1 atm pressure. The velocity scale was calibrated using a spectrum of Dy metal at liquid-helium temperature.

203

Dy3Ni

3xlO -a

500 0e r.

"~ 2x10-3

T~

wN

°'°

rt II c %%

O

3. Results

'%"*'~'~,,,,~.[

ZFC~T....'" . . . . .o,'°

-~ lxlO -a =a

l

3.1. Magnetic susceptibili O, 01 The magnetization versus temperature curves of Dy3Ni show complicated behavior depending on the applied field and the experimental history. Fig. 1 shows the temperature dependence of magnetizations along three crystallographic axes of the single crystal, which were measured under an applied field of 500 Oe with field cooling (FC) and after zero-field cooling (ZFC) below 80 K. The FC and ZFC curves branch off below the N6el temperature TN = 52 K, and the separation is enhanced below the order-order transition temperarures T,2 = 34 K and Ttl = 22 K. The TN and Ttl values are higher than 42 K and 20 K, respectively, which are reported by Talik. The transition at Tt2 was newly found out in the present experiment. The fact that the M/H values along the three axes are comparable may suggest that the Dy moment align in directions apart from the three crystallographic axes by nearly the same angles. The temperature dependence of reciprocal susceptibility 1/z along the three crystallographic axes are shown in Fig. 2, which were measured under an applied field of 10kOe. All reciprocal susceptibilitiy curves satisfy the Curie Weiss law above 200 K. The paramagnetic Curie temperatures along a the three axes are 0v = 1.2 K, 0bp = - 17.9 K and 0~ = 16.5 K, respectively. The effective paramagnetic moments are P~fr = 11.7 laB/Dy,/~hff = 11.8 gB/ Dy and I~;ff = 11.6 g~/Dy, respectively, which are larger than the theoretical value of 10.6 lab for the Dy 3 + free ion.

3.2. Magnetization process Fig. 3 shows magnetization processes at 4.2 K measured in high magnetic fields up to 230 kOe, There occur field-induced transitions at H~ = 48 kOe (up) and 43 kOe (down) with small hystere-

3xlO -3

o o o ~ ........ !............ i...... 2xlO-a ~D

lxl0 -:t

,,°°"°

",~Oo

1 3x10:1

2x10-'~ E lxl0 -a

0

0

10

20

30

40

50

6()

70

80

T (K) Fig. 1. Temperature dependence of the magnetic susceptibility along three crystallographic axes of single-crystalline Dy3Ni, where the magnetic field of 500 Oe is applied with cooling tFC) and after zero-field cooling (ZFC).

sis along the a-axis, Hb~ = 7 8 k O e along the b-axis, and H~, = 5 4 k O e (up) and 48 kOe (down) along the c-axis. Above the critical fields, the three magnetizations increase linearly by dM/dH ~ 15.0 emu/g kOe (a-axis), 19.0 emu/g kOe (b-axis) and 12.3emu/gkOe (('-axis), and reach unsaturated values of 6.8 lan/Dy (a-axis), 5.8 la~/Dy (b-axis) and 7.7 gB/Dy (c-axis) at 230kOe. In order to examine whether the easy direction of Dy moments coincides with any crystallographic axis or not, the magnetization behavior was examined for the powdered sample as shown

204

H. Onodera et al. / Journal of Magnetism and Magnetic Materials 170 (1997) 201-210

4. OxlO 3

Dy3Ni 3. OxlOa

0p (K) 1.2

o a-axis [b-axis c-axis

~eff ( ~ / D y N i i/3 )

11.66 11.82 ii. 57

-17.9 16.5

2. OxlO 3

"7

~.

i::[::

jj~:; ~,f/,¢¢¢~ ~ j

.....

.....-

i. Oxl03

0.0017;"

'

.

.

.

50

.

.

.

.

.

.

.

.

100

.

.

.

.

.

'

150

. . . . . . . . .

200

Temperature

250

'

'

300

(K)

Fig. 2. Temperature dependence of the reciprocal susceptibility along three crystallographic axes of single-crystalline Dy3Ni, where the magnetic field of 10 kOe is applied. 250

i

i

I

I

H[[o ........................... ~oooQ~o~o 200

~-~ 150

o

.;°

- . - - - - ' - ' - " ....

Hlla

20

15

g

~A

0 v

(D

I00

•o

ooj ~

DyaNi

i0

4.2K 50

,

I

5

0

15

i0

20

25

~oH (T) Fig. 3. Magnetization curves of single-crystalline Dy3Ni at 4.2 K under high fields.

in Fig. 4. The powder sample was the same to that used for the M6ssbauer experiment which was prepared by grinding the polycrystalline button. The powder was sealed in a polytetrafluoroethylene (Teflon) capsule with helium gas and BN powders so as to achieve a homogeneous temperature and to rotate freely in the magnetic field. Although the process with increasing field is more

complicated than those of single crystal, the maximum magnetization coincides well with that along the c-axis, that is the easy direction of Dy moments does not coincide with any crystallographic axis and the maximum component of moments appears along the c-axis. It is, therefore, supposed that the noncollinear antiferromagnetic structure is forced to be canted-ferromagnetic above the critical fields,

H. Onodera et al. / Journal of Magnetism and Magnetic Materials 170 (199D 201--210

250

'

I

'

I

'

205

I

20

200 l st .~.

run -~ 15 "~"

150 .¢

lO

lOO

~

DY3Ni

:~

free powder 50

5

4.2K

0

,

0

I

I

,

50

i

100

,

I 150

0

H (kOe) Fig. 4. Magnetization curves of powdered Dy3Ni at 4.2 K under high fields. The powder particles are free to rotate in the applied field.

and the canting angle decreases gradually as the field increases. Fig. 5 shows the temperature variation of the M - H curve, where each critical field was determined as a field having the maximum dM/dH value. The critical field increases slightly with increasing temperature, and the metamagnetic transition becomes unclear and smears out around 40 K. The hysteresis was observed in the low-temperature M - H curves along the a- and c-axis. Fig. 6 shows the M - T phase diagram made by plotting the critical fields of metamagnetic transitions. A small remanent magnetization which does not exceed 6 emu/g (0.20 gB/Dy) are observed for the all axes as shown in Figs. 3-5. This remanence occurs after the initial magnetization process below the critical field as shown in Fig. 7. It is noticeable that the initial magnetization increases steeply

around 6 kOe, and it seems that the magnitude of remanence relates to this steep increase of magnetization. 3.3.

161Dy

M'dssbauer effect

Fig. 8 shows ~61Dy M6ssbauer spectra of Dy3Ni measured at various temperarures. In the figure, the observed and calculated spectra are shown together by circles and solid lines, respectively. As the temperature increases, the absorption intensities of the central peaks increase and those of the outer peaks decrease. This fact implies that the relaxation rate of 4f electrons increases as temperature increases [3]. the analyses were done by a static model and a relaxation model for the spectra below and above 25 K, respectively. All the spectra are interpreted by a single set of hyperfine parameters, although the

206

H. Onodera et al. / Journal of Magnetism and Magnetic Materials 170 (1997) 201 210

250 DY3Ni

~

~

~

200

'20

1

Hllc 150

100

i

o[

501-

~

J

"

. 4.2K

:

o 13.0 K

'

15

, 16.0K

~ 19.8 K

10

• 24.9K , 30.8K

-15

0 4.2K

200

10.1 g

HIIb

20 15

150[

rv

100

o 15.3K

10

• 19.7K

(:1)

Z~

24.9K 35.5K

50

• 44.5K 0 ~¢''

,

I

i

I

I

L

20

200

15

150 100

o*~i

,10. 1 K

*y

o 15.1 K

nq

.2L9

K

10 5

50

0 0

0

J

40

,

I

,,

80

I

120

i

0 160

H (kOe) Fig. 5. Temperature variation of magnetization curves of single-crystalline Dy3Ni under high fields.

H. Onodera et al. /Journal of Magnetism and Magnetic Materials 170 (1997) 2 0 l - 2 1 0

100

,

207

, 25

Dy3Ni

4. 2 K

2O 80

G) G

h0

Hl[o

-._./ 10

60 ~

5

~°~

He a

40

25 2O

20

, 0

i i0

,

I 20

,

I 30

, 40

T (K) Fig. 6. Magnetic H T phase diagram of Dy3Ni when the magnetic fields are applied along the three axis. The same symbols at the same temperature denote the critical fields of the transitions showing the hystereses in increasing and decreasing temperature, respectively.

"---" i0 5

J

otJu o~ n

20

Dy atoms occupy two nonequivalent crystallographic sites. The hyperfine field 9NPNHhf/h, is 841 MHz at 4.2 K which is larger than the theoretical value of 832 MHz for the pure J~ = I ~ ) state, where the small excess is attributable to a transferred hyperfine field originating from the neighboring magnetic moments. The quadrupole splitting, ¼e2qQ/h,are 557 MHz at 4.2 K which is rather smaller than 714 MHz of [ ~ ) . The difference of - 157 MHz originates from the lattice contribution as discussed later. The relaxation rate increases from 4.2 x l0 s s - t at 30.0 K to 6.9 x 1 0 9 S- I at 49.5 K as tempearature increases. Fig. 9 shows the temperature dependence of the magnetic hyperfine field and the quadrupole splitting. It is remarkable that both the values are nearly constant and show no anomaly at the magnetictransition temperatures. The obvious change around the magnetic-transition temperature is observed in the transmission rate of M6ssbauer v-ray at zero relative velocity as shown in Fig. 10, where the values are corrected for intensity change due to y-source decay. The transmission rate decreases rapidly as the temperature closes to T,~, although there is no anomolous change above T,x. As mentioned above, the analysis of M6ssbauer spectrum

Jo

II

5

10

15

20

H (ROe) Fig. 7, Behaviors of the initial magnetization and remanence single-crystalline Dy3Ni at 4.2 K.

of

below T,t was done by the static model. However, the rapid decrease of transmission rate with increasing temperature is attributable to the spin relaxation, since the magnetic hyperfine field is nearly constant in this temperature range as shown in Fig. 9.

4. Discussion The magnetic hyperfine field Hhf may be decomposed into contributions: the field due to 4f elec4f tron, Hhf, the core polarization field, H~p, the field

208

H. Onodera et al. /

'

.f

'

I

'

i

,

I

Journal of Magnetism and Magnetic Materials 170 ( l 997) 2 O1 - 2 l 0 ,

;

I

1000

.

I

I

i

Ttl

i

I

Tt2

TN

900

c~

o

-0

o

o~

_

~

800

gN~NHhf/h

o=

.P-I

700

O]

600

0a

soo

22.1 K

1/4e2qQ/h t

400

-g

I

I0

4.

i

I

t

I

20

,

30

I

,,

40

I

50

60

T (K)

K

Fig. 9. Tempearature dependence of the magnetic hyperfine field (gNpNHhe/h) and the quadrupole splitting (¼e2qQ/h) of Dy3Ni. -300

-200

-100

0

100

200

300

Velocity (ram/s) Fig. 8. 161Dy M6ssbauer spectra of D y 3 N i at various temper-

atures.

8.4x10 s © •~

Dy3Ni Jr

8.2x10 s

(y-rays at v=O) i

=~

8. OxlO 5

due to conduction electron polarization, *'hf~s°~P,and the transferred field from neighboring magnetic moments, H~'f. The Hh4f by 4f orbital angular momentum and dipole interaction of 4f spin is directly proportional to the magnetic moments 9JPSJz. The core polarization field H~,F is estimated theoretically to be gNltNH~/h ~ -- 14(gs - l)J~ ( - 35 MHz for Jz = ~ ) and therefore is a relatively small contribution compared with Hh*~. The (H~[ + H~p) value for the free Dy 3 + ion of the pure [~> state has been calculated to be 5700 kOe [5] whose value is converted to 832 MHz using the value of 9N = 0.1916 nuclear magneton [6]. Although the value of 9NPNHhf/h = 841 MHz of Dy3Ni is larger than that of the pure }~> state, the /cep small excess of 9 MHz is attributable to L",he and H~%. When the 3d moments participate in the magnetic ordering, the transferred hyperfine field become, in general, larger by one order of magnitude than the present excess value. Conclusively, the Dy moments at the both sites have the full moment of 10 rta.

>

~

Ttl Yt2

TN

7.8xlO s

7.6x10 ~

7.4x10 s

0

i0'

' 2~0

' 30

~ ' 5'0 ' 60' 40

' ' - -80 70

Temperature (K) Fig. 10. Transmission velocity in Dy3Ni.

rate of the Mbssbauer y-rays at zero

The paramagnetic effective moment per Dy atom is rather larger than the theoretical value of Dy 3 + ion. This difference may be attributed to the paramagnetic moment on the Ni atom as pointed by Talik [1]. As mentioned above, the magnitude of hyperfine field reveals that the ground state of Dy ion is the pure I - ~ ) state below TN, implying no contribution of Ni moment to the transferred hyperfine field. Furthermore, the temperature-dependence of gNpNHhf/h and ¼eZqQ/h exhibits no

H. Onodera et al. / Journal of Magnetism and Magnetic Materials 170 (1997) 201-210

anomalous change at T,~ and T~, and the relaxation rate increases monotonously with increasing temperature. When the 3d moments participate in the magnetic ordering, the spin relaxation of Dy ions is suppressed through the magnetic 3d-Dy interaction which is rather stronger than the magnetic D y - D y interaction [7]. And hence it is supposed that the Ni moments remain in the paramagnetic state even below TN. Consequently, there is no evidence that the Ni moments participate in the magnetic ordering below TN down to 4.2 K. It is supposed that the molecular fields produced by the Dy moments are zero or very weak by compensating each other at the Ni site which locates at the center of Dy trigonal prism. As shown in Fig. 3, the magnetizations along the three axes increase linearly above the critical fields and do not saturate even at 230kOe. This fact implies that the magnetic structure is noncollinear and the magnetic anisotropy is so large as to prevent ferromagnetic arrangement of the Dy moment under the applied field up to 230 kOe. Above the critical field, the Dy moments are forced to arrange noncollinearly in a canted ferromagnetic structure, where the moment directions may differ among the sites depending on the CEF parameters and the applied field. By extrapolation from the magnetizations above the critical fields to 0 kOe in order to eliminate the effect of applied field, three component of the Dy moments along the crystallographic axes are obtained to be/~, = 5.71 laB, l~b ----4.37 lab and it,, = 6.77 gB, respectively. These values correspond to the Dy moment of 9.88 gB with the direction of 4 7 from the c-axis and 37 ° from the a-axis on average among the canted Dy moments with different directions. Talik and Mydlarz have reported that in Y3Ni a metamagnetic transition occurs around 100kOe at 4.2 K [2]. When it is assumed that the molecular field acting on the Ni atom in Dy3Ni is enough to cause the metamagnetic transition at the critical fields and that the Dy moment is 10 lab as derived from the magnetic hyperfine field, the Ni moment of ~ - 0 . 2 lab should be yielded along the applied field direction. However, it is not conclusive how the Ni moment behaves, since its magnitude is so small to conceal the accurate behavior of Ni moment in the experimental precision.

209

It is noticiable that the 16~Dy M6ssbauer spectra of Dy3Ni are interpreted by a single set of hyperfine parameters while the Dy atoms occupy two nonequivalent crystallographic sites. The ¼e2qQ/h contains two contributions due to different sources of electric field gradient (EFG), a nonspherical 4f electron contribution q4f and a lattice-charge contribution q|au- The q4f is described as qcf = e~j(r-3)[3J

2 -

Ill

J(J + 1)].

Chappert et al. have derived the q4f value of a pure ]-~) state as ¼e2qQ/h = 714 MHz [8]. Since the ground state is considered to be [ - ~ ) from the magnetic hyperfine field, the difference, -157MHz, between the observed value of 557 MHz and the above value may be ascribed to the contribution of qlatt. The fact that the spectra are interpreted well by a single set of hyperfine parameters is presumably due to the probability that the qlatt at the 4c and 8g sites have the close values undistinguished in the experimental precision. The EFG produced by charged ions surrounding D y 3 + ion relates to the crystalline electric field (CEF) parameter as follows: qla,, =

4

-- e

(1 - ),~)A ° = - - -

4

e~j(r

2)

l - )'~ r~o ,,,, 1 -

0" 2

-

(2) where ),~ is a shielding factor given by (1 - 7~,) = 60, 0.2 a screening coefficient to be about 0.6 and ~j the Stevens factor. Assuming that the principal axes describing qlatt and q4f are in the same direction, the qlatt of 157 MHz corresponds to A ° ~ 800 K/a 2. This large A ° value and its sign explain well the experimental results as follows. The magnetization curves are interpreted by postulating that the Dy moments are fixed strongly along the principal axis of CEF, since the single-ion magntic anisotropies at both the crystallographic sites are large due to the strong CEF. The strong CEF interaction brings forth the 4f ground state to be pure I - ~ ) , and then the Dy moment is the full moment of 10 P-n. Below T N , DyaNi shows no spontaneous magnetization but the small remanent magnetization. -

-

210

H. Onodera et al. / Journal o f Magnetism and Magnetic Materials 170 (1997) 201-210

T h e r e m a n e n c e increases as the t e m p e r a t u r e decreases, a n d does n o t exceed 6 e m u / g (0.20 ~tB/Dy). T h e m o s t plausible origin for this small r e m a n e n c e is i n c o m m e n s u r a t i o n of a l o n g - p e r i o d i c antiferromagnetic structure. T h e i n c o m m e n s u r a t e l y m o d u lated m o l e c u l a r field m a y b e c o m e very w e a k within a certain p e r i o d where D y m o m e n t m a y be unstable in s o m e directions which are e q u i v a l e n t with respect to C E F .

Acknowledgements T h e a u t h o r s w o u l d like to t h a n k the staff of H F L S M , I M R , for o p e r a t i n g the high-field m a g n e t . T h a n k s are also due to the staff of the H o t L a b o r a t o r y in the I r r a d i a t i o n E x p e r i m e n t a l Facilities at O a r a i , I M R , for their k i n d s u p p o r t in p r e p a r i n g the M 6 s s b a u e r sources b y n e u t r o n i r r a d i a t i o n at JMTR.

References [I] E. Talik, Physica B 193 (1994) 213. [2] E. Talik, T. Midlarz, J. Alloys Compounds 215 (1994) L7. [3] H.H. Wickman, in: I.J. Gruverman (Ed.), M6ssbauer Effect Methodology, vol. 2 (Plenum, New York, 1966), p. 39; H.H. Wickman, G.K. Wertheim, in: V.I. Goldanskii, R.H. Herber (Eds.) Chemical Applications of M6ssbauer Spectroscopy (Academic Press, New York, 1968), p. 548. [4] L. F6ron, R. Lemaire, D. Paccard, R. Pauthenet, C.R. Acad. Sci. Paris B 267 (1968) 371. [5] 137.Bleaney, in: R.J. Elliott (Ed.), Magnetic Properties of Rare Earth Metals (Plenum Press, London, 1972) p. 383. [6] J.G. Stevens, V.E. Stevens, M6ssbauer Effect Data Index (IFI/Plenum, New York, 1975), p. 44. 1-7] H. Kobayashi, H. Onodera, H. Yamamoto, J. Magn. Magn. Mater. 109 (1992) 17; H. Onodera, M. Ohashi, H. Yamauchi, Y. Yamaguchi, J. Magn. Magn. Mater. 109 (1992) 249; H. Onodera, T. Ono, M. Ohashi, Y. Yamaguchi, H. Kobayashi, Nucl. Instr. and Methods B 76 (1993) 55; H. Onodera, T. Ono, M. Ohashi, Y. Yamaguchi, H. Kobayashi, J. Magn. Magn. Mater. 124 (1993) 96. [8] J. Chappert, L. Asch, M. Boge, G.M. Kalvius, B. Boucher, J. Magn. Magn. Mater. 28 0982) 124.