Perpendicular exchange bias in ferrimagnetic spin valves

Abstract

The exchange bias effect refers to the shift of the hysteresis loop of a ferromagnet in direct contact to an antiferromagnet. For applications in spintronics a robust and tunable exchange bias is required. Here we show experimental evidence for a perpendicular exchange bias in a prototypical ferrimagnetic spin valve consisting of DyCo 5 /Ta/Fe 76 Gd 24 , where the DyCo 5 alloy has the role of a hard ferrimagnet and Fe 76 Gd 24 is a soft ferrimagnet. Taking advantage of the tunability of the exchange coupling between the ferrimagnetic layers by means of thickness variation of an interlayer spacer, we demonstrate that perpendicular unidirectional anisotropy can be induced with desirable absolute values at room temperature, without making use of a field-cooling procedure. moreover, the shift of the hysteresis loop can be reversed with relatively low magnetic fields of several hundred oersteds. This flexibility in controlling a robust perpendicular exchange bias at room temperature may be of crucial importance for applications.

Double exchange bias in ferrimagnetic heterostructures

“…If the two coupled layers exhibit the same dominating elements (RE/RE or TM/TM), a negative EB occurs. These two cases have been recently reported for DyCo 5 /Fe 76 Gd 24 heterostructures [19]. In other recent papers, large EB has been observed in FI Ru 0.25 Cr 0.75 O 2 thin films [28] and FI Heusler alloys [29].…”

“…Ferrimagnetic Tb 19 Fe 81 (20 nm − x)/Tb 36 Fe 64 (x) thin films with x = 5, 7.5, 10, 12.5, and 15 nm, exhibiting strong perpendicular magnetic anisotropy, were prepared by dc magnetron cosputtering at room temperature on SiO 2 (100 nm)/ Si(001) substrates. The base pressure of the deposition chamber was below 8 × 10 −8 mbar, and during the deposition, an Ar pressure of 1.5 × 10 −3 mbar (up to 5.0 × 10 −3 mbar) was used.…”

“…In addition, the magnetic properties of the individual FI layers of a Tb 19 Fe 81 (10 nm)/Tb 36 Fe 64 (10 nm) film sample were studied by soft x-ray magnetic circular dichroism (XMCD) [31]. To allow for sufficient transmission of soft x-rays, this film sample was prepared on a 200-nm-thick Si 3 N 4 membrane.…”

“…In addition to AFM/FM interfaces, EB has also been reported in systems with ferrimagnetic (FI)/FM layers [10][11][12][13][14][15][16][17][18][19][20][21][22][23], resulting in giant EB fields in the order of several tens of kilo-Oersteds [13,14,[24][25][26]. In particular, FI layers consisting of amorphous heavy rare earth (RE)-3d transition metal (TM) alloys provide further benefits as a pinning layer since these alloys can exhibit large interfacial exchange interaction and zero moment at the compensation temperature T comp .…”

“…In this paper, the reversal characteristics of exchange coupled FI Tb 19 Fe 81 /Tb 36 Fe 64 heterostructures, consisting of a Tb-dominated and a Fe-dominated FI layer with perpendicular magnetic anisotropy, are investigated. Most striking, below 160 K, two simultaneously shifted hysteresis loops of different shape and magnitude occur in positive and negative field directions.…”