Abstract
Optical control of magnetization using femtosecond laser without applying any external magnetic field offers the advantage of switching magnetic states at ultrashort time scales. Recently, all-optical helicity-dependent switching (AO-HDS) has drawn a significant attention for potential information and data storage device applications. In this work, we employ element and magnetization sensitive photoemission electron microscopy (PEEM) to investigate the role of heating in AO-HDS for thin films of the rare-earth transition-metal alloy TbFe. Spatially resolved measurements in a 3–5 μm sized stationary laser spot demonstrate that AO-HDS is a local phenomenon in the vicinity of thermal demagnetization in a ‘ring’ shaped region. The efficiency of AO-HDS further depends on a local temperature profile around the demagnetized region and thermally activated domain wall motion. We also demonstrate that the thickness of the film determines the preferential switching direction for a particular helicity.
Highlights
The direct control of magnetization using light at ultrashort timescales has the potential to revolutionize the future magnetic data storage technologies
We investigate all-optical magnetic switching using a stationary femtosecond laser spot (3–5 μm) in TbFe alloys via photoemission electron microscopy (PEEM) and x-ray magnetic circular dichroism (XMCD) with a spatial resolution of approximately 30 nm
We find that all-optical helicity-dependent switching (AO-HDS) occurs only in a ‘ring’ shaped region surrounding the thermally demagnetized region formed by the laser spot and the formation of switched domains relies further on thermally induced domain wall motion
Summary
The RE and TM magnetic sublattices in TbxFe1−x alloys are anti-ferromagnetically coupled to each other and exhibit a perpendicular magnetic anisotropy. The samples will be referred by TbXY where X specifies the Tb concentration in % (either 22 or 30) and Y specifies the thickness of TbFe magnetic alloy in nm. The PEEM provides a lateral resolution of 30 nm using x-rays which are incident at 16° to the sample surface. Magnetic images are recorded at Fe L3 (706.6 eV) absorption edge, exploiting the XMCD for left and right circularly polarized x-rays (σ− and σ+). The XMCD magnetic contrast is calculated as the difference between the images taken by left and right circularly polarized x-rays normalized by their sum. 1(c) shows a schematic displaying the two modes and their expected temperature profiles build on the sample surface during laser exposure
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