NMR MEASUREMENTS ON LIQUID ³He CONFINED IN ALUMINA AND PLATINUM POWDERS AND GRAFOIL

Abstract

Nous présentons des mesures de la susceptibilité et du temps de relaxation Ti de l' 3 He liquide confiné dans du grafoil, dans de la poudre d'alumine de 400 A et dans de la poudre de platine de 8u. Nous observons une susceptibilité de Curie-Weiss correspondant à une monocouche d'^He adsorbé qui serait responsable du fort taux de relaxation. Ces effets sont supprimés par quelques couches d ,l *He.

Model nuclear relaxation time of inhomogeneous fluids near a substrate: Liquid 3He in confined geometries or physisorbed molecular systems

“…The features described in (i) and (ii) agree qualitatively with the observed behavior for TI(T) of Ref. 5. In the case where 4He was introduced to coat the walls, one still finds a small Curie-Weiss contribution to the susceptibility, indicating that part of the high-density fluid 3He is still present.…”

Pressure-induced ferromagnetic solidHe3layer onHe4preplated graphite

“…On the other hand, the surface magnetism for various materials filled with liquid 3 He was investigated in the 1970s and the magnetization was found to show a ferromagnetic tendency with Weiss temperature around 0.5 mK. [2][3][4] A very recent study on liquid 3 He magnetization in Grafoil has revealed that the third and the fourth layers grow as solid with increasing the liquid pressure. 5 These upper solid layers show a strong ferromagnetic tendency that depends on the liquid pressure.…”

“…The introduced 4 He gas corresponds to 2.5 and 3.5 layers of 4 He ͑total 4 He densities of 26.6 and 35.8 nm −2 ͒, respectively, if we use 12.8 and 9.2 nm −2 as the maximum 4 He areal density of graphite for the first layer and the upper layer. Preferentially, adsorbed 4 He was annealed for several hours at 4.2 K. To avoid 4 He desorption, 3 He gas was liquefied slowly at temperatures below 100 mK. The results of 3 He magnetization did not change even after a few months, indicating that the pressure induced solid 3 He layer is expected to reach its equilibrium, owing to its close contact with bulk liquid 3 He.…”

“…In particular, 3 He films adsorbed on graphite have extensively been studied, owing to the atomically flat surface and large surface area of graphite. 1 The previous investigations on the adsorbed film have revealed that the first and the second atomic layers solidify on the graphite surface, while the upper layers above the second one exist as liquid.…”

“…It shows a strong ferromagnetic tendency, probably due to the intralayer exchange interaction. 3 He atoms bound on the surface of various materials form a unique system to study two-dimensional magnetism. In particular, 3 He films adsorbed on graphite have extensively been studied, owing to the atomically flat surface and large surface area of graphite.…”