Birgit Hebler

Thermally Assisted All‐Optical Helicity Dependent Magnetic Switching in Amorphous Fe100–xTbx Alloy Films

All-optical switching (AOS) in ferrimagnetic Fe(100-x)Tb(x) alloys is presented. AOS is witnessed below, above, and in samples without a magnetic compensation point. It is found that AOS is associated with laser heating up to the Curie temperature and intimately linked to a low remanent sample magnetization. Above a threshold magnetization of 220 emu/cc helicity dependent AOS is replaced by pure thermal demagnetization.

Ferrimagnetic Tb–Fe Alloy Thin Films: Composition and Thickness Dependence of Magnetic Properties and All-Optical Switching

Ferrimagnetic rare earth - transition metal Tb-Fe alloy thin films exhibit a variety of different magnetic properties, which depends strongly on composition and temperature. In this study, first the influence of the film thickness (5 - 85 nm) on the sample magnetic properties was investigated in a wide composition range between 15 at.% and 38 at.% of Tb. From our results, we find that the compensation point, remanent magnetization, and magnetic anisotropy of the Tb-Fe films depend not only on the composition but also on the thickness of the magnetic film up to a critical thickness of about 20-30 nm. Beyond this critical thickness, only slight changes in magnetic properties are observed. This behavior can be attributed to a growth-induced modification of the microstructure of the amorphous films, which affects the short range order. As a result, a more collinear alignment of the distributed magnetic moments of Tb along the out-of-plane direction with film thickness is obtained. This increasing contribution of the Tb sublattice magnetization to the total sample magnetization is equivalent to a sample becoming richer in Tb and can be referred to as an “effective” composition. Furthermore, the possibility of all-optical switching, where the magnetization orientation of Tb-Fe can be reversed solely by circularly polarized laser pulses, was analyzed for a broad range of compositions and film thicknesses and correlated to the underlying magnetic properties.

Controlling the magnetic structure of Co/Pd thin films by direct laser interference patterning

Pulsed two beam direct laser interference patterning (DLIP) is used to generate two-dimensional temperature patterns on a magnetic sample. In contrast to other methods like electron beam lithography, DLIP offers the possibility to pattern large areas on a timescale of a few nanoseconds in a one-step process. Usually DLIP is used to pattern surfaces [1,2], but here we focus on local periodic heating on the nanoscale.

All-optical helicity dependent magnetic switching in Tb-Fe thin films with a MHz laser oscillator.

We demonstrate all-optical magnetic switching (AOS) in an amorphous Tb30Fe70 thin film, triggered by a 5.1 MHz laser oscillator. The magnetic layer is grown on SiO2/Si substrate. An identical magnetic film deposited on a microscope glass slide reveals no AOS but solely thermally induced demagnetization. This effect is due to heat accumulation by multiple laser pulses because of the low thermal conductivity of the glass substrate. In contrast, the use of a proper heat sink (e.g. SiO2/Si) avoids the need for low repetitive laser amplifier systems to induce AOS and paves the way for a cheap and simple technical implementation using conventional laser oscillators.

Nanoscale magnetic imaging using circularly polarized high-harmonic radiation

We introduce laboratory-scale magneto-optical imaging with sub–50-nm resolution using high-harmonic radiation. This work demonstrates nanoscale magnetic imaging using bright circularly polarized high-harmonic radiation. We utilize the magneto-optical contrast of worm-like magnetic domains in a Co/Pd multilayer structure, obtaining quantitative amplitude and phase maps by lensless imaging. A diffraction-limited spatial resolution of 49 nm is achieved with iterative phase reconstruction enhanced by a holographic mask. Harnessing the exceptional coherence of high harmonics, this approach will facilitate quantitative, element-specific, and spatially resolved studies of ultrafast magnetization dynamics, advancing both fundamental and applied aspects of nanoscale magnetism.

Nanoscale magnetic imaging using a compact high-harmonic source

Compact sources based on high harmonic generation (HHG) offer experimental access to ultrafast dynamics, high-resolution imaging and spectroscopy, and also provide for a simultaneous probing of element-specific spin and charge carrier dynamics. Here, we extend the capabilities of compact EUV sources to the nanoscale imaging of magnetic structures by using circularly polarized harmonics in conjunction with Fourier transform holography.

Control of the magnetic structure of Co/Pd thin films by direct laser interference patterning

Pulsed two beam direct laser interference patterning (DLIP) is used to generate two-dimensional temperature patterns on a magnetic sample. In contrast to other methods like electron beam lithography, DLIP offers the possibility to pattern large areas on a timescale of a few nanoseconds in a one-step process. Usually DLIP is used to pattern surfaces [1,2], but here we focus on local periodic heating on the nanoscale.

Thermally Assisted All-Optical Helicity Dependent Switching of Ferrimagnetic Amorphous Fe 100− x Tb x Thin Films

We observe all-optical switching (AOS) in ferrimagnetic Fe100−x Tb x alloy films below, above, and in samples without a magnetic compensation point. AOS is linked to a low remanent magnetization M R and associated with laser heating up to the Curie temperature. Above M R = 220 emu/cc AOS is replaced by pure thermal demagnetization.