The experimental techniques for obtaining reliable enthalpies of formation and migration of vacancies in pure metals and the importance of achieving high accuracy are critically discussed, with emphasis on studies based on the quenching-in of 'thermal' vacancies. From measurements of the residual electrical resistance introduced into high-purity Al foils (thickness 0.1 mm) by ultrafast quenches (initial quenching rate ≈ 2 × 10 6 K s −1 ) from temperatures T between 800 K and 530 K and the literature data on high-temperature differential dilatometry, the enthalpy,

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Mossbauer effect studies (ME) for members of the alkylene-diammonium series, (CH2)n(NH3)2Fe(II)Cl4, where n=3, 4, 5, and 6 are presented. At 78 K the ME spectra reveal similar general features showing an 8 line well split hyperfine spectra; the effective magnetic field is in the range 18.5–20 T. Fitting the magnetization curves to the theoretical models showed that all compounds are best fitted to a 2d Ising system with β values in the range of 0.124–0.151, D=1.05–1.12, and TN=102.2–105.2 K for n=3 to n=6, respectively. Structural phase transitions have been found for the n=3 and 6 compounds at Ts=230 and 242 K, respectively. Electric permittivity of two members of the series is presented and related to the ME results.

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