Magnetoresistance of non-180° domain wall in the presence of electron-photon interaction
International Nano Letters
Magnetoresistance of non-180° domain wall in the presence of electron-photon interaction
Roya Majidi 0
0 Department of Physics, Shahid Rajaee Teacher Training University , Lavizan, Tehran 16788-15811 , Iran
In the present paper, influence of photon on resistance of non-180° domain wall in metallic magnetic nanowires has been studied using the semiclassical approach. The analysis has been based on the Boltzmann transport equation, within the relaxation time approximation. The one-dimensional Néel-type domain wall between two ferromagnetic domains with relative magnetization angle less than 180° is considered. By increasing this angle, the contribution of the domain wall in the resistivity of the nanowire becomes considerable. It is also found that the fundamental contribution of the domain wall in resistivity can be controlled by propagating photon. These results are valuable in designing spintronic devices based on magnetic nanowires.
Magnetoresistance; Non-180° Néel-type domain wall; Metallic nanowire; Magnetization rotation angle; Electron-photon interaction
Background
Spintronics is an emerging technology with a great
promise to provide a new generation of electronic
devices where spin of carriers would play a crucial role in
addition to or in place of their charge [
1,2
]. The design
and manufacture of such new spintronic devices require
a proper understanding of spin-dependent transport
especially in magnetic systems [
1,2
]. In recent years,
investigating the unique spin transport property and determining the
magnetoresistance (MR) of magnetic nanostructures such
as nanowires have attracted much attention. Results
indicate that MR as a characteristic property of the magnetic
nanostructures can be modified significantly by the
presence of non-collinear magnetization regions named domain
walls (DWs) [
3
]. From both scientific and technological
points of view, understanding the resistance caused by
DWs and determining the effect of different scattering
sources on the DW resistance (DWR) are essential. For that
reason, many research efforts have been made to
understand the role of DW in resistivity [
4-15
]. Experiments on
iron whiskers demonstrate that DWs are a source of
electrical resistance [4]. Contrary to bulk samples, it has been
found that the MR associated with nanosize DWs can be
significantly large [
4,5
]. Theoretically, Levy and Zhang, by
studying MR effect due to the magnetic DW scattering,
found that the DWs are a source of spin channel mixing
and MR enhancement [6]. In addition, investigation of the
effect of Rashba spin orbit interaction on the resistance of
DW indicates that this interaction causes an increase in the
DWR [
7,8
]. The temperature dependence of the resistivity
of DWs has been also studied. The results clarify that the
positive contribution of DWs in increasing the resistivity
is enhanced by increasing temperature [
10-12
]. In recent
years, applying an external magnetic field or propagating a
photon to control the DWR has been investigated [
13-15
].
It should be mentioned that most of the present studies
[
4-15
] have focused on the ideal 180° DWs despite the fact
that DWs with a magnetization rotation of less than 180°
appear in artificial materials [
16,17
]. Meanwhile, realization
of spintronic devices with improved functionality and
performance requires controlling DW configurations and
understanding their role in electronic transport. In recent
years, contributions of 90°, 180°, and 360° DWs in the
resistivity of samples in the presence of external magnetic
field are compared [18]. It is found that that resistance of
360° DW is more considerable than that of 90° and 180°
DWs. In the present paper, we have studied the influence
of photon on the resistivity of the non-180° DW in metallic
magnetic nanowires.
Methods
Theoretical considerations
We have studied a metallic magnetic nanowire containing
a Néel-type DW. For this DW, the angle between the local
direction of the magnetization and the z-axis can be
expressed as θ(z) = ϕ z/d, where φ is the magnetization
rotation angle of the DW and considered less than 180°. It
means that the DW is confined between two magnetic
domains with relative magnetization angle of φ, and in such
DW, θ changes smoothly from zero to φ over the DW
width, d. In Figure 1, the 180° DW with φ = 180° and
non180° DW with φ < 180° are shown.
The following Hamiltonian has been used to describe
the DW in the presence of photon:
H ¼ H0 þ Hex þ Hel ph:
The first term, H0, contains kinetic energy and
nonmagnetic periodic potential. The second term, Hex,
represents the exchange interaction between the spin of
conduction electrons and the localized magnetic
moments. These terms are given by
H0 ¼
Hex ¼
ħ2 d2
2m dz2 þ V ðzÞ;
Δexσ^:M^ ðzÞ;
ð1Þ
ð2Þ
ð3Þ
ð4Þ
in which V(z) is the lattice periodic potential, Δex
represents the exchange interaction strength, σ^ denotes the
Pauli spin matrices, and M^ ðzÞ (...truncated)