Anisotropic Effects in Antiferromagnetic MnSb 2 O 4 and NiSb 2 O 4 : Structural and Vibrational Evolution Studies
- PDF / 268,531 Bytes
- 6 Pages / 416.88 x 635.4 pts Page_size
- 117 Downloads / 205 Views
ANISOTROPIC EFFECTS IN ANTIFERROMAGNETIC MnSb 2 0 4 AND NiSb 2 0 4 : STRUCTURAL AND VIBRATIONAL EVOLUTION STUDIES
J.R. Gavarri, R. Chater, F. Genet E.R.A. au CNRS no 456, Ecole Centrale des Arts et Manufactures 92290 CHATENAY-MALABRY et Laboratoire de Chimie Physique Universit6 Paris 13, 93430 VILLETANEUSE, France
ABSTRACT Powdered samples and crystals of the antimony isomorphous MnSb 2 0 4 and NiSb 2 0 4 have been prepared using hydrothermal synthesis. The anisotropic elastic and magnetic properties of these tetragonal structures are compared, using low temperature diffraction techniques (X-ray and neutron) and Raman scattering experiments. Magnetostrictive effects in MnSb 2 0 4 are interpreted. An anomalous frequency shift is observed below 70 K and the change of the Gruneisen constant is interpreted.
INTRODUCTION The antimony isomorphous oxides MnSb 2 0 4 and NiSb 2 O4 belong to the 4 4 2 2 2 2 general family MeX 2 0 4 (Me=Pb , Sn 4 and X=Pb + or Me=Zn , Ni , Mn , 2 2 3 3 Fe +, Co + and X=Sb +, As +) ; the structures are tetragonal (space group P4 2 /mbc) [1]. Previous works using X-ray and neutron diffraction [2-7] showed that some of these materials could present interesting anisotropic elastic or magnetic properties. Using elementary models [5], it has been possible to evaluate the compressibility, several elasticity constants sij(Pa-),
the Griineisen constants y = 0
Debye temperatures ( a,
0c). In MnSb
-c
x (
-1 and the anisotropic
2 04
a thermal expansion anomaly was 1 dc . observed at low temperatures (T < 115 K) : mc = c-T is maximum at about 70 K. On the contrary a negative ac value is observed in NiSb 2 0 4 in this temperature range. Magnetic spin orderings have been evidenced in these two isomorphous oxides [7].
SYNTHESIS Using solid solid reactions (MeO + Sb 2 0 3 ) under nitrogen flux it has been possible to prepare powders of ZnSb 2 0 4 , NiSb 2 0 4 but not of MnSb204. This last compound was firstly prepared using mixtures Mn + Mn3 0 4 + 4 Sb 2 0 3 under static vacuum, at 475'C [7]. The reaction was not complete. Recently we have synthesized MnSb 2 0 4 using hydrothermal conditions [8]; the initial products have been successively Mn + Mn3 0 4 + 4Sb 2 03 and MnO + Sb 2 0 3 . In a recent TABLE I.
(a)
Previous results : Ref [7]
; (b)
Synthesis
MnSb
Conditions
Mn + Mn3 0 4 + 4Sb 2 03 (b) hydrothermal conditions, 495°C, 1000 bar, 8 days (b) MnO + Sb 2 0 3
2 04
NiSb 2 04
hydrothermal conditions 0 510 C, ' 1000 bar, 8 days
Mat. Res. Soc.Symp.
Proc. Vol.
Present results and Ref [101.
(a) nitrogen flux, 500'C, 4 days (b) hydrothermal conditions 0 1% HF, 500 C, 1000 bar 10 days
21 (1984) OElsevier Science Publishinq Co., Inc.
214
study we have characterized the non stoichiometry of MnO [9] which is very stable under normal conditions. Using MnO + Sb 2 03 mixtures, various sizes of 2 crystals were obtained (maximum dimensions = xO.IxO.1 mm) in ten days. The most common habit is prismatic and the colours vary from light green to dark green. The Table I reassembles the principal res
Data Loading...
