Theory of Colossal Magnetoresistance in Doped Manganites

Abstract

The exchange interaction of polaronic carriers with localized spins leads to a ferromagnetic/paramagnetic transition in doped charge-transfer insulators with strong electron-phonon coupling. The relative strength of the exchange and electron-phonon interactions determines whether the transition is first or second order. A giant drop in the number of current carriers during the transition, which is a consequence of local bound pair (bipolaron) formation in the paramagnetic phase, is extremely sensitive to an external magnetic field. Below the critical temperature of the transition, $T_c$, the binding of the polarons into immobile pairs competes with the ferromagnetic exchange between polarons and the localized spins on Mn ions, which tends to align the polaron moments and, therefore, breaks up those pairs. The number of carriers abruptly increases below $T_c$ leading to a sudden drop in resistivity. We show that the carrier density collapse describes the colossal magnetoresistance of doped manganites close to the transition. Below $T_c$, transport occurs by polaronic tunneling, whereas at high temperatures the transport is by hopping processes. The transition is accompanied by a spike in the specific heat, as experimentally observed. The gap feature in tunneling spectroscopy is related to the bipolaron binding energy, which depends on the ion mass. This dependence explains the giant isotope effect of the magnetization and resistivity upon substitution of ${}^{16}$O by ${}^{18}$O. It is shown also that the localization of polaronic carriers by disorder {\em cannot} explain the observed huge sensitivity of the transport properties to the magnetic field in doped manganites.

14 pages, REVTeX 3.0, 7 EPS-figures embedded via epsf

References in corpus (3)

• Carrier Density Collapse and Colossal Magnetoresistance in Doped Manganites
• Polaron Absorption in a Perovskite Manganite La0.7Ca0.3MnO3
• Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides

Cited by in corpus (13)

• Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides
• Ferromagnetism and electron-phonon coupling in the manganites
• Phase coexistence and resistivity near the ferromagnetic transition of manganites
• Modelling colossal magnetoresistance manganites
• Correlation Between Phase Competition and the Nucleation of a Griffiths Phase in (La1-yPry)0.7Ca0.3Mn16/18O3
• The Essential Interactions in Oxides and Spectral Weight Transfer in Doped Manganites
• Non-adiabatic small polaron hopping in the n=3 Ruddlesden-Popper compound Ca4Mn3O10
• Temperature- and quantum phonon effects on Holstein-Hubbard bipolarons
• Doped Manganites Beyond Conventional Double-Exchange Model
• Thermopower peak in phase transition region of (1-x)La${}_{2/3}$Ca${}_{1/3}$MnO${}_3$/xYSZ
• Oxygen isotope effect and phase separation in the optical conductivity of (La${}_{0.5}$Pr${}_{0.5}$)${}_{0.7}$Ca${}_{0.3}$MnO${}_3$ thin films
• Role of the superexchange interaction in magnetic transition and polaron crossover
• Coherence of polaronic transport in layered metals