LOW TEMPERATURE MAGNETIC SUSCEPTIBILITY OF [(CH3)3NH] 3Cu2Cl7 A ONE DIMENSIONAL S = 1/2 FERROMAGNET

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LOW TEMPERATURE MAGNETIC

SUSCEPTIBILITY OF [(CH3)3NH] 3Cu2Cl7 A ONE

DIMENSIONAL S = 1/2 FERROMAGNET

C. Landee, R. Willett

To cite this version:

JOURNAL DE PHYSIQUE _{Colloque C6, supplPment au no 8, Tome 39,} aolit 1978, page

C6-741

LOW

TEMPERATURE

MAGNETIC SUSCEPTlBl

LlTY

O F

~ c H ~ )

3 ~ q

3 C ~ 2 C 1 7

A

ONE-DIMENSIONAL

S

= 112 FERROMAGNET

C.P. ~andee+ and R.D. Willett

Department of Chemical Physics, Washington S t a t e University, PulZman, Washington,99169, U.S.A.

Gsum6.- On a mesur6 la susceptibilit6 magn6tique d'un composd. en poudre de

U C H ~ ) ~ ~

3 ~ ~ 2 ~ 1 7 de 2

1 300 K. La susceptibilitd diverge fortement 1 basse temperature et on l'a interprstde c o m e due B

une chaTne ferromagndtique fortement couplde (J/k = 72 K) d'ions de cuivre en coordination octaddri- que plus une chaine antiferromagndtique plus faiblement couplde (J/k =

-

13 K) d'ions de cuivre en coordination tdtraddrique. Les interactions antiferromagndtiques entre chaines se traduisent par un maximum de XT observe

a

3,8 K. Un modPle pour expliquer ce maximum indique un dchange trPs faible

(3' /k %

-

0,l K) entre les chatnes.

Abstract.- The magnetic susceptibility of a powdered sample of

UCH~)~NH~

3C~2C1,ha~ been measured from 2-300 K. The susceptibility is strongly divergent at low temperatures and has been interpreted as due to a strongly coupled (J/k = 72 K) ferromagnetic chain of octahedrally coordinated copper ions plus a weakly antiferromagnetic (J/k =

-

13 K) chain of tetrahedrally coordinated copper ions. Evi- dence for antiferromagnetic interactions between chains isseenin the maximum of XT observed at 3.8

K. A model to account for this maximum indicates very weak (J'/k

2

-

0.1 K.) interchain exchange.

INTRODUCTION AND EXPERIMENTAL- This paper reports

r

I 1

3.0

on the magnetic susceptibility measurements made on

ECH~)

3 ~ ~ 1

3C~2C17, the fourth known example of a ferromagnetic, S 1/2 Heisenberg linear chain. The

other such compounds reported are

UCH~)

3 ~ H 7 CuC13.

-

_{2 6}

2H20 /1,2/, CuCl2.~MS0/3/ and CuC12.TMSO 131.

g

2.4 The crystal structure of the present compound Y

¶ consists of two types of copper chains well separa- 2.2

1

o \

ted by trimethylananonium groups/4/ : one chain con- sists of Eucl3-Jn arranged in face sharing octa-

edra and the other chain consists of distorted te- 18

trahedral groups P U C ~ I , ~ ~ stacked over one another.

The present compound is the copper analogue of the 16

I

1

RCH~)

3 ~ ~ 1

3Mn2X7 compounds which have recently been 2 4 6 8 10 12 14 l6 18

studied for X = C1 /5,6/ and X = Br 171. TEMPERATURE (K) The magnetic susceptibility of a powdered sam

ple was measured between 2 and 300 K in a PAR Vi- brating Sample Magnetometer in a field of 5 kOe. The susceptibility increases much more rapidly than Cu- rie-like behaviour and continues to rise rapidly at 2 K. The product XT (figure I) rises rapidly as temperature is lowered, indicating ferromagnetic (FM) interactions. However, XT shows a maximum at 3.8 k 0.15 K. The Curie sum of Coct = 0.449 from the octahedral and Ctet = 0.437 for the tetrahedral copper ions.

DISCUSSION.- The data for T > 1 0 0 K have been fit

-P

Present address : CNRS, Groupe des Transitions de Phases, Avenue des Martyrs, Grenoble, France

Fig. 1 : The product of susceptibility times tempe- ratures (xT) is plotted against temperature (T). The data show a maxima at 3.8 i: 0.15 K. The solid line is the best fit to the data over the temperature range 2-300 K for the molecular field &del as des- cribed in the text.

to the high temperature series expansion results of the FM S = 112 linear chain of Baker et a1.181. With the tetrahedral ions assumed paramagnetic, a value Jik = 59 K was found. However, antiferromagnetic

(AFM) interactions are likely within the tetrahedra chain /6,7/, so 59 K m s t be considered as the sum of Jm (the*FM exchange parameter of the octahedral chain) and Jm (the AFM exchange of the tetrahe-

dral chain). Fitting the data to a sum of Baker's expression/8/ for the I-D FM susceptibility and an expression for the I-D S 112 AFM susceptibility /8,9/ gave a fit within one percent between 50 and 300 K for values J /k = 72 K and Jm/k P

-

12 K.

FM

However, at lower temperatures the calculated sus- ceptibilities increase much more rapidly than the data.

The distinctive feature of the data at low temperatures is the maximum of kT at 3.8 K. The simple model of two independent chains cannot ac- count for this feature since the I-D FM model in- creases far more rapidly than the I-D AM decreases. It has been assumed that weak interchain AFM cou- pling is present in the compound. A simple molecu- lar field correction/lO/ to the susceptibility was used to account for this coupling and was able to produce a maximum in XT with a reasonable overall fit. Allowing Jm and Z'J' (the molecular field pa- rameter) to vary,

( I

J

~

"8s constrained to equal

I

Jm- 59) the best fit occurred for Jm/k = 73 K (Jm/k =

-

14 K) and Z'J1/k = : 0.45 K. This fit appears as the solid line in figure 1. The predicted peak of XT appeared at 3.8 K, disagreeing with the data by three percent. Systematic deviations as lar- ge as six percent appeared between 10 K and 30 K with the fit better than two percent from 70 K to

140 K and within one percent above 170 K. These de- viati'ons are consistent with a small amount of Ising

like anisotropy in the exchange.

These results do indicate the presence of

weak

interchain AFM coupling in

ECH~)

3 ~ ~ 7

3Cu2C17. Exa- mination of the crystal structure shows the closest

D

C 1 4 1 distances between neighboring chains is 5.8 A. The small interchain exchange parameter observed does not seem inconsistent with these distances. In conclusion, TMA3Cu2C17has been found to consist of a strongly ferromagnetic S = 112 Heisen- berg linear chain and a more weakly coupled antifer- romagnetic chain. In addition, a weak interchain AFM cpupling,

I

J'

1

/k

2

0.1 K causes the product XT to reach a maximum at low temperatures.

References

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/ 2 / Algra,H.A., De Jongh,L.J., Huiskamp,W.J.,and Carlin,R.L., Physica (1 977) 187

/3/ Willett,R.D., Swank,D.D. and Landee,C.P., Am. Chem. Soc. 175th Nat. Meet. Anaheim, Ca. Mar.

12-17 1978

/4/ Clay,R.M., Murray-Rust,P. and Murray-Rust,J., J. Chem. Soc. (London); Dalton Trans. 1973(6) (1973) 595

/5/ Caputo,R.E., Roberts,S.A.. Willett,R.D. and Gerstein,B.C., Inorg. Chem.

15(4)

(1976) 820 ' /6/ McElearney,J.N., Inorg. Chem. 15(4) (1976) 823 /7/ McE1earney.J.N.. Inorg. Chem.

17(2)

(1977) 248 /8/ Baker,G.A.Jr., Rushbrooke,G.S. and Gilbert,H.F.,

Phys. Rev. 135(5A) (1964) 1272

/g/ Bonner,J.C. and Fisher,M.E., Phys. Rev. 135(3A) (1964) 640