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

Abstract

Ferrimagnetic rare earth -transition metal Tb-Fe alloy thin films exhibit a variety of different magnetic properties, which depend 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 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.

Double exchange bias in ferrimagnetic heterostructures

“…1(a). As expected, both layers do not show a compensation temperature for these compositions and stay either Tb or Fe dominant [32,33]. We also determined the uniaxial magnetic anisotropy constant K U of both layers as a function of temperature using the expression…”

“…Growth-induced variations in the short range order, resulting in a redistribution of the orientation of the Tb magnetic moments, are responsible for the thickness dependence, as discussed in detail in Ref. [32].…”

“…Furthermore, the interfacial layer can only act as a pinning layer if its coercivity gets larger than the available field range (up to ±80 kOe) at a certain temperature. Apparently, this perquisite depends strongly on the thickness of the FI layers, which is typically associated with a strong variation of the magnetic properties present in this thickness range [32]. Please note that, also, the order of the layer stack plays an important role.…”

“…In addition, the presence of a compensation point is not required for the occurrence of the EB effect. It is assumed that this interfacial region is formed during the growth process due to interface mixing and re-sputtering effects, where for certain Tb-Fe compositions, hard magnetic properties can be achieved [32]. An example of a 20-nm-thick Tb 22 Fe 78 single layer is included in Fig.…”

Perspective: Ultrafast magnetism and THz spintronics

“…All-optical writing was demonstrated for ferrimagnetic rare-earth transition metal alloy films GdCoFe or TbCoFe around the compensation temperature of the rare-earth and transition metal moments, Figure 6(a) shows single shot switching with two helicities. 73 It was found that the situation is quite complex, 78,79 and it became evident that the demagnetization (memory loss of the spin system) together with some symmetry-breaking mechanism determines the physics of the all-optical switching. 80 The magnetization is not reversed by a 180 rotation, as in a standard recording media (transverse relaxation).…”