ESR spectrum of Fe+3 in topaz (Al2SiO4F2) has been investigated at X- and K-band frequencies. The spectrum, in addition to large zero-field splitting, also shows well-resolved h.f.s. due to 19F at some orientations. The spin-Hamiltonian parameters, which include b21 and b41, are given in the text. The spectrum has been interpreted to originate from Fe+3 impurity located at Al+3 sites. The implications of these results are considered briefly. The results of the analysis of the h.f.s. are to be published in the near future.
The superhyperfine structure (shfs) aspect of the ESR spectrum of Fe+3 impurity in topaz (A12Si0,F2) has been investigated at X-band frequencies. The shfs tensors of the two inequivalent 19F nuclel have been determined. The experimental results were analyzed in the fornlalisnl of the effective spin. The isotropic contributions to shfs tensors were found to be (in cm-') 25.6 and 30.0 and the dipolar contribution, 6.8 and 5.9, with errors of k 0 . 5 (see Table V). The calculations leading to these values assume considerable distortions at the Fe+3 site.
The temperature variation of the spin-Hamiltonian parameters of Mn" in Ca{OH)2 single crystals was studied. The parameters 52 (=D) and the isotropic part of the hyperfine-structure tensor A showed marked variation in the range 80-800'K. b2 showed a reversal of sign around 450 'K. The theory of orbit-lattice interaction and the theory of covalent reduction of A through spin polarization was applied to the interpretation of the temperature variance of A.The temperature variations of 52 were interpreted as originating from the phonon modulations of the crystal field. The calculated values were comparable to the experimental values. Implicit temperature variations of b2 were also found to be significant. Included also are the results of the velocities of sound in Ca(OH)2 as functions of temperature.
A robust apparatus, which includes a microcomputer to control the release of a body, perform the necessary timings, and measure its average speed, is used by freshman students to study free-fall motion. A procedure is suggested that enables students in one laboratory period to collect data to find ‘‘g’’ from least-squares fits of the functions s=v0t− 1/2 gt2, v=v0−gt, and v2=v20−2gs.
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