Magnetic inhomogeneity and magnetotransport in electron-dopedCa1−xLaxMnO3

Abstract

The dc magnetization (M ) and electrical resistivity (ρ) as functions of magnetic field and temperature are reported for a series of lightly electron doped Ca1−xLaxMnO3(0 ≤ x ≤ 0.10) specimens for which magnetization [Phys. Rev. B 61, 14319 (2000)] and scattering studies [Phys. Rev. B 68, 134440 (2003)] indicate an inhomogeneous magnetic ground state composed of ferromagnetic (FM) droplets embedded in a G-type antiferromagnetic matrix. A change in the magnetic behavior near x = 0.02 has been suggested to be the signature of a crossover to a long-ranged spin-canted phase. The data reported here provide further detail about this crossover in the magnetization, and additional insight into the origin of this phenomenon through its manifestation in the magnetotransport. In the paramagnetic phase (T ≥ 125 K) we find a magnetoresistance ∆ρ/ρ = −C(M/MS) 2 (MS is the low-T saturation magnetization), as observed in many manganites in the ferromagnetic (FM), colossal magnetoresistance (CMR) region of the phase diagram, but with a value of C that is two orders of magnitude smaller than observed for CMR materials. The doping behavior C(x) follows that of MS(x), indicating that electronic inhomogeneity associated with FM fluctuations occurs well above the magnetic ordering transition. 75.47.Lx, 75.30.Et, I.

Electron transport in CaMnO3 − δ at elevated temperatures: a mobility analysis

“…4. As expected, the concentration of Mn 3+ cations noticeably increases with temperature due to reaction (2). For instance, the straightforward contribution of non-stoichiometry in the right hand side of Eq.…”

“…where ΔS°and ΔH°designate entropy and enthalpy, respectively, for reaction (2). The temperature variations of parameters n and g can be calculated from (3) and (4) with the use of ΔS°and ΔH°obtained elsewhere [30].…”

“…Substitution of calcium for higher-charged cations and formation of vacancies in the oxygen sub-lattice both result in partial reduction of Mn 4+ to Mn 3+ cations and appearance of n-type conductivity [1][2][3][4][5][6]. The electrondoped derivatives Ca 1−x R x MnO 3−δ , where R is a rare earth metal, are stable in different atmospheres and exhibit rather large values of conductivity (σ) and negative thermopower (S) up to 1000°C.…”

Impurity conduction and magnetic polarons in antiferromagnetic oxides

“…The latter behavior appears to be associated with FM polarons [7], whereas the former may be attributed to an additional FM contribution in CMO from Dzyaloshinsky-Moriya coupling (allowed by symmetry). These materials exhibit band-like, largepolaron transport with mobilities ∼ 1 cm 2 /V s at T ≥ T N [9,13], which contrasts with the small polaronic character of the paramagnetic phase of hole-doped manganites [14]. Figure 1 shows resistivity data (in zero magnetic field), plotted versus inverse temperature, illustrating the sensitivity of the charge transport in these materials to applied current (I) at low T where impurity conduction is predominant.…”

Charge-Carrier Hopping in Highly Conductive CaMn1–xMxO3−δ Thermoelectrics

“…23 Although, the electronic transport phenomena of the electron doped CaMn 1-x M x O 3-δ compounds are often described by a small adiabatic polaron hopping process, 21,[24][25][26] there is some debate if the polarons are either localized small adiabatic or Fröhlich (continuum or larger) polarons. [27][28] Nevertheless, the small adiabatic polaron model provides a good starting point for a further analysis of the transport properties. 15 The hopping model depends on the Jahn-Teller active Mn 3+ O 6 octahedra due to their t 2g 3 e g 1 electron configuration which renders the transport properties.…”