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Magnetic properties of some tetragonal uranium compounds
R. Trok, Z. Żolnierek
To cite this version:
R. Trok, Z. Żolnierek. Magnetic properties of some tetragonal uranium compounds. Journal de
Physique Colloques, 1979, 40 (C4), pp.C4-79-C4-81. �10.1051/jphyscol:1979426�. �jpa-00218822�
JOURNAL DE PHYSIQUE Colloque C4, supplément au n° 4, Tome 40, avril 1979, page C4-79
Magnetic properties of some tetragonal uranium compounds
R. Trod and Z . Zolnierek
Institute for Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw, POB 937, Poland
Résumé. — On présente les résultats de mesures de susceptibilité magnétique effectuées dans un large intervalle de températures pour une série de composés tétragonaux d'uranium sous forme de poudres, ayant les structures cristallographiques de type PbFCl ou anti-Cu2Sb (de groupe spatial P4/nmm). On analyse ces résultats en utilisant la théorie du champ cristallin.
Abstract. — The results of susceptibility measurements in a wide temperature range (4.2-900 K) on a series of the tetragonal uranium compounds in a powder form, having either the PbFCl or anti-Cu2Sb type crystal structures (with P4/nmm space group), are presented with the crystal field analysis.
U r a n i u m f o r m s with t h e e l e m e n t s of I V , V a n d V I g r o u p a large class of t e t r a g o n a l , b i n a r y a n d t e r n a r y c o m p o u n d s w h i c h a r e closely related t o o n e a n o t h e r . T h e c o m m o n f e a t u r e for t h e m is t h e s a m e C4 v point s y m m e t r y of u r a n i u m central ion. This allows for analysing their m a g n e t i c p r o p e r t i e s in a similar m a n n e r . T o this class of c o m p o u n d s , a m o n g o t h e r s , b e l o n g t h e o x y - ( U O Y ) a n d nitro- ( U N Y ) chalcogenides with t h e P b F C l s t r u c t u r e (c/a < 2) a n d simple or m i x e d dipnictides U X2 a n d U X X ' as well as t h e only o n e existing u r a n i u m tin- chalcogenide : U S n T e . All t h e latter c o m p o u n d s crystallize in t h e anti-Cu2Sb t y p e crystal s t r u c t u r e (c/a > 2 ) .
T h e U O Y a n d U N S e or U N T e ( U N S d o e s n o t exist) t e r n a r i e s w e r e o b t a i n e d in t h e r e a c t i o n of
U 02 + U Y2 a n d U N + (Se or T e ) , r e s p e c t i v e l y , at t e m p e r a t u r e s of a b o u t 900 °C. T h e U X2 s a m p l e s w e r e s y n t h e s i z e d directly b y heating a m i x t u r e of u r a n i u m p o w d e r a n d r e s p e c t i v e p n i c t o g e n , w h e r e a s t h e U X X ' samples — b y mixing a n d heating t h e c o n s t i t u e n t binary c o m p o u n d s .
X - r a y m e a s u r e m e n t s indicated t h a t all t h e s a m - p l e s , e x c e p t for U N S e a n d U S b B i , w e r e single p h a s e . F o r t h e latter c o m p o u n d s s o m e additional w e a k reflections w e r e also s e e n o n X - r a y d i a g r a m s .
T h e p o w d e r magnetic susceptibility or magnetiza- tion a t l o w e r t e m p e r a t u r e s w e r e m a d e b y m e a n s of a n e l e c t r o n i c C a h n b a l a n c e or of a F o n e r vibrating s a m p l e m a g n e t o m e t e r . T h e m a g n e t i c susceptibility at higher t e m p e r a t u r e s ( a b o v e r o o m t e m p e r a t u r e ) w e r e m e a s u r e d o n an a d a p t e d analytical b a l a n c e .
T a b l e I. — Magnetic characteristic of some tetragonal uranium compounds.
C o m p .
U O S U O S e U O T e U N S e * U N T e * U P2
U A s2
U S b2
U B i2
U P A s U A s S b U S b B i * U S n T e
S t r u c t .
P b F C l
—
—
—
— anti- C u2S b
—
—
—
—
—
—
—
A / e m u \
' molj
0.828 0.798 0.828 0.517 0.437 0.490 0.724 0.760 1.019 0.386
— 1.250*
2.069**
1.046
B x 106
/ e m u \
^ m o l / 490 540 420 400 400 320 340 580 770 570
—
~ 0
~ 0 270
A / m o l \ ' e m u /
~ 0
~ 0
~ 0 - 8 0 - 1 0 0 - 1 8 0 - 1 0 0 - 9 0
~ 0 - 3 2 0
— - 1 2 0
- 5 0
~o
0P
(K)
~ 0
~ 0
~ 0 43 44 94 72 72
~ 0 151
— 150
~ 0 52
MP O B )
2.57 2.53 2.57 2.03 1.87 1.98 2.40 2.47 2.85 1.76
— 3.16 4.07 2.89
^ a f ( M B )
2.0 2.2 2.0
—
— 2.0 1.6 1.9 2.1
—
—
—
—
TN
(K)
56 75 164 90 59 202 273 205 180 264 259 140 70
* Ferromagnets.
* From 170-330 K.
** From 330-900 K.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979426
Fig. 1. -Temperature susceptibility fitting for UOSe to the following expressions : a ) the paramagnetic region :
b ) the antiferromagnetic region :
Results are plotted in figures 1 to 3 and summarized in the table I.
High temperature magnetic susceptibility measu- rements up to 900 K have shown that the function x-I(T) almost for all the compounds investigated is curvilinear and follows very well the equation :
where A, B and A are the constants defined in reference [I].
1. The PbFC1-type compounds. - The UOY compounds were found to be antiferromagnetic ma- ny years ago
[a].
As the table indicates the striking feature of the fitting of the experimental results to eq. (1) is the fact that for all the UOY compounds A .= 0 and the paramagnetic moment of uranium is almost the same and amounts to about 2.6 pB, and is higher than the ordered one. This means that at least the first excited crystal field level in the uranium oxychalcogenides is, in contrast, e.g., to the U,N,Z type compounds [I], not far in energy (300-400 K) from the ground state doublet T,,.UNSe and UNTe have been investigated magneti- cally for the first time. It was found that both of them are ferromagnetic below 90 and 59 K, respecti- vely. The high temperature susceptibility behaviour is for them similar to the UOY type compounds.
2. The anti-Cu,Sb type compounds.
-
The anti- ferromagnetic properties of the uranium dipnictideswere recognized also many years ago [I]. However, the low temperature magnetic properties of these compounds was not known up to now. It was found that for UP, and UAs, some increase in the suscepti- bility, whereas for USb, and U B i slight maxima, occur at low temperatures. The mixed UXX' pnicti- des show similar behaviour, except for USbBi which seems to be ferromagnetic below 140 K.
USnTe was magnetically investigated for the first time and it was found in the temperature dependence of susceptibility to exhibit two maxima ; one at 12-17 K and the second at 63-72 K, depending pro- bably on a slight difference in stoichiometry (Fig. 2).
These two maxima in susceptibility indicate likely
USnTe
3
0 20 40 60 80
T(K1 Fig. 2. -Temperature dependence of susceptibility for several samples of USnTe.
Fig. 3. -High temperature susceptibility fitting for UPAs, USbBi, UNSe and USnTe.
MAGNETIC PROPERTIES OF SOME TETRAGONAL URANIUM COMPOUNDS C4-81
the antiferromagnetic properties of this compound with a complex magnetic structure, which is now under investigation.
High temperature magnetic susceptibility fitting (Fig. 3) gives good accordance with eq. (I), like for the UOY and UNY compounds. However, a value of A determined from eq. (1) for the anti-Cu,Sb type compounds turned out to be very large (except for
UBi, where h = 0) and negative (see the table).
According to the crystal field diagram displayed in reference [I], which fits very well to the compounds considered here, only for UP, the ground state doublet
r,,
is very well separated from the others (paf=
pp) crystal field levels. On pro- ceeding from UP, to UBi, difference between these moments increases.References
[I] ZOLNIEREK, Z . and TRoC, R., J. Magn. Magn. Mater. 8 (1978) 210.
[ 2 ] LAM, D. J. and ALDRED, A. T., in The Actinides : Electronic
Structure and Related Properties, eds. A. J . Freeman and J. B. Darby (Academic Press, New York) 1974, Vol. 1, Chapter 3.
