Magnetism of VxTiS2 compounds

1175

Journal of Magnetism and Magnetic Materials 31-34 (1983) 1175-1176 MAGNETISM Y. T A Z U K E

O F V~TiS2 C O M P O U N D S a n d T. E N D O

Department o/Physics, Faculty of Sctem e, Ho~aMo Umversltv, Sapporo 060, Japan

Powder samples of V,TIS2 (0 _
V a n a d i u m atoms show interesting magneuc properties when they are incorporated into sulphides and selenldes [1-4] In these c o m p o u n d s the vanadium atoms, whether accompanied by other metal atoms or not, are distributed m a r a n d o m manner in the metal sites Susceptlbfltxes of these c o m p o u n d s show paramagnetic behavior and the data obey a C u r i e - W e i s s

I

5.72

0

C 0 0

571 0 0

5.70

0

law~

X = Xo + C / ( T -

O)

(1)

There have been several discussions as to the m a g m t u d e of the vanadium m o m e n t on the various sites [1-3]. In these c o m p o u n d s there are two kinds of metal sites' those m the full layers and those in the partmlly occupied layers The vanadium atoms are located in both kinds of layers, and this complicates the determination of their m o m e n t s T,tanium dlsulph, de, TIS 2, ~s composed of a repetition of three layers, two sulphur layers and a t~tanlum layer located between the sulphur layers There is an empty metal layer between adjacent sulphur layers We prepared powder samples of TIS z d o p e d with vanadium which is intercalated in the originally empty metal layer (hereafter we call this a vanadium layer) These samples are ideal magnetic systems for &scusslng the above problem V~TIS2 samples (0 < x _< 0.33) were prepared m vacuum at 500°C from a mixture of v a n a d m m powder and T I S 2 powder, the latter having been prepared in vacuum at 900°C. It took about 10 days to prepare samples with x < 0 2 and more than 20 days for x > 0 2. The color of the TIS 2 was gold, and that of the d o p e d samples became increasingly darker as x increased. The X-ray patterns of the d o p e d samples were the same as that of TIS 2 [hexagonal Cd(OH)2 type]. When samples were prepared at 900°C from the same starting mixture as above, different X-ray patterns corresponding to that of a sample prepared at 900°C from a mixture of the three elements were obtained, and the color of this sample was black These crystallographic data are explained in the following manner The arrangement of u t a m u m and sulphur atoms m the samples prepared at 500°C is the same as that m TIS 2 and the vanadium atoms are distributed randomly in the vanadium layers Titanium and vanadium atoms are distributed In all of 0304-8853/83/0000-0000/$03

342

341 •

I

340 0

I

0 []

I

02

•

l I

03

I

J

× Fig h Compos*tlon dependences of latticeparameters c (open circles) and a (closed circles)

the metal layers in the samples prepared at 900°C We report here experimental data on the samples prepared at 500°C Fig. 1 shows the x-dependences of lattice parameters a and c As the parameters are constant for x < 0.2, the vanadium atoms enter the T1S 2 crystal without expandmg it for x < 0.2 Interactions between the vanadium atoms and the host crystal for x < 0 2 may be weaker than that for x > 0.2, and this situation may influence the magnetic properties. The susceptlblhty X follow eq. (1) in the temperature range 10 K < T < 300 K Fig. 2 shows typical data. Fig 3 shows the x-dependences of the parameters X0, C and 0 determined by a least-squares fitting Full hnes m fig 2 show calculated values The X0 values seem to follow two straight lines one for x < 0.2 and the other for x > 0 2 This change at x - 0 2 may be connected with the change in the behavior of the lattice parameters at x - 0 . 2 It is hard to detect such a change m the behavior of C because of the large scatter of the data In the following we &scuss the effect of vanadium doping on the magneuc properties The 3d band is e m p t y at x = 0 because TI 4+ has no 3d electrons. The

00 @ 1983 N o r t h - H o l l a n d

1176

Y

Tazuke, T Endo / Magnemm of V TIS: ~ompound~

% (xlO-3emu/mo[e)

*j

%0( x10-4emu/mote) 2 It

0 25 t x=O * 33 * 01 0

o

÷

O 002 ~" :

2, I( ~.--o

o

)1 a

T(K) Fig 2 Typical susceptlblhty data measured at 16 1 kOe Compositions of the samples are shown in the figure Full lines show calculated values

o

C(emuK/mole) O

0,01

O o o

o

d o p e d v a n a d m m c o n t r i b u t e s electrons, w l u c h e n t e r t h e relatively wide t i t a n i u m 3d b a n d [5]. T h i s b a n d gives t h e c o n s t a n t s u s c e p t l b d t t y X0 T h e n u m b e r o f e l e c t r o n s t r a n s f e r r e d f r o m a v a n a d m m a t o m to t h e 3d b a n d for x < 0 2 m a y be d i f f e r e n t f r o m t h a t for x > 0 2, b e c a u s e t h e s l o p e s o f the Xo-X d e p e n d e n c e are d i f f e r e n t in the t w o r e g i o n s o f x W e c a n n o t be e x c l u d e the p o s s i b i l i t y o f a b a n d s t r u c t u r e c h a n g e at x - 0 2 A s a result of this b e h a v i o r of X0 we are led to t h e c o n c l u s i o n t h a t t h e t e m p e r a t u r e - d e p e n d e n t s u s c e p t i b i l i t y C / ( T - O) arises f r o m t h e v a n a d i u m a t o m s W e also c o n c l u d e t h a t a m a g n e t i c m o m e n t a p p e a r s o n every v a n a d i u m a t o m , at least for x < 0 2 T h i s c o n c l u s i o n IS d e d u c e d f r o m two e x p e r i m e n t a l facts t h e C u r i e c o n s t a n t C is p r o p o r t i o n a l to x a n d t h e v a n a d i u m a t o m s are d i s t r i b u t e d r a n d o m l y in t h e v a n a d i u m layers T h e r e h a v e b e e n d i s c u s s i o n s [1,2 ] in w h i c h a m o m e n t a p p e a r s on a v a n a d x u m a t o m t h a t h a s a s m a l l n u m b e r of m e t a l a t o m s as ~ts n e a r e s t n e i g h b o r s If a m o m e n t a p p e a r e d o n s u c h v a n a d i u m a t o m s m t h e p r e s e n t case, a n o n linear C - x d e p e n d e n c e w o u l d h a v e b e e n o b t a i n e d . T h e r e f o r e we c o n c l u d e t h a t a m a g n e t i c m o m e n t o f (0.63 _+ 0 05)/% is o b s e r v e d on e v e r y v a n a d i u m a t o m for x < 0 2. A d e v i a t i o n f r o m eq

0

I

9

° I. -5 i

O(K)

"

-10 0. . . .01 . . . 02 ×

o

•

0'3

Fig 3 C o m p o s m o n dependences of the parameters X0, C and 0 determined by a least-squares fitting in 10 K < T < 300 K (1) IS o b s e r v e d in t h e s a m p l e s with x > 0 1 at T < 10 K [3,4] T t u s b e h a v i o r will be r e p o r t e d in f u t u r e

References

[1] A B de V r i e s a n d C Haas, J Phys Chem Sohds 34 651 [2] S Funahash~, H NozaM and I Kawada, J Phys Solids 42 (1981) 1009 [3] Y Tazuke, K Watanabe and T Suzuki, J Phys Soc 50 (1981) 2900 [4] C Schlenker, C Landee, R Buder and F L~vy, J Magn Mat 15-18 (1980) 91 [5] J A Wdson, Phys Star Sol (b) 86(1978)11

(1972) Chem Japan Magn