Heat diffusivity of Nd1−xSrxMnO3−δ and La1−xCaxMnO3−δ compounds

Abstract

Phase evolution and the multiple metal-insulator transitions in epitaxially shear-strained La 0.67 Ca 0.33 MnO 3 / NdGaO 3 ( 001 ) filmsThe thermal diffusivity of bulk and epitaxial layer samples of the giant magnetoresistance compounds Nd 0.67 Sr 0.33 MnO 3Ϫ␦ and La 0.67 Ca 0.33 MnO 3Ϫ␦ is investigated in a comparative study for temperatures between 35 and 350 K in order to detect preparational differences and to correlate the thermal transport with magnetization M and resistivity . We find for Nd-Sr an anomaly of the heat diffusivity D near 145 K ͑80 K La-Ca͒ which we attribute to a temperature-induced canted metal to AFM insulator transition and a second anomaly in D(T) near 250 K ͑300 K͒ which we assign to the transition to paramagnetism. The low-temperature anomaly can be a step of up to five times in the heat conductivity, which makes these compounds potential magnetic field activated heat switches, as this transition can also be induced by a magnetic field.

Investigation of thermophysical properties of alates (swarmers) termite wing as potential raw material for insulation

“…This agrees with the expression of [40]. Several researchers and authors including [10], [15], [28], [41], [42], and [43] have severally defined thermal diffusivity  as the ratio of thermal conductivity k to thermal capacity…”

Unusual electroresistive effect in ceramic La0.49Ca0.51MnO3

“…Both is found experimentally, A 1 corresponds to [6], A 4 and A 6562 correspond to [7] and the ER-effect in oxygen deficient bulk NSMO is indeed very large as compared to that of comparable epitaxial layers [8,9]. For LCMO, the comparison of epitaxial layers [10,11] and ceramic samples [7,12] yields the same equivalency.…”

“…1 mV per barrier. Taking the other data from the literature [7], we obtain a 25 K temperature change per barrier, which cannot nearly explain the ER-effects observed. Even if a single surface layer would be dominant, we would only have a 25 mK temperature change at the surface.…”

“…For LCMO, the comparison of epitaxial layers [10,11] and ceramic samples [7,12] yields the same equivalency. There are, of course, exceptions from these rules if the parameter ranges of the interface layers cease to overlap; for example when the layer thickness gets very low (<150 nm), so that the nature of the connecting interfaces becomes the controlling factor.…”

Bond-valence analysis on the structural effects in magnetoresistive manganese perovskites

“…The compounds falling in the TMI region often exhibit unusual magnetic and electronic properties. For this region, in particular, the details of the electrical and magnetic behaviour must depend on other factors [22] that are not discussed in this letter.…”