Analysis Of Magnetoresistance Research Articles

Probing electron-electron interaction along with superconducting fluctuations in disordered TiN thin films

In two-dimensional (2D) disordered superconductors prior to superconducting (SC) transition, the appearance of a resistance peak in the temperature dependent resistance $R(T)$ measurements indicates the presence of weak localization (WL) and electron-electron interaction (EEI) in the diffusion channel and SC fluctuations in the Cooper channel. Here, we demonstrate an interplay between SC fluctuations and EEI by low-temperature magnetotransport measurements for a set of 2D disordered TiN thin films. While cooling the sample, a characteristic temperature ${T}^{*}$ is obtained from the $R(T)$ at which SC fluctuations start to appear. The upturn in $R(T)$ above ${T}^{*}$ corresponds to WL and/or EEI. By the temperature and field dependences of the observed resistance, we show that the upturn in $R(T)$ originates mainly from EEI with a negligible contribution from WL. Further, we have used the modified Larkin's electron-electron attraction strength $\ensuremath{\beta}(T/{T}_{\mathrm{c}})$, containing a field-induced pair-breaking parameter, in the Maki-Thompson SC fluctuation term. Here, the temperature dependence of $\ensuremath{\beta}(T/{T}_{\mathrm{c}})$ obtained from the magnetoresistance (MR) analysis shows a diverging behavior close to ${T}_{\mathrm{c}}$, and it remains almost constant at higher temperature within the limit of $\mathrm{ln}(T/{T}_{\mathrm{c}})<1$. Interestingly, the variation of $\ensuremath{\beta}(T/{T}_{\mathrm{c}})$ on the reduced temperature $(T/{T}_{\mathrm{c}})$ offers a common trend which has been closely followed by all the concerned samples presented in this paper. Finally, the temperature dependence of inverse phase scattering time (${\ensuremath{\tau}}_{\ensuremath{\phi}}^{\ensuremath{-}1}$), as obtained from the MR analysis, clearly shows two different regimes; the first one close to ${T}_{\mathrm{c}}$ follows the Ginzburg-Landau relaxation rate $({\ensuremath{\tau}}_{\mathrm{GL}}^{\ensuremath{-}1})$, whereas the second one at high temperature varies almost linearly with temperature, indicating the dominance of inelastic electron-electron scattering for the dephasing mechanism. These two regimes are followed in a generic way by all the samples despite being grown under different growth conditions.

Spin current related magnetoresistance in epitaxial Pt/Co bilayers in the presence of spin Hall effect and Rashba-Edelstein effect

We analyze the experimentally obtained spin current related magnetoresistance (MR) in epitaxial Pt/Co bilayers by using a drift-diffusion model that incorporates both bulk spin Hall effect and interfacial Rashba-Edelstein effect (REE). The MR analysis yields, for the Pt/Co interface, a temperature-independent Rashba parameter in the order of ${10}^{\ensuremath{-}11}\phantom{\rule{0.16em}{0ex}}\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\mathrm{m}$ that agrees with theoretical calculations, along with an effective interfacial REE thickness of several angstroms, which is in overall consistency with our previous spin-orbit torque analysis. Our results suggest that both bulk and interface charge-spin current interconversions need to be taken into account for the spin current related MR analysis in highly conductive magnetic heterostructures such as the epitaxial Pt/Co bilayers.

Low-temperature quantum magnetotransport of graphene on SiC (0 0 0 1) in pulsed magnetic fields up to 30 T

Resistivity, ρ(T), and magnetoresistance (MR) are investigated in graphene grown on SiC (0 0 0 1), at temperatures between T ~ 4–85 K in pulsed magnetic fields of B up to 30 T. According to the Raman spectroscopy and Kelvin-probe microscopy data, the material is a single-layer graphene containing ~20% double-layer islands with a submicron scale and relatively high amount of intrinsic defects. The dependence of ρ(T) exhibits a minimum at temperature Tm ~ 30 K. The low-field Hall data have yielded a high electron concentration, nR ≈ 1.4 × 1013 cm−2 connected to intrinsic defects, and a mobility value of µH ~ 300 cm2 (Vs)−1 weakly depending on T. Analysis of the Shubnikov–de Haas oscillations of MR, observed between B ~ 10–30 T, permitted to establish existence of the Berry phase β ≈ 0.55 and the cyclotron mass, mc ≈ 0.07 (in units of the free electron mass) close to expected values for the single-layer graphene, respectively. MR at 4.2 K is negative up to B ~ 9 T, exhibiting a minimum near 3 T. Analysis of MR within the whole range of B = 0–10 T below the onset of the SdH effect has revealed three contributions, connected to (i) the classical MR effect, (ii) the weak localization, and (iii) the electron–electron interaction. Analysis of the ρ(T) dependence has confirmed the presence of the contributions (ii) and (iii), revealing a high importance of the electron–electron scattering. As a result, characteristic relaxation times were obtained; an important role of the spin–orbit interaction in the material has been demonstrated, too.

Evaluation of the effect of various mechanisms on the magnetoresistance of lanthanum manganites La0.85Sr0.15MnO3 with activation-type conductivity

A method is proposed that allows one to divide the magnetoresistance (MR) observed in manganites into three mechanisms: dimensional, orientational, and magnetic. The first two mechanisms are associated with the stratification of a substance into ferromagnetic and nonferromagnetic phases, which significantly differ in electric resistivity. The dimensional mechanism of MR is attributed to the effect of a magnetic field on the size of magnetic inclusions. The orientational mechanism of MR is determined by the dependence of electric resistivity on the mutual orientation of the magnetizations of magnetic inclusions. The magnetic mechanism of MR is determined by the properties of the magnetization of a ferromagnet, in particular, by the Curie–Weiss singularity on the temperature dependence of magnetic susceptibility at the Curie point. This mechanism exists in homogeneous substances, although its value may depend on the magnetic properties of inhomogeneities. The method is developed for substances with activation-type conductivity and is applied to the analysis of MR of La0.85Sr0.15MnO3 manganite near the Curie point, where the MR attains its maximum. The dimensional mechanism turns out to be dominant in magnetic fields H greater than the saturation field Hs (H > Hs). The orientational, dimensional, and magnetic mechanisms have a comparable effect on the MR for H < Hs. The effect of the orientational mechanism on MR is relatively weak (does not exceed the third part of the total MR), although this mechanism determines the giant MR in multilayered metal films. The possibility of application of the method to the analysis of MR near the insulator–metal transition is analyzed.

Magnetoresistivity of R 2Rh 3Al 9 (R=Ce, La) and A 2Rh 3Ga 9 (A=U, Th)

The anomalous properties of Ce 2Rh 3Al 9 and of U 2Rh 3Ga 9 are investigated by magnetoresistivity (MR) measurements of these alloys and of their non-f electron counterparts La 2Rh 3Al 9 and Th 2Rh 3Ga 9 between room temperature and T=1.4 K, and in magnetic fields up to 8 T. In U 2Rh 3Ga 9 there is a large, negative MR prevalent up to 80 K where the electrical resistivity ρ( T) reaches a maximum. The MR in Ce 2Rh 3Al 9 is small and negative below 8 K, then turns positive at the shoulder-like anomaly in ρ( T) and remains positive towards the peak seen in ρ(T≃140 K). The analysis of MR( T, B) for U 2Rh 3Ga 9 in the paramagnetic Kondo-lattice region yields a Kondo temperature of T K =5.3(1) K which is of the same order as the magnetic ordering temperature.