All of the ferrimagnetic garnets studied to date have been found to be transparent to visible light down to wavelengths of about 5200 A. Thin sections (e.g., 0.005 cm) have been examined to determine the absorption and the specific Faraday rotation through that part of the visible spectrum where they transmit light. These measurements have been made at temperatures down to 4.2°K. They are interpreted as giving us information on electronic energy levels. A magnetic birefringence and a circular dichroism have been observed. The Faraday rotation permits observation of the domain structure in these crystals at any temperature below the Curie point. Possible microwave‐optical experiments are discussed briefly.

1.
A preliminary report of this work was presented at the meeting of the American Physical Society, April 27, 1957 [see
J. F.
Dillon
, Jr.,
Bull. Am. Phys. Soc.
Ser. II,
2
,
238
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1957
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2.
J. R. Partington, Advanced Treatise on Physical Chemistry (Longmans Green and Company, London, 1953), Vol. IV, p. 606, reference 1.
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Williams
,
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1957
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4.
P. A. Miles, Prog. Rep. XXI, Laboratory for Insulation Research M.I.T., p. 19;
H. J. Williams and R. Sherwood (private communication),
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Sherwood
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5.
Specimens used in these experiments were all made from single crystals grown by J. W. Nielsen. An oriented plane was ground and polished, the opposite plane was then treated similarly with care taken that it be parallel. Polishing was done with automatic polishing machines using Linde A alumina. When practicable a reasonable thickness of material (e.g., 0.0025 cm) was removed by polishing beyond removal of the grinding pits in order to obtain a more nearly strain free surface.
6.
Note that a byproduct of this experiment can be a light beam modulated at microwave frequencies.
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© 1958 The American Institute of Physics.
1958
The American Institute of Physics
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