Tuning exchange bias

Physical Review Letters, 2000

Polarized neutron reflectometry is used to probe the in-plane projection of the net-magnetization vector M of polycrystalline Fe films exchange coupled to twinned (110) MnF 2 or FeF 2 antiferromagnetic (AF) layers. The magnetization reversal mechanism depends upon the orientation of the cooling field with respect to the twinned microstructure of the AF, and whether the applied field is increased to (or decreased from) a positive saturating field; i.e., the magnetization reversal is asymmetric. The reversal of the sample magnetization from one saturated state to the other occurs via either domain wall motion or magnetization rotation on opposite sides of the same hysteresis loop.

Low Temperature Physics, 2012

The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is studied. Hysteresis behavior in the 2-spin model of a ferro/antiferromagnet (FM/AFM) bilayer with exchange bias has been investigated in detail. In this model a half-space of AFM with fixed magnetic configuration contacts with a 2-layer FM film. Twelve different types of magnetization curves M(H) (both with and without hysteresis) have been found. Some of the M(H) curves demonstrate unusual features, such as plateaus and inclined segments. The hysteresis loop becomes asymmetric if the surface anisotropy is taken into account. 0 2 2 0 J J J J H .

2009

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.

Physical Review B, 1999

We consider three mechanisms of hysteresis phenomena in alternating magnetic field: the domain wall motion in a random medium, the nucleation and the retardation of magnetization due to slow (critical) fluctuations. We construct quantitative theory for all these processes. The hysteresis is characterized by two dynamic threshold fields, by coercive field and by the so-called reversal field. Their ratios to the static threshold field is shown to be function of two dimensionless variables constituted from the frequency and amplitude of the ac field as well as from some characteristics of the magnet. The area and the shape of the hysteresis loop are found. We consider different limiting cases in which power dependencies are valid. Numerical simulations show the domain wall formation and propagation and confirm the main theoretical predictions. Theory is compared with available experimental data. 75.70.Ak,75.60.Ej, 75.60.Ch

Low Temperature Physics, 2009

Magnetization field-dependences and the "exchange bias" in ferro/antiferromagnetic systems. I. Model of a bilayer ferromagnetic Low Temperature Physics 35, 476 (2009);

APS, 1998

A theory of the hysteresis loop in ferromagnets controlled by the domain wall motion is presented. Domain walls are considered as plane or linear interfaces moving in a random medium under the action of the external ac magnetic field H = H 0 sin ωt. We introduce important characteristics of the hysteresis loop, such as dynamic threshold fields, reversal field etc. together with well known

Physical Review B, 2004

The strength of exchange bias and rotatable anisotropy in polycrystalline NiFe− IrMn ferromagnet/ antiferromagnet systems is quantified from dc down to the picosecond time scale by regular quasistatic and microwave magnetometry, as well as magnetic domain observation. A transition from superparamagnetic to antiferromagnetic behavior with increasing IrMn thickness is derived from the magnetic resonance frequency and the effective magnetic damping parameter. A discrepancy between magnetic loop shift and dynamically obtained exchange bias strength is explained by asymmetric rotatable anisotropy contributions with different relaxation times in the antiferromagnetic layer. The time-dependent relaxation is directly confirmed by magnetic domain observations. Partially switching in the IrMn layer even with strong exchange bias is concluded. The increase of coercivity rises solely from the rotatable anisotropy contribution.

Dynamic magnetization reversal measurements at room temperature have been performed by magneto-optical effect on Au/Co/Au sandwiches with perpendicular anisotropy. Domain wall displacement and domain nucleation regimes govern the magnetization reversal at low and high-applied field sweep rates, respectively. The transition between the two regimes occurs at 200 Oe/s.

Low Temperature Physics, 2009

Field dependences of the magnetization and exchange bias in ferro/antiferromagnetic systems. II. Continuum model of a ferromagnetic layer

Journal of Applied Physics, 1983

We have obtained theoretical expressions for the ferromagnetic magnetization curve and hysteresis loop using an extension of the general ideas of the Globus model for polycrystalline ferrimagnets. In this work we take into account the force which resul ts from the variation of the total energy (magnetic energy plus surface energy) in order to find the value of the critical field . Our theoretical magnetization curve agrees well with the experimental curve and our hysteresis loop has the general qualitative features of the corresponding experimental loops.