Phase effects in magnetic second-harmonic generation on ultrathin Co and Ni films on Cu(001)
Abstract
Phase relations in second-harmonic generation (SHG) have been studied systematically for Ni and Co films on Cu(001) as a function of thickness in the range 1-12 ML. Below two monolayers we observe, with s-polarized fundamental light and P-polarized second-harmonic light, phase shifts close to 180° of both films against the Cu substrate. Such large phase shifts in this polarization combination appear to be characteristic of the transition from s- to d-band metals. In the ferromagnetic thickness range the relative phase between odd and even tensor elements becomes important. For Ni films it is independent of film thickness for both p-->P and s-->P polarizations, and leads to the ratio χoddxyy /χevenzyy=0.047+/-0.013, in agreement with theoretical predictions. In the case of Co films the relative phase differs dramatically between these two polarization combinations. It is nearly independent of film thickness for p-->P polarized SHG. However, for s-->P polarization it varies from 135° at 3 ML to 60° at 10 ML, causing a sign change of the magnetic contrast at 90° near 6 ML. The ratio of odd to even second-harmonic field amplitudes was found to vary from 22% at 3 ML to 12.5% above 6 ML. From these results we conclude that measurements of the relative phase are necessary for deriving reliable information from SHG about the magnetization state of a sample.
- Publication:
-
Physical Review B
- Pub Date:
- April 2001
- DOI:
- 10.1103/PhysRevB.63.144417
- Bibcode:
- 2001PhRvB..63n4417C
- Keywords:
-
- 75.70.Ak;
- 42.65.Ky;
- 78.47.+p;
- Magnetic properties of monolayers and thin films;
- Frequency conversion;
- harmonic generation including higher-order harmonic generation;
- Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter