Abstract
The in-plane temperature dependence of exchange bias was studied through both dc magnetometry and ferromagnetic resonance spectroscopy in a series of [NiFe/IrMn]n multilayer films, where n is the number of layer repetitions. Major hysteresis loops were recorded in the temperature range of 300 K to 2 K to reveal the effect of temperature on the exchange bias in the static regime while temperature-dependent continuous-wave ferromagnetic resonance for frequencies from 3 to 16 GHz was used to determine the exchange bias dynamically. Strong divergence between the values of exchange bias determined using the two different types of measurements as well as a peak in temperature dependence of the resonance linewidth were observed. These results are explained in terms of the slow-relaxer mechanism.
Highlights
The phenomenon of exchange bias discovered over 60 years ago[1] remains a topic of interest in applications and basic research
major hysteresis loop (MHL) were measured along the exchange bias (HEB) axis using a Quantum Design Magnetic Properties Measurement System (MPMS) in the temperature range 300 K to 2 K
Static measurements yield an expected increase in the value of HEB as temperature decreases which has been explained as temperature dependence of the number of grains contributing to HEB.[14,18]
Summary
The phenomenon of exchange bias discovered over 60 years ago[1] remains a topic of interest in applications and basic research. Marked by a shifted major hysteresis loop (MHL), exchange-biased systems display subtle properties requiring deeper exploration, including a non-monotonic variation of the ferromagnetic resonance (FMR) linewidth (∆H) as a function of temperature. This property had been observed in rare-earth (RE)-doped iron garnets,[2,3,4,5,6,7] and a theory was developed by Teale and Tweedale[2] and Van Vleck and Orbach[8] based on earlier work of Galt[9] and Clogston,[10] describing a slow-relaxation due to the paramagnetic impurities. Others have suggested that the impurities are paramagnetic ions present at the interface of the ferromagnetic and antiferromagnetic layers.[13,14,15] In this work, the theory of paramagnetic ion relaxation is used to describe experimental observations
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