Effect of Cu-Substitution on the Epitaxial Growth for La_2-2xSr_1+2xMn₂O₇ Bilayer Manganates

Abstract

c-Axis epitaxial thin films of the bilayer manganates La 2À2x Sr 1þ2x Mn 2 O 7 (LSMO327) and La 2À2x Sr 1þ2x Mn 2Ày Cu y O 7 (x ¼ 0:3, y ¼ 0:2) (LSMCO327) have been fabricated. It is found that Cu-substitution is effective in improving the c-axis epitaxy, which is difficult to attain in this layered system.

Growth of c-Axis Epitaxial Thin Films with Reduced Intergrowths for the Bilayer Manganate La2-2xSr1+2xMn2O7 Using a New Sputtering Configuration

“…At a magnetic field of 7 T, the magnetoresistance ÀÁ= 0 , defined as ÀÁ= 0 ¼ À½ðBÞ À ð0Þ=ð0Þ, reached the highest value of more than 60% around 120 K. Here, ðBÞ denotes the film resistivity in the presence of a magnetic field B. The magnetoresistance is greater than 50% at all temperatures below the MI transition temperature of 144 K. These values are much larger than those obtained in previous sputtered films, 5) but smaller than the value of 98% observed at 7 T for a c-axis film grown by pulsed laser deposition. 8)…”

“…The present films show much smaller values for the full width at half maximum (FWHM) than the films grown previously. 4,5) For example, the FWHM value is $0:3 for the diffraction peak (0010) and $0:6 for (008), while they were $0:5 and $3:0 , respectively, for earlier films. 4) The values of the shift of the XRD peak position and those for FWHM are listed in Table I and Table II for as-grown and annealed films together with the simulation result.…”

“…These peaks are sensitive to the lattice constants of the included intergrowths. 5) It is supposed that a better agreement can be obtained by taking into account the uncertainty in the lattice constants of the included LSMO113 and LSMO214 phases.…”

“…A partial Cu-substitution of the Mn site helps to improve the crystallinity of the films to some extent, but it degrades their magnetic properties. 5) Considering the layered structure of these materials, one can say that their growth needs a special care. Namely, one has to be sure that the layered structure formed during the growth is not destroyed by energetic events such as the bombardments of the film by high-energy particles that normally exist in the sputtering of oxides such as negative oxygen ions.…”