Magnetic Transition Temperature Tc Research Articles

Electrical transport behavior and thermo electric power studies of Nd0.67Sr0.33MnO3/ZrO2 CMR composites

In this work, we reported structural, morphological, electrical, magnetic transport and thermo electric power properties of (1-x) Nd0.67Sr0.33MnO3 - x ZrO2 (abbreviated as NSMO, where × = 0%, 5%, 10%, 15%, and 20% mol.%) composites and were synthesized by a double stage sol–gel method. The X-ray diffraction (XRD) revealed a pure perovskite phase of NSMO. The Scanning electron microscopy (SEM) studies displayed uniform microstructure and the average grain size of NSMO was estimated to be 30 nm and was increased to 80 nm with the substitution of ZrO2. With addition of ZrO2 the metal to insulator transition temperature (Tp) shifted towards lower temperature and the resistivity order of the samples are enhanced from 5 to 10 times. The magnetic transition temperature (Tc) is shifted to higher temperature with increase the ZrO2. The temperature dependent resistivity data is well fitted with polynomial equation, which indicates that the high temperature resistivity behavior has been explored with adiabatic small polaron and variable range hopping (VRH) models.

An emergence of chiral helimagnetism or ferromagnetism governed by Cr intercalation in a dichalcogenide CrNb3S6

A synthesis of single crystals of chiral dichalcogenides TM3X6 (T: 3d transition metal, M: Nb or Ta, X: S or Se) remains an intriguing issue for the investigation of emergent quantum properties such as chiral helimagnetism. In this study, we investigated a correlation between the quantity of Cr intercalation x and the magnetic property in single crystals of a chromium (Cr) intercalated chiral disulfide CrxNb3S6 in order to optimize the synthesis condition for the intercalation-controlled single crystals. The magnetic properties, including a magnetic transition temperature Tc, take different values depending on the samples. We systematically grew single crystals of CrxNb3S6 with x ranged from 0.89 to 1.03 and found that the amount of the Cr intercalation x is an essential factor in controlling the magnetic properties of the grown crystals. The magnetization anomaly, which appears in the temperature dependence as evidence of the formation of chiral magnetic soliton lattice (CSL), was observed only in a narrow region of x from 0.98 to 1.03. The single crystals with x being 0.98 and 0.99 showed the CSL behavior with the highest Tc of 133 K. These results indicate that the small number of defects on the sites for T ions dramatically affects the quality of the single crystals in the synthesis of TM3S6. We also discuss the importance of synthesizing enantiopure single crystals of chiral dichalcogenides in order to observe chiral physical properties unique to chiral compounds such as magneto-chiral effect and chiral-induced spin selectivity.

Ferromagnetic Cd(1-x)CuxCr2S4 thin films: Synthesis, characterization, and first-principles calculations

The magnetic chromium-based chalcogenide spinel system has been proposed for development of a new class of spintronic devices. They have been extensively investigated because of their unique electrical, magnetic, and optical properties. For example, CdCr2S4 is a well-established ferromagnetic semiconductor, while CuCr2S4 is a ferromagnetic metal. Their solid solution, Cd(1-x)CuxCr2S4, offers an exciting possibility to tailor the magnetic and optical properties. In bulk form, they exhibit ferrimagnetic ordering with Curie temperature of about 85 K (for x = 0.1). However, thin films of these mixed magnetic chalcospinels materials have not been investigated. We have deposited Cd(1-x)CuxCr2S4 thin films using a versatile and simple chemical spray deposition (CSD) method combined with post-annealing in a sulfur atmosphere. The Cd(1-x)CuxCr2S4 thin films are deposited over a range of 0 ≤ x ≤ 0.2 using simple inorganic salts of Cd, Cu, and Cr. Systematic changes in the unit cell volume, lattice parameter, bandgap, and magnetic properties are observed with Cu incorporation. A decrease in the saturation magnetic moment and transition temperature (Tc) are noted with increasing Cu substitution. First principles spin-polarized calculations within GGA and PBE approximation have been performed to determine the electronic and magnetic structure as a function of composition. The results suggest that an antiparallel alignment between Cu and Cr spins decreases the magnetization with increasing Cu substitution. The theoretical results are in qualitative agreement with the experimental findings and highlight the development of Cd(1-x)CuxCr2S4 (0 ≤ x ≤ 0.2) thin films with tunable magnetic and semiconducting properties.

Effects of Cr,Co,Ni substitution at Mn-site on structural, magnetic properties and critical behaviour in Nd0.67Ba0.33MnO3 mixed-valent manganite

This work investigates on the crystal structure, magnetic nature and critical behaviour with the partial replacement of transition (Tr) elements (ie., 10% of Cr, Co, Ni) at the Mn-site of Nd0.67Ba0.33MnO3 (NBMO) synthesised via conventional solid-state-method. NBMO compound is crystallised into an orthorhombic crystal structure and possess a magnetic transition temperature (Tc) at 145 K. Crystal structure of NBMO remains the same with partial substitution of Tr elements but, the Tc is found to be slightly increased with the doping of Cr, while decreases with the doping of Co and Ni. The magnetic isotherms are traced, and critical exponents are studied using modified Arrott plots (MAP) and power law. All the substituted samples show a second-order nature of Tc similar to that of the parent compound. The critical parameters are identified and verified through MAP, critical isotherms, Kouvel-Fisher method and field dependence of entropy change. All the substituted compounds govern the 3D Heisenberg with short-range order.

Control of Magnetic Properties of Barium Ferrite Thin Films With Unusual Valence Fe

Thin films of BaFe1-xMxO3 (M = Hf, Zr, and Ce; 0.0 ≤ x ≤ 0.75) were fabricated using pulsed laser deposition and their magnetic properties were investigated. X-ray diffraction analysis indicated that oxygen-deficient BaFeOx (x < 3.0) with a monoclinic structure was formed when the deposition was conducted using a non-substituted target (x = 0.0). The as-grown BaFeOx films were converted into fully oxidized BaFeO3 with a perovskite structure by low-temperature oxidation in an ozone atmosphere. In contrast, the as-deposited films of Hf, Zr, and Ce-substituted films exhibited a perovskite structure, and their crystallinity did not change after low-temperature ozone annealing. The magnetic transition temperature Tc of the BaFeO3 film was 115 K, whereas the substituted BaFeO3 films showed ferromagnetic behavior even at 300 K. These results can be attributed to the weakening of the antiferromagnetic super-exchange coupling among Fe ions owing to the lattice expansion in the substituted BaFeO3. In addition, the magnetization of the films was found to increase with the decreasing ionic ratio of Fe4+/Fe3+, suggesting that the inherent carrier-induced ferromagnetic interaction is dominant in the films.

Magnetic properties and non-fermi liquid behaviour in mechanically alloyed FeCu

FexCu100−x alloys where x (wt%) = 25, 35, 50, 65, and 75 were prepared via mechanical alloying. Microstructural characterization revealed a single-phase face-centered cubic structure for a wide range of compositions. Atomic volumes were estimated from measured lattice parameters suggesting a high volume state consistent with Weiss model predictions of the ferromagnetic ground state. Saturation magnetic moments at 2 K monotonically decreased from 2.28 μB/Fe for starting Fe powder to 0.65 μB/Fe in Fe25Cu75 alloy. Samples with Fe content higher than 35% exhibited magnetic transition temperatures (Tc) higher than 350 K. On the other hand, the Fe25Cu75 sample exhibit a Tc around 250 K as determined from the gradient method. According to Banerjee's criterion, the magnetic transition is determined to be second order for the Fe25Cu75 alloy. Moreover, modified Arrott plots were used to reveal the critical behavior of the Fe25Cu75. Temperature dependencies of the resistivity were measured for all samples. At low temperatures, the Fe25Cu75 alloy exhibited T3/2 dependence of the resistivity. At higher temperatures (100–300 K) all mechanically alloyed FeCu exhibited unusual T linear dependence resistivity. Such behavior is often called “strange metallicity” or non-Fermi Liquid behavior. The possible origin of such behavior was also discussed.

Spin glass behavior and exchange bias effect in GaFeO3‐type iron oxide

AbstractGaFeO3‐type iron oxide is a promising room‐temperature multiferroic material due to its large magnetization and polarization. To expand the scope of its application, it is crucial to control the magnetic properties. Based on introducing the ferromagnetic (FM) Fe3O4 in the antiferromagnetic (AFM) GaFeO3 to build the FM‐AFM interface by changing the Ga/Fe ratio, Ga0.69Fe1.31O3 (GFO) was successfully grown by the floating zone method. The resulting sample was characterized by X‐ray diffraction (XRD), and its magnetic properties were measured using a superconducting quantum interference device (SQUID). The temperature‐dependent AC susceptibility measurement shows that the spin glass‐like behavior of GFO at temperatures close to 50 K is a manifestation of the geometrical frustration arising from cation site disorder. In addition, the magnetic property measurement shows that the magnetic transition temperature Tc is at 650 K, which is introduced by Fe3O4 and suppresses the ferromagnetic transition around 320 K of GFO. Interestingly, the observed exchange bias effect, which does not exist in the bulk GaFeO3‐type family, is attributed to the formation of an FM/AFM interface due to the existence of FM Fe3O4 in the GFO. This study provides a new perspective on the properties of the GaFeO3‐type family for potential applications in spintronic devices.

Transition metals co-doped induced ferromagnetism in SnO2: First-principles characterization

The possibility of ferromagnetism in SnO2 is explored by (Fe,TM= Sc, Ti, V, Cr, Mn, and Co) co-doping strategy using ab-initio calculations. Our results revealed that (Fe,Sc), (Fe,V), (Fe,Cr), (Fe,Mn), and (Fe,Co) co-doped SnO2 materials exhibit stable FM ground state, while (Fe,Ti) co-doped system attains the FiM. Furthermore, the calculated magnetic transition temperatures (Tc) show the reasonable range and (Fe,Mn) co-doped system having the highest of 884 K. The most striking feature of the present study is that (Fe,V) co-doped structure displayed the half-metallic behavior with a Tc of 207 K, which makes it promising candidates for potential applications in magnetic memory devices. The V dz2/dxy orbitals are mainly responsible for conductivity in the spin-majority channel with small contributions from Fe 3d. Spin-magnetization density iso-surface plots exhibit that magnetism mainly originated from the admixture of dxy, dxz, and dyz orbitals of Fe/V ions.

Prediction of the Properties of the Rare-Earth Magnets Ce2Fe17−xCoxCN : A Combined Machine-Learning and Ab Initio Study

We employ a combination of machine learning and first-principles calculations to predict magnetic properties of rare-earth lean magnets. For this purpose, based on training set constructed out of experimental data, the machine is trained to make predictions on magnetic transition temperature (Tc), largeness of saturation magnetization ({\mu}0Ms), and nature of the magnetocrystalline anisotropy (Ku). Subsequently, the quantitative values of {\mu}0Ms and Ku of the yet-to-be synthesized compounds, screened by machine learning, are calculated by first-principles density functional theory. The applicability of the proposed technique of combined machine learning and first-principles calculations is demonstrated on 2-17-X magnets, Ce2Fe17-xCoxCN. Further to this study, we explore stability of the proposed compounds by calculating vacancy formation energy of small atom interstitials (N/C). Our study indicates a number of compounds in the proposed family, offers the possibility to become solution of cheap, and efficient permanent magnet.

Observation of relaxor-ferroelectric behavior in gallium ferrite thin films

We report a detailed investigation on magnetic and electrical properties of the multiferroic GaFeO3 (GFO) thin films grown on SrRuO3 (SRO) buffered SrTiO3 (1 1 1) substrates. The magnetic transition temperature (Tc) of GFO thin films is observed ∼240 K, which is higher by 20 K than in GFO ceramic. The clear and reversible out-of-plane phase-contrast seen in the Piezoresponse Force Microscopy (PFM) phase and amplitude images measured within positive and negative poling confirms the polarization reorientation and hence piezoelectric nature of the compound. The temperature and frequency dependence of permittivity studies demonstrates the relaxor behavior of these thin films. The observed near room temperature (RT) magnetic phase transition with RT piezoelectric nature of these thin films elucidates the possible potential candidates for a multiferroic world with spintronics device applications.

Magnetic, magnetocaloric and critical behavior investigations of 0.8BiFeO3-0.2BaTi0.95(Yb0. 5Nb0.5)0.05O3 multiferroïc ceramic

Abstract The magnetic, magnetocaloric and critical behavior properties of 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroic ceramic are studied around its magnetic transition temperature: TC. The Rietveld Refinement of X-ray diffraction data, recorded at room temperature, revealed that our sample crystallizes in the tetragonal P4mm space group. The dependence of magnetization on temperature reveals a magnetic transition at TC = 365 K, which was confirmed via in-situ Mossbauer measurements. Around the magnetic transition temperature TC, the magnetic entropy change reached maximum value of Δ S M M a x of 10.0066 J. kg−1 K−1 and the relative cooling power (RCP) value is of 278.4014 J. kg−1, when a magnetic field of 5T is applied. The critical exponents β, γ and δ have been deduced via various methods: the modified Arrott plots (MAP), Kouvel-Fisher method (KF) and critical isotherm (CI) analysis. These critical exponent values confirm that δ values is between the mean-field model and the 3D-Heisenberg model, the β value is so close to the 3D-Heisenberg model while that γ value is proximate to the mean-field model. These critical parameters associated with the critical magnetic transition region predict the presence of both short and long magnetic range order in our sample. The precision of the deduced critical exponents is highlighted through the follow-up of the dependence of magnetization on temperature and magnetic field to the scaling theory. All the obtained results confirm the coexistence of the effect of two networks in our ceramics, the ferromagnetic ordering spin contribution, resulting in modulating the antiferromagnetic AFM canted spin, and the AFM ones, with both contributions of short- and long-range interactions, respectively, embedded in the spin glass like matrix BiFeO3. A number of attractive features made our 0.8BiFeO3-0.2BaTi0.95(Yb0.5Nb0.5)0.05O3 multiferroics as a potential candidate in a large area of modern applications.

Room-temperature skyrmion phase in bulk Cu2OSeO3 under high pressures

A skyrmion state in a noncentrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high-density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic field-temperature phase space and often in the low-temperature region near the magnetic transition temperature Tc We have expanded and enhanced the skyrmion phase region from the small range of 55 to 58.5 K to 5 to 300 K in single-crystalline Cu2OSeO3 by pressures up to 42.1 GPa through a series of phase transitions from the cubic P213, through orthorhombic P212121 and monoclinic P21, and finally to the triclinic P1 phase, using our newly developed ultrasensitive high-pressure magnetization technique. The results are in agreement with our Ginzburg-Landau free energy analyses, showing that pressures tend to stabilize the skyrmion states and at higher temperatures. The observations also indicate that the skyrmion state can be achieved at higher temperatures in various crystal symmetries, suggesting the insensitivity of skyrmions to the underlying crystal lattices and thus the possible more ubiquitous presence of skyrmions in helimagnets.

Spin-pair correlation driven the colossal magnetoresistance effect in multiferroics CdCr2S4

To understand the anomalous conductivity and colossal magnetoresistance effect of multiferroics CdCr2S4 around magnetic transition temperature TC, we propose the spin-pair correlation dependence of magnetic polarons model. In CdCr2S4, system shows the spontaneous magnetic order at TC and the magnetic order promotes the delocalization of magnetic polarons. According to the proposed model of a dual-conduction behavior, the normal and delocalized magnetic polarons coexist below TC due to the gradual delocalization process of magnetic polarons. Compared to the conductivity of normal magnetic polarons, the conductivity from the delocalized magnetic polarons is dominant. It is suggested that the spin-pair correlation modifies the hopping activation energy of delocalized polarons to realize the anomalous conductivity and colossal magnetoresistance effect. In addition, the applied magnetic field, which promotes the magnetic order and delocalization of magnetic polarons, also leads to the increase of conductivity via spin-pair correlation. It is found that the obtained conductivity and colossal magnetoresistance are in agreement with the experimental results.

Electrochemical development of magnetic long-range correlations with Tc = 128 K in a tetraoxolene-bridged Fe-based framework

The generation of the paramagnetic radical (Cl2An3−) in the framework-edge moieties of an Fe-based two-dimensional honeycomb framework with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinonate (Cl2Ann−), (H3O)2(phz)3[Fe2(Cl2An)3] (phz = phenazine), allowed the formation of long-range magnetic correlations over the network with a relative high magnetic phase transition temperature (Tc) of 128 K. The original compound is a paramagnet with a diamagnetic Cl2An2− linker that significantly separates paramagnetic FeII ions (S = 2), where the [(H3O)2(phz)3]2+ cation is located between layered frameworks. Post-synthetic electron-doping, i.e., reduction in the solid state, using a lithium-ion battery (LIB) system, finally produced (Li+)3(H3O+)2(phz)3[(Fe2+)2(Cl2An3−)3], which demonstrated a drastic magnetic change.

Electronic and magnetic properties of B-Doped XS (X = Zn and Cd): A density functional theory study

Ab-initio calculations were performed to study the electronic and magnetic properties of boron doped XS (X = Zn and Cd) systems. The structural stability of doped systems is analyzed in terms of formation energy and found that B@S site in ZnS is more energetically favorable than that of B@S in CdS system. Our calculations show that B-doping at S-site (B@S) induced magnetism in XS structures, which can be explained on the basis of electronegativity difference between the dopant and host atoms. It is evident that B 2p orbitals are playing the major role to generate magnetism in both (ZnS and CdS) doped systems. In contrast, B-doping at Zn/Cd sites in XS structures, leads the systems to n-type non-magnetic conductor. Furthermore, the impact of B-doping at different S sites is studied to probe the stable magnetic ground state. Finally, the magnetic transition temperature (Tc) is also computed.

Enhanced magneto-electric coupling and energy storage analysis in (BiFeO3–BaTiO3)/CoFe2O4 composites

Enhanced magneto-electric coupling and energy storage density analysis of solid-state route derived (BiFeO3–BaTiO3)/CoFe2O4 composites were investigated for memory application under the variation of the magnetic phase of CoFe2O4. The powder X-ray diffraction data, SEM–EDX, Raman spectroscopy, and FTIR measurements were carried out to investigate the crystalline structure, composite formation and phase purity of all the samples. Magnetic measurements showed very high magnetization values obtained from 0.063 emu/g for 0.7BF–0.3BT to 18.14 emu/g for (0.7BF–0.3BT)/30CF composite near room temperature. The weak but countable maximum ferroelectric polarization (Pmax) was achieved due to the change in the area of the loops with the variation of frequencies from 50 to 200 Hz. The highest value of energy storage density (Ju) and efficiency (η) for (BF–BT)/30CF (Ju = 37.08 mJ/cm3 and η = 89.40%) composite was achieved. The dielectric anomaly near the magnetic transition temperature (Tc ~ 425 °C) and the variation in the maximum polarization values from 4.63 to 6.6 µC/cm2 with respect to the applied magnetic field confirmed the strong evidence of magneto-electric coupling in (BF–BT)/CF composite samples. The highest values of magneto-electric coefficients (α) were achieved 9.039 mV/cm Oe at 600 Oe, 9.039 mV/cm Oe at 1100 Oe and 22.59 mV/cm Oe at 1600 Oe for (BF–BT)/10CF, (BF–BT)/20CF and (BF–BT)/30CF composites respectively.

Magnetic properties of sintered CoFe2O4–BaTiO3 particulate magnetoelectric composites

Abstract The magnetic properties of sintered particulate magnetoelectric CoFe2O4−BaTiO3 composites have been studied. The particulate composites are sintered in the temperature range 1000–1300 °C, for a short duration of 10 min. The magnetic transition temperature (Tc) of CoFe2O4 is found to decrease with increasing the sintering temperature and sintering time, as well as on increasing the BaTiO3 content in the composites. Similarly, a reduced saturation magnetization at room temperature, compared to that expected for the CoFe2O4 content, is also observed. Powder X-ray diffraction studies showed the presence of the impurity phase related to the hexagonal ferrite BaFe12O19 in all the composites. Ba2Fe2Ti4O13 is observed as a second impurity phase in the BaTiO3−rich composites. The present studies suggest that the composition of the piezomagnetic (CoFe2O4) phase in the CoFe2O4−BaTiO3 magnetoelectric composite is affected during the sintering process.

Coupled phonons and magnetic orderings in GaFeO3: Raman and magnetization studies

Magnetoelectric (ME) materials with ferroelectric and magnetic transition temperatures near room temperature are of current interest in research due to their technological importance and potential applications. Herein, we report the coupled magnetic ordering and phonons in gallium ferrite (GaFeO3), a near room temperature ME perovskite, using magnetization and inelastic light scattering measurements as a function of temperature. Temperature-dependent magnetization behavior studied in a wide temperature range of 5–395 K at both field-cooled (FC) and zero-field-cooled (ZFC) conditions using different static magnetic fields confirms the magnetic transition temperature Tc at 220 K. On temperature dependent Raman spectroscopy, no significant changes in Raman spectra were observed at an elevated temperature that can be attributed to the absence of structural phase transition. Instead of expected anharmonic behavior, several librational (rigid rotation) and stretching modes of rigid BO6 units were found to be hardening below Tc, suggesting the significant magnetoelastic coupling contributions to phonon frequencies. The asymmetric stretching mode at 753 cm−1 is found to have larger spin-phonon coupling contribution (λ∼2.93), while the lattice mode at 153 cm−1 and external librational mode at 240 cm−1 had the lowest effect (λ∼0.88).

Investigation of Spin Reorientation in Ga Substituted Y-type Hexaferrite based on Mössbauer Spectroscopy

The polycrystalline sample of Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 Y-type hexaferrite, doped with Ga-cation, was prepared by using the solid-state reaction method. The crystalline structure of sample was investigated by x-ray diffractometer (XRD), and the magnetic properties of sample were measured by vibrating sample magnetometer (VSM), and Mossbauer spectrometer. The crystal structure of prepared sample was determined to be rhombohedral with space group R-3m. From the temperature dependence of the magnetization curves under 100 Oe between 4.2 and 740 K, two temperature-dependent magnetic transitions occurred in the Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 sample. Mossbauer spectra of the sample were analyzed at various temperatures ranging from 4.2 to 620 K, and the Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 sample showed abrupt changes in Hhf and EQ at 200 K, indicating the spin transition effect. We have also determined the magnetic transition temperature TC, in addition to the temperature dependent magnetization and ZVC measurements.

Elastic properties of SmPt2Cd20 probed by ultrasound measurements

Ultrasound measurements have been carried out to investigate the elastic and low-temperature 4f-electronic properties of the Sm-based 1-2-20 system SmPt2Cd20. It was found that SmPt2Cd20 shows a pronounced elastic softening toward the magnetic transition temperature Tc = 0.64 K in the temperature dependence of the transverse elastic constant CE = (C11 -C12)/2. The clear elastic softening behavior is suppressed gradually with increasing a magnetic field. The obtained results can be explained reasonably by a deformation potential approximation in which a coupling between conduction electrons and elastic strains caused by sound waves leads to a temperature dependence of elastic constants. This suggests possibly that the 4f electrons would become itinerant in the ground state in SmPt2Cd20. The nature of the low-temperature elastic and electronic states involving the ground state multiplets of Sm ions are discussed.