Liquidlike Spatial Distribution of Magnetic Droplets Revealed by Neutron Scattering inLa1−xCax<

Abstract

Elastic neutron scattering experiments performed in semi-conducting La1−xCaxMnO3 single crystals (x=0.05, 0.08), reveal new features in the problem of electronic phase separation and metal insulator transition. Below TN , the observation of a broad magnetic modulation in the q-dependent scattering intensity, centered at nearly identical qm whatever the q direction, can be explained by a liquid-like spatial distribution of similar magnetic droplets. A semi-quantitative description of their magnetic state, diameter, and average distance , can be done using a two-phase model. Such a picture can explain the anomalous characteristics of the spin wave branches and may result from unmixing forces between charge carriers predicted from the s-d model.

Magnons in ferromagnetic metallic manganites

“…This anomalous central component has been interpreted [26] as the signature of the formation of spin polarons similar to the ferromagnetic 'droplets' observed in the La 1−x Ca x MnO 3 with lower doping levels [57], thus suggesting a magnetic phase inhomogeneity near T C [58]. Such a phase inhomogeneity scenario should be invoked for understanding the unusual magnon behaviour and transport properties in manganites including CMR effects.…”

Evidence of anisotropic magnetic polarons inLa0.94Sr0.06MnO3Hennion1, Moussa2, Biotteau3 et al. 2000Phys. Rev. BSelf Cite759410View full textAdd to dashboardCite

“…In La 1−x Ca x MnO 3 , interesting observations have been recently reported: a "static" ferromagnetic modulation has been observed at small wave-vectors q, interpreted in terms of magnetic inhomogeneities or droplets, with a distribution analogous to that of a liquid 11 . Moreover, below the gap of the spin wave branch with an anisotropic dispersion typical of the AF layered structure, an additional spin wave branch with an isotropic dispersion was observed [11][12][13] .…”

“…Moreover, below the gap of the spin wave branch with an anisotropic dispersion typical of the AF layered structure, an additional spin wave branch with an isotropic dispersion was observed [11][12][13] . Whether these findings are restricted to Ca substitution, in relation with the stronger induced lattice distortion, or are more general, is an important question.…”

“…Its full expression which uses the average inter-cluster distance d m and a minimal distance of approach d min , has been previously given 11 . F (Q) is the Mn magnetic form factor.…”

Effect of disorder in an orbitally ordered Jahn-Teller insulator

“…Hole doping leads to progressive loss of orbital order (OO), a reduction of the transport gap, increasing isotropy in the effective magnetic exchange, and an insulator (I) to metal (M) transition [2,18,19]. Beyond transport and thermodynamic indicators, NMR and neutron scattering experiments have revealed an inhomogeneous -possibly phase separated -state in the low doping regime [20,21]. The interplay of doping, disorder, and thermal fluctuations thus presents an intriguing problem even in the insulators.…”