Is Magnetic Circular Dichroism Surface Sensitive in the Manganese Perovskites?
- PDF / 376,443 Bytes
- 6 Pages / 418.68 x 637.2 pts Page_size
- 50 Downloads / 248 Views
While roughly similar materials, we anticipate that the Pb doped material has a larger number of valence electrons than the Sr doped material. EXPERIMENTAL The Lao.65Pbo.3sMnO 3 films, and Lao.65AO. 35MnO 3 (A=CaSrBa) films with a nominal thickness of 1000 A, were grown on a (100) LaAIO 3 substrates by RF sputtering in a 4:1 argon/oxygen atmosphere maintained at 15 mTorr. The Pb samples were subsequently annealed in two steps in order to prevent Pb evaporation: at a temperature of 6500 C for 10 hours, at 8500 C for 2 hours and then again for 10hrs at 650' C in an oxygen pressure of 1 atmosphere. The bulk chemical composition was determined from energy dispersive analysis of the X-ray emission (EDAX). The XAS and MCD spectra were recorded by monitoring the sample current, which corresponds to the total electron yield. For magnetizing the sample, a 400 Oe pulse field was applied along the in-plane easy axis. The spectra for two different helicities were recorded by alternating the magnetization at every photon energy. In the total electron yield mode, the XAS spectra probes approximately 100 A in depth, which is an intermediate length scale between the bulk and the surface boundary. RESULTS It is evident that the magnetization determined from MCD is not the same as that determined from SQUID magnetometry in the 0.8
lanthanum manganates LalAMnO 3 [14], Sr [12]), as seen in
......
1.0
0.8 *,.~
-Figure
.(A=Pb
1. These results, with the that the electron mean free
.knowledge
0.6
"path of even very low kinetic electrons is limited, suggests that the MCD signal does have, at least, a
0.4
rMn 0.2
0
0.3
limited surface contribution.
3
S0.0
....
In Figure 2, we compare inverse
photoemission La1_xAMnO 3 (A = Pb, Ca, Sr, Ba) and the photoemission Sfor Lao. 65Ao. 35MnO 3 (A = Ca, Sr, Ba). While S0.8the inverse spectra are similar in many respects, the position of the La/D/O inverse peak about 8 eV
b1.0
0.6
0.4 0.2
La0 6 5 Pbo. 35MnO33 .
0.0 0.8
0.6
0.4
0.2
0.0
-0.2
1-TfT^
302
Figure 1: Magnetic circular dichroism magnetization from the Mn 2p cores (A) "compared to the magnetization versus The (4%. magnetometry SQUID comparison is shown for Lao.6sPboasMnO 3 with the previously reported Lao. 7Sro.3MnO 3 (data taken from ref. 1121).
above the Fermi level differs slightly for the different dopants, with the smallest energy above E• for the Pb doped material. The same is true for the Mn-O occupied feature below the Fermi level. In addition, the Pb doped material has an apparent density of states, at Ef, 3 to 5 times larger than is observed for the Sr doped material. Both of these results support the reasonable premise that the Pb doped material has a larger number of valence electrons that the Sr doped material. DISCUSSION We need to address the surface sensitivity of the MCD signal. One method for determining mean free path of the secondary electrons are to grown uniform films of varying thickness on a well defined substrate of a different material and measure the attenuation of the signal with inc
Data Loading...
