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Submitted on 1 Jan 1979
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MÖSSBAUER EFFECT OF 125Te IN MnTe2 - SPIN AXIS IN NON-COLLINEAR
ANTIFERROMAGNETIC ORDERING OF THE FIRST KIND IN FCC LATTICE
Y. Nishihara, S. Ogawa
To cite this version:
Y. Nishihara, S. Ogawa. MÖSSBAUER EFFECT OF 125Te IN MnTe2 - SPIN AXIS IN NON- COLLINEAR ANTIFERROMAGNETIC ORDERING OF THE FIRST KIND IN FCC LATTICE.
Journal de Physique Colloques, 1979, 40 (C2), pp.C2-221-C2-222. �10.1051/jphyscol:1979279�. �jpa-
00218677�
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n° 3, Tome 40, mars 1979, page C2-221
MOSSBAUER EFFECT OF l25
TeIN MnTe
2SPIN AXIS IN NON-COLLINEAR ANTIFERROMAGNETIC ORDERING OF THE FIRST KIND IN FCC LATTICE
Y. Nishihara and S. Ogawa
Mleotroteohnioal Laboratory, Tanashi, Tokyo, Japan
Résumé.- L'effet Mossbauer de 2 5Te dans Mnlea^ui est antiferromagnêtique au-dessous de 85 K, a été mesuré de 4.2 K à 90 K. On observe une variation brutale de l'effet quadrupolaire et du champ hyper-
fin à 60 K. L'angle entre la direction du champ hyperfin et l'axe principal du gradient de champ électrique est 23 degrés à 4 K, s'accroît à 30 degrés à 60 K, et décroît à 0 degré à 70 K.
Abstract.- Mossbauer effect of 1 2 5T e in MnTe2> which is antiferromagnetic below 85 K, was measured from 4.2 to 90 K. At 60 K the hyperfine field and the quadrupole splitting change discontinuously.
The angle between the direction of hyperfine field and the principal axis of electric field gradient increases from 23° at 4 K to 30° at 60 K and decreases to 0° at 70 K.
1. Introduction.- Antiferromagnetic MnTe2 and N1S2 have the spin structure of the first kind ordering of fee lattice /1,2/. Neutron diffraction patterns obtained from powders or aultidomain single crys- tals cannot distinguish between the collinear and the non-collinear structures. In this case, Moss- bauer experiment gives information for determina-
tion of the magnetic structure /3,4/.
Pasternak and Spijkervet measured the hyperfi- ne field at 1 2 5Te in MnTe2 /3/. The analysis of the transferred hyperfine field from the nearest- neighbor Mn atoms revealed that MnTe2 has the non- collinear first kind ordering and the direction of spin makes an angle 8 which is about 30° at 4.2 K and nearly 0° at 77 K with the symmetry axis at Mn site /3/. A similar spin structure is observed in NiS2 by the Mossbauer effect of 5 Fe doped in NiS2 /5/. Recently, the effect of the fourth order in- teractions between localized spins in antiferroma- gnetic fee lattices has been studied theoretically by Yoshimori and Inagaki /6/. It appears that the effect of the higher order interactions is appre- ciable in 3d-metal dichalcogenides with the pyrite structure.
We have made Mossbauer measurement of 1 2 5Te to investigate the temperature dependence of spin direction in MnTe2, and have found anomalous chan- ges in the spin direction and the hyperfine field below T„.
N
2. Mossbauer spectrum.- The sample was a polycrys- talline MnTe2 prepared by a sintering method. The Neel temperature of this sample was determined to be 85 K from resistivity and magnetic susceptibility measurements.
The y-ray source was 5 mCi 1 2 5Sb in rhodium.
All measurements were performed with the source kept below 77 K.
Figure 1 shows the temperature dependence of Mossbauer spectrum of 1 2 5Te in MnTe2. The hyperfine field H, quadrupole splitting E (=e2qQ/2)) angle 9, isomer shift and line width were determined from the computer fitting of the spectrum. Solid curves in the figure were obtained from the fitting.
Fig. 1 : Mossbauer spectra o f1 2 5T e in MnT2.
An average line width 2T of the Lorentzian was
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979279
c2-222
JOURNAL DE PHYSIQUE5.5 m m / s . T h i s v a l u e i s 2%3 m/s s m a l l e r t h a n t h a t of Pasternak and S p i j k e r v e t / 3 / .
3. R e s u l t s and Discussion.- Temperature dependences of t h e quadrupole s p l i t t i n g and h y p e r f i n e f i e l d a r e shown i n f i g u r e s 2 and 3, r e s p e c t i v e l y .
Fig. 2 : Temperature dependence of quadrupole s p l i t - t i n g
.
Fig. 3 : Temperature dependence of t h e h y p e r f i n e f i e l d a t ' " ~ e i n MnTen.
A t about 60 K both t h e quadrupole s p l i t t i n g and t h e h y p e r f i n e f i e l d change d i s c o n t i n u o u s l y . The hyper- f i n e f i e l d d e c r e a s e s from about 125 t o 75 kOe and t h e quadrupole s p l i t t i n g from -5.8 t o -8.0 mm/s a t 60
K
w i t h i n c r e a s i n g temperature. These changes were n o t observed by Pasternak and S p i j k e r v e t 131.T h i s i s because t h e v a l u e of quadrupole s p l i t t i n g was f i x e d a t t h e v a l u e of 90 K i n t h e i r a n a l y s i s of t h e spectrum a t 4.2 K
The thermal expansion of MnTen was measured by Kasai and Waki / 7 / . An anomalous i n c r e a s e i n l a t t i c e cons-
t a n t of t h e o r d e r of lo-'
1
was observed a t 60 K w i t h i n c r e a s i n g temperature.The h y p e r f i n e f i e l d a t1 2 ' ~ e i s t h e t r a n s f e r r e d h y p e r f i n e f i e l d from t h e n e a r e s t neighbor Mn and t h e quadrupole s p l i t t i n g i s caused by t h e molecular n a t u r e of t h e ~ e ' - - ~ e ' - a n i o n p a i r i n MnTe2 131. Therefore, b o t h t h e hyper- f i n e f i e l d and t h e quadrupole s p l i t t i n g a r e s e n s i - t i v e t o t h e p o s i t i o n of t e l l u r i u m atoms i n t h e crys- t a l . Since t h e c r y s t a l s t r u c t u r e of MnTe2 i s t h e p y r i t e type down t o 4.2 K / I / , i t i s most l i k e l y t h a t t h e i n t e r n a l parameter of c r y s t a l l a t t i c e changes a t 60 K i n &Ten.
Figure 4 shows the temperature dependence of 9 i n MnTez. The 6 i n c r e a s e s from about 23" t o 30° with i n c r e a s i n g temperature up t o 60 K. Above t h i s tem- p e r a t u r e 8 r a p i d l y d e c r e a s e s t o 0'. The experimental r e s u l t s show t h a t t h e d i r e c t i o n of Mn s p i n begins t o r o t a t e toward a body diagonal d i r e c t i o n w i t h in- c r e a s i n g temperature above t h e temperature a t which t h e i n t e r n a l parameter changes. F u r t h e r work i s r e q u i r e d t o make c l e a r t h e mechanism of t h e tempera- t u r e dependence of s p i n a x i s .
F i g . 4 : Temperature dependence of t h e s p i n a x i s i n MnTe2.
References
/ I / H a s t i n g s , J.M., E l l i o t t , N . and Corliss,L.M., Phys.Rev. 115 (1959) 13.
/ 2 / H a s t i n g s , J . M . and Corliss,L.M., I B M J. Deve- lopm. 14 (1970) 227.
/3/ Pasternak,M. and Spijkervet,A.L. ,Phys .Rev. 18 1 (1969) 574.
/ 4 / Hastings,J.M., Corliss,L.M., Blume,M. and Pas- ternak,M., Phys.Rev. B1 (1970) 3209.
/5/ N i s h i h a r a , Y., Ogawa,S. and Waki,S., J.Phys.Soc.
Japan 39 (1975) 63.
/ 6 / Yoshimori,A., and Inagaki,S., J.Phys.Soc.Japan
44 (1978) 101.
171 Kasai,N. and Waki,S., p r i v a t e communication.
