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Spin chiral systems with Dzyaloshinskii–Moriya (DM) interaction due to broken inversion symmetry are extensively studied for their technological applications in spintronics and thermoelectrics. Here, we report an experimental study on the magnetization, magnetoresistance (MR) and electronic structure of a non-centrosymmetric compound CrSi with B20 crystal structure. Both magnetization and MR shows competing ferromagnetic (FM) and antiferromagnetic (AFM) correlations with the FM correlations being comparatively weaker indicating the presence of DM interaction in CrSi. A large positive MR ∼ 25 % obtained at 5 K and 5 T magnetic field arises due to the stronger AFM correlations. Resonant photoemission shows both localized and itinerant nature of Cr 3d electrons to be present in CrSi and this is supported by the temperature dependence of magnetic susceptibility. Drastic variation in the density of states along with valence band broadening at low temperature indicates the increase in hybridization between Cr 3d and Si 3s–3p states which enhances the localization effects. Spin polarized itinerant Cr 3d electrons give rise to AFM spin density wave in CrSi. Magnetic interaction between the localized and itinerant Cr 3d electrons are found to be crucial for realizing DM interaction in this system. Spectral density of states derived from high resolution valence band measurements provides evidence of electronic topological transition in CrSi. Large density of polarized itinerant electrons which varies with temperature and the large positive MR with AFM correlations suggests CrSi as a potential candidate for both the thermoelectric and spintronics applications. [ABSTRACT FROM AUTHOR]

We demonstrate interface energy level engineering, exploiting the modification in energy band structure across Verwey transition temperature (TV) of Fe3O4, in a Fe3O4(111)/Alq3/Co spin-valve (SV). I-V characteristics exhibit a transition in conduction mode from carrier injection to tunneling across TV of Fe3O4 electrode. Both giant magneto-resistance (GMR) and tunneling MR (TMR) have been observed in a single SV, below and above TV, respectively. We have achieved room-temperature SV operation in our device. We believe that the tuning of charge gap at Fermi level across TV resulting in a corresponding tuning of conduction mode and a unique cross over from GMR to TMR. [ABSTRACT FROM AUTHOR]

We demonstrate interface energy level engineering, exploiting the modification in energy band structure across Verwey transition temperature (TV) of Fe3O4, in a Fe3O4(111)/Alq3/Co spin-valve (SV). I-V characteristics exhibit a transition in conduction mode from carrier injection to tunneling across TV of Fe3O4 electrode. Both giant magneto-resistance (GMR) and tunneling MR (TMR) have been observed in a single SV, below and above TV, respectively. We have achieved room-temperature SV operation in our device. We believe that the tuning of charge gap at Fermi level across TV resulting in a corresponding tuning of conduction mode and a unique cross over from GMR to TMR. [ABSTRACT FROM AUTHOR]

We report room temperature giant baroresistance (≈128%) in Fe49(Rh0.93Pd0.07)51. With the application of external pressure (P) and magnetic field (H), the temperature range of giant baroresistance (≈600% at 5K, 19.9 kilobars and 8 T) and magnetoresistance (≈ ~85% at 5K and 8 T) can be tuned from 5 K to well above room temperature. It is shown that under external pressure, antiferromagnetic state is stabilized at room temperature and shows giant magnetoresistance (≈~55%). Due to coupled magnetic and lattice changes, the isothermal change in resistivity at room temperature under pressure (at constant H) as well as magnetic field (at constant P) can be scaled together to a single curve, when plotted as a function of X = T + 12.8 x H -- 7.3 x P. [ABSTRACT FROM AUTHOR]

Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with negligible hysteresis loss have been observed in ErNiSi compound, which undergoes metamagnetic transition at low temperatures. Magnetization, heat capacity, and resistivity measurements confirm the metamagnetic transition. Both MCE and MR follow H² dependence in the paramagnetic regime. The maximum value of isothermal entropy change (ΔSM) and MR for a field change of 50 kOe are found to be 19.1 J/kg K and ~34%, respectively. Large MCE with negligible magnetic hysteresis loss could make this material promising for low temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

We have achieved giant enhancement of magnetoresistance (MR) by the formation of La0.67Sr0.33MnO3 (LSMO)-Pr0.67Ca0.33MnO3 (PCMO) core-shell nanostructure. Astonishingly, 1143% enhancement of MR in the core-shell nanostructure has been observed with respect to the parent PCMO nanoparticles at 100 K and 2 T magnetic field. The observed giant enhancement is the result of significantly weaken the charge ordered state in the created ferromagnetic-charge ordered core-shell nano structure. Our study clearly indicates a method to achieve huge enhancement of magnetoresistance that can eventually give rise artificially created superior materials important for magnetic field sensor technology. [ABSTRACT FROM AUTHOR]

Spin valves have revolutionized the field of magnetic recording and memory devices. Spin valves are generally realized in thin film heterostructures, where two ferromagnetic (FM) layers are separated by a nonmagnetic conducting layer. Here, we demonstrate spin-valve-like magnetoresistance at room temperature in a bulk ferrimagnetic material that exhibits a magnetic shape memory effect. The origin of this unexpected behavior in Mn2NiGa has been investigated by neutron diffraction, magnetization, and ab initio theoretical calculations. The refinement of the neutron diffraction pattern shows the presence of antisite disorder where about 13% of the Ga sites are occupied by Mn atoms. On the basis of the magnetic structure obtained from neutron diffraction and theoretical calculations, we establish that these antisite defects cause the formation of FM nanoclusters with parallel alignment of Mn spin moments in a Mn2NiGa bulk lattice that has antiparallel Mn spin moments. The direction of the Mn moments in the soft FM cluster reverses with the external magnetic field. This causes a rotation or tilt in the antiparallel Mn moments at the cluster-lattice interface resulting in the observed asymmetry in magnetoresistance. [ABSTRACT FROM AUTHOR]

Abstract: The origin of anomalous thermomagnetic irreversibility in rare earth germanide has been addressed. Open hysteresis observed in magnetoresistance (MR) at low temperature is shown to decrease with increasing temperature which correlates with the corresponding isothermal magnetostriction (MS) measurements. These thermomagnetic irreversibilities are interpreted in terms of kinetic arrest of magnetic field induced first order transition. The minor loop study of isothermal MS suggests that open loop in MS and MR is associated with large magnetostriction across metamagnetic transitions. The magnetoresistance associated with the second metamagnetic transition at higher field is reversible where magnetostriction variation with field is negligible. [Copyright &y& Elsevier]

Abstract: We report the effects of local structure on the electrical transport and magnetic properties of La0.67Ca0.33Mn1− x Ti x O3 (0⩽x⩽0.10) system. Linear increase in the lattice parameters, consequent expansion of unit cell and a monotonic decrease in the relative Mn4+ concentration with x suggest that Ti4+ predominantly replaces Mn4+ in La0.67Ca0.33Mn1− x Ti x O3 (x⩽0.10). The ferromagnetic-metallic ground state modifies to a glassy insulator for x⩾0.05. No field induced metallic state could be discerned for x=0.10 even at a field of 8T and at as low a temperature as 4.2K. Ti substitution significantly enhances the colossal magnetoresistance (CMR) effect. Both the metal to insulator transition temperature and Curie temperature (T c) decrease at a rate of ∼26K/at% up to x=0.05. T c levels off for higher compositions. Modification of the major carrier concentration (decreased Mn4+ concentration) seems to be insufficient to account for the observed reduction in the transition temperatures. This in turn emphasizes the significance of local structural effects: systematic elongation of the Mn–O bond lengths and decrease of Mn–O–Mn angles leading to strong suppression of itinerant ferromagnetism and metallicity of the compounds. The additional features in the ac susceptibility, viz., a broad shoulder just below T c followed by a sharp decrease in the susceptibility signal at low temperatures and a non-closure of MR at zero field as high as ∼75% at 5K indicate a frustrated magnetic ground state for x=0.07. Based on the inter-comparison of the structural, electrical transport and magnetic properties of the Mn site substituted La0.67Ca0.33MnO3 with iso-valent diamagnetic and paramagnetic ions, we argue that local structural effects have a decisive role to play, compared to the local spin coupling effects, in the ferromagnetic-metallic ground state of the CMR manganites. [Copyright &y& Elsevier]

Abstract: Conductivity vs. temperature (σ–T) at zero and 8-T field, magneto-resistance (Δρ/ρ), magnetization vs. temperature (M–T) and magnetization vs. field (M–H) of Al70.5Pd22Mn7.5 quasicrystal have been studied in the temperature range of 1.4K to 300K. The σ–T variations in both the field conditions show a σ–T minima. In addition to this the σ–T variation at 8T shows a maxima also at ∼6K. Comparative analysis shows that the observed σ–T minima arises due to competing inelastic scattering events in the presence of weak-localization effect. These events are e–ph scattering in the dirty-metallic limit (τ i ∝ T −2), and the Kondo-type spin-flip scattering (τ sf). The maxima observed for the σ–T variation at 8T, has been attributed to suppression of the spin-flip scattering in the presence of field. The magneto-resistance is found to be large and positive. It was properly accounted only when the Stoner-enhancement, found in the case of spin fluctuating systems, was taken into consideration. [Copyright &y& Elsevier]

The electrical conductivity and magnetization behaviour of single-phase Al 70-x B x Pd 20 Mn 10 (x?=?0, 0.5, 1, 2 and 4) quasicrystals have been measured. We observe that boron substitution for aluminium causes large changes in the s vs. T behaviours. s vs. (ln?T) -1 plots shows linear behaviour. Scaling was achieved by plotting {(s(T)?-?s min )/(s 4 ?-?s min )} vs. [ln(T/T min )] -1 . These samples show large positive magnetoresistance with H 2 behaviour. In the Al–B–Pd–Mn and Al–Pd–Mn quasicrystals, the observed s(T) behaviour has been explained using the weak localization theory, including Kondo-type spin-flip scattering and not due to spin-orbit scattering. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature resistivities, in zero-field and 8T field, and magnetoresistance have been measured down to 1.4–300K for stable icosahedral quasicrystals Al65Cu20+x Ru15−x (x =1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect (τ so ∼10−12 s). But the sample with x =−0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down (τ so to be 10−15 s). The in-field σ–T between 5K and 20K, for x =1.0, 0.5, 0.0 and −0.5 samples, and between 1.4K and 40K for x =1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal–insulator (MI) transition, dominated by electron–electron and electron–phonon inelastic scattering events respectively. In samples with x =1.0, 0.5, 0.0 and −0.5 the in field σ–T has been found to follow ln σ-vs-T 1/4 below 5K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal–insulator transition in these Al–Cu–Ru quasicrystal samples. [Copyright &y& Elsevier]

Zero-field and in-field (at 8T) conductivity vs temperature (σ–T), magneto-resistance (Δρ/ρ), magnetization vs temperature (M–T) and magnetization vs field (M–H) of unannealed Al70Pd20Mn10 and annealed Al70Pd20Mn10, Al70Pd21Mn9 and Al70Pd22Mn8 quasicrystalline alloys have been studied in the temperature range of 1.4–300K. Room temperature resistivity and the low-temperature magneto-resistance show a correlation with the corresponding magnetization. The σ–T for all the studied samples shows a pair of minima and maxima. The σ–T maxima show a correlation with the total magnetization. The analysis shows that σ–T is dominated by weak-localization effects. The minima are arising due to competing inelastic scattering times τi (e–ph scattering in the dirty metallic limit, τi∝T−2) and the Kondo-type spin-flip scattering time τsf whereas the maxima has been attributed to ‘Kondo-maxima’, occurring due to maxima in the spin-flip rate . The magneto-resistance of these samples shows a changeover from negative to positive where the negative component shows a correlation with the magnetization of the sample. The values of parameters derived from refinement give spin-flip scattering fields, which are found to be correlated with the total sample magnetization. [Copyright &y& Elsevier]

Zero-field and in-field (at 8 T) conductivity vs. temperature (σ–T) and magnetoresistance (Δρ/ρ) of as-prepared and unannealed Al70Pd20Mn10, annealed Al70Pd20Mn10, and annealed Al70Pd21Mn9 quasicrystalline (qc) alloys have been studied in the temperature range of 1.4–300 K. From room temperature to 30 K, σ–T appears to be dominated by weak-localization effects including electron–phonon (e–ph) scattering as the inelastic process. σ–T minima are possibly due to the dephasing arising from temperature dependent spin–spin scattering, resulting from a cluster-glass-like transition as indicated by the χ–T and M–H measurements. The σ–T maxima at ∼9 K and the negative Δρ/ρ at 1.4 K originate probably from some ferromagnetic type magnetic interaction in the sample, which quenches the spin–spin scattering effects. [Copyright &y& Elsevier]

Ni2-xMnGa1+x (0.4 ≤ x ≤ 0.9) show the existence of modulated crystal structure at room temperature (RT) in the martensite phase, exhibit ferromagnetic behavior and have high martensitic transition temperature. The saturation magnetic moment decreases as Ga content increases, and this is related to antisite defects between Mn and Ga atoms leading to Mn-Mn nearest neighbor antiferromagnetic interaction. Negative magnetoresistance is observed at RT that increases linearly with magnetic field. These properties of Ga excess Ni-Mn-Ga show that it is a potential candidate for technological applications. [ABSTRACT FROM AUTHOR]

5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni2+xMn1-xGa. This indicates the possibility of using Ni2+xMn1-xGa as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0–0.2) in the austenitic, premartensitic, and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and premartensitic phases, in the martensitic phase it shows a cusplike shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model. [ABSTRACT FROM AUTHOR]

In the present work, we have studied the effect of Fe composition on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) of FeSe1/2Te1/2. The polycrystalline samples have been prepared via solid state reaction route with nominal compositions FexSe1/2Te1/2 (x = 0.95, 1.00, 1.05 and 1.10). The x-ray diffraction results show the presence of tetragonal α-FeSe phase with the p4/nmm space group symmetry in all the samples. The zero resistance temperatures, Tczero, measured in zero magnetic field, have been found to be 10.0, 12.4, 12.3, and 11.7 K for x = 0.95, 1.00, 1.05, and 1.10, respectively. The temperature dependence of Hc2(T) and Hirr(T) have been calculated from the magnetoresistance data using the criteria of 90% and 10% of normal state resistivity (ρn) values, respectively. The values of Hc2(0) are 121.3 T, 142.8 T, 82.7 T, and 79.3 T for x = 0.95, 1.00, 1.05, and 1.10, respectively. The possible reasons for the variation of superconducting properties with Fe composition (x) have been described and discussed in this paper. [ABSTRACT FROM AUTHOR]

Thin films of layered perovskites Sr 1.5 RE 0.5 CoO 4 (RE = La, Gd) were grown on MgO (0 0 1) substrate using pulsed laser ablation method. Structural, electrical and magnetic properties of single phase oriented films were studied. Films reveal semiconducting behavior in the entire measured temperature range. The films show thermally activated behavior at high temperature regime, with a higher value of activation energy for SGCO than that for SLCO. The low temperature behavior is well fitted with 3D-variable range hopping mechanism. Both films showed negative magneto-resistance measured in temperature range of 10–200 K. The value of MR is large for SGCO film as compared to its bulk counterpart as well as SLCO film, suggesting its high potential in the spintronics applications. A pinch-shaped M−H behaviour as observed in both the films, suggests the presence of two-magnetic phases. Occurrence of pinch-shape behaviour is although in line with that of SLCO bulk counterpart, interestingly, it was absent in SGCO polycrystalline powder. It suggests major role of film growth kinetics in modifying the magnetic properties in cobaltites. [ABSTRACT FROM AUTHOR]

The magnetic, magneto-transport and magnetocaloric properties of antiferromagnetic intermetallic compound NdCo 2 Si 2 ( T N = 32 K ) have been studied. The compound yields a positive magnetoresistance (MR) of about ∼ 123 % at ∼ 5 K in 8 T magnetic field. The MR value is significantly large vis – a – vis earlier reports of large MR in intermetallic compounds, and possibly associated with the changes in magnetic structure of the compound. The large MR value can be explained in terms of field induced pseudo-gaps on Fermi surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • TS500 CFAS film has the highest B2 structural order and lowest residual resistivity. • Diffuson and WL effects (e-m and e-p scattering) dominate for T < T min (T > T min) • Phonon-induced non-spin-flip two-band (s↑↓- d↑↓) scattering accounts for. ρ e - p • Thermal renormalization of spin-wave stiffness significantly contributes to. ρ e - m (T) • Suppression of WL an d e – m scattering by magnetic field results in negative MR. An exhaustive study of the effect of anti-site disorder on the 'zero-field', ρ(T , H = 0), and 'in-field', ρ(T , H = 80 kOe), electrical resistivity in 50 nm thick Co 2 FeAl 0.5 Si 0.5 (CFAS) Heusler alloy thin films (deposited on the Si(1 0 0) or SiO 2 /Si(1 0 0) substrates at fixed substrate temperatures in the range 27 ° C ≤ T S ≤ 550 ° C), has been carried out. Irrespective of the strength of disorder, resistivity goes through a minimum as a function of temperature at T = T min. With increasing substrate temperature, the crystalline order of the CFAS thin films improves so much so that the films deposited at 500 °C have the lowest anti-site disorder within the B2 structure and the least residual resistivity. A quantitative comparison of our results with the predictions of the existing theoretical models permits us to unambiguously identify the diffusive and ballistic transport mechanisms, responsible for ρ(T , H = 0) and ρ(T , H = 80 kOe) in different temperature ranges and accurately determine their relative magnitudes. The electron-diffuson (e – d) scattering and weak localization (WL) mechanisms, responsible for negative temperature coefficient of resistivity (TCR) for T < T min , compete with the positive TCR mechanisms, electron-magnon (e – m) and electron–phonon (e – p) scattering, to produce the resistivity minimum at T min. The e – d and WL contributions to ρ, ρ e - d and ρ wl , dominate over the e – m and e – p contributions, ρ e - m and ρ e - p , for T < T min whereas the reverse is true for T > T min . At any given temperature, ρ e - d , ρ wl and ρ e - m decrease while ρ e - p increases as the atomic order improves with increasing substrate temperature, T S. ρ e - p and ρ e - m originate from the phonon-induced non-spin-flip two-band (s↑↓- d↑↓) scattering and magnon - induced spin-flip s - d interband (s↑↓- d↓↑) transitions, respectively. In all the CFAS films, except for the one deposited at T S = 27 ° C , the thermal renormalization of the spin-wave stiffness, due to the electron - magnon interaction, contributes significantly to ρ e - m (T). Furthermore, we demonstrate that the negative magnetoresistance (MR) is a consequence of a progressive suppression of the WL effect and e – m scattering by external magnetic field. However, the WL contribution to MR turns out to be negligibly small as the e – m contribution almost entirely accounts for MR over the temperature range 5 K ≤ T ≤ 300 K. [ABSTRACT FROM AUTHOR]

The metal–insulator like transition of the ferromagnetic (FM) state in Co 1 − x Fe x S 2 (0 ≤ x ≤ 0.7) with varying x is investigated using X-ray diffraction, Mössbauer spectroscopy, and magnetoresistance measurements. The linear decrease of unit cell parameter with x confirmed Fe substitution at the Co site. The room temperature Mössbauer study showed the absence of magnetic moment on Fe and both isomer shift and quadrupole splitting were found to vary linearly with x. The temperature-coefficient-of-resistivity (TCR) in the FM state became negative for x ≥ 0.15. For intermediate compositions i.e., x = 0.05 and 0.1, TCR changed from positive to negative (T ≤ T C) to positive with an increase in temperature. By studying the temperature-dependent and isothermal magnetoresistance data around the transition region, it was shown that resultant behavior could be arising due to changes in spin polarization over a broad temperature range. [ABSTRACT FROM AUTHOR]

We have presented experimental results addressing the origin of spin valve (SV) magneto-resistance (MR), in both injection and tunnel conduction regimes, in our fabricated Fe 3 O 4 (111)/Alq 3 /Co SV device. Experimental evidences have shown that any alternative MR process, such as 'tunneling anisotropic MR' is not at the origin of this SV MR. Spin resolved density of states of electrodes indicate that both the conduction mechanisms induce different spin dependent scattering which inturn modify the MR signal of the device. This modification helped in maintaining a non-monotonous quenching of MR signal with increase in temperature. We have also proposed a phenomenological model for device operation where the concept of charge gap modification at Fermi level across Verwey transition is envisaged to offer this unique scenario of tuning the conduction mode and hence MR in this ferrite based organic SV. The model is also supported by an established theoretical study which considers high temperature phonon assisted tunneling through defect states at electrode–organic interface of the device. [Display omitted] • Conduction mechanism transition from carrier injection to multistep tunneling. • Transition due to Verwey transition of Fe 3 O 4. • Spin flip scattering at Alq 3 spacer above Verwey transition temperature. • Non-monotonous MR quenching with temperature. • Room temperature MR signal of hybrid spin valve. [ABSTRACT FROM AUTHOR]

The magnetoresistance (MR) and magnetocaloric properties of naturally occurring layered compound NdRu 2 Si 2 with a Néel temperature T N = 24 K have been investigated in the temperature range 60 ≥ T ≥ 1.8 K. It has been shown that a high external magnetic field greatly modifies the MR properties of the compound which in its low temperature ferromagnetic state (T < 10 K) exhibits an unusual positive MR instead of being negative. Although, the magnetocaloric investigations at this field and temperature range further indicates that the compound is in a predominantly ferromagnetic state. With the lowering of temperature, the MR value changes from a negative 34% near T N to a positive 5% at 5 K. Magnetocaloric (MCE) investigations on NdRu 2 Si 2 exhibit two well defined peaks corresponding to the magnetic transitions. A table like MCE behaviour has been observed in the temperature range from 5 K to 45 K. • Magnetization, transport and magnetotransport properties of NdRu 2 Si 2 have been studied. • Magnetotransport and magnetocaloric properties have been compared. • External magnetic field greatly modifies the magnetoresistance behaviour of the compound. • Unusual positive MR observed in low temperature ferromagnetic state. • Table like magnetocaloric behaviour have been observed, promising for rare earth based refrigerants. [ABSTRACT FROM AUTHOR]