Synthesis and magnetic reversal of bi-conical Ni nanostructures

Abstract

Template synthesis in polyethylene terephthalate (PET) membranes has been used to grow hour glass shaped nickel nanowires with a constriction in the range of tens of nanometers at the center. Anisotropic magnetoresistance measurements have been performed on a single nanowire to follow magnetization reversal of the structure. The results are explained via 3D micromagnetic simulations showing the appearance of a complex vortex state close to the constriction whose propagation depends on the angle between the cone axis and the applied field. The interest of this original growth process for spintronics is discussed. V

Magnetoresistance in magnetic nanoconstrictions: The role of structural defects

“…A magnetomechanical strain can modify the lattice structures (typically via dislocations) at the level of the constriction. This study is a prolongation of previous measurements performed on larger constrictions, 11 in which the different states of the domain wall have been identified. 12 …”

“…Numerical simulations are necessary in order to precisely describe the magnetic configurations measured through the magnetoresistance. 11 Nevertheless, the profile R(H) gives the mean value of the resistance averaged over a cone section, and the general shape follows approximately that of a uniformly magnetized wire, as shown in Fig. 3(a).…”

“…4 shows a typical hysteresis loop of the resistance at an intermediate angle of the applied field (h ¼ 35 with respect to the cone axis) measured between 1.2 and 1.2 T. As for the measurements at h ¼ 90 , the hysteretic behavior (with a coercivity of about 0.1 T) is restricted to the same field interval as that measured and studied in usual biconical samples. 11 The main shape is reproducible while cycling the magnetic field, with some significant statistical fluctuations of the position of the jumps (6 superimposed hysteresis loops are shown in Fig. 4(b)).…”

Magnetic nanoconstrictions made from nickel electrodeposition in polymeric bi-conical tracks: Magneto-transport behavior

“…Numerical simulations are necessary in order to describe precisely the magnetic configurations measured through the magnetoresistance. 11 Nevertheless, the profile R(H) gives the mean value of the resistance averaged over a cone section, and the general shape follows approximately that of an uniformly magnetized wire, as shown in Fig. 5 (a).…”

“…Details about the method is described elsewhere. 11,12 As the constriction is extremely small in an hydrophobic matrix, the electrodeposition time is long. At least 2000s are necessary to fill the 10 µm length of the biconical wire.…”