Variations in the electrical resistivity of La0.67Ca0.33MnO3 films and induced interconversions of ferromagnetic and nonferromagnetic inclusions in their bulk

A significant (∼1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion (a ⊥/a ‖ ≈ 1.04) and reduction in the volume of the unit cell of La0.67Ca0.33MnO3 films (15 nm) quasicoherently grown on the (001) surface of a LaAlO3 substrate. The films consist of single-crystal blocks with the lateral size of 30–50 nm. The atomically smooth LaAlO3-La0.67Ca0.33MnO3 interphase boundary has no misfit dislocations. At T = 4.2 K, the transformation of nonferromagnetic phase inclusions into ferromagnetic ones in a constant magnetic field H is accompanied by a stable reduction in the electrical resistivity ρ of manganite films with time, so that the curve ρ(t) is well approximated by the relationship ρ(t) ∼ ρ1(t − t 0)1/2, (where t 0 is the time for establishment of the specified value (μ0 H = 5 T) of the magnetic field and ρ1 is a coefficient independent of H). The magnetocrystalline anisotropy due to the elastic deformation of films by the substrate and stratification of electronic phases are the reasons of the distinct hysteresis in the dependences ρ(μ0 H, T < 100 K) obtained on μ0 H scanning in the sequence 5 T → 0 → −5 T → 0 → 5 T. At T = 50 K and μ0 H = 0.4 T, the magnetoresistance MR = 100% [ρ(μ0 H) − ρ(μ0 H = 0)]/ρ(μ0 H = 0) of LCMO films attains 150%.