ELECTRON >I1HH()K MICROSCOPY 



Fig. 4. Electron mirror stereomicrograph pair 

 of the electrical potential gradient across a low 

 angle grain boundary in germanium. 



Fig. 5. Magnetic pattern recorded on magnetic 

 tape as revealed by electron mirror microscopy. 

 The double track pattern was recorded with an 

 audio frequency of 1000 cps, the upper track at a 

 tape speed of l}-i, in. /sec and the lower one at a 

 speed of 3% in. /sec. 



microscopy can, in general, be used for this 

 purpose. One can, for instance, observe the 

 magnetic pattern recorded on magnetic 

 computer tapes or the magnetic pattern 

 recorded by conventional audio frequency 

 recording (7). Figure 5 shows as an example 

 a magnetic pattern recorded on magnetic 

 tape as revealed by electron mirror micros- 

 copy. The double track pattern was recorded 

 on a 3'4-inch wide tape with an audio fre- 

 quency of 1000 cps, the upper trace at a 



tape speed of 73^2 inches/sec, the lower one 

 at a speed of 3^^ inches/sec. 



For the observation of magnetic domain 

 patterns electron mirror microscopy is par- 

 ticularly well suited. Electron mirror micros- 

 copy reveals magnetic domain patterns in 

 materials with a uniaxial direction of easy 

 magnetization (4) as well as in materials with 

 several directions of easy magnetization, ex- 

 hibiting basically flux closure domain con- 

 figurations (8). Figure 6 shows as an example 

 of the first type of material an electron mirror 

 micrograph of a magnetic domain pattern on 

 barium ferrite at a magnification of about 

 1500 X. 



Electron mirror microscopy is inherently 

 suited for the instantaneous depiction of 

 domain patterns in motion. A few micro- 

 graphs cannot, of course, adequately portray 

 the quite impressive view of domains in mo- 

 tion as viewed directly on the microscope 

 screen. Motion pictures taken from the 

 screen portray the appearance of domain pat- 

 terns in motion quite well but are still slightly 

 inferior to direct viewing, particularly in 

 cases where domain walls at very low applied 

 magnetic fields are to be observed. Direct 



Fig. 6. Electron mirror micrograph of magnetic 

 domain pattern on barium ferrite. Magnification 

 approx. 1500X 



320 



