Surface physics, thin films

Variations in the electrical resistivity of La$_{0.67}$Ca$_{0.33}$MnO$_3$ films and induced interconversions of ferromagnetic and nonferromagnetic inclusions in their bulk

Yu. A. Boikov^a, T. Lilenfors^b, T. Claeson^b, E. Olsson^b, V. A. Danilov<sup>a

a</sup> Ioffe Institute, St. Petersburg
^b Chalmers University of Technology, Sweden

Abstract: A significant ($\sim$1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion ($a\perp/a\parallel$ $\approx$ 1.04) and reduction in the volume of the unit cell of La$_{0.67}$Ca$_{0.33}$MnO$_3$ films (15 nm) quasicoherently grown on the (001) surface of a LaAlO$_3$ substrate. The films consist of single-crystal blocks with the lateral size of 30–50 nm. The atomically smooth LaAlO$_3$–La$_{0.67}$Ca$_{0.33}$MnO$_3$ 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 $\rho$ of manganite films with time, so that the curve $\rho(t)$ is well approximated by the relationship $\rho(t)\sim\rho_1(t-t_0)^{1/2}$, (where $t_0$ is the time for establishment of the specified value ($\mu_0H$ = 5 T) of the magnetic field and $\rho_1$ 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 $\rho(\mu_0H,T<$ 100 K) obtained on $\mu_0H$ scanning in the sequence 5 T $\to$ 0 $\to$ -5 T $\to$ 0 $\to$ 5 T. At $T$ = 50 K and $\mu_0H$ = 0.4 T, the magnetoresistance MR = 100% $\cdot$ $[\rho(\mu_0H)-\rho(\mu_0H=0)]\rho(\mu_0H=0)$ of LCMO films attains 150%.

Received: 29.03.2011

 English version: Physics of the Solid State, 2011, 53:10, 2168–2173

Bibliographic databases:

•