Double exchange bias in ferrimagnetic heterostructures

Abstract

We report on the magnetic reversal characteristics of exchange coupled ferrimagnetic (FI) Tb 19 Fe 81 /Tb 36 Fe 64 heterostructures. Both layers are amorphous and exhibit strong perpendicular magnetic anisotropy. The investigated heterostructures consist of a Tb-dominated and a Fe-dominated FI layer. Thus, in the magnetic ground state the net moments of the individual layers are oppositely aligned due to antiferromagnetic coupling of Fe and Tb moments. By cooling the system below 160 K, a large positive and negative exchange bias (EB) effect appears for the Tb-and Fe-dominated layers, respectively. The biasing depends only on the initial magnetization state and is neither affected by a cooling field nor by loop cycling. The phenomenon can be explained by the presence of a hard magnetic Fe-dominated interfacial layer, which forms during the sputter deposition process due to interface mixing and resputtering effects. This interfacial layer acts as a pinning layer below a certain temperature, where its coercivity increases to values larger than the accessible magnetic field range. This assumption is further supported by introducing a 0.9-nm-thick Ru spacer layer, which causes the EB effect to vanish. The EB effect was further investigated for a sample series, where the thickness ratio of the two Tb-Fe layers was varied, while keeping the total thickness of the bilayers constant. Only samples where the individual layers are sufficiently thick reveal double shifted loops, indicating the high sensitivity of the observed bias effect with respect to the magnetic properties of the individual layers and their interfacial area.

Pervasive artifacts revealed from magnetometry measurements of rare earth-transition metal thin films

“…[1][2][3][4][5] These properties make them attractive pinning layers as an alternative to conventional antiferromagnets such that when coupled with perpendicular FI or ferromagnetic (FM) layers, they can be exploited in exchangebias systems and heat-assisted magnetic recording applications. 4,[6][7][8][9][10][11][12][13][14] More recently, RE-TM alloys have been investigated in the vicinity of their magnetization and angular momentum compensation points for high-speed domain wall-and skyrmion racetrack-type memory devices. [15][16][17][18][19][20] The high magnetic tunability of RE-TM ferrimagnet-based heterostructures allows them to be tailored to specific applications, provided that their magnetic parameters are determined accurately.…”

Observation of a Chirality-Induced Exchange-Bias Effect

“…It is generally considered to form from an uncompensated spin configuration at the ferromagnetic-antiferromagnetic interface with both frozen and rotatable spins [6][7][8][9][10]. Besides the classic system, EB-related effects have also been observed in ferrimagnetic-based materials with compensated interfaces [11][12][13][14][15][16][17]. Moreover, an atomic EB has been reported in a single ferrimagnetic DyCo 4 thin film where the magnetic surface region pins the magnetization of the bulk [18].…”

Applied Trends in Magnetic Rare Earth/Transition Metal Alloys and Multilayers

“…Another related aspect that could be worthy of study in the close future is the appearance of giant exchange bias shifts (of up to tens of kOe) in ferrimagnetic/ferromagnetic [ 48 , 49 , 50 ] and ferrimagnetic/ferrimagnetic [ 51 ] bilayers, which could be extremely useful for spin valves and other spintronic applications. Unfortunately, these exchange bias phenomena are usually observed at low temperatures, which decreases its potential for applications (usually requiring a working range of temperatures close to room temperature).…”