Ferromagnetism of 3He Films

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Ferromagnetism of 3He Films
Hans M. Bozler Collaborators Christopher M.
Gould Jinshan Zhang Yuan Gu Kevin White
Funded by the National Science Foundation
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Towards understanding ordering in

• Introduction to the ferromagnetic region of
  3He on grafoil
• USC experiments on grafoil using SQUID NMR
• Progress report on using ZYX graphite

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In 2-d
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Short digression on techniques.
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Pulse CW NMR drive circuit and pick-up circuit.
Red outlines are shields.
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Advantages of the very wide bandwidth from SQUID
NMR
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Typical NMR signals
Coverage 26 atoms/nm2
T4.6 mK
T1.6 mK
T4.6 mK
T0.8 mK
T0.37 mK
Requires CW NMR for analysis
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Field dependence
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NMR absorption lines for 22.5 atoms/nm2 under
0.35 mT applied field.
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The platelet angles distribution can be described
as
The effective field Heff is the combination of H0
and ?M0., and ?m in the angle relative to
platelet normal.
The static field H0 is applied at an angle ?h off
the normal to the Grafoil plane. The
magnetization points at an angle ?m off the
normal.
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Linewidth and dipolar field extracted from
lineshapes
Dipolar field
Linewidth
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Comparison with the Nearest Neighbor Heisenberg
Model
Also note that the when used to fit data, the
Heisenberg spin wave theory gives N as a function
of H0 not physical.
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These results do not conflict with the Multiple
Spin Exchange Model except weak effects can
dominate in the case of the two phase region
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• Length scales
• Structural coherence
• Typically 10 -20 nm
• Based on scattering measurements
• Long range effects?
• Should be greater than 10-20 nm
• Perhaps facet size
• Magnetic correlation length

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Estimated coherence length from P.
Kopietz, P. Scharf, M.S. Skaf, and S.
Chakravarty Europhys. Lett.
(1989).
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Progress report on high coherence substrate (ZYX)

• Coherence length is approximately 10 times
  greater
• Angular dispersion is much less
• Isotropic background?
• Experiments are difficult
• Small surface
• Poor thermal contact

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Improved SQUIDs
Quantum Design modulation Peter Day 2-stage SQUID STAR Cryo 2-stage SQUID
Input coil coupling 0.18 ?A/?0 2.2 ?A/?0 7.63 ?A/?0
BandWidth 30-50 KHz 1-1.2 MHz 1.3 MHz
Noise (no load) 3.84 ??0/?Hz 0.8 ??0/?Hz 4.8 ??0/?Hz
   
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4.2 K 3He pressure isotherm
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Very recent USC data
Original Grenoble data
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• Conclusions on present state of ZYX study
• It can be done
• There may be differences in phase diagram
• Further studies of equilibrium are needed

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Magnetization results
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