Isotropic FMR frequency enhancement in thin Py/FeMn bilayers under strong magnetic proximity effect

Abstract

Exchange biasing in ferromagnet/antiferromagnet bilayers is known to enhance the material’s ferromagnetic resonance frequency and make it strongly angle dependent due to the unidirectional anisotropy induced at the interface. We observe a ten-fold enhancement in frequency and angle-independent ferromagnetic resonance in bilayers of Py/FeMn with ultrathin FeMn, accompanied by a significantly enhanced magnetic moment. The observed isotropic frequency enhancement is consistent with rotatable rather than unidirectional magnetic anisotropy and the induced magnetic moment links this anisotropy with the ferromagnet-proximity effect. The estimated effective anisotropy field acting on the proximity-induced moment in ultrathin FeMn can be as high as 0.5 T at room temperature. Our results show the potential of the ferromagnetic proximity effect combined with the inherent exchange anisotropy in antiferromagnets for high-speed spintronic applications.

Spin wave excitations in exchange biased IrMn/CoFe bilayers

“…This supports the idea that the frequency overlap of the ferromagnet and antiferromagnet response is essential in correctly propagating spin waves into a coupled antiferromagnet. 25 The resonance in the 10 GHz range is close to reported experimental values for a similar material system. 26…”

“…This suggests a natural frequency dependence of the attenuation of spin waves propagating in the antiferromagnet, with higher frequency modes being dissipated more strongly. Interestingly, the data show a significant coupling of spin waves between the ferromagnet and antiferromagnet, and a similar behavior has been observed in recent experiments for the FeMn/Py system 25 with broad implications for tuning the dynamic response of materials in the 5-200 GHz frequency range.…”

Oscillatory Exchange Bias Controlled by RKKY in Magnetic Multilayers

“…The difference in thickness of the two Py layers makes it easy to distinguish them using magnetometry. The thickness of the FeMn layer is chosen to be small enough to exhibit strong finite size effects [10,15], such that the magnetic state of its interfaces would significantly affect its AF ordering; 6 nm was found to be optimal in our case. The normal metal spacer (N) thickness was varied through the entire RKKY range, to investigate the effect of the oscillating indirect exchange mediated by the conduction electrons in N (RKKY) on the AF-ordering strength in the FeMn layer.…”

Магнітні Нанокомпозити Для Новітніх Технічних Та Медичних Застосувань

“…Показано, що поведінку таких систем визначає конкуренція двох механізмів: зростання обертової анізотропії, притаманної полікристалічному шару FeMn, коли температура АФМ-впорядкування наближається до температури вимірювання зі зменшенням товщини, та наведення значного додаткового магнітного моменту у FeMn (~15 %) завдяки ефекту близькості до ФМ-шару [22]. Одержано експериментально та підтверджено аналітичними розрахунками істотне (на порядок величини) ізотропне підсилення частоти феромагнітного резонансу, що є перспективним для розроблення функціональних елементів субтерагерцового частотного діапазону [22,23].…”