Research Interests

Exchange bias systems

 

Introduction

 

This characteristic shift of the magnetic hysteresis loop away from zero field has initially been found in ferromagnetic (FM) Co particles having an antiferromagnetic (AFM) CoO coating. This phenomenon, which has been called exchange bias, is often observed after field cooling FM/AFM systems below the Néel temperature. In the past two decades, exchange bias has been studied intensively in thin films where it has a high potential for technological applications.

 

Results for the Co/CoO system

We investigated a (16.4 nm Co / 2 nm CoO / 3.4 nm Au)20 multilayer prepared on a Al2O3(0001) substrate with PNR to study the magnetization reversal process. PNR has the property to distinguish between different magnetization reversal models because the neutrons are sensitive to the parallel as well as perpendicular magnetization component with respect to an external magnetic field. The perpendicular component causes a spin-flip intensity (I+- and I-+), whereas the parallel component causes a difference between the non-spin flip intensities I++ and I--.

For the unbiased state (T = 300 K), reversal is due to rotation on both sides of the hysteresis loop. For the biased state (T = 10 K), rotation is the main mechanism only for increasing fields. For the decreasing field branch, which is the direction opposite to the bias (cooling field), the mechanism changes to domain wall motion.

 

References:

K. Temst, E. Girgis, R. D. Portugal, H. Loosvelt, E. Popova, M. J. Van Bael, C. Van Haesendonck, H. Fritzsche, M. Gierlings, L. H. A. Leunissen, and R. Jonckheere

Magnetization and polarized neutron reflectivity experiments on patterned exchange bias structures
Eur. Phys. J. B 45, 261 (2005)

M. Gierlings, M. J. Prandolini, H. Fritzsche, M. Gruyters, and D. Riegel

A PNR study of the off-specular scattering during the asymmetric magnetization reversal in an exchange-biased Co/CoO multilayer

Physica B 356, 36 (2005)

M. Gierlings, M. J. Prandolini, H. Fritzsche, M. Gruyters, and D. Riegel

Change and asymmetry of magnetization reversal for a Co/CoO exchange-bias system

Phys. Rev. B. 65 , 092407 (2002)

 

M. Gierlings, M. J. Prandolini, H. Fritzsche, M. Gruyters, and D. Riegel

Observation of magnetization rotation during the reversal in Co/CoO exchange-bias multilayers

Appl. Phys. A, 74 [Suppl.], S1523 (2002)