Evidence of Spin-Glass state in Molecular Exchange-Bias System

Abstract: In conventional exchange-bias system comprising of a bilayer film of ferromagnet (FM) and antiferromagnet (AFM), investigating the role of spin-disorder and spin-frustration inside the AFM and at the interface has been crucial in understanding the fundamental mechanism controlling the exchange-bias -- an effect that leads to a horizontal shift in the magnetization hysteresis response of the FM. Similarly, in the recently reported monolayer molecular exchange-bias effect requiring no AFM layer, probing magnetic-disorder at the FM/molecule interface or inside the FM layer can provide new insights into the origin of molecular exchange-bias and the associated physics. In this article, by cooling the Fe/metal-phthalocyanine devices in oscillating magnetic field, we demonstrate a characteristic temperature dependent response of exchange-bias shift and ferromagnet coercivity that is supportive of a spin-glass behavior. Here, the origin of spin-glass is attributed to the spin frustration created in the magnetic structure of the Fe layer, which was absent in our reference-Fe studies. These results highlight the strong influence of FM/molecule interface pi-d hybridization on the magnetic exchange interactions extending deeper into the FM layer.