The Effect of Oxygen Deposition Pressure on the Structure and Properties of Pulsed Laser Deposited LaxCa1−xMnOδ Films

Thin films (∼1000 Å) of LaxCa1−xMnOδ (x=0.67) were deposited onto LaA1O3 (100) substrates at of 600 and 700°C. Varying the oxygen deposition pressure between 15 and 400 mTorr systematically changed the oxygen concentrations in the as deposited films. Asdeposited films exhibited an orthorhombic structure with an oxygen pressure dependent lattice parameter. The films were highly oriented as characterized by narrow x-ray ω-scans (FWHM ≤ 0.16 −0.70°). At low pressures, the films were preferentially (202) oriented while at high pressures deposited films had a (040) preferred orientation. A 900°C anneal in flowing oxygen for a film deposited at low oxygen pressures resulted in a decrease in the lattice parameter (associated with an increase in δ) and a change in the preferred orientation from (202) to (040). The resistivity as a function of temperature (R(T)) showed a significant variation as a function of growth conditions. At 600°C, the peak in the resistivity curve (Tm) varied between 73 and 93 K for P(O2) = 15 to 400 mTorr, while at 700°C, Tm was ∼150 K. For films deposited at 600°C, the resistivity was reduced by a factor of 103 for H = 9T and Tm was shifted to 150 K. The activation energy associated with the semiconducting phase was approximately the same for all as-deposited films (∼100 meV).