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Anisotropic susceptibilities of UP, UAs and USb single crystals
G. Busch, F. Hulliger, O. Vogt
To cite this version:
G. Busch, F. Hulliger, O. Vogt. Anisotropic susceptibilities of UP, UAs and USb single crystals.
Journal de Physique Colloques, 1979, 40 (C4), pp.C4-62-C4-63. �10.1051/jphyscol:1979418�. �jpa-
00218814�
JOURNAL DE PHYSIQUE Colloque C4, supplkment au no 4, Tome 40, avril1979, page C4-62
Anisotropic susceptibilities of UP, UAs and USb single crystals
G. Busch, F. Hulliger and 0. Vogt
Laboratorium fur Festkorperphysik, ETH, CH-8093 Zurich, Switzerland
R6sum6. - Les susceptibilit6s de UP, UAs et USb ont 6t6 mesurkes.
Abstract.
-
Susceptibilities of UP, UAs and USb are reported.Susceptibility measurements on ( 100) single crys- tals are plotted in figure 1. Diamagnetic corrections (UP : -64, UAs : -83, USb : - 105 x loe6 cm3/mole) were applied. For UP and UAs the slopes of the reciprocal susceptibility curves slightly de- crease at higher temperatures in good agreement with data of TroC and Lam [I]. For USb, however, we obtained a perfect straight line from 300 to 1 200 K with n, = 3.64 pB,
ep
=+
140 K. Our single crystal data thus fairly well agree with earlier powder measurements. Arguments have been put forward which favour 5fZ and others that plead for 5f3, and possibly truth lies between. Extrapolating from Th to U tetravalency was first assumed for all U monopnictides [2, 33. Roughly one free electron per formula was indeed derived from Hall measure- ments, namely 0.88 for UN and 0.7 for UP [3].Lemmer and Lowther [4] analysed the magnetic data of UN based on a 5f2 configuration. TroC and Lam [I] obtained a reasonable 'fit between theoreti- cal and experimental data for UP and UAs only based on 5f3 with
r:)
lying lowest. For USb Lander et al. [5] calculated the cross-section for various ground-state configurations and obtained agreement only with 5f3 and ary'
ground-state, i.e. with acrystal-field potential of opposite sign to that assumed above for UP and UAs.
The appearance of U monopnictides discredits a pure 5fZ configuration. However, if we trust in the ionic radii of Shannon [6] then the U configuration is not pure 5f3 either. In figure 2 we have plotted the lattice constants of the Th and U rocksalt phases versus those of the Gd compounds. For isovalent pnictide (MY) or chalcogenide (MX) series one would expect 45" straight lines, as found for ThX and Thy. The dotted line below the experimental points stems from GdX, GdY. Since
it corresponds to a Th4'Y series without the excess valence electron. The observed shift then should be
Fig. 1 . -Inverse susceptibilities of UP, UAs and USb single Fig. 2. -Lattice constants of the Th and U rocksalt phases crystals oriented with H 11 ( 100 ). versus those of the Gd compounds.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979418
ANISOTROPIC SUSCEPTIBILITIES OF UP, UAS AND USb SINGLE CRYSTALS C4-63
due to the 6d electron. The radius of U3+ lies giving us the true value of the susceptibility which between that of La3' and Ce3', while differs by more than a factor of 2 from the multido- main susceptibility. At 60 K the critical field is r(U43 = r(Er3+)
.
lower, decreasing further with increasing tem- Assuming similar features of the Th4' and U4' curvesand fixing UN as true SfZ we obtain a shift down- wards for U4'Y. Then the points for UP, UAs, USb and UBi well lie between the U 4 Y and the U3'Y line, thus pointing to a mixed valency.
Below T , it is difficult to align the domains, due to the fact that anisotropy is strong and consequently the Bloch walls are extremely narrow. As can be seen in figure 3 we measure on a virgin UAs crystal at 4.2 K magnetic moments which depend strictly linearly on the applied field up to 40 kOe. Above 70 kOe only do we obtain a single domain crystal
perature.
We have found that all samples under investiga- tion could be made. single domain crystals by field cooling through TN in a field of at least 100 kOe.
This method allows us to determine reproducible
x
values. Figure 4 shows for the example of UP that below TN the susceptibilities depend strongly on the direction of the applied field. Our experiments confirm that the magnetic moments are confined to the ( 100 ) axis since this is the direction of maximum moment for a given applied field. Earlier powder measurements of other authors fall somewhere between our curves for the ( 100 ) and ( 1 1 1 ) d' uec-
References tion.
[I] TRoC, R. and LAM, D. J., Phys. Status Solidi ( b ) 65 (1974) [4] LEMMER, R. H. and LOWTHER, J. E., J. Phys. C 11 (1978)
3 17. 1145.
PB
- -
[2] GRUNZWEIG-GENOSSAR, J., KUZNIETZ, M. and FRIEDMAN, F . , [5] LANDER, G. H., MUELLER, M. H., SPARLIN, D. M. and VOGT,
Phys. Rev. 173 (1968) 562. O . , Phys. Rev. B 14 (1976) 5035.
[3] KUZNIETZ, M., Rare Earth C o d . , Durham 1971, p. 162. [6] SHANNON, R. D., Acta Cryst. A 32 (1976) 751.
I I
- 1UAs I I X
(100) 0 8 -
300
06 -
-
-
UPH = 6 0 hoe
04 -
0 10 20 30 40 50 60 70 HlkOe)
0 I
-
0 5 0 I 0 0 150 200 250 T ( K )
Fig. 3. -Magnetization (in magnetons per U atom) of a virgin
UAs crystal for increasing and decreasing field applied along the Fig. 4.
-
Inverse molar susceptibility (in emu) of UP versus( 100) axis. temperature as a function of crystal orientation.
