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Magnetic susceptibility and 31p nuclear magnetic resonance in Mn2P
Volume 28A, number 9
PHYSICS
can d e t e r m i n e t h e e n e r g y l o c a t i o n of the c h a r a c t e r i s t i c p o i n t s b e l o n g i n g to the s i g n a l s A, B and C to be 2.788 eV, 2.804 eV and 2.760 eV, r e s p e c t i v e l y . T h e e n e r g y v a l u e s of 2.788 eV and 2.804 eV a g r e e in f a i r l y good w i t h t h o s e a s s o c i a t e d with e x c i t o n g r o u n d s t a t e E x l and the f i r s t e x c i t e d s t a t e E x 2 a s s i g n e d a l r e a d y by t h e p r e vious investigators |1,3]. The structure C might c o r r e s p o n d to the s i g n a l a s s o c i a t e d with an L0 phonon a s s i s t e d d i r e c t e x c i t o n c r e a t i o n p r o c e s s . "Then the e n e r g y of phonon b r a n c h ~w l is d e t e r m i n e d to be 28 m e V . T h i s v a l u e is a l i t t l e bit s m a l l e r a s c o m p a r e d with 31.4 m e V o b t a i n e d by H i t e et al. [3]. T h e r e m a i n i n g s t r u c t u r e D in t h e h i g h e s t e n e r g y r e g i o n m i g h t b e a r i s e n f r o m the e l e c t r o - r e f l e c t a n c e of the f u n d a m e n t a l e d g e of ZnSe. T h e l i n e s h a p e of t h i s s i g n a l h a s a s h a p e of G(-~) t y p e e l e c t r o - o p t i c a l f u n c t i o n [4]. T h u s t h e e n e r g y of the f u n d a m e n t a l e d g e (Eg) can b e d e t e r m i n e d to b e 2.811 eV at 90OK. By u s i n g t h i s d i r e c t e d g e e n e r g y , one can c a l c u l a t e the e x c i t o n b i n d i n g e n e r g y ; E B = (Eg - E x l ) = 23 m e V o r ~(Ex2 - E x l ) = 21 m e V . T h e s e v a l u e s a r e c o n s i s t e n t with t h a t o b s e r v e d by H i t e et al. A t e n t a t i v e m o d e l of the p r o b a b l e t r a n s i t i o n p r o c e s s and t h e i r e n e r g i e s a s s i g n e d f r o m the a n a l y s i s of d a t a a r e s u m m a r i z e d in fig. l(c). One d i s c r e p a n c y of
31p
LETTERS
10 February 1969
t h e r e s u l t a n t c u r v e f r o m fig. l(a) i s a n e g a t i v e d r i f t of the ~ R / R a p p e a r e d in the h i g h e r e n e r g y r e g i o n . T h i s r e a s o n m a y be due to a shift of z e r o l i n e in t h e AR m e a s u r e m e n t by s o m e u n known e f f e c t s (like a p h o t o - e l e c t r o - l u m i n e s c e n c e a b o v e t h e d i r e c t edge). A m o r e d e t a i l e d a n a l y s i s on both t h e e l e c t r i c f i e l d and t e m p e r a t u r e d e p e n d e n c e f o r v a r i o u s k i n d s of s a m p l e s (like i m p u r i t i e s d o p e d c r y s t a l s ) is now in p r o g r e s s . T h e a u t h o r s w i s h to thank M r . H. K i m u r a of the C e n t r a l R e s e a r c h L a b o r a t o r i e s , M i t s u b i s h i E l e c t r i c C o r p o r a t i o n , f o r his h e l p in s a m p l e preparation.
References 1. R.A. Forman and M. Cardona, II-VI semiconducting compounds, ed. D.G. Thomas {Benjamin Inc., New York, 1967) p. 100. 2. Y. Hamakawa, F.A. Germano and P. Handler, Phys. Rev. 167 (1968) 703 and in Proc. Intern. Conf. on the Physics of semiconductors, Moscow, July 1968 I-C-4, to be published. 3. G. E. Hire, D . T . F . Marple, M. Aven and B. Segall, Phys. Rev. 156 (1967) 850. 4. D.E.Aspnes, Phys. Rev. 153 {1967) 972.
MAGNETIC SUSCEPTIBILITY AND NUCLEAR MAGNETIC RESONANCE IN
Mn2P
S. K. M A L I K and R. V I J A Y A R A G H A V A N Tara Institute of Fundamental Research, Bombay, India Received 1 January 1969
The magnetic susceptibility of Mn2P shows a peak around ll0OK, indicating antiferromag~etic ordering. F r o m susceptibility and 31p Knight shifts in the paramagnetic state the hyperfine fields at two phosphorus sites have been found to be +3.5 and +21.8 kOe p e r ~tfl of Mn. NMR of 55Mn was observed from one of the manganese sites.
T h e m a n g a n e s e - p h o s p h o r u s s y s t e m f o r m s the c o m p o u n d s M n P , M n 2 P and M n 3 P [1]. We h a v e m e a s u r e d t h e m a g n e t i c s u s c e p t i b i l i t y (×) of M n 2 P w h i c h o r d e r s a n t i f e r r o m a g n e t i c a l l y at 103°K, and 3 1 p Knight s h i f t s (K) in M n 2 P and Mn3P. M n 2 P w a s p r e p a r e d by h e a t i n g t o g e t h e r s t o i c h i o m e t r i c a m o u n t s of m a n g a n e s e p o w d e r and r e d p h o s p h o r u s in an e v a c u a t e d s i l i c a t u b e at 8 0 0 ° C 648
f o r one day [2]. F i g . 1 c o n t a i n s a plot of 1 / × versus temperature, where 1/× (corrected for p o s s i b l e f e r r o m a g n e t i c i m p u r i t i e s [3]) s h o w s a b r o a d m i n i m u m a r o u n d l l 0 ° K c o r r e s p o n d i n g to an a n t i f e r r o m a g n e t i c o r d e r i n g . T h i s t e m p e r a t u r e is h i g h e r than the N ~ e l t e m p e r a t u r e (T N) of 103°K found by n e u t r o n d i f f r a c t i o n [2,4]. A b o v e N d e l t e m p e r a t u r e , × c o u l d b e f i t t e d to a C u r i e - W e i s s
Volume 28A. number 9
PHYSICS
law × = C / ( T - O) g i v i n g C = 1 . 8 5 ± 0 . 1 ( c o r r e s p o n d i n g to ~ D a r a = 3.8 + 0.2 p e r M_n) and 8 = = - 115 ± 10n01K. M n 2 P is h e x a g o n a l w i t h r e v i s e d F e 2 P ( C 2 2 ) s t r u c t u r e type. T h e r e a r e two i n e q u i v a l e n t Mn s i t e s Mn I and M n i i and two i n e q u i v a l e n t P s i t e s P I and PII, t h e l a t t e r in the r a t i o of 2 : 1. C o n s e q u e n t l y two 31p N M R l i n e s w e r e o b s e r v e d w i t h t h e i n t e n s i t y r a t i o of 2 : 1 f r o m P I and PII r e s p e c t i v e l y . T h e PII N M R l i n e had a h i g h f i e l d a n i s o t r o p y in line shape. Knight shift K I and KII f r o m the two s i t e s w a s p o s i t i v e and t e m p e r a t u r e d e p e n d e n t ( s e e fig. 1). T h e l i n e s e v e n t u a l l y d i s a p p e a r e d at 104 ± 2OK w h i c h a g r e e s v e r y w e l l w i t h T N found by n e u t r o n d i f f r a c t i o n . A g e n e r a l e x p r e s s i o n f o r the 31p Knight shift [5] m a y b e w r i t t e n a s K(T)
=g o + (N~)-IHhfX(T)
,
10 February 1969
LETTERS
40 I
80 I
120 I
TEMP. ( ° K ) 200
160 l
I
240
280
I
1
320
I~ x Id' ~M
22
20 ®
5"0
"22
®
4.0 ~0 K 3.
(1)
w h e r e Hhf i s t h e n e t h y p e r f i n e f i e l d p e r /1/3 at P s i t e . Fig. 1 c o n t a i n s K v e r s u s X p l o t s f o r P I and PII, f r o m t h e s l o p e s of w h i c h we get Hhf a s + 3 . 5 ± 0.2 k O e / g l 3 f o r P I and + 2 1 . 8 ± 0.5 k O e / f l ~ f o r PII r e s p e c t i v e l y . Mn I and P I a t o m s a r e in z = 0 p l a n e and M n i i and P H a r e in z = ½ p l a n e . E a c h p h o s p h o r u s a t o m h a s nine Mn n e i g h b o r s . T h e y a r e 3 Mn I at 2.30 and 6 M n i i at 2.52 A f o r PI and 6 Mn I at 2.32 and 3 M n i i at 2.46 ~, f o r PII. In o r d e r e d s t a t e [2] at 4OK, two M n i i a t o m s c a r r y l a r g e r m o m e n t (0.84 ± 0.03 ~ ) t h a n two Mn I a t o m s (0.01 ± ± 0.04 ~ ) w h i l e t h i r d Mn I and t h i r d M n i i c a r r y z e r o m o m e n t . F r o m N M R , we find t h a t PII n u c l e i e x p e r i e n c e a m u c h l a r g e r h y p e r f i n e f i e l d than P I i n s p i t e of t h e i r h a v i n g s i m i l a r m a n g a n e s e s u r r o u n d i n g s . T h i s c l e a r l y s u g g e s t s that M n - P i n t e r a c t i o n in b a s a l p l a n e i s m u c h s t r o n g e r t h a n out of p l a n e i n t e r a c t i o n . F u r t h e r it is i n t e r e s t i n g to n o t e t h a t we h a v e o b s e r v e d one 55Mn N M R at r o o m t e m p e r a t u r e w i t h a shift of - 0 . 4 ± 0.1%, p r e s u m a b l y f r o m t h o s e Mn a t o m s w h i c h c a r r y a s m a l l o r no m a g n e t i c m o m e n t . H o w e v e r , the l i n e w a s w e a k and b r o a d and so i t s t e m p e r a t u r e d e p e n d e n c e c o u l d not b e s t u d i e d . 31p N M R w a s o b t a i n e d in t e t r a g o n a l M n 3 P w h i c h h a s o n l y one p h o s p h o r u s site. T h i s c o m -
6'-
1.0
2.0
3"0
4.0
5,0
6.0
7.0
8-0
'X. xlO 3 e m u / m o l e
Fig. 1. 1/x(T ) versus T for Mn2P lower two curves are K(T) versus ×(T) for PI and PII"
pound w a s found not to o r d e r m a g n e t i c a l l y t i l l 77°K. T h e 31p Knight s h i f t s a r e - 0 . 3 1 + 0.02% at 300OK and - 0.45 + 0.02% at 77OK. We thank M i s s S. D. D a m l e f o r a s s i s t i n g in susceptibility measurements.
References 1. M. Hansen, Constitution of binary alloys {McGraw Hill, New York 1958} p.941. 2. M. Yessik, Phil. Mag. 17 (1968} 623. 3. L. F. Bates, Modern magnetism {Cambridge University P r e s s , London, 1951} p.133. 4. D.H. Martin, Magnetism in solids (The MIT P r e s s . Cambridge, Mass., U.S.A. 1967} p.65. 5. E.D. Jones and J. I. Budnick, J. Appl. Phys. 37 (1966} 1250.
649
PHYSICS
can d e t e r m i n e t h e e n e r g y l o c a t i o n of the c h a r a c t e r i s t i c p o i n t s b e l o n g i n g to the s i g n a l s A, B and C to be 2.788 eV, 2.804 eV and 2.760 eV, r e s p e c t i v e l y . T h e e n e r g y v a l u e s of 2.788 eV and 2.804 eV a g r e e in f a i r l y good w i t h t h o s e a s s o c i a t e d with e x c i t o n g r o u n d s t a t e E x l and the f i r s t e x c i t e d s t a t e E x 2 a s s i g n e d a l r e a d y by t h e p r e vious investigators |1,3]. The structure C might c o r r e s p o n d to the s i g n a l a s s o c i a t e d with an L0 phonon a s s i s t e d d i r e c t e x c i t o n c r e a t i o n p r o c e s s . "Then the e n e r g y of phonon b r a n c h ~w l is d e t e r m i n e d to be 28 m e V . T h i s v a l u e is a l i t t l e bit s m a l l e r a s c o m p a r e d with 31.4 m e V o b t a i n e d by H i t e et al. [3]. T h e r e m a i n i n g s t r u c t u r e D in t h e h i g h e s t e n e r g y r e g i o n m i g h t b e a r i s e n f r o m the e l e c t r o - r e f l e c t a n c e of the f u n d a m e n t a l e d g e of ZnSe. T h e l i n e s h a p e of t h i s s i g n a l h a s a s h a p e of G(-~) t y p e e l e c t r o - o p t i c a l f u n c t i o n [4]. T h u s t h e e n e r g y of the f u n d a m e n t a l e d g e (Eg) can b e d e t e r m i n e d to b e 2.811 eV at 90OK. By u s i n g t h i s d i r e c t e d g e e n e r g y , one can c a l c u l a t e the e x c i t o n b i n d i n g e n e r g y ; E B = (Eg - E x l ) = 23 m e V o r ~(Ex2 - E x l ) = 21 m e V . T h e s e v a l u e s a r e c o n s i s t e n t with t h a t o b s e r v e d by H i t e et al. A t e n t a t i v e m o d e l of the p r o b a b l e t r a n s i t i o n p r o c e s s and t h e i r e n e r g i e s a s s i g n e d f r o m the a n a l y s i s of d a t a a r e s u m m a r i z e d in fig. l(c). One d i s c r e p a n c y of
31p
LETTERS
10 February 1969
t h e r e s u l t a n t c u r v e f r o m fig. l(a) i s a n e g a t i v e d r i f t of the ~ R / R a p p e a r e d in the h i g h e r e n e r g y r e g i o n . T h i s r e a s o n m a y be due to a shift of z e r o l i n e in t h e AR m e a s u r e m e n t by s o m e u n known e f f e c t s (like a p h o t o - e l e c t r o - l u m i n e s c e n c e a b o v e t h e d i r e c t edge). A m o r e d e t a i l e d a n a l y s i s on both t h e e l e c t r i c f i e l d and t e m p e r a t u r e d e p e n d e n c e f o r v a r i o u s k i n d s of s a m p l e s (like i m p u r i t i e s d o p e d c r y s t a l s ) is now in p r o g r e s s . T h e a u t h o r s w i s h to thank M r . H. K i m u r a of the C e n t r a l R e s e a r c h L a b o r a t o r i e s , M i t s u b i s h i E l e c t r i c C o r p o r a t i o n , f o r his h e l p in s a m p l e preparation.
References 1. R.A. Forman and M. Cardona, II-VI semiconducting compounds, ed. D.G. Thomas {Benjamin Inc., New York, 1967) p. 100. 2. Y. Hamakawa, F.A. Germano and P. Handler, Phys. Rev. 167 (1968) 703 and in Proc. Intern. Conf. on the Physics of semiconductors, Moscow, July 1968 I-C-4, to be published. 3. G. E. Hire, D . T . F . Marple, M. Aven and B. Segall, Phys. Rev. 156 (1967) 850. 4. D.E.Aspnes, Phys. Rev. 153 {1967) 972.
MAGNETIC SUSCEPTIBILITY AND NUCLEAR MAGNETIC RESONANCE IN
Mn2P
S. K. M A L I K and R. V I J A Y A R A G H A V A N Tara Institute of Fundamental Research, Bombay, India Received 1 January 1969
The magnetic susceptibility of Mn2P shows a peak around ll0OK, indicating antiferromag~etic ordering. F r o m susceptibility and 31p Knight shifts in the paramagnetic state the hyperfine fields at two phosphorus sites have been found to be +3.5 and +21.8 kOe p e r ~tfl of Mn. NMR of 55Mn was observed from one of the manganese sites.
T h e m a n g a n e s e - p h o s p h o r u s s y s t e m f o r m s the c o m p o u n d s M n P , M n 2 P and M n 3 P [1]. We h a v e m e a s u r e d t h e m a g n e t i c s u s c e p t i b i l i t y (×) of M n 2 P w h i c h o r d e r s a n t i f e r r o m a g n e t i c a l l y at 103°K, and 3 1 p Knight s h i f t s (K) in M n 2 P and Mn3P. M n 2 P w a s p r e p a r e d by h e a t i n g t o g e t h e r s t o i c h i o m e t r i c a m o u n t s of m a n g a n e s e p o w d e r and r e d p h o s p h o r u s in an e v a c u a t e d s i l i c a t u b e at 8 0 0 ° C 648
f o r one day [2]. F i g . 1 c o n t a i n s a plot of 1 / × versus temperature, where 1/× (corrected for p o s s i b l e f e r r o m a g n e t i c i m p u r i t i e s [3]) s h o w s a b r o a d m i n i m u m a r o u n d l l 0 ° K c o r r e s p o n d i n g to an a n t i f e r r o m a g n e t i c o r d e r i n g . T h i s t e m p e r a t u r e is h i g h e r than the N ~ e l t e m p e r a t u r e (T N) of 103°K found by n e u t r o n d i f f r a c t i o n [2,4]. A b o v e N d e l t e m p e r a t u r e , × c o u l d b e f i t t e d to a C u r i e - W e i s s
Volume 28A. number 9
PHYSICS
law × = C / ( T - O) g i v i n g C = 1 . 8 5 ± 0 . 1 ( c o r r e s p o n d i n g to ~ D a r a = 3.8 + 0.2 p e r M_n) and 8 = = - 115 ± 10n01K. M n 2 P is h e x a g o n a l w i t h r e v i s e d F e 2 P ( C 2 2 ) s t r u c t u r e type. T h e r e a r e two i n e q u i v a l e n t Mn s i t e s Mn I and M n i i and two i n e q u i v a l e n t P s i t e s P I and PII, t h e l a t t e r in the r a t i o of 2 : 1. C o n s e q u e n t l y two 31p N M R l i n e s w e r e o b s e r v e d w i t h t h e i n t e n s i t y r a t i o of 2 : 1 f r o m P I and PII r e s p e c t i v e l y . T h e PII N M R l i n e had a h i g h f i e l d a n i s o t r o p y in line shape. Knight shift K I and KII f r o m the two s i t e s w a s p o s i t i v e and t e m p e r a t u r e d e p e n d e n t ( s e e fig. 1). T h e l i n e s e v e n t u a l l y d i s a p p e a r e d at 104 ± 2OK w h i c h a g r e e s v e r y w e l l w i t h T N found by n e u t r o n d i f f r a c t i o n . A g e n e r a l e x p r e s s i o n f o r the 31p Knight shift [5] m a y b e w r i t t e n a s K(T)
=g o + (N~)-IHhfX(T)
,
10 February 1969
LETTERS
40 I
80 I
120 I
TEMP. ( ° K ) 200
160 l
I
240
280
I
1
320
I~ x Id' ~M
22
20 ®
5"0
"22
®
4.0 ~0 K 3.
(1)
w h e r e Hhf i s t h e n e t h y p e r f i n e f i e l d p e r /1/3 at P s i t e . Fig. 1 c o n t a i n s K v e r s u s X p l o t s f o r P I and PII, f r o m t h e s l o p e s of w h i c h we get Hhf a s + 3 . 5 ± 0.2 k O e / g l 3 f o r P I and + 2 1 . 8 ± 0.5 k O e / f l ~ f o r PII r e s p e c t i v e l y . Mn I and P I a t o m s a r e in z = 0 p l a n e and M n i i and P H a r e in z = ½ p l a n e . E a c h p h o s p h o r u s a t o m h a s nine Mn n e i g h b o r s . T h e y a r e 3 Mn I at 2.30 and 6 M n i i at 2.52 A f o r PI and 6 Mn I at 2.32 and 3 M n i i at 2.46 ~, f o r PII. In o r d e r e d s t a t e [2] at 4OK, two M n i i a t o m s c a r r y l a r g e r m o m e n t (0.84 ± 0.03 ~ ) t h a n two Mn I a t o m s (0.01 ± ± 0.04 ~ ) w h i l e t h i r d Mn I and t h i r d M n i i c a r r y z e r o m o m e n t . F r o m N M R , we find t h a t PII n u c l e i e x p e r i e n c e a m u c h l a r g e r h y p e r f i n e f i e l d than P I i n s p i t e of t h e i r h a v i n g s i m i l a r m a n g a n e s e s u r r o u n d i n g s . T h i s c l e a r l y s u g g e s t s that M n - P i n t e r a c t i o n in b a s a l p l a n e i s m u c h s t r o n g e r t h a n out of p l a n e i n t e r a c t i o n . F u r t h e r it is i n t e r e s t i n g to n o t e t h a t we h a v e o b s e r v e d one 55Mn N M R at r o o m t e m p e r a t u r e w i t h a shift of - 0 . 4 ± 0.1%, p r e s u m a b l y f r o m t h o s e Mn a t o m s w h i c h c a r r y a s m a l l o r no m a g n e t i c m o m e n t . H o w e v e r , the l i n e w a s w e a k and b r o a d and so i t s t e m p e r a t u r e d e p e n d e n c e c o u l d not b e s t u d i e d . 31p N M R w a s o b t a i n e d in t e t r a g o n a l M n 3 P w h i c h h a s o n l y one p h o s p h o r u s site. T h i s c o m -
6'-
1.0
2.0
3"0
4.0
5,0
6.0
7.0
8-0
'X. xlO 3 e m u / m o l e
Fig. 1. 1/x(T ) versus T for Mn2P lower two curves are K(T) versus ×(T) for PI and PII"
pound w a s found not to o r d e r m a g n e t i c a l l y t i l l 77°K. T h e 31p Knight s h i f t s a r e - 0 . 3 1 + 0.02% at 300OK and - 0.45 + 0.02% at 77OK. We thank M i s s S. D. D a m l e f o r a s s i s t i n g in susceptibility measurements.
References 1. M. Hansen, Constitution of binary alloys {McGraw Hill, New York 1958} p.941. 2. M. Yessik, Phil. Mag. 17 (1968} 623. 3. L. F. Bates, Modern magnetism {Cambridge University P r e s s , London, 1951} p.133. 4. D.H. Martin, Magnetism in solids (The MIT P r e s s . Cambridge, Mass., U.S.A. 1967} p.65. 5. E.D. Jones and J. I. Budnick, J. Appl. Phys. 37 (1966} 1250.
649