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ABSTRACT: Studies of the spin transition behavior of the mononuclear compound [Fe(pythiaz)(2)](BF(4))(2) have been carried out under hydrostatic pressures up to 9.13 kbar in the 5-300 K temperature range. Under ambient pressure this compound exhibits an approximately half-step (incomplete) HS [Formula: see text] LS transition with T(1/2) = 146 K without any thermal hysteresis. At pressures up to 4.5 kbar the behavior remains similar but with an upward displacement of T(1/2) and a slight decrease in the residual high spin fraction at low T. Application of higher pressures resulted in an almost complete two-step spin transition with several unusual pressure effects. Along with the expected pressure dependence of T(1/2) the surprising appearance of hysteresis in the spin transition curves was observed. It is suggested that the likely origin of this unprecedented behavior is a pressure-induced structural change.
Journal of Physics Condensed Matter 01/2009; 21(2):026011. · 2.55 Impact Factor
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ABSTRACT: (57)Fe Mössbauer spectroscopy of the mononuclear [Fe(II)(isoxazole)(6)](BF(4))(2) compound has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S = 0) and high-spin (S = 2) states. A temperature-dependent spin transition curve has been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures in the 240-60 K range during the cooling and heating cycle. The compound exhibits a temperature-dependent two-step spin transition phenomenon with T(SCO) (step 1) = 92 and T(SCO) (step 2) = 191 K. The compound has three high-spin Fe(II) sites at the highest temperature of study; among them, two have slightly different coordination environments. These two Fe(II) sites are found to undergo a spin transition, while the third Fe(II) site retains the high-spin state over the whole temperature range. Possible reasons for the formation of the two steps in the spin transition curve are discussed. The observations made from the present study are in complete agreement with those envisaged from earlier magnetic and structural studies made on [Fe(II)(isoxazole)(6)](BF(4))(2), but highlights the nature of the spin crossover mechanism.
Journal of Physics Condensed Matter 10/2007; 19(40):406202. · 2.55 Impact Factor
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ABSTRACT: Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) thiocyanate dihydrate undergoes a two-step singlet (1A1) ⇄ quintet (5T2) transition in which both steps are associated with thermal hysteresis. Thermal cycling of the sample results in its conversion to a second phase which displays a single-step transition with a very narrow hysteresis loop. This second phase slowly reverts to the initial phase on standing at 300 K. The interconversions are completely reversible. The spin state changes have been monitored by measurement of magnetism and Mössbauer spectra and by differential scanning calorimetry (DSC) studies.
Advanced Functional Materials 11/2003; 13(11):877 - 882. · 10.18 Impact Factor
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ABSTRACT: The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided.
Journal of Physics and Chemistry of Solids.
