Ca1−xYxMnO3 manganites: synthesis and ESR characterization

Agüero, O.; Leyva, A.G.; König, P.; Vega, Daníel; Polla, G.; Aliaga, H.; Causa, M.T.

doi:10.1016/s0921-4526(02)00617-8

Cited by 8 publications

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“…The experimental T mo (x) shows a minimum at about x c = 0.05. According to equations ( 9) and (10) this crossover concentration corresponds to γ 43 ≈ γ 43 and the values calculated for T mo in this case are shown in figure 5(b).…”

Section: Mean Field Modelmentioning

confidence: 68%

“…In spite of the differences between the ionic radii of Y 3+ and Ca 2+ (r Y < r Ca ) in our compounds, a volume increase is observed along the series, as is seen in figure 1(b). In this figure we compare the x dependence of the cell-volume in our samples [10] with that of other Ca 1-x A x MnO 3 (A = La, Pr, and Tb) manganites [11][12][13]. A linear dependence with a positive slope is found in all cases.…”

Section: Resultsmentioning

confidence: 86%

“…(i) The initial slope of T mo (x) versus x is rather larger than the effect expected on the basis of Mn 4+ dilution alone, even if the always positive second term in equation ( 9) completely disappears on assuming γ 43 = γ 43 . (ii) The observed increase of T mo for x > x c is much smaller that predicted by equation (10). (iii) The CW temperatures (x) calculated using equation ( 6) (shown in figure 5(a)) indicate a high temperature behaviour that is mainly AFM-like.…”

Section: Monte Carlo Simulationsmentioning

confidence: 84%

“…In the same way, the susceptibility of the x = 1 sample would allow us to estimate (γ 33 +γ´3 3 ). The measurement in the G-type AFM YMnO 3 [10] gives (γ 33 +γ´3 3 ) = -16 mol/emu. However, the YMnO 3 compound is a much distorted perovskite and the tilting and rotation angles, related to the magnitude of the exchange interactions, are much larger than those measured in our case.…”

Section: Mean Field Modelmentioning

confidence: 97%

“…Our experimental results show that the initial effect of doping is a decrease of T mo , indicating that the weakening of the AFM interaction is dominant. As x increases, T (2) mo is expected to become larger than T (1) mo and T mo is given by equation (10). Thus, T mo should present a minimum at a crossover concentration x c .…”

Section: Mean Field Modelmentioning

confidence: 98%

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High temperature susceptibility in electron doped Ca_1 xY_xMnO₃: double exchange versus superexchange

Aliaga

Causa

Tovar

et al. 2002

J. Phys.: Condens. Matter

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Abstract. We present a study of the magnetic properties of the electron doped manganites Ca 1-x Y x MnO 3 (for 0 ≤ x ≤ 0.25) in the paramagnetic regime. For the less doped samples (x ≤ 0.1) the magnetic susceptibility, χ(T), follows a Curie-Weiss (CW) law only for T > 450 K and, below this temperature, χ -1 (T) shows a ferrimagnetic-like curvature. We approached the discussion of these results in terms of a simple mean-field model where double exchange, approximated by a ferromagnetic Heisenberg-like interaction between Mn 3+ and Mn 4+ ions, competes with classical superexchange. For higher levels of doping (x ≥ 0.15), the CW behaviour is observed down to the magnetic ordering temperature (T mo ) and a better description of χ(T) was obtained by assuming full delocalization of the e g electrons. In order to explore the degree of delocalization as a function of T and x, we analyzed the problem through Montecarlo simulations. Within this picture we found that at high T the electrons doped are completely delocalized but, when T mo is approached, they form magnetic polarons of large spin that cause the observed curvature in χ -1 (T) for x ≤ 0. IntroductionManganites, responding to the formula B 1-x A x MnO 3 (with B = divalent alkaline earth and A = trivalent rare earth), have prompted a burst of research activity in the last decade, as they enclosed not only very rich physics but also interest in technological applications. The dynamics of these systems is mainly governed by the Mn ions, whose average valence changes with x between 4+ and 3+. The Mn 4+ ions have noncompensated spins in t 2g 3 configuration that give rise to localized S = 3/2 spins. On the other hand, the Mn 3+ ions have an extra e g electron (with s = ½), that couples ferromagnetically (FM) to the t 2g spins. The e g electrons tend to be itinerant and lower their kinetic energy by polarizing with FM character the localized t 2g spins. This process is known [1] as double exchange (DE) and in these materials competes with the classical superexchange (SE) interaction between Mn ions.In Ca 1-x La x MnO 3 were the whole series, from x = 0 to x = 1, can be obtained with the perovskite structure, the behaviour in the electron and hole doping regions were found different. The parent compounds are indeed quite different: while LaMnO 3 , a Jahn-Teller system, displays A-type [2] antiferromagnetism, where ferromagnetic (FM) planes order antiferromagnetically (AFM), the non Jahn-Teller CaMnO 3 is a G-type antiferromagnet, where each magnetic moment orders AFM with his nearest neighbours [2]. Most studies have been performed on hole doped compounds where ferromagnetism and colossal magnetoresistance (CMR) were found. In the range of electron doping, transport and magnetization studies on Ca 1-x La x MnO 3 showed that a complete FM state is never reached and different models were discussed in order to explain the magnetic properties at low temperatures [3,4]. These studies showed that in this region of doping new and very interesting phenomena appear as a conseq...

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Section: Mean Field Modelmentioning

confidence: 68%