Alexander Hassdenteufel

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.

All-optical helicity dependent magnetic switching in an artificial zero moment magnet

Low remanent magnetization as key prerequisite for the ability of helicity dependent all-optical magnetic switching (AOS) is demonstrated for an artificial zero moment magnet. A heterostructure consisting of two amorphous ferrimagnetic Tb36Fe64 and Tb19Fe81 alloy layers is designed to yield a zero remanent net magnetization at room temperature by means of an antiparallel interfacial exchange coupling of the dominant magnetic moments. The canceling layer magnetizations provide vanishing demagnetization fields and the ability of AOS. Contrary to this, no all-optical switching is observed for single Tb36Fe64 and Tb19Fe81 films. This study provides further evidence that the ability for all-optical magnetic switching is correlated to the remanent sample magnetization and thus to the difference in magnetic moment of the rare-earth and transition-metal sublattices.

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.

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.

Magneto-optical response of ferrimagnetic Tb-Fe thin films in the visible and ultraviolet range

We present wavelength-dependent measurements of Kerr rotation and ellipticity for ferrimagnetic Tb30Fe70 thin films in the optical range of 225 nm–726 nm (1.7 eV to 5.5 eV). The thicknesses of the magnetic layers vary from 19 nm to 83 nm. Strong optical interference effects in the magneto-optical spectra are observed for films grown on commonly used SiO2/Si substrates, which may easily be misinterpreted as spectral signatures of Tb. This strong optical interference feature can be fully suppressed by depositing magnetic Tb-Fe films on glass substrates.

Dependence of all-optical magnetic switching on the sublattice magnetization orientation in Tb-Fe thin films

We demonstrate that the direction of all-optical switching (AOS) in rare-earth transition-metal (RE-TM) alloy Tb-Fe thin films depends on the orientation of the sublattice magnetization and not on the direction of the resulting net magnetization.

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.