Low-temperature Magnetic Studies Research Articles

Magnetocaloric effect in aluminum doped ErCr1−xAlxO3 orthochromites

Aluminum-doped ErCr1-xAlxO3 orthochromites prepared via autocombustion technique were investigated for their magnetic and magnetocaloric properties. X-ray diffraction confirmed that samples were orthorhombic phases with the Pbnm space group without a trace of any impurity. As analyzed via Rietveld refinement of XRD data, structural parameters such as lattice parameters, volume, bond angle, and bond lengths were affected by doping nonmagnetic Al3+ in the compound. ErCrO3 possesses the long-range antiferromagnetic ordering with a weak display ferromagnetism at TN =133 K. Low-temperature high-field magnetic study shows a decrease in Neel temperature (TN ∼ 114 K for x = 0.5), suggesting magnetic ordering suppression due to Al3+ doping. The asymptotic paramagnetic Curie temperature Tcw = −25 K suggests the predominance of antiferromagnetic interactions in ErCrO3 orthochromites, which was observed to increase with Al3+ doping. Isothermal magnetization data show changes in magnetic entropy (−ΔSMmax) and relative cooling power (RCP). The magnetic entropy change, −ΔSMmax, for ErCrO3 estimated from magnetization measurements show 11.60 J kg−1 K−1 at 11 K and a relative cooling power (RCP) of 209.4 J kg−1 at 5 T applied field. While ErCr0.75Al0.25O3 show a maximum magnetic entropy of 11.52 J kg−1 K−1 at 11 K with a 5 T applied field and RCP of 186.66 J kg−1, whereas ErCr0.5Al0.5O3 displayed −ΔSMmax of 11.63 J kg−1 K−1 at 5 K with a 5 T applied field and RCP value of 160.78 J kg−1. The results show that nonmagnetic doping, such as Al3+, could maintain the compound’s magnetocaloric property to an extent.

Spontaneous Hall effect in the magnetic Weyl semimetallic Eu2Ir2O7 (111) thin films

Here, we have carried out a low-temperature magnetization and magnetotransport study on epitaxial antiferromagnetic Eu2Ir2O7 (111) thin films with an all-in-all-out/all-out-all-in spin structure to delve into the possibility of realizing spontaneous Hall effect that can provide strong experimental evidence for the existence of the Weyl semimetallic phase. The temperature-dependent resistivity on Eu2Ir2O7 (111) thin films indicates a semimetallic transition below 90 K and the existence of a correlated metallic state in the high-temperature regime (90–300 K). Magnetoresistance measurements suggest that at a low temperature (below 10 K), the all-in-all-out (AIAO) spin structure is stable enough against the applied magnetic field, whereas above 10 K, application of magnetic field causes field-induced modification of the spin structure and plastic domain deformation. Hall resistivity shows a spontaneous Hall effect (SHE) in the low-temperature semimetallic phase of Eu2Ir2O7 (111) thin films with minimal magnetization (AIAO/all-out-all-in spin structure). The observed SHE provides strong evidence for the emergent Weyl semimetallic phase in the (111) thin film geometry of antiferromagnetic Eu2Ir2O7.

Dependence of WAL effect and enhancement of spin-orbit coupling effect in Bi1.2Sb0.8Te0.4Se2.6 low-temperature magnetic transport

The strong spin-orbit coupling and time-reversal symmetry in topological insulators (TIs) produce a new quantum state known as the topological surface state (TSS). The study of low-temperature magnetic transport in the TSS provides opportunities to explore exotic physical phenomena such as the spin Hall effect and the topological phase transition. An important goal in obtaining intrinsic TI systems is to eliminate internal defects and thereby reduce the contributions of metallic states in transport measurements. In this work, we are committed to overcoming this difficulty by elemental alloying. This paper reports the successful preparation of high-quality and stoichiometrically stable Bi1.2Sb0.8Te0.4Se2.6 (BSTS) thin films by innovatively combining the hybrid target structure with the laser molecular beam epitaxy (LMBE) system and low-temperature magnetic transport tests conducted on BSTS thin films of different thicknesses. Due to stronger spin-orbit coupling, we observed a weak anti-localization (WAL) effect, and the strength of the effect was affected by the film thickness and temperature in the low-temperature magnetic transport study. The dependence of the WAL effect provides a way to regulate the TSS.

Temperature Dependent Crystal Structure of Nd2CuTiO6: An In Situ Low Temperature Powder Neutron Diffraction Study

Herein we reported the crystal structure and crystal chemistry of orthorhombic perovskite type Nd2CuTiO6 in between 2 K and 290 K as observed from the in situ temperature-dependent powder neutron diffraction (PND) studies. It is observed that the cations in octahedral sites are statistically occupied, and the ambient temperature orthorhombic structure is retained throughout the temperature range of the study. Absence of any long-range magnetic ordering down to 2 K is confirmed by both low-temperature PND and magnetization studies. The lattice shows strong anisotropic thermal expansion with increasing temperature, viz. almost no or feeble negative expansion along the a-axis while appreciably larger expansion along the other two axes (αb = 10.6 × 10−6 K−1 and αc = 9.8 × 10−6 K−1). A systematic change in the rotation of octahedral units with temperature was observed in the studied temperature range, while the expansion of unit cells is predominantly associated with the polyhedral units around the Nd3Ions. The temperature-dependent relative change in unit cell parameters as well as coefficients of axial thermal expansion show anomalous behavior at lower temperatures, and that seems to be related to the electronic contributions to lattice expansion.

High-temperature solution growth of large size chalcogenide FeTxSe (T: Fe, Co) superconducting single crystals

We report the growth of high quality Fe excess and Co doped, Fe T x Se single crystals in nominal ratio via slow cooling method of high temperature solution growth technique and, their structural and physical properties through the X-ray diffraction, Raman spectroscopy, magnetic and transports measurements. Selective area electron diffraction (SAED) patterns and X-ray diffraction of cleavage piece confirm the growth of single crystals in ( h0l ) orientations. Observations of phonon vibration modes (A 1g and B 1g ) in Raman spectroscopy measurements mark the qualitative analysis of these single crystals. Low temperature magnetic and electrical transport studies manifest the superconducting nature of both single crystals.

Structural evolution-enabled BiFeO3 modulated by strontium doping with enhanced dielectric, optical and superparamagnetic properties by a modified sol-gel method

Multiferroic (BFO) nanoparticles doped with strontium with the general formula Bi1–x Sr x FeO3 (x = 0, 0.3, 0.5, 0.7) were synthesized using a modified sol-gel auto-combustion process. The structural, electrical, optical, and magnetic properties of the samples are discussed. The structural analysis, carried out using the x-ray powder diffraction technique, shows a structural transition from rhombohedral (R-3c) to cubic (Pm-3m) for the doping amount of strontium (Sr) equal to x = 0.3. Morphological analysis of the prepared samples were carried out using scanning electron microscopy (SEM). Frequency-dependent dielectric constant and ac conductivity were studied. The doped samples, with improved dielectric properties, can be used to fabricate different optoelectronic devices. Strong dielectric dispersion and broad relaxation were exhibited by all the samples. Cole–Cole plots were employed as an effective tool to study the dispersion parameters, namely, the optical dielectric constant, static dielectric constant, relaxation time, and spreading factor. The activation energy was calculated from the relaxation peaks and Cole–Cole plots, which were found to be compatible with each other. The bandgap of the samples was calculated using diffuse reflectance spectral (DRS) analysis. Sharp and strong photoluminescence in the IR region was observed in the samples, similar to ZnO, which was reported for the first time. Room-temperature and low-temperature magnetization studies point towards the superparamagnetic nature of the samples, with an improvement in magnetic properties with doping. The antiferromagnetic behavior of bulk bismuth ferrite transforms to superparamagnetic in nature for both pure and Sr-substituted bismuth ferrite nanoparticles due to the close dimensions of crystallite size with magnetic domains leading to the break-down of the frustrated spin cycloidal moment.

High-Performance Luminescence Thermometer with Field-Induced Slow Magnetic Relaxation Based on a Heterometallic Cyanido-Bridged 3d-4f Complex.

The 1:1:1 reaction of DyCl3·6H2O, K3[Co(CN)6] and bpyO2 in H2O has provided access to a complex with formula [DyCo(CN)6(bpyO2)2(H2O)3]·4H2O (1) in a very good yield, while [DyFe(CN)6(bpyO2)2 (H2O)3]·4H2O (2) was also precipitated (also in a high yield) using K3[Fe(CN)6] instead of K3[Co(CN)6]. Their structures have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses and IR spectra. Combined direct current (dc) and alternating current (ac) magnetic susceptibility revealed slow magnetic relaxation upon application of a dc field. μ-SQUID measurements and CASSCF calculations revealed high-temperature relaxation dynamics for both compounds. Low-temperature magnetic studies show the relaxation characteristics for 1, while for compound 2 the dynamics corresponds to an antiferromagnetically coupled Dy···Fe pair. High-resolution optical studies have been carried out to investigate the performance of compounds 1 and 2 as luminescence thermometers. For 1, a maximum thermal sensitivity of 1.84% K-1 at 70 K has been calculated, which is higher than the acceptable sensitivity boundary of 1% K-1 for high-performance luminescence thermometers in a broad range of temperature between 40 and 140 K. Further optical studies focused on the chromaticity diagram of compound 1 revealed a temperature shift from warm white (3200 K) at 10 K toward a more natural white color near 4000 K at room temperature.

Low temperature magnetic study and first principle calculation in ‘Mo’ doped CoFe2O4 for magnetic information storage applications

Structural and low temperature magnetic properties of CoFe2−xMoxO4 (x = 0.01, 0.03 and 0.05) were studied in the present work. Rietveld refinement of XRD patterns of CoFe2−xMoxO4 (x = 0.01, 0.03 and 0.05) confirm the pure phase cubic crystal structure in Fd3m space group. The decrease in lattice parameters (a contraction of the lattice) has been observed with doping, which confirms the probability of substitution of ‘Mo’ at the octahedral site of parental CoFe2O4 (CFO). The micro-strain via W-H plots was found to be enhanced for CoFe1.95Mo0.05O4 (CMFO5) sample which confirms the incorporation of ‘Mo’ atoms at Fe-site and subsequently reducing impurities as observed from refined patterns. The low temperature (2K) magnetic parameters were found to be greatly enhanced with ‘Mo’ substitution. We observed the decrease in anisotropy constant of Co2+ ions with ‘Mo’ doping and Mo6+ ions concentration at the tetrahedral site of CFO, increases the magnetization of the samples. Both M-H and ZFC-FC measurements confirm the ferrimagnetic behavior of all the samples. The maximum value of information storage parameter ‘S’ achieved around 0.442 for x = 0.03 sample at 2K. The structural parameters, electronic (density of states and band structure) and magnetic properties of pure CFO have also been investigated via computational first principle based density functional theory (DFT) calculations. The computational results are in good agreement with the experimental outputs.

Experimental and theoretical analysis of magnetocaloric behavior ofDy1−xErxNi2intermetallics(x=0.25,0.5,0.75)and their composites for low-temperature refrigerators performing an Ericsson cycle

In the present work, the structural, magnetic, and thermodynamic properties of ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$ $(x=0.25,\phantom{\rule{0.16em}{0ex}}0.5,\phantom{\rule{0.16em}{0ex}}0.75)$ Laves-phase intermetallics, being continuous solid solutions in the ${\mathrm{DyNi}}_{2}\text{\ensuremath{-}}{\mathrm{ErNi}}_{2}$ system, synthesized by arc melting, are experimentally studied and analyzed in accordance with mutual substitution within the rare-earth sublattice. The existence of Laves-phase superstructure (space group $F\overline{4}3m$) in the substituted ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$ compounds was found by x-ray diffraction analysis. Low-temperature magnetic studies showed the ferromagnetic behavior of the compounds; their Curie temperatures correlate with the erbium content; namely, they decrease from 16.8 K for ${\mathrm{Dy}}_{0.75}{\mathrm{Er}}_{0.25}{\mathrm{Ni}}_{2}$ to 10.0 K for ${\mathrm{Dy}}_{0.25}{\mathrm{Er}}_{0.75}{\mathrm{Ni}}_{2}$. Heat capacity measurements performed in magnetic fields of 1 and 2 T allowed us to estimate the isothermal magnetic entropy and adiabatic temperature changes for ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$. Independently, a theoretical analysis was performed for a polycrystalline sample in the frame of a model Hamiltonian taking into account the Zeeman exchange interaction and crystal electric field anisotropy and was expanded to experimental results. Composites with optimum proportions of the individual ${\mathrm{Dy}}_{0.75}{\mathrm{Er}}_{0.25}{\mathrm{Ni}}_{2}$, ${\mathrm{Dy}}_{0.5}{\mathrm{Er}}_{0.5}{\mathrm{Ni}}_{2}$, and ${\mathrm{Dy}}_{0.25}{\mathrm{Er}}_{0.75}{\mathrm{Ni}}_{2}$ components were theoretically determined. The results indicate that the proposed composites are good candidates to be used as the refrigerant material in a magnetic refrigerator performing an Ericsson cycle at low temperatures. The relative cooling power RCP, refrigerant capacity RC, temperature averaged entropy change TEC, and the changes of emitted or absorbed quantity of heat \ensuremath{\Delta}Q were calculated for investigated samples. Direct measurements of the adiabatic temperature change in the vicinity of the magnetic transition temperature were carried out in magnetic fields up to 14 T. The regularities found are discussed in terms of Landau's theory of second-order magnetic phase transitions.

Revealing three-dimensional quantum criticality by Sr substitution in Han purple

Classical and quantum phase transitions (QPTs), with their accompanying concepts of criticality and universality, are a cornerstone of statistical thermodynamics. An exemplary controlled QPT is the field-induced magnetic ordering of a gapped quantum magnet. Although numerous "quasi-one-dimensional" coupled spin-chain and -ladder materials are known whose ordering transition is three-dimensional (3D), quasi-2D systems are special for several physical reasons. Motivated by the ancient pigment Han Purple (BaCuSi$_{2}$O$_{6}$), a quasi-2D material displaying anomalous critical properties, we present a complete analysis of Ba$_{0.9}$Sr$_{0.1}$CuSi$_{2}$O$_{6}$. We measure the zero-field magnetic excitations by neutron spectroscopy and deduce the magnetic Hamiltonian. We probe the field-induced transition by combining magnetization, specific-heat, torque and magnetocalorimetric measurements with low-temperature nuclear magnetic resonance studies near the QPT. By a Bayesian statistical analysis and large-scale Quantum Monte Carlo simulations, we demonstrate unambiguously that observable 3D quantum critical scaling is restored by the structural simplification arising from light Sr-substitution in Han Purple.

Low temperature magnetic study of α-NiS nanoparticles synthesized via hydrothermal technique

Synthesis of material with nano-order anisotropy has always been a tricky task for the researchers, since there has to be some property-based inhomogeneity present within the homogeneous material. In this report, we discuss the emergence of Exchange Bias (EB), which is itself a case of magnetic property based anisotropy. Here, a thorough low temperature magnetic study of nickel sulfide (NiS) nanoparticles synthesized via solution based hydrothermal technique was performed. To introduce nano-order inhomogeneity we played with different feeding flow rate of the starting materials. The synthesized samples were of highly crystalline mixed phase nature with α-NiS as a dominant phase. Variation in energy bandgap as a function of feeding rate suggests the possibility of the formation different-sized seed cluster. For sample with maximum α-NiS content, presence of strong magnetic coupling at T < Tb arising from uncompensated spins at the surface of the nanoparticles suggest its weak ferromagnetic character with a paramagnetic background. For the first time, an unusual phenomenon of exchange bias (EB) was also observed for the sample with maximum α-NiS content. The presence of EB suggests FM-AFM coupling occurring over the particle surface, which is also prudent from the fact that NiS is intrinsically an antiferromagnetic material. In short the present study opens up the possibility for the use of NiS a possible material spin based device applications.

Role of charge doping and distortions on the structural, electrical, and magnetic properties of modified CuFeO2 compounds

Single phase CuFeO2, CuFe0.96M0.03V0.01O2 (M = Ti, Mn, and Ga), and CuFe0.96V0.04O2 compounds with space group R3¯m were prepared through a newly developed solid-state technique using annealing under high vacuum. Raman studies demonstrate, for the first time, a minor shift in Ti and Mn-doped samples as well as the Jahn–Teller effect induced distortions around 500 cm−1 along with well-documented peaks of Eg and A1g modes. Mössbauer studies confirm the presence of iron in high spin Fe3+ and quadruple splitting values endorsing the presence of octahedron distortions. An increase in the electrical conductivity at low temperatures is observed due to the enhanced charge doping with minor variations related to local distortions. Low-temperature magnetic studies of pristine and Ti-doped samples demonstrate paramagnetic nature up to 25 K. However, on one hand, the pristine sample shows a sharp rise in magnetization values at low applied fields and on the other side, Ti-doped samples exhibit nearly linear behavior. Dielectric measurements confirm weakening of electrical ordering near the magnetic transition in distorted Ti-doped samples, compared to pure CuFeO2 sample. Level of charges along with its local distortions affected mobility has significant effects on transport and multiferroic nature of these samples.

Splitting of antiferromagnetic resonance modes in the quasi-two-dimensional collinear antiferromagnet Cu(en)(H2O)2SO4

Low-temperature magnetic resonance study of the quasi-two-dimensional antiferromagnet Cu(en)(H$_2$O)$_2$SO$_4$ (en = C$_2$H$_8$N$_2$) was performed down to 0.45~K. This compound orders antiferromagnetically at 0.9K. The analysis of the resonance data within the hydrodynamic approach allowed to identify anisotropy axes and to estimate the anisotropy parameters for the antiferromagnetic phase. Dipolar spin-spin coupling turns out to be the main contribution to the anisotropy of the antiferromagnetic phase. The splitting of the resonance modes and its non-monotonous dependency on the applied frequency was observed below 0.6K in all three field orientations. Several models were discussed to explain the origin of the nontrivial splitting and the existence of inequivalent magnetic subsystems in Cu(en)(H$_2$O)$_2$SO$_4$ was chosen as the most probable source.

Evidence for the coexistence of spin-glass and ferrimagnetic phases in BaFe12O19 due to basal plane freezing.

We present here the results of low-temperature magnetization and X-ray magnetic circular dichroism studies on the single crystals of BaFe12O19 which reveal for the first time the emergence of a spin glass phase, in coexistence with a long-range ordered ferrimagnetic phase, due to the freezing of the basal plane spin component.

Investigation on the role of thermo-magnetic history/hysteresis on the isothermal magnetic entropy change property of EuSe

Low temperature magnetization studies on polycrystalline EuSe have been performed. The system shows anti-ferromagnetic magnetic ordering with Neel temperature TN ∼4.6 K and exhibits a field induced meta-magnetic transition, for temperatures below the TN. Arrot plot analysis indicates first order nature for both these magnetic phase transitions. Using the isothermal magnetization measurements, the isothermal magnetic entropy change (−ΔSM) is evaluated. The magnetization measurements were done for two different measurement protocols to check the effect of thermo-magnetic history/hysteresis on the magneto caloric properties. Results indicate negligible effect of thermo-magnetic history/hysteresis on magnetic and magneto-caloric properties of the EuSe system.

Dielectric, impedance, AC conductivity and low-temperature magnetic studies of Ce and Sm co-substituted nanocrystalline cobalt ferrite

Abstract In this study, we report frequency and temperature dependent dielectric, electrochemical impedance and low temperature magnetic properties of Sol-gel auto-combustion synthesized rare-earth (Ce and Sm) co-substituted cobalt ferrite, CoCexSmyFe2-x-yO4 (x = y = 0.00, 0.1, 0.12 and 0.25). The surface morphology and particle size as obtained by XRD studies was confirmed by HRTEM measurements for a representative sample. The dielectric properties such as dielectric constant, loss tangent and AC conductivity have been measured using LCR meter, variation of dielectric parameters with substituent concentrations, frequency range from 0.1 to 10 MHz at room temperature (RT) and temperatures 100–400 °C have been well supported by Maxwell-Wagner interfacial polarization. The AC conductivity increased with applied frequency suggesting that the conduction mechanism is owing to small polaron hopping between cations. Impedance studies shows that, the addition of RE (Ce and Sm) cause a decrease in the Z′ value, with increasing frequency which can be attributed to the space charge polarization effect in the material. Low temperature magnetic measurements in ZFC-FC mode and magnetic isotherms at 20 and 310 K reveals the ferromagnetic nature of RE (Ce, Sm) substituted cobalt ferrite nano particles. The coercive field has been increased at low temperature 20 K compared to that at 310 K, the samples shows super paramagnetism beyond room temperature.

Structural, surface morphological and low temperature studies on gadolinium tri chloride (GdCl3)

Gd3+ compounds receive special interest because of the maximum number of unpaired spins and they are useful in NMR spectroscopy and MRI. So, study on Gadolinium tri chloride has been reported here. The compound crystallizes in hexagonal structure. The particles are spherical and exhibit flake like structure. Low temperature magnetic study from 300 K to 20 K shows decrease of magnetic susceptibility with increase of temperature. M-H curve shows paramagnetic behavior. The compound can be used for UV filters and for optoelectronic applications. Low temperature magnetic study indicates cooperative interaction between the gadolinium spins in the compound.

Low temperature magnetic and x-ray diffraction studies of YBa1-xSrxCuFeO5 (x = 0, 0.5)

We report low temperature magnetic and structural properties of Sr doped layered perovskite material YBaCuFeO5. YBaCuFeO5 is the antiferromagnetic compound with commensurate to incommensurate transition temperature at 200 K. Low temperature x-ray diffraction shows the lattice contraction effect with decreasing temperature. Below 15 K a strong bifurcation between the ZFC and FC curves has been observed in YBa0.5Sr0.5CuFeO5, which may arise due to lattice contraction effect which changes the interaction between the spin and the lattice.

Structural, Spectroscopic, and Magnetic Studies on Copper Tartrate Crystals

Abstract Copper tartrate crystals were grown by the gel growth method and characterised by energy-dispersive X-ray (EDAX), scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, Fourier transform infrared, photoluminescence (PL), electron paramagnetic resonance, and low-temperature magnetic studies in the temperature range 300–20 K. The XRD study confirmed the orthorhombic structure of the crystal and the XPS study established the Cu2+ ions in the crystal. UV-vis study deduced the energy gap as 2.15 eV, confirming the semiconducting nature, and Urbach energy as 0.4686 eV. PL showed the presence of Cu2+ vacancy-related defects. Low-temperature magnetic study confirmed the paramagnetic nature in the temperature range 300–77 K, and the crystal showed a weak ferromagnetic signal at 20 K, which is interesting. The magnetic field along with the low temperature caused an ordered spin orientation.

Structural, optical, room-temperature and low-temperature magnetic properties of Mg–Zn nanoferrite ceramics

ABSTRACTMg–Zn nanocrystalline ferrites (Mg1−xZnxFe2O4, where x = 0.0 to 1.0) were synthesized by the citrate gel auto-combustion route. XRD revealed the formation of nano-sized particles with cubic spinel structure. Lattice constant and specific surface area increased with Zn substitution. SEM micrographs revealed inhomogeneous grains with agglomerates; EDS spectra confirmed the stoichiometry. HRTEM images showed agglomerated nanoparticles with average particle sizes of 21 nm and 16 nm for x = 0.6 and 1.0, respectively, and lattice fringe images and SAED patterns showed nanocrystalline characteristics corroborating the XRD results. FTIR and Raman spectra recorded at room temperature confirmed the spinel structure of ferrites. VSM technique at room temperature used to measure magnetic properties. MS and HC were found to decrease with increases in the Zn concentration in Mg–Zn ferrites due to a weakening of the A–B interaction and decrease in the particle size and surface effect. Low-temperature magnetic studies were carried out in the ZFC and FC modes using SQUIDS by applying 100 Oe between temperatures of 5 and 400 K, and magnetic isotherms were recorded at temperatures of 51 and 310 K. The study revealed the superparamagnetic nature of the synthesized samples showing that the blocking temperature (TB) depends on interparticle interactions.