Abstract
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.
Highlights
For Fe rich Tb–Fe films where the Fe moment is dominating, no pronounced magnetic field dependent increase of the magnetization was observed due to the stronger TM–TM exchange coupling of Fe (Heiman, 1976). Please note that this approach does not allow determining the exact fanning cone angle of the Tb moments, as the Tb fanning cannot be fully compressed and the Fe cone will certainly expand at the same time, these results should be treated with care and serve only as a first indicator
magnetization versus temperature (MR–T) curves are exemplarily plotted in Figures 3A,B for the 5- and 85-nm-thick Tb–Fe film with varying Tb content between 15 and 35 at.%, respectively
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, while variations in composition with film thickness are insignificant
Summary
Ferrimagnetic amorphous rare earth (RE)–transition metal (TM) Tb–Fe alloy thin films gained considerable attention in the past as a potential medium for thermomagnetic recording (Mimura et al, 1976a,b; Mansuripur, 1986; Hansen, 1987; Jamet et al, 1996; Suits et al, 1998) due to its low Curie temperature (Mimura et al, 1976a; Iijima et al, 1989) and tunable magnetic properties by varying composition (Mimura et al, 1976a, 1978; Satoh et al, 1985; Hassdenteufel et al, 2013). Today’s significance lies primarily in the field of exchange-biased heterostructures (Radu et al, 2012; Romer et al, 2012; Schubert et al, 2013; Tang et al, 2015), giving rise to giant exchange bias fields, and all-optical switching (AOS) (Stanciu et al, 2007; Hassdenteufel et al, 2013), where the Ferrimagnetic Tb–Fe Alloy Thin Films orientation of the magnetization can be reversed by circularly polarized femtosecond laser pulses without any external magnetic field This ability depends strongly on the material properties and underlying microstructure; its characterization and their dependence on growth conditions, film thickness, and composition is of great importance for the understanding of the underlying mechanism. On the contrary, Malmhäll and Chen (1982) ascribed the thickness dependence to a microstructure-induced variation in the short range order during growth, which causes a change in the effective composition with increasing film thickness
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