Magnetoresistance of a domain wall at a submicron junction

Autor: Yongbing Xu, C. A. F. Vaz, C.C. Yao, H. T. Leung, J. A. C. Bland, Atsufumi Hirohata, F. Rousseaux, H. Launois, Edmond Cambril
Rok vydání: 2000
Předmět:
Zdroj: Physical Review B. 61:R14901-R14904
ISSN: 1095-3795
0163-1829
DOI: 10.1103/physrevb.61.r14901
Popis: A local magnetoresistance ~MR! effect associated with the switching of a coherent spin block confined in a cross-shaped junction of mesoscopic ferromagnetic NiFe wires was probed with the voltage pads attached close ~,1.5 mm! to the junction. A positive intrinsic MR effect, i.e., an increase in resistance, associated with local spin noncollinearity, or a 45° domain wall, in a 0.5 mm cross was demonstrated while the anisotropic MR and the Lorentz MR were unambiguously excluded. The spin configurations of magnetic domain walls~DW! in ferromagnets have the same feature of noncollinearity found in antiferromagnetically coupled magnetic multilayers or magnetic granular systems, both of which display giant magnetoresistance ~GMR!. 1 Accordingly, spin-dependent transport effects associated with the presence of the DW are expected. This idea was explored by Gregg et al. 2 and a positive magnetoresistance ~MR! effect due to DW scattering was observed in continuous Co films with regular stripe domains. Hong and Giordano 3 observed discontinuous changes of the resistance upon sweeping the field in Ni wires. This was attributed to the nucleation and movement of DW, which transverse the wire during magnetization reversal. Ru ¨diger et al. 4 has investigated the effect of the domain wall on the MR in micron size Fe wires with a controlled stripe domain structure. A negative MR effect was identified at the temperature where the anisotropic MR ~AMR! and Lorentz MR compensate each other. The negative MR effect of DW was also observed by Ohtani et al. 5 in wires with a ‘‘neck.’’ Several theoretical models 6‐9 based on new physical mechanisms have been proposed to explain the experimental observations. Levy and Zhang 6 calculated the spin flip, as well as nonflip scattering present in DW with the same Hamiltonian used to explain the GMR effect. The positive MR observed in continuous Co films was attributed to an admixture of spin states in the presence of the DW. van Hoof 8 made ab initio calculations of the specular electron transmission through DW and proposed that the MR effect of the DW is due to the change in the electronic band structure of the ferromagnets brought about by spin rotation. Tatara and Fukuyama 7 on the other hand found that the DW contributes to the decoherence of electrons and the nucleation of a wall leads to a decrease of resistance ~negative MR! in the weakly localized regime which occurs at less than about 20 K. More recently, Lyanda-Geller et al. 9 discussed the importance of the electron-electron interaction quantum corrections and universal conductance fluctuations along with weak localization for the electron transport through regions of spatially varying magnetization, such as domain walls. We can see from the above arguments that there are striking disagreements between the different experimental reports as well as between the various proposed theoretical models concerning the sign, the temperature range, and the mechanism causing the MR effect. These conflicting theoretical and experimental studies now call for further observations of the DW MR under conditions in which domain structure can be well defined and both the Lorentz MR and AMR effects excluded. Nanofabrication of mesoscopic magnets provides a key opportunity to address this spin-dependent electron-transport effect associated with the local spin noncollinearity, as the domain structure can be controlled by varying the shape and lateral dimensions. In this paper, we have designed and fabricated a simple cross shape wire structure using advanced e-beam lithography. The electric pads were fabricated to be as close as possible to the junction of the crosses to probe the local MR response of regions with controlled spatially varying magnetization. The aim was to confine domain walls in a junction of submicron size and to clarify unambiguously the intrinsic MR effect due to spin noncollinearity.
Databáze: OpenAIRE
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