Atomistic origin of exchange anisotropy in noncollinear γ-IrMn3 -CoFe bilayers

TY - JOUR

T1 - Atomistic origin of exchange anisotropy in noncollinear γ-IrMn3 -CoFe bilayers

AU - Jenkins, Sarah

AU - Fan, Wei Jia

AU - Gaina, Roxana

AU - Chantrell, Roy W.

AU - Klemmer, Timothy

AU - Evans, Richard F.L.

N1 - This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2020/10/13

Y1 - 2020/10/13

N2 - Antiferromagnetic spintronic devices could offer ultrafast dynamics and a higher data density than conventional ferromagnetic devices. One of the challenges in designing such devices is the control and detection of the magnetization of the antiferromagnet due to its lack of stray fields, and this is often achieved through the exchange bias effect. In exchange biased systems, the pinned spins are known to comprise a small fraction of the total number of interface spins, yet their exact nature and physical origin has so far been elusive. Here we show that in the technologically important disordered γ-IrMn3-CoFe structure, the pinned spins arise from the small imbalance in the number of spins in each magnetic sublattice in the antiferromagnet due to the naturally occurring atomic disorder. These pinned spins are strongly coupled to the bulk antiferromagnet, explaining their stability. Moreover, we find that the ferromagnet strongly distorts the interface spin structure of the antiferromagnet, causing a large reversible interface magnetization that does not contribute to exchange bias but does increase the coercivity. We find that the uncompensated spins are not localized spins which occur due to point defects or domain walls but instead constitute a small motion of every antiferromagnet spin at the interface. This unexpected finding resolves one of the long-standing puzzles of exchange bias and provides a route to developing optimized nanoscale antiferromagnetic spintronic devices.

AB - Antiferromagnetic spintronic devices could offer ultrafast dynamics and a higher data density than conventional ferromagnetic devices. One of the challenges in designing such devices is the control and detection of the magnetization of the antiferromagnet due to its lack of stray fields, and this is often achieved through the exchange bias effect. In exchange biased systems, the pinned spins are known to comprise a small fraction of the total number of interface spins, yet their exact nature and physical origin has so far been elusive. Here we show that in the technologically important disordered γ-IrMn3-CoFe structure, the pinned spins arise from the small imbalance in the number of spins in each magnetic sublattice in the antiferromagnet due to the naturally occurring atomic disorder. These pinned spins are strongly coupled to the bulk antiferromagnet, explaining their stability. Moreover, we find that the ferromagnet strongly distorts the interface spin structure of the antiferromagnet, causing a large reversible interface magnetization that does not contribute to exchange bias but does increase the coercivity. We find that the uncompensated spins are not localized spins which occur due to point defects or domain walls but instead constitute a small motion of every antiferromagnet spin at the interface. This unexpected finding resolves one of the long-standing puzzles of exchange bias and provides a route to developing optimized nanoscale antiferromagnetic spintronic devices.

UR - http://www.scopus.com/inward/record.url?scp=85094585569&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.102.140404

DO - 10.1103/PhysRevB.102.140404

M3 - Article

AN - SCOPUS:85094585569

SN - 2469-9950

VL - 102

JO - Physical Review B

JF - Physical Review B

IS - 14

M1 - 140404(R)

ER -