Saturated Hall Resistivity Research Articles

Anomalous Hall effect in CoxSi1−x granular films deposited by magnetron co-sputtering

In this research, CoxSi1−x granular films with Co volume fraction (x) varying from 0.36 to 1 were prepared by using a magnetron co-sputtering method. The influence of x on the temperature-dependent longitudinal resistivity ($${\rho _{xx}}$$) and anomalous Hall effect (AHE) in CoxSi1−x granular films were systematically studied. The dependence of $${\rho _{xx}}$$ on measuring temperature could be explained by the superposition of fluctuation-induced tunneling (FIT) process and temperature-dependent scattering. Interestingly, the contribution from scattering and FIT can be distinguished. The saturated Hall resistivity ($$\rho _{{xy}}^{A}$$) increased monotonically with decreasing x. In addition, the $$\rho _{{xy}}^{A}$$ amplified nearly 26-fold as x decreased from 1 to 0.4. For the pure Co film (x = 1), the intrinsic and side jump mechanisms dominated the Hall transport. However, the deviation of classical scaling relation was observed in other samples, which was mainly ascribed to the influence of interfacial scattering.

Effect of MgO/Co interface and Co/MgO interface on the spin dependent transport in perpendicular Co/Pt multilayers

Effect of the metal/oxide interface on spin-dependent transport properties in perpendicular [Co/Pt]3 multilayers was investigated. The saturation Hall resistivity (ρxy) is significantly increased by 45% with 1.4 nm thick CoO layer inserted at the top Co/MgO interface; whereas it is increased only 25% with 1 nm thick CoO layer at the bottom MgO/Co interface. The interfacial structures characterized by X-ray photoelectron spectroscopy show that the MgO/Co interface and Co/MgO interface including chemical states play a dominant role on spin-dependent transport, leading to different anomalous Hall behavior.

Enhanced anomalous Hall effect in Fe nanocluster assembled thin films

An enhanced anomalous Hall effect is observed in heterogeneous uniform Fe cluster assembled films with different film thicknesses (ta = 160-1200 nm) fabricated by a plasma-gas-condensation method. The anomalous Hall coefficient (Rs) at ta = 1200 nm reaches its maximum of 2.4 × 10(-8) Ω cm G(-1) at 300 K, which is almost four orders of magnitude larger than bulk Fe. The saturated Hall resistivity (ρ(A)xy) first increases and then decreases with the increase of temperature accompanied by a sign change from positive to negative. Analysis of the results revealed that ρ(A)xy decreases with increasing longitudinal resistivity (ρxx) on a double-logarithmic scale and obeys a new scaling relation of log(ρ(A)xy/ρxx) = a0 + b0 log ρxx.

Giant Hall effect of (Ni90Co10) x (SiO2)1− x nanogranular films at percolation threshold

The series of (Ni90Co10) x (SiO2)1− x nanogranular films were fabricated using the magnetron sputtering technique. The Hall effect of these films increased as the fraction of permalloy metal composition decreases near percolation. The maximum saturated Hall resistivity was found to be 4.32 µΩ cm in (Ni90Co10)55(SiO2)45 film at room temperature, about two orders of magnitude larger than that of pure ferromagnetic metallic films. The atomic fraction at the quantum percolation threshold was accurately proved with the Rutherford backscattering (RBS) for the first time.

Effect of interfacial structures on anomalous Hall behavior in perpendicular Co/Pt multilayers

A large enhancement of anomalous Hall resistivity was obtained in the perpendicular [Co/Pt]3 multilayers sandwiched by MgO/CoO hybrid bilayers. For example, the saturation Hall resistivity (ρxy) is greatly increased, which is 250% and 67% larger than that in pure [Co/Pt]3 multilayers and that in [Co/Pt]3 multilayers sandwiched by pure MgO layers, respectively. Meanwhile, the perpendicular magnetic anisotropy in the multilayers with MgO/CoO hybrid bilayers was enhanced. The large enhancement of ρxy originates from the modified metal/oxide interfacial structures, together with improved crystallization of core [Co/Pt]3 multilayers, due to the insertion of hybrid bilayers.

Extraordinary Hall effect on Fe-rich amorphous thin films and Fe-rich/Cu multilayers

In this study we investigated the magnetic and transport properties of thin Fe-rich amorphous films and Fe-rich/Cu multilayers. We compared the extraordinary Hall effect in these two types of samples and discussed it in terms of thickness and sample structure. The thicker films exhibited a strong in-plane magnetic anisotropy, and by decreasing film thickness both saturated Hall resistivity and Hall sensitivity increase. A Hall resistivity value of 20μΩcm is observed in 100nm thick Fe-rich films at 12K and a sensitivity of 1.3Ω/T is obtained at room temperature. Electrical conductance increases and Hall resistivity decreases when the films are sandwiched with Cu.

Enhancement of Extraordinary Hall Effect in Pt/CoFe Multilayers With a Small Amount of Fe Doped Into Pt Layers

The extraordinary Hall effect (EHE) is investigated for the Pt/CoFe multilayers with a small amount of Fe doped into Pt layers. It is found that, through varying CoFe layer thickness and/or the content of Fe in Pt layers, high sensitivity linear EHE can be achieved in the Fe doped Pt/CoFe multilayers at room temperature. Most remarkably, both the saturation Hall resistivity and the Hall angle are significantly enhanced upon adding a small amount of Fe into Pt layers, reaching 1.2 μΩ·cm and 1.8%, respectively. The EHE sensor based on the Fe doped Pt/CoFe multilayers has the field sensitivity over 400 V/A T, which is twice as large as that of the pure Pt/CoFe multilayers and much higher than the best value ever achieved in Pt-based ferromagnetic alloy thin films. The present results suggest that, due to the large Hall effect and the adjustable interface anisotropy, the Fe doped Pt/CoFe multilayer film should be a potential candidate for magnetic field sensor application.

Room Temperature Giant Hall Effect in (Ni61Fe39) x (Al2O3)1−x Percolating Nanogranular Films

A series of (Ni61Fe39) x (Al2O3)1−x films were prepared using the magnetron sputtering technique. The maximum of saturated Hall resistivity 4.06 μΩ⋅cm was observed in (Ni61Fe39)60(Al2O3)40 nanogranular film at room temperature, which was about two orders larger than that of pure ferromagnetic metallic films. For the first time, the composition in the atomic fraction at the quantum percolation threshold was accurately characterized by the Rutherford backscattering (RBS) channelling technique in order to substantiate the newly metal-insulator fraction of percolation threshold in the Giant Hall Effect. It also was identified from the TEM image of an as-deposited sample that this large enhancement of the Hall resistivity coefficient was interrelated with the percolation threshold. With a different annealing temperature (T A ) up to 300 °C , the saturated Hall resistivity of (Ni61Fe39)60(Al2O3)40 granular film decreased only a little, which showed its good thermal stability for potential application.

Spin injection in GaAs and giant Hall effect

In spintronics, general spin injection is achieved by the superlattice, spin valve, tunnel junction, other typical method of spin injection is to dilute magnetic semiconductor such as: GaMnAs. In this paper, spin Fe particles are injected into the GaAs matrix by using the magnetron sputtering to form the granular film (GaAs)19Fe81, in which saturated Hall resistivity ρxys is shown to be 15 μΩ·cm at room temperature, which is about 2 orders larger than that of pure Fe. So the spin injection is successfully realized.

Structure, magnetic and electrical transport properties of cosputtered Fe 0.5Ge 0.5 nanocomposite films

Fe 0.5Ge 0.5 nanocomposite films with different film thicknesses were fabricated using cosputtering. The films are composed of Ge, Fe and Fe 3Ge 2, and are ferromagnetic at room temperature. The saturation magnetization and magnetic interaction including dipolar interaction and exchange coupling increase with the increasing film thickness. The electrical conductance mechanism turns from metallic to semiconducting and the saturation Hall resistivity ρ xys increases with the decreasing film thickness. At 28 nm, ρ xys is ∼137 μΩ cm at 2 K, about 150 times larger than that of pure Fe film (0.9 μΩ cm) and four orders larger than that of bulk Fe. The ρ xy – H curves of all the films show the same linearity character in low-field range even though the temperature-independent slope is different at different film thicknesses. At high temperatures, the skew scattering mechanism is dominant. At low temperatures, side-jump effect should be dominant at large resistivity ρ xx regime for the thin films, and the skew scattering is dominant at small ρ xx regime for the thick films.

Giant Hall effect in (GaAs)Fe granular films

A series of (GaAs) 1 − x Fe x ( x: volume fraction) films with Fe granules embedded in GaAs matrix were prepared by magnetron sputtering. Hall Effect of the films was characterized. The largest saturated Hall resistivity of 17.3 μ Ω cm was observed in (GaAs) 30Fe 70 film at room temperature, which is over 2 orders larger than that of pure Fe, about 1 order larger than that of (NiFe)–(Al 2O 3) and (NiCo)–(SiO 2) granular films prepared under the same preparation conditions, and 150% larger than that of Ge 30Fe 70.

Anomalous Hall effect and magnetoresistance of (FexSn1−x)1−y(SiO2)y films

Structural, magnetic and transport properties were investigated for heterogeneous (FexSn1−x)1−y(SiO2)y films deposited on oxidized silicon substrates at room temperature with RF magnetron sputtering. X-ray diffraction indicated that the films consist of a nanocrystalline phase of FeSn2 embedded into an amorphous background. For (FexSn1−x)92.33(SiO2)7.67, it was demonstrated that with the increase in the Fe component an evolution from negative isotropic magnetoresistance (MR) behaviour to one with a mixture of anisotropic magnetoresistance and isotropic negative MR occurs. On fixing the SiO2 percentage and decreasing the Fe–Sn ratio, the negative transverse MR first increases and then decreases. For samples having a fixed Fe–Sn ratio, the negative transverse MR increases with the increase in SiO2. Compared with the Fe–Sn system, the addition of 7.67 at.% SiO2 enhances the saturated Hall resistivity. Further increase in SiO2 introduces a complicated saturated Hall resistivity dependence on the concentration of SiO2.

Investigation on the giant Hall effect of (Fe xSn 100− x) 1− y(SiO 2) y granular films

(Fe x Sn 100− x ) 1− y (SiO 2) y granular films have been fabricated by a magnetron-sputtering technique and the Hall resistivity of the films has been investigated in the Fe concentration range from x = 71 to 73, and in the SiO 2 volume fraction range from y = 0.45 to 0.65. Compared with the Fe–Sn system, a significant enhancement has been observed for the Hall resistivity at room temperature for x = 71, y = 0.65, as high as 75 μΩ cm. This value of the saturated Hall resistivity is almost three orders larger in magnitude than that of pure Fe and about 10 times higher than that of the Fe 68Sn 32 granular alloy films reported earlier. The magneto-resistance of the films has also been studied.

Extraordinary Hall effect in FexSn100-x granular alloy films

A series of FexSn100-x granular alloy films with different atomic fractions were fabricated by ion beam sputtering. The highest value ever observed for ferromagnetic metal/non-magnetic metal systems has been obtained. The extraordinary Hall effect was studied systemically by varying the atomic fractions and the thickness of the samples. With the power law between the saturated Hall resistivity and the resistivity the mechanism of the extraordinary Hall effect was also discussed.

Giant Hall effect in FexSn100−x granular alloy films

The Hall resistivity of FexSn100−x granular alloy films fabricated by ion-beam sputtering has been studied. A saturated Hall resistivity up to 8.68 μΩ cm, the highest value ever observed for ferromagnetic metal/nonmagnetic metal system, has been obtained for the sample with Fe concentration x=68 at. %. This value is almost 60 times higher than that of pure Fe and eight orders higher than that of pure Sn, respectively. The scale relation between ρxys and ρxx was also investigated. The effect of both the concentration and average grain size of the films on the Hall resistivity has been discussed. Magnetoresistance measurement indicated no giant magnetoresistance effect has been found in this system.

Hall Effect of(Co0.34Fe0.66)0.42(SiO2)0.58 Granular Films

The(Co0.34Fe0.66)0.42(SiO2)0.58 (volume fraction)granular films were fabricated by using the magnetron sputteringtechnique, and a saturated Hall resistivity ρxys of about29 µΩ·cm was observed at room temperature, which wasalmost three orders of magnitude greater than that in the pureferromagnetic sample. The measured linear dependence of resistivityρxx versus log10T and magnetoresistance effect indicated thatthe the Co0.34Fe0.66 volume fraction in the films was nearpercolation threshold. The giant Hall effect in the(Co0.34Fe0.66)0.42(SiO2)0.58 granular film mayoriginate from the percolation phenomenon.

The Hall effect of Co0.35Fe0.65-Al2O3nanogranular films

A series of (Co0.35Fe0.65)x(Al2O3)(1-x) (volumefraction) nanogranular films was fabricated using magnetron sputtering. TheHall effect of the films increases as the volume fraction ofCo0.35Fe0.65 decreases near percolation. The saturated Hallresistivity of (Co0.35Fe0.65)0.43(Al2O3)0.57 isabout 5.5 µΩ cm at room temperature. This suggests that the giantHall effect (GHE) may be due to the percolation phenomenon. The correlation ofthe Hall effect and tunnelling magnetoresistance (TMR) with the alloy volumefraction is discussed.

The Hall effect of Fe–Al–O thin film

A series of Fe45.51(Al2O3)54.49 (volume fraction) nanogranular films were prepared using the ion-beam sputtering technique. A saturated Hall resistivity of about 12.5 μΩ cm was observed at room temperature. With different annealing temperature TA up to 300 °C, the saturated Hall resistivity of the sample decreases only a little, which shows good thermal stability. The transmission electron microscopy image shows that very small Fe particles (smaller than 1 nm) embedded in the Al2O3 matrix, and connected into the network, with the ρ–T curve indicates that this Hall effect may originate from the percolation phenomenon.

Giant Hall Effect of Fe45.51(Al2O3)54.49 Nano-granular Film

A series of Fe45.51(Al2O3)54.49 nano-granular films were prepared using ion-beam sputtering technique. A saturated hall resistivity of about 12.5 μΩ·cm at room temperature was observed. The transmission electron microscopy image showed that very small Fe particles of smaller than 1 nm are embedded in Al2O3 matrix, and connected into network. The measured ρ - T curve indicated that this giant Hall effect may originate from the percolation phenomenon. With different annealing temperature (TA) up to 300°C, the saturated Hall resistivity decreased only a little. The good thermal stability of Fe45.51(Al2O3)54.49 nano-granular Films showed potential application for magnetic sensor.

The Hall Effect in Ni0.8Co0.2-SiO2 Granular Film

The Hall effect in Ni0.8Co0.2-SiO2 granular films which were fabricated by ion beam sputtering technique was studied. The saturated Hall resistivity reached 6.3μΩ·cm in an applied field of 9.5×105 A/m at room temperature when NiCo volume fraction x is near the metal-insulator transition threshold. The temperature dependence of resistivity in these samples with different NiCo compositions was also investigated. It showed-lg T dependence in low x samples, which gradually showed metallic as x increased. Transmission electron microscopy and vibrating sample magnetometer were used to study the microstructures and magnetic properties, the dependence of transport properties on microstructure was also discussed.