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Hydrostatic pressure effects and neutron diffraction studies of CeBi phase diagram
H. Bartholin, P. Burlet, S. Quezel, J. Rossat-Mignod, O. Vogt
To cite this version:
H. Bartholin, P. Burlet, S. Quezel, J. Rossat-Mignod, O. Vogt. Hydrostatic pressure effects and neutron diffraction studies of CeBi phase diagram. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-130-C5-131. �10.1051/jphyscol:1979547�. �jpa-00218964�
JOURNAL DE PHYSIQUE Colloque C5, supplément au n° 5, Tome 40, Mai 1979, page C5-130
Hydrostatic pressure effects and neutron diffraction studies of CeBi phase diagram
H. Bartholin (*), P. Burlet, S. Quezel, J. Rossat-Mignod and O. Vogt (**)
DRF/DN, C.E.N.G., 85X, 38041 Grenoble Cedex, France
(*) Laboratoire Louis-Neel et S.N.C.I., C.N.R.S., 166X, 38042 Grenoble Cedex, France
(**) E.T.H. Laboratorium fur Festkoperphysic, Eidgenossische Technische Hochschule, Zurich, Switzerland
Résumé. — Le diagramme de phase de CeBi a été déterminé avec le champ magnétique appliqué suivant un axe < 100 y par mesure d'aimantation et diffraction neutroniqxie. Parmi les sept phases magnétiques observées certaines disparaissent sous pression.
Abstract. — The phase diagram of CeBi for a magnetic field applied along a < 100 > axis has been determined by magnetization experiments and neutron diffraction scattering. Some of the seven observed magnetic phases disappear under pressure.
The cerium monopnictides of CeSb and CeBi exibit unusual magnetic behaviours which are not under- stood at the present time. In CeSb an original magnetic ordering consisting of sandwiches of ferromagnetic and non magnetized (100) planes has been reported [1,2]. In CeBi neutron experiments in zero [3] and in high magnetic field [4] have shown the existence of three magnetic structures described by stacking sequences of ferromagnetic (100) sheets. However magnetization experiments give a more complicated phase diagram. In order to define the magnetic structures of these phases neutron experiments have been performed at the Siloe reactor of the C.E.N.
Grenoble. The hydrostatic pressure effects on the phase diagram have been investigated by means of magnetization experiments.
The phase diagram of CeBi for an increasing magnetic field applied along a < 100 > direction is shown in figure 1. The critical field values have been deduced from magnetization measurements (S.N.C.I.
Grenoble). In zero field, below JN = 25.5 K CeBi orders with a type I structure -1 1— down to T = 12.5 K where a first order transition occurs giving a type IA structure + -\ [3]. At low tempe- rature we confirm the existence of an intermediate phase having a net magnetization of one half the saturation value. It has been characterized by Lander et al. [4] and corresponds to the + + H— sequence.
But in addition four other phases have been evidenced by Bartholin et al. [5].
Therefore in order to know the nature of these phases a detailed investigation of the phase diagram has been performed by neutron diffraction scattering.
For all the value of the magnetic field and temperature the wave vector of the magnetic structure is along a
< 100 > axis (k = [00&]) which is also the direction of
CeBi
50. H / / < 1 0 0 > Increasing field
40. \
I k= 1.1.0. [ A f k T l 2 . . 1 0 .
s~* 2 \ 3 3 AS * * * - h • • • - • -
~30. / / M , , -
~° flli k= 1.2.2.1. i.o.
•Ju / If 1
5 5 5 5n_ / P / 9 * • • - * • • - • - W20 llHined phases. I I J^P " I
* ' r E*; k=s- fl I
\ rTTT I / , _ 'K-—o a ^ r^~n
_ ^' / i
* * — / i •»-•»-1 i
0 10 20 30 Temperature ( K )
Fig. 1. — (H, T) magnetic phase diagram of CeBi.
the magnetic moment. Thus all the magnetic struc- tures can be described as stacking sequences of ferromagnetic (100) sheets of magnetic moments which have a magnetization parallel or antiparallel to the < 100 > axis.
At low temperature, from the intensity of the superlattice peaks we deduce that the magnetic
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979547
HYDROSTATIC PRESSURE EFFECTS AND NEUTRON DIFFRACTION C5-131
moment value (2.1
+
0.1 h) is equal to the free-ion moment for all cerium ions. The two intermediate phases between the+ +
- - and+ + +
- phasesare characterized by several Fourier components, the value of the most intense component is successively
k = 0.545
+
0.005 = 6/11and
when the field increases. These phases are in fact the addition of the two units
+ +
- - and+ +
-, :the phases k = 6111 and k = 518 corresponds respectively to the
+ +
- -+ +
- -+ +
- and+ +
- -+ +
-+ +
-+ + - + +
- sequences.These structures give a net magnetization of 111 1 and 114 of the saturated value in agreement with magnetic measurements.
At high temperature the two phases observed between the
+ + +
- and+
-+
- phases are also combination of the two+ + +
- and+
-+
- units.In increasing field we observe first the Fourier components m, with k = f 113,
+
213, 1, 0 leading to the+ + +
-+
- sequence, in higher field the components with k = f 115,+
2/5,+
315,+
415, 1, 0 with amplitudes compatible with the+ + +
-+ + +
-+
- sequence. An accurate measu- rement of the superlattice peak intensities in these two phases and in the phase+ + + -
indicates that the moment value is not constant from plane to plane ; however this variation is rather small, about 0.2 p,.The exact structure cannot be determined because of the lack of the phase knowledge of each Fourier component.
Pressure effects on CeBi have been studied in high magnetic field and low temperature up to 8 kbar (S.N.C.I. Grenoble). At T = 4.2 K magnetization in the saturated paramagnetic phase and in the
+ + +
- phase are not changed by pressure : whereas the highest critical field increases (+ 0.44 kOe/kbar) and the lowest one decreases with pressure (- 0.24 kOe/kbar). At higher temperature the pressure effects are shown in figure 2 which represents the magnetization versus temperature at 1 bar and 7.6 kbar for several
-
1 Ce BiI
5
H I / <loo> Increasing temperatureTemperature (K)
Fig. 2. - Magnetization versus temperature for several magnetic fields and pressure.
values of the magnetic field. We must notice first an increase of the Nee1 temperature with pressure ( + 0.31 Klkbar). In high fields (b, c) the critical fields between the
+ + +
- and+
-+
- phasesincrease with pressure whereas they decrease at H = 12.2 kOe (a). In lower field the pressure induces a sharp decrease of the temperature at the first order transition between the type I and the type IA struc- tures (30 % for 10 kbar at low pressure). Moreover in high pressure intermediate phases disappear. We can summarize the pressure effects on the phase diagram as increasing the stability range of the
+ + +
- and+
-+
- structures and decreasing those of the+ +
- - structure. It must disappear at about 10 kbar.CeBi has a complex magnetic properties, many phases have been observed, their magnetic structures cannot be described as CeSb by ferromagnetic and non magnetized (100) planes. However the small modulation of the magnetic moment value observed at high temperature can have the same physical origin than the non-magnetized planes in CeSb. The pressure effects are similar in both compounds, the stability range of FP phases in CeSb and of the modulated phases in CeBi decreases with pressure.
References
[I] ROSSAT-MIGNOD, J., BURLET, P., VILLAIN, J., BARTHOLIN, H., [3] CABLE, J. W., KOEHLER, W. C., AIP Conf: Proc. 5 (1972) 1381.
WANG TCHENG-SI, FLORENCE, D. and VOGT, O., Phys. [4] LANDER, G. H., MUELLER, M. H. and VOGT, O., AIP Con$
Rev. B 16 (1977) 440. Proc. (1975).
[2] BARTHOLIN, H., FLORENCE, D. and VOGT, O., J. Phys. Chem. [5] BARTHOLIN, H., FLORENCE, D., WANG TCHENG-SI and VOGT, O.,
Solids 39 (1978) 89. Phys. Status Solidi (a) 24 (1974) 631.
