Coexistence Of Ferromagnetism Research Articles

Unveiling the magnetic and transport properties of La0.5Sr0.5Co1−xVxO3−δ (x = 0, 0.01, 0.02 and 0.1)

La0.5Sr0.5CoO3−δ system displaying coexistence of metallicity and ferromagnetism, and the interplay between distinct spin states of Co ions has gained significant attention from the fundamental as well as the applications point of view. In this regard, the effect of V5+ doping on the dynamics of spin and oxidation states of Co ions in the La0.5Sr0.5CoO3−δ system has been studied using structural, X-ray photoemission spectroscopy, magnetic and transport measurements. The La0.5Sr0.5Co1−xVxO3−δ (x = 0, 0.01, 0.02 and 0.1) series was prepared by conventional solid-state reaction method and its chemical homogeneity was established by inductively coupled plasma mass spectroscopy. The increase of lattice parameters/volume with increasing V5+ content in rhombohedrally crystallized (R3-c) samples is attributed to the presence of Co2+ ions . The presence of Co2+ ions and the reduction of Co3+ ion concentration with V substitution is verified from the results of core-level photoemission spectra of Co. Detailed magnetic measurements show an increase in Curie temperature, effective magnetic moment, soft magnetic nature and suggesting strengthening of underlying magnetic interactions. As a result of multiple oxidation states of Co ions and the delocalization of electrons, rise in the conductivity is noticed. Such enhancement in the conductivity and ferromagnetic ordering temperature, simultaneously, with V doping implies a strong coupling between spin and charge degrees of freedom. To understand the underlying mechanism more clearly, different possible scenarios have been discussed. The most appropriate scenario i.e., the conversion of Co3+ ions into Co2+ ions and admixture of Co4+ ion spin states with V5+ doping was found to be consistent with all the experimental observations.

Pairing symmetry in monolayer of orthorhombic CoSb

Ferromagnetism and superconductivity are generally considered to be antagonistic phenomena in condensed matter physics. Here, we theoretically study the interplay between the ferromagnetic and superconducting orders in a recent discovered monolayered CoSb superconductor with an orthorhombic symmetry and net magnetization, and demonstrate the pairing symmetry of CoSb as a candidate of non-unitary superconductor with time-reversal symmetry breaking. By performing the group theory analysis and the first-principles calculations, the superconducting order parameter is suggested to be a triplet pairing with the irreducible representation of 3B2u, which displays intriguing nodal points and non-zero periodic modulation of Cooper pair spin polarization on the Fermi surface topologies. These findings not only provide a significant theoretical insight into the coexistence of superconductivity and ferromagnetism, but also reveal the exotic spin polarized Cooper pairing driven by ferromagnetic spin fluctuations in a triplet superconductor.

Understanding the ferromagnetic-insulator phase in manganites through a localized band model

Understanding the coexistence of ferromagnetism and insulating behavior in manganites is an unsolved problem. We propose a localized band model involving effective intermediate-range electron-electron (electron-hole) repulsion (attraction) generated by cooperative electron-phonon interaction. A double-exchange mechanism, involving holes virtually hopping to nearest neighbors and back, produces magnetic polarons in an antiferromagnetic environment; when these magnetic polarons coalesce and percolate the system, we get a ferromagnetic insulator. Ferromagnetism gets more pronounced when the concentration of holes (doping) increases or when the ratio of hopping to polaronic-energy dominates over the ratio of superexchange-coupling to hopping.

Magnetic characteristics of LaMnO3+δ thin films deposited by RF magnetron sputtering in an O2/Ar mixture gas

In this work, LaMnO3+δ thin films have been successfully fabricated by RF magnetron sputtering using different O2/Ar flux ratios. The crystal structures, morphologies, stoichiometry, surface chemical states and magnetic properties of films are thoroughly characterized by x-ray powder diffraction (XRD), Raman spectrometer, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The magnetic characteristics of LaMnO3+δ films are systematically studied with the transformation from Mn3+ to Mn4+, which is strongly controlled by the deposited O2/Ar flux ratios. We demonstrate that LaMnO3+δ films undergo an antiferromagnet, the coexistence of ferromagnetism and antiferromagnetism and a robust ferromagnetism ordering by the variation of Mn3+/Mn4+ ratios. The LMO film deposited in pure argon atmosphere shows negligible FM signal and an inconspicuous TC. With the increase of deposited O2/Ar flux ratios, the Curie temperature of LMO films increases from 100 K to 224 K and then decreases to 140 K and meanwhile the irreversibility temperature fluctuates between 24 K and 100 K. The appearance of cluster glass state and the unexpected exchange bias phenomenon where the film deposited at highest O2/Ar flux ratio has a HEB ∼ 115 Oe is observed. All these evolutions of magnetization characteristics are discussed in terms of the strength of ferromagnetic interactions and the degree of competition between ferromagnetic and antiferromagnetic interactions in LaMnO3+δ films. Our work serves as prerequisites for LaMnO3-based magnetic heterostructures grown by RF magnetron sputtering.

Evolution of diverse Hall effects during the successive magnetic phase transitions in Mn2.5Fe0.6Sn0.9 Kagome-lattice alloy

Evolution of diverse Hall effects due to successive magnetic transitions has been observed in Mn2.5Fe0.6Sn0.9 by suitable chemical substitution of Fe in Mn3.1Sn0.9. This noncollinear antiferromagnetic alloy exhibits a Neel temperature of 325 K. Upon cooling from 325 K, a magnetic phase transition from noncollinear antiferromagnetism to ferromagnetism occurs at 168 K due to the tilting of magnetization towards c axis. Above this temperature, anomalous Hall resistivity ranged from 0.6 to 1.3 μΩ cm has been observed in noncollinear antiferromagnetic state. Below this temperature, a topological Hall effect (THE) starts to appear due to the non-vanishing scalar spin chirality arising from the noncoplanar spin structure. Further decreasing temperature to 132 K, another magnetic transition happens, resulting in the coexistence of ferromagnetism and antiferromagnetism, so that a Hall plateau with large hysteresis below 70 K is yielded. A hysteresis as high as ∼80 kOe is obtained in ρ xy -H at 15 K. However, the Hall plateau disappears and only anomalous Hall effect (AHE) persists when further decreasing the temperature to 5 K. The present study provides a picture of diverse magneto-transport properties correlated to the variable spin structures driven by magnetic phase transitions.

Evolution of microstructure, defect, optoelectronic and magnetic properties of Cu1-xCaxFeO2 ceramics

Microstructures, defect characteristics, optoelectronic, and magnetic properties of polycrystalline delafossite Cu1-xCaxFeO2 (x = 0.00–0.08) samples have been systemically investigated. Our investigation results distinctly show that divalent Ca2+ ions can successfully substitute partial Cu+ ions and prompt the grain size and induce the partial Fe3+ valence variation to Fe2+. The positron annihilation lifetime spectra signifies that the cation vacancy clusters exist in all samples, the size and concentration of vacancy defects are redistributed with increasing Ca2+ ions content, while the overall defect environment of CuFeO2 system is not changed. The Hall-effect measurement results indicate the transition of semiconductor type from p-type to n-type. The UV–Visible absorption spectroscopy results indicate that the calculated band gap of the prepared samples is estimated to be 3.42–3.58 eV, indicating the series can be applied to the transparent conductive oxide materials. The magnetic measurements reveal that the transition temperature TN1 and TN2 are independent of Ca2+ content x, while the coexistence of antiferromagnetism and weak ferromagnetism for all the doped samples are observed. A moderate Ca2+ content, i.e. x = 0.02, can distinctly promote weak ferromagnetism. The above internal mechanism is probably relevant to the evolution of lattice structure and defect characteristics caused by Ca2+ ions doping.

Metallic ferroelectric-ferromagnetic multiferroics in strained EuTiO3−xHx

Polar metals are defined by the coexistence of metallicity and polar crystal structure. They have potential applications in non-linear optics, ferroelectric devices, and quantum devices. Meanwhile, ferroelectric-ferromagnetic (FE-FM) multiferroics display simultaneous ferroelectricity and ferromagnetism, leading to new technologies in information storage. It remains an open question whether metallicity, ferroelectricity, and ferromagnetism can coexist in a single domain of a material. EuTiO$_3$ is actively studied for potential applications in magnetic sensors, memories, magneto-optical devices, and energy conversion devices. It stabilizes at a multi-critical equilibrium and exhibits a rich range of intriguing properties. Here, using the results from hybrid density functional theory calculations, we report metallic FE-FM multiferroics in strain-engineered epitaxial EuTiO$_3$ with H doping. The emergence of the magnetism in polar metals provides a new degree of freedom to control these materials in applications. The underlying mechanism for the coexistence of metallicity, ferroelectricity, and ferromagnetism is discussed. The ferromagnetism in metallic EuTiO$_{3-x}$H$_x$ is explained by the Ruderman-Kittel-Kasuya- Yosida (RKKY) interaction, which agrees with experiments. The coexistence of metallicity and ferroelectricity is allowed because the electrons at the Fermi level are weakly coupled to the ferroelectric distortion. Our results suggest that the combined effect of strain and doping is responsible for achieving EuTiO$_3$-based metallic FE-FM multiferroics and may provide a new way for obtaining metallic FE-FM multiferroics in other materials.

Multiferroic and magnetoelectronic polarizations in BaFe12O19 system

Coexistence of ferroelectricity and ferromagnetism in one single phase of a solid is of great interest because of the potential application for novel electronic devices. We report on the enhanced ferroelectricity jointly co-existing with excellent magnetic performance in M-type barium hexaferrite (BaFe12O19), which demonstrating a classic electric polarization (P-E) hysteresis loop with full saturation. Two nonlinear current peaks in the I–V curve for polarization switch and giant abnormal change of dielectric constant near Curie temperatures provide sufficient experimental evidences to verify the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant polarization of 55.7 μC/cm2 and a suitable coercive field at 441 kV/cm. Two peaks at 194 °C and 451 °C in the temperature-dependent dielectric spectrum of BaFe12O19 ceramics are considered to be the phase transition from ferro-to antiferro- and antiferro-to para-electric structures. A conventional strong magnetic hysteresis loop was also observed. The influence of oxygen vacancies on the band structure, electric and magnetic properties has been discussed in detail. The magnetically induced E-polarization upon the BaFe12O19 ceramics was achieved in the form of alternating spin current waves. These combined multiple functional responses of large ferroelectrics and strong ferromagnetism reveal the excellent multiferroic features of BaFe12O19, which would bring forth the great opportunity to create novel electric devices with active coupling effect between magnetic and electric orders.

Exchange Bias in Antiferromagnetic Mn3Sn Monolayer Films

${\mathrm{Mn}}_{3}\mathrm{Sn}$ is an antiferromagnet with a noncollinear spin order, and the spin structures can be controlled by an external magnetic field. When a magnetic field is applied, ${\mathrm{Mn}}_{3}\mathrm{Sn}$ with the inverse triangular spin structure exhibits the coexistence of antiferromagnetism and weak ferromagnetism. Here we observe that both the magnetization hysteresis loops and anomalous Hall curves of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ single-layer films present exchange bias after field cooling, which are generally observed in ferromagnet/antiferromagnet bilayers. A part of the antiferromagnetic spin structure of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ with negligible net moments is frozen by the field-cooling process, while for the other part of ${\mathrm{Mn}}_{3}\mathrm{Sn}$, the switching of the inverse triangular spin structure with weak moments by external magnetic fields results in sizable anomalous Hall curves. The stable frozen antiferromagnetic part pins the weak moments and the inverse triangular spin structures can explain the exchange bias in magnetization hysteresis loops and anomalous Hall curves. The finding of exchange bias in antiferromagnetic ${\mathrm{Mn}}_{3}\mathrm{Sn}$ single-layer films with noncollinear spin order adds a different dimension to antiferromagnetic spintronics.

First-principles study of a Mn-doped In2Se3 monolayer: Coexistence of ferromagnetism and ferroelectricity with robust half-metallicity and enhanced polarization

Two-dimensional (2D) materials with coexistence of ferromagnetism (FM) and ferroelectricity (FE) are rare. By using first-principles modeling, here we report that doping of magnetic transition metal (TM) atoms in FE monolayer In2Se3 could introduce giant local FM magnetic moments (4μB per Mn atom). The exchange splitting energy, and the C3ν crystal field together with the hybridization of the Mn−d and Se−p orbitals result in spin-polarized states near the Fermi surface. More interestingly, the asymmetric charge distribution of the Jahn-Teller ion (Mn3+d4) further lift the twofold degeneracy of the Mn-d e1∗ states. This affects the band structure and enhances the FE polarization in monolayer In2Se3. Our work paves the way for tailoring FM in 2D FE via doping magnetic moments from TM atoms. The half-metallicity combined with the enhanced FE polarization make Mn-doped In2Se3 a candidate for potential applications in information technology and spintronic devices.

Crystalline and magnetic structures, magnetization, heat capacity, and anisotropic magnetostriction effect in a yttrium-chromium oxide

We have studied a nearly stoichiometric insulating Y$_{0.97(2)}$Cr$_{0.98(2)}$O$_{3.00(2)}$ single crystal by performing measurements of magnetization, heat capacity, and neutron diffraction. Albeit that the YCrO$_3$ compound behaviors like a soft ferromagnet with a coersive force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions between Cr$^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and antiferromagnetism may indicate a canted AFM structure. The AFM phase transition occurs at $T_\textrm{N} =$ 141.5(1) K, which increases to $T_\textrm{N}$(5T) = 144.5(1) K at 5 T. Within the accuracy of the present neuron-diffraction studies, we determine a G-type AFM structure with a propagation vector \textbf{k} = (1 1 0) and Cr$^{3+}$ spin directions along the crystallographic \emph{c} axis of the orthorhombic structure with space group \emph{Pnma} below $T_\textrm{N}$. At 12 K, the refined moment size is 2.45(6) $\mu_\textrm{B}$, $\sim$ 82\% of the theoretical saturation value 3 $\mu_\textrm{B}$. The Cr$^{3+}$ spin interactions are probably two-dimensional Ising like within the reciprocal (1 1 0) scattering plane. Below $T_\textrm{N}$, the lattice configuration (\emph{a}, \emph{b}, \emph{c}, and \emph{V}) deviates largely downward from the Gr$\ddot{\textrm{u}}$neisen law, displaying an anisotropic magnetostriction effect and a magnetoelastic effect. Especially, the sample contraction upon cooling is enhanced below the AFM transition temperature. There is evidence to suggest that the actual crystalline symmetry of YCrO$_3$ compound is probably lower than the currently assumed one. Additionally, we compared the $t_{2\textrm{g}}$ YCrO$_3$ and the $e_\textrm{g}$ La$_{7/8}$Sr$_{1/8}$MnO$_3$ single crystals for a further understanding of the reason for the possible symmetry lowering.

Coexistence of Surface Ferromagnetism and a Gapless Topological State in MnBi_{2}Te_{4}.

Surface magnetism and its correlation with the electronic structure are critical to understanding the topological surface state in the intrinsic magnetic topological insulator MnBi_{2}Te_{4}. Here, using static and time resolved angle-resolved photoemission spectroscopy (ARPES), we find a significant ARPES intensity change together with a gap opening on a Rashba-like conduction band. Comparison with a model simulation strongly indicates that the surface magnetism on cleaved MnBi_{2}Te_{4} is the same as its bulk state. The inability of surface ferromagnetism to open a gap in the topological surface state uncovers the novel complexity of MnBi_{2}Te_{4} that may be responsible for the low quantum anomalous Hall temperature of exfoliated MnBi_{2}Te_{4}.

Study of the low-field irreversibility line in the transverse component spin-glass phase of the amorphous Fe90Zr10 alloy

Amorphous FexZr100−x alloys display a complex magnetic phase diagram, particularly in the range 89% ≲ x ≲ 93% in which the phase transition from the paramagnetic to a soft ferromagnetic (FM) state at a critical temperature Tc precedes a second transition at Txy < Tc to a transverse spin-glass (SG) phase, with frozen spin components transverse to the magnetization. The softness of the FM phase and the coexistence of FM and SG orderings complicate exploring the low-temperature and low-field critical properties of the glassy transition. Here we study the irreversibility Almeida-Thouless (AT) line that marks the onset of the transverse SG phase in the Fe90Zr10 alloy in the low-field regime up to H = 60 Oe. While ZFC measurements give rise to an AT exponent ϕ = 4.6, similar to that of another amorphous FM compound with random local anisotropy, the induction of magnetic shiftings upon cooling the sample in a large field, − 85 kOe, displaces down the AT line and separates it into two distinct regimes: one also with ϕ = 4.6 for H above 20 Oe, nearly corresponding to the typical field to flip the remanent magnetization, and a new second regime at lower H, with field-induced remanent clusters and exponent ϕ = 3.6 that approaches the mean-field value ϕ = 3. Our findings are discussed on the light of the results from a random nonuniform anisotropy model with FM exchange interactions, which also reported the existence of a two-regimes scenario in the AT line with similar exponents.

Effect of Mn doping on the microstructure and magnetic properties of CuFeO2 ceramics

The effects of Mn doping on the microstructure and magnetic properties of CuFeO2 systems were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), and a physical property measurement method. The microstructure measurements demonstrated that the substitution of Mn for Fe can cause lattice distortion, promote grain growth, and change the valence state of Fe and Mn ions. Ceramic samples with doping content x = 0.00−0.03 exhibited two successive magnetic transition temperature (TN) at TN1 ≈ 14 K and TN2 ≈ 10 K. TN decreased gradually with the Mn4+ content, and TN2 was not observed in the x > 0.05 samples within a temperature range of T = 5−300 K. Magnetic hysteresis loops revealed that only anti-ferromagnetic behavior occurred in the low-doped samples (x = 0.00−0.03), and the coexistence of ferromagnetism and anti-ferromagnetism was observed in the high-doped samples (x = 0.05−0.10). Besides, the x = 0.10 sample had a maximum magnetization of 5.98 emu/g. This study provides basic experimental data for investigating the relationship between the microstructure and magnetic properties of CuFeO2 systems.

Synthesis and Magnetic Characterization of La&lt;sub&gt;2-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Sr&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;CuO&lt;sub&gt;4&lt;/sub&gt; Nanoparticles

Non-doped and strontium-doped lanthanum cuprates (La2CuO4 (LCO) and La1.85Sr0.15CuO4 (LSCO15)) in nano-sized particles were synthesized by the chemically dissolved technique employing HNO3 as the dissolving agent. The structural and magnetic properties were investigated by using an x-ray diffraction (XRD) apparatus and a superconducting quantum interference device (SQUID) magnetometer, respectively. The XRD patterns of LCO and LSCO15 show the formation of the single phase without impurities after the calcinations in air at 1100°C for 15 h and the post-annealing in oxygen at 800 °C for 24 h. The average crystallite sizes of LCO and LSCO15 samples were in a range of around 100 nm confirming nano-sized particles. The LCO and LSCO15 nanoparticles exhibit superconductivity at the superconducting (SC) transition temperature, Tc, of 23 K and 38 K, respectively. The magnetization curve measurements have revealed that both samples show the appearance of ferro- and dia-magnetic behavior at room temperature and the appearance of superconductivity at low temperatures. This result may indicate the coexistence of ferromagnetism and superconductivity below Tc in the nano-sized cuprates.

Coexistence of Weak Ferromagnetism and Paramagnetism in T’-Pr&lt;sub&gt;2-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Ce&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;CuO&lt;sub&gt;4+α-δ &lt;/sub&gt;Nanoparticles

The coexistence of ferromagnetism and paramagnetism of T’-Pr2-xCexCuO4+α-δ (T’-PCCO) nanoparticles with x = 0, and 0.10 have been studied intensively in the normal state. All samples were synthesized by a chemically dissolved method using HNO3 as a dissolving agent. The calcination process was performed at 1000°C for 15 h in air and followed by reduction annealing at 700°C in argon atmosphere for 10 h. All samples were first characterized by an x-ray diffraction (XRD) measureemnts followed by Rietveld and Maximum Entropy Method (MEM) analyseis. The result confirms the Ce-dependence and reduction annealing effect on the electron density at around the Cu site. The magnetic characterization was performed by using vibration sample magnetometer (VSM) indicating weak ferromagnetic properties at x = 0 and dominant paramagnetic properties at x = 0.10 at room temperature. Moreover, the weak ferromagnetic feature seems to remain after the annealing process. This signifies the coexist of weak ferromagnetism and paramagnetism at the normal state due to a number of oxygen vacancies in the crystal structure.

Coexistence of Ferromagnetism and Paramagnetism in Graphene with Boron-vacancy Complex

Defect induced magnetism in a single layer graphene with Boron-vacancy complex is studied using highly precise ab initio full-potential linearized augmented plane wave (FLAPW) method. From energetics, it is most stable when Boron and vacancy are the nearest neighbor. Furthermore, we propose both paramagnetic and magnetic states, with negligible energy difference, can coexist in defected graphene. The k resolved band structure reveals that the magnetism is mainly from different occupation of very localized impurity bands. Moreover, calculated STM image associated with defect is presented to provide some hint in experimental verifications.

Investigation on the preference of the martensitic structure in off-stoichiometric Ni-Mn-In alloys by first-principle calculations

In order to figure out the effect of excess Mn atoms on the preference of the martensite structure, the tetragonal distortion was employed in the off-stoichiometric Ni-Mn-In alloys with different Mn contents using the Extra Muffin-tin Orbital combined with the Coherent Potential Approximation (EMTO-CPA). The calculations were conducted with the optimization of the magnetic structure, where the stoichiometric Ni2MnIn alloy was served as the reference. The ground state-energy-resolved tetragonal distortion reveals that the excess Mn changes the preferred stable structure from the perfect cubic L21 structure to the tetragonally distorted structures. The stable tetragonal structure could shift from c/a < 1 to c/a > 1 with the increase of the Mn concentration. Furthermore, to find out more accurate preference of the martensite structure, the formation energies were calculated using different relaxation methods. The chemical disorder method with a 4-atom cell was used for the tetragonal L10 structure by the EMTO-CPA, and the supercell method with a 96-atom cell was applied for the orthorhombic structure by the VASP at 0 K in their ferromagnetic state. The results show that, compared with the perfect cubic L21 structure of the stoichiometric Ni2MnIn alloy, the orthorhombic structure is preferred at lower Mn concentrations (between 29 at. % and 40 at. %), whereas the tetragonal L10 structure is more stable at the higher Mn concentrations (above 40 at. %). Moreover, the effect of the Mn concentration on the magnetic properties was also studied. With the increase of excess Mn content, the magnetic moment increases linearly in the ferromagnetic cubic L21 structure, whereas it varies in the two kinds of martensite. The excess Mn could lead to the coexistence of ferromagnetism and antiferromagnetism. The appearance of the antiferromagnetism could be attributed to the Ni-Mn antiferromagnetic interaction in the tetragonal martensite.

Physical and magnetic properties of (Ce1−xNdx)3Al (x = 0.3): Coexisting ferromagnetism and Kondo effect

By means of detailed electrical, magnetic and thermal studies, we illustrate the unusual coexistence of ferromagnetism and Kondo effect for the critical Nd concentration of x = 0.3 in (Ce1−xNdx)3Al. Magnetic susceptibility χ(T) confirms the ferromagnetic character with TC ~ 8 K along with Kondo effect which appears below 35 K. Non-saturating nature of magnetization (M (H)) and Hall resistivity (ρxy (H)) isotherms indicates the Kondo screening. Resistivity ρ (T) curves exhibit nonlinear temperature dependence; ~Tn (0.48 < n < 1) below 40 K. Higher values of Sommerfeld coefficient γ (=321 mJ/Ln - mol-K2) and Seebeck coefficient S (T) as compared to the parent compound Ce3Al and other Nd doped compounds in the series (Ce1−xNdx)3Al (x = 0–1) indicate the role of critical Nd concentration namely, 0.3 in the anomalous behavior. The high value of γ observed in this critical concentration is unusual for a ferromagnetic compound and appears to be partially contributed by the exchange interaction due to Nd doping along with the Kondo hybridization. Suppression of γ value with field corroborates with the resistivity data i.e., weakening of Kondo screening. Like in the case of Ce3Al, Nd doped compound also shows structural transition attributed to the valence fluctuation of Ce. χ (T), ρ (T), S (T) and 4f part of specific heat, C4f (T) data show peculiar temperature dependence and confirm the non-Fermi liquid behavior due to Ce (4f) – Nd (4f) interaction. Change in the relative strengths of Coulomb repulsion (U) and Kondo hybridization (Vfd) is found to determine the temperature dependence of thermal and thermoelectric behavior in this compound.

Effect of Transition Metal Ion Doping on the Microstructure, Defect Evolution, and Magnetic and Magnetocaloric Properties of CuFeO2 Ceramics

The polycrystalline CuFeO2 (CFO) and CuFe1-xMxO2 (M = Ti, Hf, Zr, M-CFO) samples are synthesized by solid-state reaction method. The doping effect of tetravalent nonmagnetic transition metal M4+ ions on the microstructure, defect evolution, and magnetic and magnetocaloric properties of the CFO system are comparatively investigated. The substitution of M4+ for Fe3+ increases lattice parameters, changes the bond length of Fe/Cu-O and bond angle of Fe-O-Fe, and improves the microstructure to some extent. Positron annihilation spectroscopy results indicate that M4+ doping induces the agglomeration of small-sized vacancy defects manifested as the increase in vacancy-type defect size and the suppression of inherent defect concentration. Magnetic measurements show that the antiferromagnetic stability of CFO system is clearly affected by M4+ doping, and Ti4+ doping has a more noticeable impact than Hf4+ and Zr4+ doping. Meanwhile, the coexistence of weak ferromagnetism and antiferromagnetism is detected in all doped samples, while Ti-doped system exhibits extraordinary magnetic properties. Especially for Ti-CFO2 (x = 0.03) sample, the maximum magnetization reaches as high as 11.81 emu/g at 0.5 T, which enhanced one order of magnitude than that of undoped CFO. Isothermal M-H data at different temperatures show that entropy change (ΔSM) and refrigerant capacity (RC) for CFO and M-CFO2 samples are significantly weakening with M4+ substitution in bulk CFO. The maximum ΔSM = 4.79 J·kg−1 K−1 and RC = 12.79 J·kg−1 for undoped CFO are obtained near the transition temperature TN2 = 12 K, with the applied fields up to 6 T. The possible reasons for the above observations are discussed in detail.