Magnetization dynamics and spin-glass-like origins of exchange-bias in Fe–B–Nb thin films

• Published in: Journal of applied physics 2023-12, Vol.134 (24)
• Main Authors: Masood, Ansar, Belova, L., Ström, V.
• Format: Article
• Language: English
• Subjects: Amorphous alloys; Atomic structure; Bias; Exchanging; Glass; Grain boundaries; High temperature; Hysteresis loops; Low temperature; Magnetization; Metallic glasses; Niobium; Nuclei; Origins; Spin dynamics; Spin glasses; Thermal evolution; Thin films
• ISSN: 0021-8979; 1089-7550; 1089-7550
• DOI: 10.1063/5.0179602

The phenomenon of exchange bias has been extensively studied within crystalline materials, encompassing a broad spectrum from nanoparticles to thin-film systems. Nonetheless, exchange bias in amorphous alloys has remained a relatively unexplored domain, primarily owing to their inherently uniform disordered atomic structure and lacking grain boundaries. In this study, we present a unique instance of exchange bias observed in Fe–B–Nb amorphous thin films, offering insights into its origins intertwined with the system's spin-glass-like behavior at lower temperatures. The quantification of exchange bias was accomplished through a meticulous analysis of magnetic reversal behaviors in the liquid-helium temperature range, employing a zero-field cooling approach from various initial remanent magnetization states (±MR). At reduced temperatures, the appearance of asymmetric hysteresis, a hallmark of negative exchange bias, undergoes a transformation into symmetric hysteresis loops at elevated temperatures, underscoring the intimate connection between exchange-bias and dynamic magnetic states. Further investigations into the magnetic thermal evolution under varying probe fields reveal the system's transition into a spin-glass-like state at low temperatures. We attribute the origin of this unconventional exchange bias to the intricate exchange interactions within the spin-glass-like regions that manifest at the interfaces among highly disordered Fe-nuclei. The formation of Fe-nuclei agglomerates at the sub-nanometer scale is attributed to the alloy's limited glass-forming ability and the nature of the thin-film fabrication process. We propose that this distinctive form of exchange bias represents a novel characteristic of amorphous thin films.