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Submitted on 1 Jan 1978
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ANOMALOUS THERMAL BEHAVIOR AND
NUCLEAR SPIN RELAXATION OF LIQUID 3He IN
CONTACT WITH
LINEAR-CHAIN-ANTIFERROMAGNETS
S. Saito, M. Hanawa, K. Sato, T. Sato, Y. Nishina, T. Sugawara
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplement au n° 8, Tome 39, aout 1978, page C6-269
ANOMALOUS THERMAL BEHAVIOR AND NUCLEAR SPIN RELAXATION OF LIQUID 3He IN CONTACT WITH LINEAR-CHAIN-ANTIFERR0MA6NETS
S. S a i t o , M. Hanawa, K. Sato , T. Sato, Y. Nishina and T. Sugawara
The Research Institute for Iron, Steel and Other Metals Tohoku Univ., Sendai 980, Japan, and the Institute for Solid State Physios, Univ. of Tokyo Roppongi, Minato-Ku, Tokyo 106, Japan
Résumé.- On a observé des anomalies dans le comportement thermique et la relaxation nucléaire de He liquide en contact avec des substances antiferromagnétiques unidimentionnelles à des températures voisines de la température de transition magnétique, T .
A b s t r a c t . - Anomalies i n the thermal behavior and the n u c l e a r spin r e l a x a t i o n of l i q u i d He in con-t a c con-t wicon-th magnecon-tically one-dimensional ancon-tiferromagnecon-ts have been observed near con-t h e i r con-t r a n s i con-t i o n temperature, T N
The magnetic Kapitza conductance, h , has been theoretically explained in terms of the magne-tic dipole coupling through the boundary between liquid (or solid) 3He and the magnetic solid. The coupling is so weak that the effect has been detec-ted usually in the region of mK. Recently, one of the present authors has rported the observation of an anomalously strong magnetic coupling between li-quid 3He and a linear-chain-antiferromagnet Cu
(NH^^SO^.^O (hereafter denoted as CTS) /l/. The anomaly has been observed at a relatively higher temperature, 0.43 K. The experiment was motivated by the theoritical suggestion by Mills et al /2/.
In this report, we present the experimental results of anomalous thermal behaviors and the nu-clear relaxations Tj and T2 of liquid 3He in contact with linear-chain-antiferromagnets 4-hydro-xy-2,2,6,6,-tetramethyl piperidinoxy (TANOL) and CTS. Also, we discuss the reason why such a weak magnetic interaction causes a drastic thermal be-havior at a temperature so high as the order of 400 mK.
TAN0L-3He SYSTEM.- Figure 1 shows a typical experi-mental result on TAN0L-3He system. A single crystal of TANOL (T = 0.49 ± 0.01 K) in a cylindrical form
(y 4.5mm.d, 10.4mm.h), is immersed in liquid He
_2
(^ 1.7 x 10 mol, 99.995 %) contained in a Pyrex glass cell (8mm.i.d). A carbon resistance thermome-tern, R„, and an electrical heater are embedded in the crystal. Another thermometer, R^, is immersed in liquid He. The temperature of the system is controlled with a very slow increase from "v 1/2 T
upon the thermal balance between electrical heating (Q=6.7uW) and cooling by a dilution refrigerator.
TAN0L
?He
He,: 25930s )ft:8.41 MHz 6:6.7/.Wf H e N M R
10 t(min)
Fig. 1 : Experimental cell for TANOL- He system and the anomalies observed for R_, R^, R^ , and the satured line of 3He NMR. The temperature of the system is increased with time.
A multi-pen recorder is used for monitoring the saturated 3He NMR line by the CW method and the re-sistances of R„, R, and of R ™ , the thermometer immersed in the mixing chamber. An anomaly is ob-served near 0.48 K of R and 0.45 K of 1 as shown in figure 1. At the occurence of the anomaly, the temperature R_'once goes up, and then sharply drops down. At the same time the 3He NMR line shows a drastic decrease in the nuclear spin lattice rela-xation time, T .
CTS-3He SYSTEM.- Figure 2 shows an example of the experimental results for CTS-3He system. A single
crystal of CTS (TN = 0.43
+
0.01 K) in a cylindri- cal form (4.5 Q 6mm.d, 15mm.h), is immersed in 2.7 X 10-2 m01 of liquid 3 ~ e (99.9995 %) containedin a Pyrex glass cell (8mmi.d).
Fig. 2 : Experimental cell for C T S - ~ H ~ system and the anomalies observed for R piHRs. Rdo and the height of spin-echo signal o e NMR. R e tempera- ture of the system is increased with time.
Two carbon resistance thermomerters, R
UP and Rdown are immersed in liquid 3 ~ e . R is set near the
UP
top end of CTS, while Rdom near the bottom and the thermometer RS is embedded in the CTS crystal. An electrical heater is immersed a.t the bottom of li- quid 3 ~ e . The temperature of the system is increa- sed as in the case of TANOL-3~e. During the expe-
R and the intensity of rimental run, RUp, Rdown, S
spin-echo signal (after 90'-180' pulse) of the sa- tured 3 ~ e NMR are simultaneously recorded. An ano- maly is observed near 0.44 K of RS as shown in fi- gure 2. In the temperature region between 0.15 K and 0.7 K, T1 of liquid 3 ~ e is about 100 s and T, is 5 ms. No temperature dependence in T1 and T, has been observed in the region between 0.15 and 0.7 K except the region of the anomaly.
DISCUSSION.- From many experiments such as shown in figures1 and 2, we have concluded that an ef- fective way to observe the anomaly is to keep a temperature gradient in liquid 3 ~ e more than 20 m ~ / c m in the vertical direction of the cell. Presumably, the thermal conductibities, K, of these antiferromagnets are similar to that of CMN salt, while K of liquid 3 ~ e (7 X I O - ~ W / K ~ ) is several
hundreds times smaller. In the present experiments, we have both electrical heating near the bottom of liquid 3 ~ e and extraction of heat through the ther-
mal link. Hence, the large magnitude of K makes the temperature of the crystal rather homogeneous. The temperature of the whole parts of the crystal, therefore reaches TN simultaneously in the heating process. If such is the case, the temperature gra- dient in the liquid 3 ~ e near the top end of the crystal would be fairly large. In these circums- tances, a drastic change in h takes place.
mag
However, this change does not induce a drastic change in T1 of bulk liquid 3 ~ e , because 3 ~ e atoms at the boundary are only several tens of ppm at maximum compared with the bulk. Sucj consideration necessitates the presence of the second mechanism, by which the energy flow propagates to the bulk liquid 3 ~ e . One of the probable phenomena in the liquid is a very rapid convection driven by the magnetic coupling.
One of the authors (S.S.) wishes to thank Prof. D.M. Lee and Prof. J.C. Wheatley and Prof. S. Nakajima for many hepful discussions on the ex- perimental results. This work was supported by the Research Grant of the Iwatani Naoji Foundation
(1977).
References
/l/ Saito, S. Phys. Rev. Lett.
