Domain wall

Domain walls

2000 Five month project for my master degree at the Service de Physique de l’Etat Condensé (SPEC/DRECAM/DSM/CEA Saclay) [4]

Supervisors: O. Klein and M. Viret

Referees: A. Fert and B. Roulet

Subject: Contributions to the resistivity of an individual magnetic domain wall

Part of my postgraduate diploma, the project consisted of measuring the contributions to the resistivity of a single domain wall in a FePd nanostructure. We created a nanostructure in which a finite number of domain walls could be measured. Combining transport and magnetic imaging measurements, the intrinsic domain wall resistance is quantified. It is found positive and of a magnitude consistent with that predicted by models based on spin scattering effects within the walls. This magnetoresistance at a nanometer scale allows a direct counting of the number of walls inside the nanostructure. The effect is then used to measure changes in the magnetic configuration of submicron stripes under application of a magnetic field. These measurements are in good agreement with the model of Viret et al. [1] and Levy and Zhang [2]. To my knowledge, this experiment is still the most accurate measurement of the resistance of a single domain wall in a ferromagnetic material. This work was published two years later (see list of publications).

[1] M. Viret, D. Vignoles, D. Cole, J. M. D. Coey, W. Allen and J. F. Gregg, Phys. Rev. B 53, 8464 (1996).

[2] P. M. Levy and S. Zhang, Phys. Rev. Lett. 79, 5110 (1997).

Resistivity of a single domain wall
Virgin magnetic configuration observed by MFM inside the FePd stripe. The dark and clear ribbons correspond to up and down magnetic domains. The current flows through the two segments of the elbow (arrows), and the resistance of each configuration, CPW and CIW, is measured between four lateral contacts. From R. Danneau et al., Phys. Rev. Lett. 88, 157201 (2002) [1] .
Variation of resistance and Hall effect during the first magnetization sweep for the CPW configuration shown in the MFM picture. The excess resistance from the saturation value is due to domain walls. The steps are indicative of individual domain wall disappearance during the reversal process. The Hall resistance varies only during the low field single jumps, indicating that the magnetization saturates first in the contacts. The measurements were done at T = 17 K. From R. Danneau et al., Phys. Rev. Lett. 88, 157201 (2002) [2] .
The black curves are measurements of the resistance and Hall effect in the CIW configuration during the first magnetization process. The left inset is a MFM picture of the initial magnetic configuration. The grey curve shows the same quantities as the field is swept back to zero. The abrupt jump at 0.213 T corresponds to the nucleation of domains. The right inset is a MFM image of the nucleated domain configuration in the remanent state. From R. Danneau et al., Phys. Rev. Lett. 88, 157201 (2002) [3] .

Related publications:

  • R. Danneau, P. Warin, J. P. Attané, Y. Petej, C. Beigné, C. Fermon, O. Klein, A. Marty, F. Ott, Y. Samson and M. Viret

Individual domain wall resistance in submicron ferromagnetic structures

Phys. Rev. Lett. 88, 157201 (2002) [5]