Effect of Co and Mg doping at Cu site on structural, magnetic and dielectric properties of α-Cu2V2O7

We have studied the effect of doping of both magnetic (Co) and nonmagnetic (Mg) ions at the Cu site on phase transition in polycrystalline α-Cu2V2O7 through structural, magnetic, and electrical measurements. x-ray diffraction reveals that Mg doping triggers an onset of α- to β-phase structural transition in Cu2−xMgxV2O7 above a critical Mg concentration xc=0.15, and both the phases coexist up to x=0.25. Cu2V2O7 possesses a non-centrosymmetric(NCSM) crystal structure and antiferromagnetic (AFM) ordering along with a non-collinear spin structure in the α phase, originated from the microscopic Dzyaloshinskii-Moriya(DM) interaction between the neighboring Cu spins. Accordingly, a weak ferromagnetic behavior has been observed up to x=0.25. However, beyond this concentration, Cu2−xMgxV2O7 exhibits complex magnetic properties. A clear dielectric anomaly is observed in α-Cu2−xMgxV2O7 around the magnetic transition temperature, which loses its prominence with the increase in Mg doping. The analysis of experimental data shows that the magnetoelectric coupling is nonlinear, which is in agreement with the Landau theory of continuous phase transitions. Co doping, on the other hand, initiates a sharp α to β phase transition around the same critical concentration xc=0.15 in Cu2−xCoxV2O7 but the ferromagnetic behavior is very weak and can be detected only up to x=0.10. We have drawn the magnetic phase diagram which indicates that the rate of suppression in transition temperature is the same for both types of doping, magnetic (Co) and nonmagnetic (Zn/Mg).

Effect of Mn Substitution Fe on the Formability and Magnetic Properties of Amorphous Fe88Zr8B4 Alloy

Elemental substitution is commonly used to improve the formability of metallic glasses and the properties of amorphous alloys over a wide compositional range. Therefore, it is essential to investigate the influence of element content change on the formability as well as magnetic and other properties. The purpose is to achieve tailorable properties in these alloys with enhanced glass forming ability. In this work, the glass-forming ability (GFA) and magnetic properties of the minor Mn-substituted Fe88Zr8B4 amorphous alloy were investigated. The addition of Mn improving the amorphous forming ability of the alloy. With the addition of Mn, the magnetic transition temperature, saturation magnetization and the magnetic entropy changes (−ΔSm) peaks decreased simultaneously, which is possibly caused by the antiferromagnetic coupling between Fe and Mn atoms. The dependence of −ΔSmpeak on Tc displays a positive correlation compared to the −ΔSmpeak- Tc−2/3 relationship proposed by Belo et al.

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.

Superconductivity-driven ferromagnetism and spin manipulation using vortices in the magnetic superconductor EuRbFe4As4

Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent phenomena, such as the reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (Tm), highlighting the impact of magnetism on superconductivity. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-critical-temperature (high-Tc) magnetic superconductor EuRbFe4As4. Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism below Tm, neutron diffraction and magnetization experiments show a ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the direction of the Eu2+ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors.

Thermomagnetic Correlation in La0.85-xBixNa0.15MnO3 Soft Ferromagnet due to Nonmagnetic Bi3+ Substitution

We report the structural, magnetic, and magnetocaloric properties of Bismuth (Bi)-substituted manganite La0.85-xBixNa0.15MnO3 (x=0, 0.1, 0.2, 0.25, and 0.3). X-ray diffraction data implicates the rhombohedral structure with $$ R\overline{3}c $$ R 3 ¯ c space group. Bi2O3 has helped in ensuring phase pure, densified compounds even at low sintering temperature and hence avoiding the evaporation of volatile sodium. The increase in grain size and decrease in magnetic transition temperature (TC) are due to the Bi chemical activity and electronic structure. The samples have shown indirect magnetic transformation from soft ferromagnet to canted ferromagnet/antiferromagnet with Bi. Griffiths phase-like behavior in the inverse magnetic susceptibility was observed for x=0.1; with further increase in Bi, the samples are found to develop the antiferromagnetic competing phase. The phenomenological model was used to model the thermomagnetic behavior of all the samples. The sample with x=0.1 shows an increase in magnetic entropy change upon Bi substitution and the maximum of magnetic entropy change is seen at 275K emphasizing its potential in room temperature magnetic refrigeration.

Ferrimagnetic Half-Metallicity of the New Quaternary Heusler Alloy CoCrScIn: FP-LAPW Method

The structural, electronic, elastic and magnetic properties of CoCrScIn were investigated using first principle calculations with applying the full-potential linearized augmented plane waves (FP-LAPW) method, based totally on the density functional theory (DFT). After evaluating the results, the calculated structural parameters reveal that CoCrScIn compound is stable in its ferrimagnetic configuration of the type-III structure. The mechanical properties show its brittle and stiffer behavior. The formation energy value showed that CoCrScIn can be experimentally synthesized. Additionally, the obtained band structures and density of states (DOS) reflect the half-metallic behavior of CoCrScIn, with an indirect bandgap of 0.43[Formula: see text]eV. The total magnetic moment of 3[Formula: see text][Formula: see text] and half-metallic ferrimagnetic state are maintained in the range 5.73–6,79 Å. The magnetic moment especially issues from the Cr-[Formula: see text] and Co-[Formula: see text] spin-polarizations. Furthermore, the calculations of Curie temperature reveal that CoCrScIn has high magnetic transition temperature of 836.7[Formula: see text]K.

Tuning magnetic and magnetocaloric properties of Pr0.6Sr0.4MnO3 through size modifications

Particle size as an effective tool for controlling the magnetic and magnetocaloric properties of Pr0.6Sr0.4MnO3 samples has been studied. In the present work, a direct influence of particle size on the magnitude of magnetization and magnetic transition temperature, TC, can be seen. The TC drops from 309 to 242 K, while the saturation magnetization (MS) decreases from 3.6 to 0.5 μB/f.u. as the particle changes from 120 to 9 nm. Concurrently, coercivity (HC) exhibits a drastic rise emphasizing the enhanced surface disorder in the nanoparticles. Another interesting observation is in the magnetic entropy change, ΔS, which though decreases in magnitude from 5.51 to 3.90 J/Kg-K as particle size decreases from 120 to 30 nm, but the temperature range of ΔS (i.e., relative cooling power, RCP) increases from 184.33 to 228.85 J/Kg. Such interplay between magnitude and wider temperature range of ΔS, which can be fine-tuned by particle size, provides an interesting tool for using surface spin disorder, as a control mechanism in modifying physical properties.

Magnetoelectric Multiferroicity and Magnetic Anisotropy in Guanidinium Copper(II) Formate Crystal

Hybrid metal-organic compounds as relatively new and prosperous magnetoelectric multiferroics provide opportunities to improve the polarization, magnetization and magneto-electric coupling at the same time, which usually have some limitations in the common type-I and type-II multiferroics. In this work we investigate the crystal of guanidinium copper (II) formate [C(NH2)3]Cu(HCOO)3 and give novel insights concerning the structure, magnetic, electric and magneto-electric behaviour of this interesting material. Detailed analysis of crystal structure at 100 K is given. Magnetization points to the copper (II) formate spin-chain phase that becomes ordered below 4.6 K into the canted antiferromagnetic (AFM) state, as a result of super-exchange interaction over different formate bridges. The performed ab-initio colinear density functional theory (DFT) calculations confirm the AFM-like ground state as a first approximation and explain the coupling of spin-chains into the AFM ordered lattice. In versatile measurements of magnetization of a crystal, including transverse component besides the longitudinal one, very large anisotropy is found that might originate from canting of the coordination octahedra around copper (II) in cooperation with the canted AFM order. With cooling down in zero fields the generation of spontaneous polarization is observed step-wise below 270 K and 210 K and the effect of magnetic field on its value is observed also in the paramagnetic phase. Measured polarization is somewhat smaller than the DFT value in the c-direction, possibly due to twin domains present in the crystal. The considerable magneto-electric coupling below the magnetic transition temperature is measured with different orientations of the crystal in magnetic field, giving altogether the new light onto the magneto-electric effect in this material.

Tracing Ti-rich titanomagnetite oxidation with low-temperature magnetic measurements

<p>Ti-rich titanomagnetite is a primary magnetic mineral in submarine basalts, as well as in some terrestrial volcanic rocks. On geological timescale, it undergoes a slow oxidation forming titanomaghemites. This natural process may be modeled to some extent by a prolonged annealing at moderately elevated temperatures. We test this by treating at 355°C for 4, 40, 110, and 375 hours a sample of submarine basalt containing titanomagnetite of approximate TM46 composition with Curie temperature of 205°C. To characterize the oxidation products emerged during annealing, we have carried out magnetic measurements between at cryogenic temperatures between 1.8 K and 300 K and at high temperatures up to 700°C.</p><p>Temperature dependences of magnetic susceptibility measured in an argon atmosphere reveal that annealing for 4 hours already leads to the formation of new magnetic phases (Phases 1 and 2 thereafter) with Curie temperatures of 420°C and 590°C, respectively. At the same time, a phase close to the initial titanomagnetite still remains in a noticeable amount, although its Curie point also shifts towards higher temperatures. Upon further annealing, the initial titanomagnetite completely disappears, the Curie temperature of Phase 1 increases, reaching 500°C after 375 hours, and the Curie temperature of Phase 2 remains practically unchanged. Phase 1 appears unstable to heating to 700°C in argon atmosphere. In samples annealed for up to 110 hours, Phase 1 disappears on cooling, and a phase with the same Curie temperature as the initial titanomagnetite reemerges. In the sample annealed for 375 hours, traces of Phase 1 are still visible in the cooling branch of the susceptibility vs. temperature curve, and the Curie temperature of the reemerged initial-like phase is 250°C. The newly formed Phase 2 remains stable when heated to 700°C in argon.</p><p>Effect of prolonged annealings is clearly seen in low-temperature magnetic properties. In the fresh sample, about one quarter of magnetization acquired at 1.8 K is demagnetized by 5 K. This feature holds for the annealed samples as well. The titanomagnetite phase in the fresh sample manifests itself in a magnetic transition at 58 K. Below this temperature, the FC and ZFC curves sharply diverge, as previously observed for titanomagnetites of intermediate composition. For the annealed samples, the shape of ZFC and FC curves and the ratio between them remain generally similar to those observed for the fresh sample, but there are also several differences. The magnetic transition temperature shifts to ~45 K, while the curves’ shape above the transition changes from concave-up to concave-down. RT-SIRM cycle to 1.8 K in zero field for the fresh sample has a characteristic convex shape and is almost reversible. Magnetization at 1.8 K is about 20% higher than the initial value at 300 K, and magnetization loss after the cycle is only 2-3%. The shape of RT-SIRM cycles changes progressively with increasing annealing time, the degree of irreversibility increasing to ~30% for the sample annealed for 375 hours. </p><p>This study is supported by Russian Foundation of the Basic Research, grants 19-05-00471 and 20-05-00573.</p>