In‐plane and perpendicular exchange bias in [Pt/Co]/NiO multilayers

Abstract

Exchange bias in [Pt/Co]/NiO multilayers were studied as a function of film thickness and [Pt/Co] layer repetition. A strong temperature dependence of the coercivity, Hc, and exchange bias field, Hex, was observed for the thick and thinnest [Pt/Co]/NiO multilayers. While the thinnest [Pt(3 nm)/Co(1.25 nm)]4/NiO multilayers exhibits no in‐plane exchange bias field, a perpendicular Hex⊥ ∼ ‐150 Oe at 80 K was measured. By contrast, the thickest [Pt(12 nm)/Co(10 nm)]1/NiO multilayers exhibited an in‐plane Hex// ∼ ‐600 Oe (with Hex// ∼ ‐1300 Oe at 5 K) with no measurable perpendicular exchange bias field. The estimated interfacial exchange coupling energy implies the effective Co layer thickness contributing to the exchange bias is effective only in Co layer in contact with NiO bottom layer. AC susceptibility and the temperature dependence of Hex show that the a 1.25 nm thick Co component enables perpendicular exchange bias with a reduced blocking temperature TB∼200 K, compared to that (TB∼250 K) for the thick [Pt/Co]/NiO multilayers. This is attributed to disordered CoPt phases that formed due to intermixing between Co and Pt during deposition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous in-plane and out-of-plane exchange bias using a single antiferromagnetic layer resolved by x-ray magnetic circular dichroism

“…2,3 It has been established that both in-plane ͑IP͒ and out-of-plane ͑OP͒ H E can be induced in the same FM-AFM stacks. [4][5][6][7][8] Moreover, in FM/AFM/FM structures, simultaneous antiparallel or perpendicular IP H E of the two FM layers has been induced. [9][10][11] Similar states have been obtained in nanostructured exchange biased systems by exploiting shape anisotropy.…”

Magnetic Anisotropies and Exchange Bias of Co/CoO Multilayers with Intermediate Ultrathin Pt Layers

“…Ferromagnetic Co/Pt multilayers and CoPt alloys present large PMA [ 22 , 23 , 24 ]. When they are in contact with an antiferromagnetic (AFM) layer such as CoO or NiO, and after field cooling through the Néel point of the AFM in an applied magnetic field, perpendicular exchange bias (PEB) is observed [ 25 , 26 , 27 , 28 , 29 , 30 ]. This well-known exchange bias (EB) effect is related to the magnetic coupling across the common interface shared by an FM and an AFM layer that was discovered by Meiklejohn and Bean in 1956 [ 31 ] and results in a shift (biasing) of the hysteresis loop to negative or positive direction with respect to the applied field and increased coercivity [ 32 ].…”

Effects of the Annealing Temperature before Cooling under Magnetic Field on Perpendicular Exchange Coupling in (Pt/Co)5/NiO

“…One proof is that the Meiklejohn and Bean model does not explain positive EB. However, it has been experimentally proven that the exchange coupling anisotropy strongly depends on the individual thicknesses of the FM and AFM layers, [11][12][13][14][15] the interface roughness, and the interface morphology. [16,17] Here, we present an experimental study of perpendicular exchange coupling in FM/AFM system.…”