Nonlinear Magnetic Field Dependence Research Articles

Electrical and thermal transport properties of the kagome metals ATi3Bi5(A=Rb,Cs)

We report electrical and thermal transport properties of single-crystalline kagome metals $A{\text{Ti}}_{3}{\text{Bi}}_{5}\phantom{\rule{4pt}{0ex}}(A=\text{Rb},\phantom{\rule{4pt}{0ex}}\mathrm{Cs})$. Different from the structrually similar kagome superconductors $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, no charge density wave instabilities are found in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$. At low temperatures below 5 K, signatures of superconductivity appear in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ as seen in magnetization measurements. However, bulk superconductivity is not evidenced by specific heat results. Similar to $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}, A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ show a nonlinear magnetic field dependence of the Hall effect below about 70 K, pointing to a multiband nature. Unlike $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ in which phonons and electron-phonon coupling play important roles in thermal transport, the thermal conductivity in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ is dominated by electronic contributions. Moreover, our calculated electronic structures of ${\mathrm{ATi}}_{3}{\mathrm{Bi}}_{5}$ suggest that van Hove singularities are sitting well above the Fermi energy. Compared with $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$, the absence of charge orders in $A{\mathrm{Ti}}_{3}{\mathrm{Bi}}_{5}$ is closely associated with minor contributions from electron-phonon coupling and/or van Hove singularities.

Transport and electron spin resonance studies in Mo-doped LaMnO3

We report the magnetic, electrical, thermoelectric, and magnetic resonance properties of the Mn-site doped manganite LaMn0.94Mo0.06O3. This sample undergoes an insulator-metal transition around 235 K, near the ferromagnetic Curie temperature (TC = 237 K) in zero external magnetic field. On the other hand, thermopower exhibits a maximum at TS = 258 K, which is 23 K higher than TC. This discrepancy is attributed to nucleation of ferromagnetic clusters (Griffiths phase) above TC, which is supported by the deviation of inverse susceptibility from Curie-Weiss from linear behavior below 270 K and non-linear field dependence of magnetization. The magnetic resonance spectra shows both paramagnetic and ferromagnetic resonance signals between 240 and 260 K. It is suggested that the ferromagnetic clusters enlarge in size with lowering temperature and percolate leading to long-range ferromagnetism and metallicity.

Higher harmonics in planar Hall effect induced by cluster magnetic multipoles

Antiferromagnetic (AFM) materials are attracting tremendous attention due to their spintronic applications and associated novel topological phenomena. However, detecting and identifying the spin configurations in AFM materials are quite challenging due to the absence of net magnetization. Herein, we report the practicality of utilizing the planar Hall effect (PHE) to detect and distinguish “cluster magnetic multipoles” in AFM Nd2Ir2O7 (NIO-227) fully strained films. By imposing compressive strain on the spin structure of NIO-227, we artificially induced cluster magnetic multipoles, namely dipoles and A2- and T1-octupoles. Importantly, under magnetic field rotation, each magnetic multipole exhibits distinctive harmonics of the PHE oscillation. Moreover, the planar Hall conductivity has a nonlinear magnetic field dependence, which can be attributed to the magnetic response of the cluster magnetic octupoles. Our work provides a strategy for identifying cluster magnetic multipoles in AFM systems and would promote octupole-based AFM spintronics.

Magnetic-field and temperature dependence of anomalous Hall effect in Pt/Cr2O3/Pt trilayer

The Pt/Cr2O3 interface exhibits a variety of spin-related phenomena. In this study, we investigated the anomalous Hall effect (AHE) of a Pt/40-nm-thick Cr2O3/Pt trilayer grown on Al2O3(0001), where Cr2O3 is an antiferromagnetic (AFM) insulator. All layers were grown epitaxially on the substrate, and X-ray reflectivity measurement showed an interfacial roughness of approximately 0.2 nm at each interface. The AHE resistance showed a nonlinear magnetic-field dependence at 300 K. Below 250 K, a clear hysteresis with coercivity was observed. The coercivity was approximately 7 T above 150 K and approximately 6 T below 100 K. The remanent AHE resistance shows a finite value below 285 K. The temperature dependence forms a broad peak with a maximum at approximately 200 K and gradually decreases with decreasing temperature. This temperature dependence is similar to that reported for the interfacial magnetic moment on Cr2O3(0001). Based on these results, the remanent AHE coupled with the AFM order parameter or the Néel vector was successfully detected in the 40-nm-thick Cr2O3 layer grown on the conductive layer.

Magnetodielectric effect and spin state of iron ions in iron-substituted bismuth pyrostannate

The magnetic and magnetodielectric properties of bismuth pyrostannate $$\hbox {Bi}_{{2}}(\hbox {Sn}_{1-{x}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ ( $$x = 0.1$$ and 0.2) have been examined. Using the Mossbauer spectroscopy and electron paramagnetic resonance, the high-spin state and crystallographic positions of iron ions have been established. The coexistence of triclinic symmetry domains in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}(x = 0.1)$$ compound with the monoclinic symmetry below 140 K has been found. For the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ composition with $$x = 0.2$$ , the nonlinear field dependence of magnetization in the paramagnetic region up to room temperatures has been observed. The electric polarization hysteresis and the magnetoelectric effect in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ compound have been disclosed. The magnetic field-dependent anomalous behavior of magnetization has been explained by the magnetoelectric effect.

Surface spin magnetism controls the polarized exciton emission from CdSe nanoplatelets.

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetic behaviour owing to the uncompensated spins of dangling bonds, as we reveal here by optical spectroscopy in high magnetic fields up to 15 T using the exciton spin as a probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the magnetization of the dangling-bond spins (DBSs), the exciton spin polarization as well as the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction depends on the nanoplatelet growth conditions.

Charging effects and anomalous resistive features of superconducting boron doped diamond films

Anomalous resistive peaks below the superconducting transition temperature in heavily boron doped nanocrystalline diamond films could have potential application in switching devices, however it’s exact origin is still under study. We establish a temperature dependence of this resistive phase similar to what has been reported for in Josephson junction arrays and other granular superconductors where the charge duel of the Berezinskii-Kosterlitz-Thouless (BKT) transition has been observed. Non-linear magnetic field dependence of the resistance with a temperature dependent peak feature below the critical field are also presented. Pronounced temperature dependent hysteresis in the current voltage sweeps at temperatures below the determined BKT critical point are related to pinning of charge defects. It is shown that these collective features allude to a Charge-BKT transition between charge and anti-charge analogues.

Negative differential resistance and quantum oscillations in FeSb2 with embedded antimony**Project supported by Guangdong Innovative and Entrepreneurial Research Team Program, China (Grant No. 2016ZT06D348), the National Natural Science Foundation of China (Grant No. 11874193), and the Shenzhen Fundamental Subject Research Program, China (Grant Nos. JCYJ20170817110751776 and JCYJ20170307105434022). The work at Brookhaven is supported by the US Department of Energy, Office

We present a systematical study on single crystalline FeSb2 using electrical transport and magnetic torque measurements at low temperatures. Nonlinear magnetic field dependence of Hall resistivity demonstrates a multi-carrier transport instinct of the electronic transport. Current-controlled negative differential resistance (CC-NDR) observed in current–voltage characteristics below ∼ 7 K is closely associated with the intrinsic transition ∼ 5 K of FeSb2, which is, however, mediated by extrinsic current-induced Joule heating effect. The antimony crystallized in a preferred orientation within the FeSb2 lattice in the high-temperature synthesis process leaves its fingerprint in the de Haas-Van Alphen (dHvA) oscillations, and results in the regular angular dependence of the oscillating frequencies. Nevertheless, possible existence of intrinsic non-trivial states cannot be completely ruled out. Our findings call for further theoretical and experimental studies to explore novel physics on flux-free grown FeSb2 crystals.

Anomalous Hall effect and re-entrant metallic transitions in epitaxial PrNiO3-δ thin films

We have deposited and studied epitaxial PrNiO3-δ thin films (12 nm) for the temperature dependent resistivity and the anomalous Hall effect. The post-deposition in situ oxygen annealing time for thin film formation was varied (0 to 5 min) in order to change the oxygen stoichiometry. One film was kept completely unannealed to create oxygen deficiency. A decrease in resistivity was observed with increasing oxygen-annealing time. In spite of different oxygen content and resistivity values, all the other films show metal to insulator transitions at the same temperature (∼100 K), except the unannealed insulating film. Before a complete insulating state was established while cooling, a re-entrant metallic state appeared at lower temperatures, where the on-set temperature was different for different films. A nonlinear magnetic-field dependence of Hall resistance manifests in the low-temperature re-entrant metallic state in contrast to the normal Hall effect in the high-temperature metallic state. The theoretical fits to temperature dependent resistivity indicate a non-Fermi liquid behavior in the high temperature metallic state. Moreover, the non-Fermi liquid behavior gets modified by the variation in oxygen content in PrNiO3-δ films.

Multigap superconductivity in ThAsFeN investigated using μSR measurements

We have investigated the superconducting ground state of the newly discovered superconductor ThFeAsN with a tetragonal layered crystal structure using resistivity, magnetization, heat capacity and transverse-field (TF) muon-spin rotation ($\mu$SR) measurements. Our resistivity and magnetization measurements reveal an onset of bulk superconductivity with $T_{\bf c}\sim$ 30 K. The heat capacity results show a very small anomaly, $\Delta$C$_{ele}$$\sim$0.214 (J/mol-K) at $T_{\bf c}\sim$ 30 K and exhibits exponential behavior below $T_{\bf c}$, which fits better to two superconducting gaps rather than a single gap. Further a nonlinear magnetic field dependence of the electronic specific heat coefficient $\gamma$(H) has been found in the low temperature limit, which indicates that the smaller energy gap is nodal. Our analysis of the TF-$\mu$SR results shows that the temperature dependence of the superfluid density is better described by a two-gap model either isotropic $s$+$s$-wave or $s$+$d$-wave than a single gap isotropic $s$-wave model for the superconducting gap, consistent with other Fe-based superconductors. The combine $\gamma$(H) and TF-$\mu$SR results confirm $s$+$d$-wave model for the gap structure of ThFeAsN. The observation of two gaps in ThFeAsN suggests multiband nature of the superconductivity possibly arising from the d-bands of Fe ions. Furthermore, from our TF-$\mu$SR study we have estimated the magnetic penetration depth, in the polycrystalline sample, of $\lambda_{\mathrm{L}}$$(0)$ = 375 nm, superconducting carrier density $n_s = 4.6 \times 10^{27}~ $m$^{-3}$, and carrier's effective-mass $m^*$ = 2.205\textit{m}$_{e}$. We will compare the results of our present study with those reported for the Fe-pnictide family of superconductors.

Magnetoresistance of electrochemically produced InSb

Classical geometric effects in disordered and inhomogeneous polycrystalline narrow bandgap semiconductors can lead to high, non-saturating, linear magnetoresistance (MR) values. It has been previously shown that polycrystalline networks of InSb produced by grinding an InSb single crystal have a large, linear, non-saturating magnetoresistance of several hundred per cent. InSb produced via electrochemical routes has not been characterised regarding their magnetoresistive response yet. Starting from a material produced by an electroless solution-phase reaction, we demonstrate that despite small crystallite size and inhomogeneous material composition, a similar effect leading to a high, linear and non-saturating MR of up to 150% can be observed. A range of InSb thin films produced via electrodeposition show much lower MR values of ∼2% and a non-linear magnetic field dependence probably due to resulting microstructure and use of a conductive substrate.

Optical and magnetotransport properties of InGaAs/GaAsSb/GaAs structures doped with a magnetic impurity

InGaAs/GaAsSb/GaAs bilayer quantum-well structures containing a magnetic-impurity δ-layer (Mn) at the GaAs/InGaAs interface are experimentally studied for the first time. The structures are fabricated by metal organic chemical-vapor deposition (MOCVD) and laser deposition on substrates of conducting (n+) and semi-insulating GaAs in a single growth cycle. The InGaAs-layer thickness is varied from 1.5 to 5 nm. The significant effect of a decrease in the InGaAs quantum-well thickness on the optical and magnetotransport properties of the structures under study is detected. Nonlinear magnetic-field dependence of the Hall resistance and negative magnetoresistance at temperatures of ≤30–40 K, circular polarization of the electroluminescence in a magnetic field, opposite behaviors of the photoluminescence and electroluminescence emission intensities in the structures, and an increase in the contribution of indirect transitions with decreasing InGaAs thickness are observed. Simulation shows that these effects can be caused by the influence of the δ-layer of acceptor impurity (Mn) on the band structure and the hole concentration distribution in the bilayer quantum well.

Semimetallic transport properties of epitaxially stabilized perovskite CaIrO3 films

We report on the synthesis and transport properties of perovskite (Pv) CaIrO3 thin films. The Pv phase of CaIrO3 was stabilized by epitaxial growth on SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and LaAlO3 substrates with strong tensile, weak tensile, and compressive strains, respectively. The resistivity of these films showed a poorly metallic behavior. The Hall resistivity exhibited a sign change as a function of temperature and a nonlinear magnetic-field dependence, which clearly indicated the coexistence of electrons and holes and hence supported that Pv CaIrO3 films are semimetallic. The observed robustness of the semimetallic ground state against tensile and compressive strains is consistent with the presence of symmetry-protected Dirac points (nodes) around the Fermi level that prohibits the system from becoming a band insulator.

Thermal emission of one-dimensional magnetophotonic crystals

Theoretical investigations of the spectral and angular characteristics of 1D semiconductor-based magnetophotonic crystal thermal emission in an external magnetic field are presented. Propagation of the emission is described by the 4 × 4 matrix method using the nonlinear magnetic-field dependence of a semiconductor dielectric tensor. The calculations are carried out for the (ZnS/KBr)2/InAs/(KBr/ZnS)10 structure in the spectral range 8–11 μm. It is established that the thermal emission is narrow-band and narrow-beam and substantially changes in the magnetic field. The results show that the magnetophotonic crystals can be used for creating tunable selective emitters for mid-wave and long-wave infrared spectral ranges.

Bulk Superconductivity in Bismuth Oxysulfide Bi4O4S3

A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) Å and c = 41.3520(1) Å. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 Å . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).

Evidence for multiple superconducting gaps in the filled skutterudite compound LaRu4As12

Superconducting properties of the filled skutterudite compound LaRu${}_{4}$As${}_{12}$ were investigated both as a function of temperature and magnetic field. At $T\ensuremath{\ll}{T}_{\mathrm{c}}=10.45$ K, the electronic contribution to the specific heat was found to be at variance with the predictions for an $s$-wave superconductor with one energy gap. In constant applied fields up to ${H}_{\mathrm{c}2}(0)\ensuremath{\approx}10.2$ T, multiple gaps have been further inferred from both a nonlinear magnetic-field dependence of the specific heat in the zero-temperature limit and a positive curvature of the upper critical field in the vicinity of ${T}_{\mathrm{c}}$. Thus, LaRu${}_{4}$As${}_{12}$ appears to be a rare multiple-gap superconductor with cubic symmetry. Intriguing evidence for multiband effects is observed in the compound with enhanced superconducting properties as compared to other skutterudite superconductors.

Strong Coupling Superconductivity at 8.4 K in an Antiperovskite PhosphideSrPt3P

We report the discovery of a family of ternary platinum phosphides APt3P (A = Ca, Sr, and La), which crystallize in an antiperovskite-based structure closely related to that of the heavy fermion superconductor CePt3Si. All three phosphides showed superconductivity at low temperatures and the highest critical temperature T(c) = 8.4 K was observed for SrPt3P. The analysis of specific heat C(T) for SrPt3P shows clear evidence for very strong coupling s-wave superconductivity with a large ratio between superconducting gap Δ0 and T(c), 2Δ0/k(B)T(c) ∼ 5, and the presence of low-energy phonons. The presence of multiple Fermi surface pockets was inferred from the nonlinear magnetic field dependence of Hall resistivity, which we argue might play a role in realizing the strong coupling of charge carriers with the low-lying phonons.

Shifting the operating frequency of magnetoelectric sensors

A method is presented for increasing the operating frequency of symmetric and asymmetric magnetoelectric (ME) sensors so that the operating frequency can be equal to the mechanical resonance frequency of the sensor. This increase improves the signal to noise ratio of a symmetric sensor by at least two orders of magnitude because it mitigates the effect of 1/f noise and the sensor has an increased response at its resonant frequency. The method is based on the strong, nonlinear magnetic field dependence of the magnetostriction. Our method has lowered the detection limit to 4 pT/Hz at 1 Hz in a magnetically unshielded environment.

Enhancing the sensitivity of magnetoelectric sensors by increasing the operating frequency

We present a field modulation technique that increases the operating frequency of magnetoelectric (ME) sensors so that it can match the mechanical resonance frequency of the sensor. This not only improves the sensitivity but also reduces the effect of 1/f noise that is inherent at low frequencies. The technique, which is shown to apply to both symmetric and asymmetric ME sensors, relies on the strong, nonlinear magnetic field dependence of the magnetostriction. The combination of a lower 1/f noise and enhanced response at resonance has increased the signal to noise ratio of a symmetric sensor by two orders of magnitude. The detection limit of this sensor was lowered from 90 to 7 pT/Hz at 1 Hz in a magnetically unshielded environment.

Nonlinear magnetic field dependence of spin polarization in high-density two-dimensional electron systems

The spin polarization (P) of high-density InSb two-dimensional electron systems (2DESs) has been measured using both parallel and tilted magnetic fields. P is found to exhibit a superlinear increase with the total field B. This P–B nonlinearity results in a difference in spin susceptibility between its real value χs and χgm∝ m*g* (m* and g* are the effective mass and g factor, respectively) as routinely used in experiments. We demonstrate that such a P–B nonlinearity originates from the linearly P-dependent g* due to the exchange coupling of electrons rather than from the electron correlation as predicted for the low-density 2DES.