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HIGH-FIELD MAGNETIZATION STUDY OF THE
ANTIFERROMAGNETIC CHAIN SYSTEMS IN
[CH3)3NH]3Mn2X7 (X=Cl, Br) AT 4.2 K
J. Smit, M. Mostafa, L. de Jongh
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, suppl4ment au tiO 8, Tome 39, aolir 1978, page C6-725
HIGH-FIELD MAGNETIZATION STUDY OF THE ANTIFERROMAGNETIC
CHAIN SYSTEMS
IN
~
c
H
~
>
~
(x=cI,B~) AT
N
~
~
M
~
4.2~
Kx
~
J.J. Smit, M. Mostafa+ and L.J. De Jongh
KmerZingh Gnnes Laboratory, University of Leiden, The NetherZands
Resumb
.-
On donne les r6sultats des mesures d'aimantation des composbsECH~)
3 ~ g
3 ~ 1 1 ~ x 7 (X=Cl,Br)sous champs magnbtiques intenses jusqu'l 40 T 2 une temperature de 4,2 K. Chaque composb peut 8tre considbrb comme dtant constitu6 de deux chalnes antiferromagnetiques indbpendantes.
Abstract.- Magnetization curves in fields up to 40 T at a temperature of 4.2 K have been measyred for
DcH~)
3 ~ H 7 3Mn2X7 (X=Cl,Br).
These materials consist of two independent antiferromagnetic ~n~ chainsystems.
It has recently been shown by Caputo et al./]/ for the intrachain exchange constants,
Joct and
that the Mn2+ ions in the compound U ~ H 3 ) 3 a 3 M n 2 ~ 1 7 Jtetr, are listed in table I (T3Mn2C17) occur in two different types of chemical
linear chains, both running parallel to the hexago- Table I : Values for the exchange constants along the octahedra and tetrahedra. Uncertainties in the nal axis. A projection of the structure as viewed last digit are given in brackets.
perpendicular to the c-axis is given in figure 1 .
Fig. 1 : Projection of the structure of T3Mn2C17, as viewed perpendicular to the chain axeslll.
The Mn atoms are either octahedrally or tetrahedral- ly coordinated by chlorine atoms, and the chains are well separated from one another by the (CH3)3NH groups.
Susceptibility experiments on powders of T3bh2C17 were also performed by Caputo et al./]/, whereas MacElearney/2/independently studied the sin- gle crystal sugceptibilities of this material, as well as of the sister compound/3/ T3Mn2Br7(which is probably isostructural)
.
All susceptibility data were analysed assuming antiferromagnetic Heisenberg interactions between M ~ Z + ions along the chains and zero magnetic coupling between chains. Values found +on leave from : Physic Dept., Cairo University,Giza, Egypt
-(l) -0.20(5) this work
-4.5(5) -0.20(5) this work
The value Joct/k =
-
8 K for the octahedra chains in T3Mn2C17 is quite close to the interchain exchan- ge J/k"
-
7 K in the prototype linear chain anti- ferromagnetDcH~)
3 g ~ n ~ 1 3 (TMMC). This is to be expected since the octahedra chains are quite simi- lar to those occuring in TMMC. The values found for Jtetr are much smaller because of the less favoura- ble superexchange paths along the tetrahedra chains(involving two C1 anions).
We have performed high-field magnetization measurements on single-crystal specimens of T3Mn2X7
(X = C1,Br)that were kin.dly provided by Dr. McElear- ny. The sampdes were in the form of long rods, with the field parallel to the rod axis, which also is the c-axis. A previously described141 pulsed-field apparatus was used, which produces field-pulses in the form of half-a-sine, with a pulse duration of 20 ms. Calibration of the signal was accomplished by comparison with the saturation moments of para- magnetic salts.
The behaviour of the magnetization, as shown
C
W
0 20 40
MAGNETIC FIELD ( T E S L A ]
Fig. 2 : Experimental magnetization curves at 4.2 K for T3Mn2C17(m) and TsMn2Br7(0). Solid curves are theoretical predictions, as discussed in the text.
in figure 2, agrees with the assumption of two in- dependent antiferromagnetic chain systems, with
IJtetrl<<l Joctl. From the value J 2
-
0.2 K onetetr
expects a saturation of the magnetization of the tetrahedra chains in relatively low fields already. Indeed, the magnetization is rapidly increasing in the low-field region, reaching a value of half the saturation moment at about 10 T. For higher fields the magnetization rises much more slowly, reflec- ting the contribution of the octahedra chains with their much large intrachain exchange.
The solid curves in figure 2 represent calcu- lations assuming again fully isolated antiferroma- gnetic chains. In a previous publication/S/ we have already presented predictions for the magnetization of the antiferromagneitc S = 5/2 Heisenberg chain at various relative temperatures kT/
I
JI,
as obtainedfrom extrapolations from finite rings containing up to 5 spins. We have used these predictions to estimate the contributions of both the octahedra and tetrahedra chains, varying the values for J and
oct Jtetr so as to obtain the best fit for each c o w pound. The results for the exchange parameters are included in table I and compare favourably with the earlier estimates. The present experiment determines more sensitively the larger exchange J than do
OC t
the susceptibility measurements. Thus both types of experiment nicely complement each other, and appear to agree with the assumption of two independent an- tiferromagnetic chain systems in these materials.
experiments, and to D. de Klerk and W.J. Huiskamp for their interest. This work is part of the re- search program of the Stichting F.O.M. with finan- cial support from Z .W.O. One of us (M.M.) thanks the Ministery of Education of the Netherlands for a grant during her stay in Leiden.
References
/I/ Caputo,R.E., Roberts,S., Willett,R.D. and Gers- tein,B.C., Inorg. Chem.
15
(1976) 820/ 2 / McElearney,J.N., Inorg. Chem.
15
(1976) 823 /3/ McElearney,J.N., To be published/4/ Jordaan,H.A., Wolf,R. and De Klerk,D., Physica 69 (1973) 129
-
/5/ Smit,J.J., De Jongh,L.J., Blgte,H.W.~. and De Klerk,D., Coll. Int. CNRS no 242 "Physique sous champs magnstiques intenses" Grenoble (1 975) 253
![PROTON RELAXATION NEAR THE SATURATION FIELD IN AN S = [MATH] ANTIFERROMAGNETIC CHAIN SYSTEM](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==)