Magnon contribution to the magnetoresistance of iron nanowires deposited using pulsed electrodeposition

Abstract

Iron nanowires with a square cross section are grown by pulsed electrodeposition within a newly developed nanochannel template that allows for easy characterization. Measurements of the magnetoresistance as a function of magnetic field and temperature are performed within a large parameter window allowing for the investigation of the magnonic contribution to the magnetoresistance of electrodeposited iron nanowires. Values for the temperature dependent magnon stiffness D(T) are extracted:Iron nanowires reveal a high magnetization that can be combined with large shape anisotropies and very high coercive fields. These features make iron nanowires particularly interesting for applications within MRAM data storage [1,2]. There have been numerous investigations on the magnetic behavior of pure iron nanowire arrays [3] and it's alloys [4][5][6][7], but only very few that deal with the electric properties of electrodeposited nanowires [8]. This is mostly due to the fact that iron is oxidized without forming a protective native oxide as soon as it is exposed to ambient air which makes electric characterization of the unaltered material impossible. The developed template presented in this publication allows us to carry out in-situ transport measurements within the same thick oxide template that is also used for the growth of the wires. Thus, the wires are completely protected against oxidation and a good ohmic contact between conduction leads and the nanowire is guaranteed. The electric transport properties of all ferromagnets and especially ferromagnetic nanowires are dependent on the applied external magnetic field. The most prominent characteristic is the anisotropic magnetoresistance (AMR) effect, which was explained by Smit [9], suggesting an angular dependence of the scattering cross section between orbitals of atoms in ferromagnetic order and conduction electrons. As soon as all magnetic moments are fully saturated, the Lorentz force is responsible for an increase in the resistance as the magnetic field increases, since it forces electrons on a curved trajectory and thus reduces the projected free wavelength in the direction of the k-vector. Above approximately T c /5 however, ferromagnets show an inverse and near linear behavior. This is due to a decrease of the total magnon population with an increasing magnetic field and thus electron-magnon scattering is suppressed. This effect is significantly stronger than the counteracting Lorentz-dependence [10].The developed template system (Figure 1) is based on a Si/SiO 2 -wafer onto which conduction leads are evaporated. On top of these, a nanochannel template is fabricated using a sacrificial polymer layer that is patterned with laser-interference-lithography [11,12], reactive ion etching and atomic layer deposition (ALD). The sacrificial polymer layer is calcinated at 350 °C and a hollow channel structure remains on top of the previously deposited conduction leads. The height and width of the perfectly rectangular nanochannels can be tuned within a large

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

“…Drawing any conclusions about the absolute coercive field strength would be elusive, because only one nanowire of each kind was measured in this case and the switching field distribution of single wires spread on a wafer can be surprisingly large due to defects and irregularities [14]. The nanowires show linear, metallic R vs T behaviors with residual resistivity ratios of (300 )/ (2 ) ≈ 4.5, which is a notably high value for electrodeposited, ferromagnetic nanowires [27,36,59,60], indicating a good sample quality (see supporting information).…”

Non-Planar Geometrical Effects on the Magnetoelectrical Signal in a Three-Dimensional Nanomagnetic Circuit

“…Second, in contrast to the odd signal, the even signal does not saturate at fields above 2 T but instead decreases further with applied field. As (ρ ∥ – ρ ⊥ ), that is, the AMR term in eq , is not expected to change significantly after saturation, we attribute the measured change to the magnon magnetoresistance (MMR), , which has been reported as a linear and nonsaturating negative MR present after all magnetic moments are fully saturated. As schematically shown in Figure h, this contribution is due to the progressive suppression of spin disorder caused by spin waves in a ferromagnet under an increasing field strength, which results in a drop of resistance due to a reduction in the electron-magnon scattering. ,, The magnitude of MMR depends on the strength, and not the sign of the applied field, and has therefore an even response to the applied field.…”

“…To understand the significant difference in the even part of the signal, we consider the angular dependence of magnon magnetoresistance as an additional contribution. The MMR results in a change of resistivity that can be described by the electron-magnon scattering model developed by Raquet et al 56,58,61 :…”

“…Although ∆𝜌 ?? @ is not dependent on the direction of the magnetisation with respect to the current 56,58 , this does not necessarily mean that no change in the ∆𝜌 ?? @ will result from different directions of the applied magnetic field.…”

Magnetic Nanowires and Nanotubes

“…It has been claimed to be used to monitor DW stochastic motion (Singh et al 2010, Mukhopadhyay et al 2011, however the results are not consistent with those expected for a DW under field of different magnitudes. One may think of using magnon magnetoresistance (Nguyen et al 2011), already demonstrated in wires by Sergelius et al (2015), to monitor the location of a wall.…”