Detection of Ferromagnetic Domains in a Two-Dimensional Nuclear-Spin System

Magnetic Phase Transition in a Nanonetwork of SolidHe3in Aerogel

“…By integrating the heat capacity peak at low fields, S ¼ R C=TdT we estimate that the entropy change per atom is $0:05k B . A transition from a ferromagneticlike high-field phase to a low-field antiferromagnetic (V 2 ) phase has also been predicted [22], and possibly observed experimentally [23], for solid 3 He films in contact with bulk liquid. Our experiments may constitute the first observations of a similar ordering in a restricted nanoscale geometry.…”

Zero-field magnetic order in the boundary layers ofHe3on Grafoil

“…This effect was seen as a spin-flop transition in a prior experiment with Ho perpendicular to the Grafoil planes. 2 The second and more interesting effect of the dipole energy is to allow long-range order at sufficiently low temperatures. Yafet, Kwo, and Gyorgy 7 have shown that the first (low-temperature) spin-wave correction to an assumed ferromagnetically ordered state is finite in two dimensions when the long-range part of the dipole energy is taken into account.…”

“…A dc SQUID is used as a preamplifier for the NMR detection. The experimental arrangement differs from prior work 2,9 in that the static Ho field is applied parallel 10 (as opposed to perpendicular) to the Grafoil planes and we may alter this HQ field even at the lowest temperatures by using a 400-turn superconducting solenoid powered from a room-temperature current source. Noise from the leads is shorted out with a superconducting shunt.…”

Two-Dimensional Ferromagnetism of aHe3Film: Influence of Weak Frustration

“…The present experiment was performed in magnetic fields B 0 ) =, where we expect the influence of the dipolar interaction to be a small perturbation compared to the Zeeman gap, and finite size effects. Our work cannot rule out the occurrence of a finite temperature phase transition in this system at B 0 < , particularly, given the interesting NMR spectra observed in surface boundary layers [20]. In the limit B 0 ( , the dipolar interaction forces the spins into the plane, and thus into the XY symmetry class, leading to a distinct ground state [32].…”

“…We note that in sufficiently low magnetic fields the magnetization vector is in general misoriented relative to the magnetic field due to the dipolar field; when B 0 ( the dipolar interaction forces the spins to lie in the plane [20]. For ¼ 0 the onset of this tilting occurs when B 0 < 2=.…”