Thermal hysteresis of ferromagnetic/antiferromagnetic compensated bilayers

Abstract

We report a theoretical investigation of thermal hysteresis of fourfold anisotropy ferromagnetic ͑FM͒ film exchange coupled to a compensated antiferromagnetic substrate. Thermal hysteresis occurs if the temperature interval includes the reorientation transition temperature, below which the frustration of the interface exchange coupling leads to a 90°rotation of the magnetization of the ferromagnetic layer. The temperature width of the thermal hysteresis is tunable by external magnetic fields of modest magnitude, with values of 43 K for an external field of 110 Oe and of 14 K for a field of 210 Oe, for a Fe͑12 nm͒ / MnF 2 ͑110͒ bilayer. For a Fe͑3 nm͒ / FeF 2 ͑110͒ bilayer the width of the thermal hysteresis is 23 K at 110 Oe and 13 K at 300 Oe. We discuss how the thickness of the iron film affects the field tuning of the thermal hysteresis width, and also how the thermal loops may be used to identify the nature of the interface exchange energy.

In-plane reorientation of magnetization in epitaxial exchange biased Fe/MnPd bilayers

“…2 However, micromagnetic calculations show that due to the spin-flop coupling the ground state for a compensated FM-AFM interface is an orthogonal magnetic orientation of the FM and AFM spins. [8][9][10][11] In this work, we experimentally observed a variety of in-plane magnetic reorientations in Fe/MnPd bilayers with various thicknesses of both FM and AFM layers. 5,6 Including the intrinsic uniaxial anisotropy, K FM , of the FM layers, which may have various origins, 7 the FM magnetic direction is determined by the combined uniaxial anisotropy K u resulting from the competition between K FM and K sf .…”

“…With increasing temperature, the loop shift is decreased and the stepped loop becomes square. 8 It is well known that the chemically ordered a-axis MnPd surface is spin uncompensated. 15 Although H aligned with the easy axis often leads to a magnetization reversal by domain nucleation, 16 a coherent rotation model of magnetization can still give us an understanding on how the shape of loops is affected by the relative orientation between K u and the EB induced unidirectional anisotropy K eb .…”

Ferromagnetic resonance of compensated ferromagnetic/antiferromagnetic bilayers

“…9,10,[16][17][18][19][20] The interface spins of the F film are subjected to exchange field of opposite directions produced by the spins in the unit cell of the AF plane. Yet, the F-exchange field is parallel to the interface AF spins of one sublattice and opposite to those of the other sublattice.…”

“…However, magnetization measurements sample large areas of the interface and thus average out the interface field strength. 6 Interface pinned domain wall resonance, 7,8 magnetic thermal hysteresis, 9 and magnetic heat capacity 10 have been proposed as local probes of the interface exchange energy.…”

Field and temperature-driven magnetic reversal of spin-flop coupled epitaxial Fe/MnPd bilayers

“…In spite of the paucity of experiments, the correlation between the observed SRT properties and their origins at the interface needs to be established. A particularly interesting characteristic in such a SRT system is the thermal hysteresis 31 , in which the magnetization switching, from the reoriented state (RS) to the aligned state (AS) and vice versa, is driven by temperature. However, such an effect has been proposed only in theory and has not been experimentally observed so far.…”