X-ray magnetic linear dichroism as a probe for non-collinear magnetic state in ferrimagnetic single layer exchange bias systems

Abstract

Ferrimagnetic alloys are extensively studied for their unique magnetic properties leading to possible applications in perpendicular magnetic recording, due to their deterministic ultrafast switching and heat assisted magnetic recording capabilities. On a prototype ferrimagnetic alloy we demonstrate fascinating properties that occur close to a critical temperature where the magnetization is vanishing, just as in an antiferromagnet. From the X-ray magnetic circular dichroism measurements, an anomalous ‘wing shape’ hysteresis loop is observed slightly above the compensation temperature. This bears the characteristics of an intrinsic exchange bias effect, referred to as atomic exchange bias. We further exploit the X-ray magnetic linear dichroism (XMLD) contrast for probing non-collinear states which allows us to discriminate between two main reversal mechanisms, namely perpendicular domain wall formation versus spin-flop transition. Ultimately, we analyze the elemental magnetic moments for the surface and the bulk parts, separately, which allows to identify in the phase diagram the temperature window where this effect takes place. Moreover, we suggests that this effect is a general phenomenon in ferrimagnetic thin films which may also contribute to the understanding of the mechanism behind the all optical switching effect.

Interface controlled thermal resistances of ultra-thin chalcogenide-based phase change memory devices

“…2g and h, respectively. This is in agreement with previous results showing that GST transforms from an amorphous phase to a face-centered cubic lattice at 155°C [32][33][34] . The 160 nm GST film thickness was measured as 160, 152, and 149 nm at 25, 240, and 400°C, respectively, and similarly the 40 nm GST film thickness as 38.7, 36.9, and 33.7 nm at 25, 240, and 400°C.…”

Magnetic moment orientation and in depth distribution of dysprosium near the surface of DyCo$_{4.6}$ thin films determined by the analysis of their X ray circularly polarized absorption Dy $M_{5}$ spectra

“…The same table gives the compensation temperatures, T Comp , of the alloys and their coercive fields at 2 K and RT. T Comp temperature was smaller in sample DCM (90 K) than in sample DCC (120 K), in agreement with their different RE concentration, and with the expected by comparing with the reported by others in DyCo alloys of similar concentrations [5,20], assuming a linear relationship between T Comp and the atomic concentration of the alloy [18]. The higher cobalt concentration in sample DCM causes a marked lower magnetic remanence at 10 K than in sample DCC.…”

“…X ray reflectometry shows rougher surfaces in DCM than in DCC thin films, suggesting that the larger H C of the DCM thin film is probably caused by its higher density of domain wall pinning defects. The coercive fields of both samples were notoriously higher than the reported in DyCo 4 by others [5,20], with H C values lower than 1 T at a similar decrement (∆T=150 K) in temperature from their T Comp (250 K). This might account for a higher PMA energy and/or domain wall pinning defects density in our samples.…”

“…The hysteresis loops of some DyCo alloys of similar concentration than the samples used in this study presented side wing loops at high applied fields as the presented in some spring magnet-like bilayer structures [3,4,19]. The effect was explained as derived from the effective different RE concentration at the bulk and the region near the surface which will yield two different T Comp for each region [5,20].…”

The exchange bias effects of CoFe2O4@NiO nanofibers fabricated by electrospinning

“…The exchange bias effect is that the hysteresis loop of the ferromagnetic(FM) layer deviates from the magnetic field direction after the system is cooled from the Neel temperature (T Neel ) of anti-ferromagnetic(AFM). The systems can consist of permanent magnetic/soft magnetic [1], permanent magnetic/anti-ferromagnetic [2], (FM)/(AFM) [3], ferrimagnetic(FIM)/(AFM) [4] film system [5], core-shell system [6], alloy system [7], etc. In 1956, Meiklejohn and Bean [8] discovered the exchange bias effect, which was due to the spin interaction at the interface of Co nanoparticles covered by CoO, and the hysteresis loop moved along the magnetic field axis after the applied magnetic field cooled.…”