http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

TOPICAL REVIEW: Nanomagnetics

https://macul.ciencias.uchile.cl/~mkiwi/CV86.pdf

Exchange bias theory

Hard/soft magnetic heterostructures: model exchange-spring magnets

The magnetic exchange between epitaxial thin films of the multiferroic (antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft ferromagnetic (FM) layer is used to couple the magnetic response of the FM layer to the magnetic state of the antiferromagnetic one. We will show that biasing the ferroelectric YMnO3 layer by an electric field allows control of the magnetic exchange bias and subsequently the magnetotransport properties of the FM layer. This finding may contribute to paving the way towards a new generation of electric-field controlled spintronic devices.

/pdf/electric-field-control-of-exchange-bias-in-multiferroic-1w65z4hk5e.pdf

Electric-field control of exchange bias in multiferroic epitaxial heterostructures.

Direct ferromagnetic antiferromagnetic exchange biasing energy is determined by small reversible rotations of the magnetization away from the unidirectional easy axis using an externally applied magnetic field. The angle the magnetization makes relative to the easy direction is determined by measuring the anisotropic magnetoresistance. This technique gives energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO. An apparent Co thickness variation of the experimentally determined exchange biasing interface energy indicates the Co magnetization is not uniform but probably spirals through the thickness of the film.

Use of the anisotropic magnetoresistance to measure exchange anisotropy in Co/CoO bilayers

Two measurement techniques, both relying on reversible rotations of the magnetization, have been used to determine the magnitude of the interfacial exchange energy (IEE) between ferromagnetic and antiferromagnetic (F/AF) layers. One technique is to use the anisotropic magnetoresistance to determine rotations of the magnetization away from the unidirectional easy axis, where the rotation is accomplished by applying external magnetic fields less than the effective F/AF exchange field. The second technique uses measurements of the ac susceptibility as a function of the angle between the ac field and the unidirectional exchange field. Both of the reversible process techniques result in values of the IEE larger (by as much as a factor of 10 in Co/CoO bilayers) than the traditional irreversible technique of measuring a shift in the hysteresis loop. The ac susceptibility technique was also used to measure one Fe/FeF2 bilayer. For this sample, the IEE values obtained by reversible and irreversible methods are equ...

Measurements of the ferromagnetic/antiferromagnetic interfacial exchange energy in CO/CoO and Fe/FeF2 layers (invited)

In studies of the giant magnetoresistance (GMR) of ferromagnetic/nonmagnetic/ferromagnetic sandwich films, both the anisotropic magnetoresistance (AMR) and the GMR change with the angle between the magnetizations of the individual layers when the current direction is fixed. A technique is presented that separates the two phenomena and shows explicitly the angular dependence of the GMR. The technique relies on layered films in which the magnetization of one or more layers is held fixed by an exchange biasing field and the magnetization of another layer is rotated by an applied field. The separation of the two magnetoresistance contributions takes advantage of the fact that the GMR has a cosine angular dependence and the AMR of the rotated layer has a cosine squared angular dependence. The results indicate the GMR can be isolated from the AMR using only data containing contributions from both.

A method of separating the giant magnetoresistance and the anisotropic magnetoresistance in multilayers

We have developed a new technique to measure the ferromagnetic antiferromagnetic exchange biasing (FAEB) energy with relatively small reversible rotations of the magnetization from the unidirectional easy direction. This new technique uses the anisotropic magnetoresistance to determine the angle the magnetization makes relative to the easy direction as a function of an externally applied magnetic field. This technique, based on reversible magnetization changes, gives FAEB energies roughly twice that of the traditional irreversible magnetization reversal measurements.

Measurement of the exchange anisotropy in Co/CoO bilayers using the anisotropic magnetoresistance

By a systematic variation of structures, recent measurements conclude the scattering associated with the high resistance giant magnetoresistance (GMR) state occurs within 0.25 nm of the magnetic interface. We have accomplished a similar measurement that does not require such stringent control of the sample structure. Instead, the present work uses measurements of the anisotropic magnetoresistance (AMR) in both the high resistance and low resistance GMR states. The samples are sandwiches of Co/Cu/Co/CoO with Co thicknesses ranging from 1 to 10 nm and Cu thickness of approximately 2.5 nm. The AMR is measured with the Co magnetizations aligned parallel to one another (the low resistance GMR state) and with the Co magnetizations aligned antiparallel to one another (the high resistance GMR state). The data show that the AMR in the antiparallel configuration is less than that in the parallel configuration. An analysis that relates the reduced AMR to the magnetic interfacial region giving rise to the high resist...

B. H. Miller

Papers

Use of the anisotropic magnetoresistance to measure exchange anisotropy in Co/CoO bilayers

Measurements of the ferromagnetic/antiferromagnetic interfacial exchange energy in CO/CoO and Fe/FeF2 layers (invited)

A method of separating the giant magnetoresistance and the anisotropic magnetoresistance in multilayers

Measurement of the exchange anisotropy in Co/CoO bilayers using the anisotropic magnetoresistance

A comparison of the giant magnetoresistance and anisotropic magnetoresistance in Co/Cu sandwich films (abstract)