The role of the wide-band-gap polymer layer for the existence of conductivity switching in the valve structure

Abstract

428Previously, the possibility of switching the conduc tivity in the metal/polymer/metal asymmetric struc ture containing only one ferromagnetic electrode and a layer of a wide band gap polymer material (poly(diphenylenephthalide), PDP) was detected [1]. It was also shown that the conductivity switching by the magnetic field is associated with partial polariza tion over the spin of charges injected from the ferro magnet [2]. However, the results of [1, 2] do not allow a conclusion on spin transport within the polymer layer. Experiments on the structure such as a spin valve could answer the question on the possibility of spin transport through a rather thick polymer film. In such a structure, the injecting electrode plays the role of a polarizer; the second ferromagnetic electrode serves as an analyzer of spin polarized current carriers. In this case, a change in the magnetization direction in the electrode analyzer should result in modulation of the current flowing in the structure under study.In this context, the objective of this research is to study the possibility of spin transport occurring through a layer of a wide band gap polymer material in an experimental configuration such as the spin valve.The main difference between the samples studied in this work and those used previously [1] is the replacement of the nonmagnetic copper electrode by the ferromagnetic metal Ni electrode. Thus, in this work, we study the "symmetric" ferromagnet/poly mer/ferromagnet structure unlike the "asymmetric" ferromagnet/polymer/non ferromagnetic metal structure previously considered in [1,2]. The elec trode with a large coercivity in the symmetric structure under consideration was fabricated by depositing a nickel layer on an antiferromagnetic Cr layer [3]. The lower two layer chromium/nickel film grown by sequential deposition of these metals on glass in vac uum was characterized in the initial state by a prefer ential direction and increased magnetic rigidity (Fig. 1a). The upper nickel film was a soft magnetic elec trode and had not a preferential direction in the initial state (Fig. 1b). Polymer was deposited in one layer or in two layers to increase the distance for possible spin transfer. The thickness of these structures was no less than 500 nm and to 1.2 μm, respectively. Measure ments were performed at room temperature, magnetic fields were less than 500 mT.Since abrupt changes in the working cell resistance (six-eight orders of magnitude) in the experimental circuit were possible, a circuit with a current generator was used.The external magnetic field could be oriented par allel or perpendicular to the structure plane. Observa Abstract-The effect of electronic switching of the conductivity by a magnetic field lower than 500 mT has been implemented in the spin valve structure in the "current perpendicular to plane" geometry with a trans port layer of a wide band gap polymer to 1200 nm thick. The problem of spin transfer through the polymer layer has been discussed in the model of ballistic charge transport over nanos...

Giant magnetoresistance of strong magnet–polymer heterostructures with a wide band gap

“…The effect of spin-polarized electrons on the giant magnetoresistance of a ferromagnetic-polymer structure was found [13]. The spin transport through a film of nonconjugated polymer with a thickness of approximately 800 nm was demonstrated by the example of the structure of a spin valve [14]. Despite the large amount of experimental data supporting the nontrivial nature of magnetoresistance phenomena in the asymmetric structure of a ferromagnet-PDF-metal, there are enough grounds for trivial explanation of the phenomenon under discussion, for example, by means of electrical breakdown or mechanical breakdown (puncture) of the polymer film and, as a result, shortcircuiting of the electrodes, branching, and other reasons.…”