Coexistence of perpendicular and in-plane exchange bias using a single ferromagnetic layer in Pt/Co/Cr/CoO thin film

Abstract

We studied the temperature dependence of magnetization and exchange bias in a Pt/Co/Cr/CoO multilayer thin film. These magnetic multilayers are of particular interest since the easy axis of ultra-thin Co is strongly affected by the interfacial anisotropies of neighbouring Pt and Cr layers. The room temperature measurements show that the sample has a magnetic easy axis only in the film plane. However, upon cooling the sample, the easy axis of the magnetization departs from its initial orientation and typical easy-axis hysteresis loops are obtained for both inplane and perpendicular directions. In accordance with this change in the magnetization direction at lower temperatures, the sample shows an unexpected coexistence of perpendicular and in-plane exchange bias below the antiferromagnetic transition of CoO. The temperature dependence of the exchange bias field for both directions is also significantly different. Along the film plane, the exchange bias field monotonically decreases and disappears at 220 K with increasing temperature. For the perpendicular direction, however, the exchange bias field increases and reaches a maximum value at 80 K. Then it decreases and disappears at 150 K with further increasing temperature. The mechanisms behind this anomalous temperature dependence of the exchange bias as well as the step-like behaviour in the hysteresis curves are discussed.

Spontaneous Formation of Core@shell Co@Cr Nanoparticles by Gas Phase Synthesis

“…The magnetism of CoCr alloys is due to the ferromagnetism of Co, with a critical superparamagnetic size of 9 nm at room temperature (RT), as Cr is an antiferromagnetic material with a Néel temperature of 311 K [17]. Most of the literature on magnetic studies of the CoCr system focuses on thin alternating Co-Cr layers for applications in magnetic recording or microwave sensing [18][19][20][21]. However, to our knowledge, there are no fundamental studies on the magnetism of CoCr NPs, whether alloyed or core@shell-structured.…”