Anomalous cyclotron mass dependence on the magnetic field and Berry's phase in (Cd1-x-y Zn x Mn y )3As2 solid solutions.

Shubnikov-de Haas (SdH) effect and magnetoresistance measurements of single crystals of diluted II-V magnetic semiconductors (Cd1-x-y Zn x Mn y )3As2 (x + y = 0.4, y = 0.04 and 0.08) are investigated in the temperature range T = 4.2 ÷ 300 K and in transverse magnetic field B = 0 ÷ 25 T. The values of the cyclotron mass m c, the effective g-factor g*, and the Dingle temperature T D are defined. In one of the samples (y = 0.04) a strong dependence of the cyclotron mass on the magnetic field m c(B) = m c(0) + αB is observed. The value of a phase shift close to ß = 0.5 indicates the presence of Berry phase and 3D Dirac fermions in a single crystals of (Cd1-x-y Zn x Mn y )3As2 in one of the samples (y = 0.08).

Variable-range hopping conductivity of La(1 - x)Sr(x)Mn(1 - y)Fe(y)O3.

The temperature dependence of the resistivity, ρ, of ceramic La(1 - x)Sr(x)Mn(1 - y)Fe(y)O(3) (LSMFO) samples with x = 0.3 and y = 0.03, 0.15, 0.20 and 0.25 (or simply #03, #15, #20 and #25, respectively) is investigated between temperatures T ∼ 5 and 310 K in magnetic fields B up to 8 T. Metallic conductivity in #03 is changed eventually to activated in #25. In #15 and #20 the behavior of ρ(T) is more complicated, comprising of two extremes, divided by an interval of metallic behavior in #15, and two inflections of ρ(T) in #20 within similar intervals ΔT below approximately 100 K. Mott variable-range hopping (VRH) conductivity is observed in #15 above the ferromagnetic Curie temperature, T(C). In #20 the Mott VRH conductivity takes place in three different temperature intervals at T > T(C), T close to T(C) and T < T(C). In #25, the Mott VRH conductivity is observed in two different intervals, above and below T(C), divided by an intermediate interval of the Shklovskii-Efros VRH conduction regime. Analysis of the VRH conductivity yielded the values of the localization radius, α, and the dependence of α and of the density of the localized states, g, near the Fermi level, on B. Above T(C) the localization radius in all samples at B = 0 has similar values, α approximately 1.0-1.2 Å, which is enhanced to α approximately 3.3 Å (#20) and 2.0 Å (#25) below T(C). The sensitivity of α and g to B depend on y and T. The complicated behavior of the mechanisms of the hopping charge transfer, as well as of the microscopic parameters α and g, is attributable to different electronic and magnetic phases of LSMFO varying with temperature and Fe doping.

Persistent photoinduced magnetization and oxygen non-stoichiometry in La(0.9)Ca(0.1)MnO(3) films.

The influence of thermal annealings on La(0.9)Ca(0.1)MnO(3) (LCMO) films in oxygen and in vacuum with low hole doping is investigated in the phase separation region where competition between AFM and FM phases is high. Measurements by x-ray diffractometry, atomic force microscopy and magnetometry reveal changes in the lattice parameters and magnetic properties of the films, depending on the oxygen content. All films show magnetic cluster glass properties with similar freezing temperatures of around 45 K. Clearly the highest increase of the magnetization is observed in the films annealed in vacuum. We attribute this effect to trapping of unpaired electrons at oxygen vacancies where they can form rigid self-trapped magnetic polarons in potential wells of local moments. As a result long-range spin distortions with local ferromagnetic order may be realized. In conformity with these results, photoinduced persistent magnetization showing different mechanisms of generation, depending on the method of thermal annealing, is observed.

Lattice distortions, magnetoresistance and hopping conductivity in LaMnO(3+δ).

Structural and transport properties of ceramic LaMnO(3+δ) are investigated for δ = 0-0.154. According to x-ray diffraction measurements at room temperature the crystal structure of this compound varies from orthorhombic (Pbnm) for δ = 0 to rhombohedrally distorted cubic (Pm3m) for δ = 0.065-0.112 and to rhombohedral ([Formula: see text]) crystal symmetry for δ = 0.125-0.154. These structural modifications are confirmed by the Raman micro-spectroscopy measurements. The resistivity displays in the range δ = 0-0.154 an activated behaviour both above and below the paramagnetic (PM) to ferromagnetic transition temperature, T(C). In the field of 8 T the relative magnetoresistance, Δρ(B)/ρ(0), reaches at δ = 0.154 the values of -88% near T(C) and -98% at [Formula: see text] K. The resistivity of the PM phase of LaMnO(3+δ) with δ = 0.100-0.154 satisfies the Shklovskii-Efros-like variable-range hopping (VRH) conductivity law between [Formula: see text] K and the VRH onset temperature [Formula: see text] K. The resistivity is governed by a complex energy dependence of the density of the localized states near the Fermi level, comprising a soft Coulomb gap [Formula: see text] eV and a rigid gap [Formula: see text] eV, the latter being connected to formation of small polarons.