Complex Magnetic Behavior Research Articles

Growth and magnetic properties of epitaxial thin films of the [formula omitted]-MAX phase (Mn[formula omitted]Sc[formula omitted])[formula omitted]GaC

i-MAX phases are quaternary variants of the nanolaminated MAX phases, with additional in-plane ordering of the M atoms. The combination of in-plane and out-of-plane ordering potentially gives rise to complex magnetic behaviour. The i-MAX phase (Mn2/3Sc1/3)2GaC has been synthesized in epitaxial thin film form on three different substrates, SiC-4H(001), MgO(111) and Al2O3(0001), by magnetron sputtering using elemental targets. Structural characterization by x-ray scattering and scanning transmission electron microscopy confirms the phase on all three substrates, although the highest crystal quality is obtained on SiC-4H(001). High-resolution images reveal the distinctive i-MAX structure, which is orthorhombic of space group Cmcm. Magnetic characterization reveals that the ground state is most likely antiferromagnetic. This confirms previous theoretical calculations which predicted an antiferromagnetic ground state and establishes the (Mn2/3Sc1/3)2GaC i-MAX phase as a potential candidate for antiferromagnetic spintronic applications.

B-site ordered and disordered phases in A-site columnar-ordered quadruple perovskites Nd2MnMn(Mn4−xSbx)O12

Solid solutions Nd2MnMn(Mn4−xSbx)O12, belonging to the A-site columnar-ordered quadruple perovskite subfamily A2A′A′′B4O12 and prepared by a high-pressure, high-temperature method at about 6 GPa and about 1700 K, were investigated in a compositional range of 0.2 ≤ x ≤ 2.0. Crystal structures were studied using synchrotron powder X-ray diffraction. Two regions with different cation orders in the B sublattice were found: a narrow region of 0.8 ≤ x ≤ 1.0 had a B-site disordered structure with space group P42/nmc (No. 137), and a wider region of 1.6 ≤ x ≤ 2.0 had a B-site rock-salt-ordered structure with space group P42/n (No. 86). Small anti-site disorder of Nd and Mn was detected among the A, A′, and A′′ sites. In the B-site rock-salt-ordered structures, one B site was solely occupied by Mn, the second B′ site had a mixture of Sb and Mn (for x < 2). The samples showed complex magnetic behavior with two ferrimagnetic transitions. TC1 monotonically increased (from 66 K to 75 K) and TC2 was almost constant (about 6–7 K) for 0.8 ≤ x ≤ 1.0. TC1 monotonically decreased (from 77 K to 63 K) and TC2 monotonically increased (from 19 K to 39 K) for 1.6 ≤ x ≤ 2.0. There was evidence for the third magnetic transition in the 1.7 ≤ x ≤ 2.0 samples, and TC3 increased from 13 K to 20 K with increasing x.

Osmium(III) Acetylacetonate and Its Missing Polymorph: A Magnetic and Structural Investigation.

Despite the potential for their application, the magnetic behavior of complexes containing 4d and 5d metal ions is underexplored, evidencing the need for benchmark multi-technique studies on simple molecules. We report here a structural and magnetic study on osmium(III) acetylacetonate [Os(acac)3]. X-ray single crystal diffraction did not allow us to determine the structure of the β-polymorph of [Os(acac)3]. The combined magnetic (dc magnetic measurements on powder and cantilever torque magnetometry on single crystal) and spectroscopic (electron paramagnetic resonance, EPR) characterization is here used to provide further evidence that its structure is indeed the one of the orthorhombic "missing polymorph", analogous to the ruthenium(III) derivative. Our study shows that all acetylacetonate complexes of the eighth group of the periodic table show dimorphism and are isomorphic. The EPR characterization allowed the experimental assessment of the easy axis nature of the ground doublet and the determination of the first hyperfine coupling in an osmium complex. Torque magnetometry, applied here for the first time on an osmium-based molecule, determined the orientation of the easy axis along the pseudo C3 axis of the complex. Ac magnetometric measurements revealed in-field slow relaxation of the magnetization further slowed by the suppression of dipolar fields via magnetic dilution in the isostructural gallium(III) analogue.

Unveiling complex magnetic behaviour and effective photo-Fenton catalytic activity in the mixed phases of spinel and wurtzite structures of Fe-incorporated ZnO nanocrystals

A comprehensive exploration was conducted on the structural features, optical bandgap, magnetic characteristics and photo-Fenton catalytic activity of chemically synthesized Fe-substituted ZnO nanocrystals. Previous studies have demonstrated that undoped ZnO adopts a hexagonal wurtzite structure. X-ray powder diffraction analysis disclosed the persistence of the wurtzite hexagonal structure in 1 % Fe-incorporated ZnO, while the presence of a secondary cubic phase of spinel type structures (ZnFe2O4) emerged in the ZnO lattice with Fe content ≥ 3 %. Remarkably, the proportion of the secondary phase is systematically increased from 2.75 % to 17.90 % as the Fe content was raised from 3 % to 10 %. Microscopy analysis unveiled hexagonal, spherical, and rod-like structures across all nanocrystals. Selected area electron diffraction patterns further confirmed the coexistence of cubic and hexagonal phases. Raman spectroscopy indicated a decline in crystalline quality and the introduction of defects and disorder in the host lattice due to Fe integration. The absorption spectra were taken to assess the impact of Fe substitution on the optical properties and revealed a decreasing trend in the optical bandgap from 3.23 to 3.21 eV and 2.21–2.05 eV with rising Fe content. The first band gap is related to the ZnO and the latter is the optical band gap of ZnFe2O4. The photoluminescence plots displayed near band edge emissions as well as visible emissions, which intensified with increased Fe-doped nanocrystal concentrations. X-ray photoelectron spectroscopy analysis affirmed the integration of Fe2+ and Fe3+ cations into the ZnO matrix. Thorough magnetic investigation uncovered complex magnetic behaviour attributed to the emergence of a secondary spin glass-like phase within the weak ferromagnetic ZnO host. The co-existence of two phases containing Fe2+ and Fe3+ ions enhanced the photo-Fenton catalytic activity, leading to the complete decomposition of various organic pollutants such as methylene blue and crystal violet. The photocatalytic test also showed the ZnO co-hosting ZnFe2O4 had a decolouration efficiency of 80.62 % and 77.88 % for methyl orange and thymol blue dyes. The coexistence of two phases in Fe-incorporated ZnO nanocrystals reveals complex magnetic behaviour and enhanced photo-Fenton catalytic activity. This finding holds potential for designing innovative materials applicable in futuristic spintronics devices and waste water treatment methodologies.

A complex magnetic study: evidence of spin-glass transition below long-range magnetic ordering and its correlation with renormalization of phonon modes

In this paper, we report a complex magnetic behavior arising due to the interplay of three active magnetic cations (Nd/Sm, Co and Ir), forming 3d-5d-4f magnetic sublattices. The B-site ordered double perovskites Nd2CoIrO6and Sm2CoIrO6were successfully prepared by conventional solid-state method. Detailed structural analysis revealed that both samples crystallized in monoclinic structure with P21/n (No.-14) space group. X-ray photoelectron spectroscopy analysis confirms the presence of multiple oxidation states of Ir (i.e. Ir4+and Ir5+). Both samples show a paramagnetic-ferrimagnetic (TFiM) transition around 100 K, additionally, a low temperature transition is observed at around 10 K in the SCIO sample. This FM-like behavior of the samples is attributed to the antiparallel alignment of the Co2+and Ir4+spins, resulting in FiM ordering. The ac susceptibility analysis confirms a spin glass type transition just below the long-range ordering temperature in NCIO sample, The obtained characteristic flipping time of a single spin from both the law (Power law and Vogel-Fulcher law) and nonzero Vogel-Fulcher temperature (T0≃ 89.1 K) further verified the existence of cluster spin-glass behavior below the ordering temperature. The temperature evolution of phonon modes (up to 4 K) suggests that the phonon mode above the magnetic ordering temperature is mainly governed by the lattice degrees of freedom; notable renormalization of the mode frequency below the ordering temperature is due to the coupling of lattice with the underlying magnetic degrees of freedom.

Magnetic properties of Co1-xFexCr2S4 (x = 0–0.4) solid solutions

The magnetic properties of the Co1-xFexCr2S4 solid solutions for compositions adjacent to CoCr2S4 were investigated using various techniques, including magnetization measurements and AC susceptibility. The results revealed that substituting Fe for Co in the CoCr2S4 compound led to changes in the magnetic behavior, such as the presence of ferrimagnetic ordering and the emergence of a cluster spin glass phase. The study found that the temperature of the ferrimagnetic transition (TC) decreased with increasing Fe concentration, indicating the influence of iron on the magnetic properties of the solid solutions. Additionally, the discovery of a cluster spin glass phase for specific compositions (x = 0, 0.1, 0.2, 0.4) suggests complex magnetic behavior in these materials. In summary, the study offers valuable insights into the magnetic properties of Co1-xFexCr2S4 solid solutions and highlights the potential for tuning their magnetic behavior through compositional variations.

Spin flop transitions and complex magnetic behaviour in CoMoO4 powders and [formula omitted]-CoMoO4 thin films

Magnetic measurements were made on α-CoMoO4 powder and β-CoMoO4 thin film samples. α-CoMoO4 powder showed antiferromagnetic ordering below 13 K and two sharp spin flop transitions with complete magnetic saturation after the second transition (>5 T). A magnetic phase diagram for α-CoMoO4 was constructed, revealing three low-temperature magnetic phases: an antiferromagnetic phase at low field, an intermediate spin-flop phase, and a paramagnetic phase at high field. Two well-defined magnetisation plateaus were observed either side of the spin-flop phase: the first occurred with a moment per Co ion of 1/3 of spin saturation (where Co moments are completely aligned to the applied magnetic field), whereas the second occurred at a moment per Co ion matching calculations for spin saturation (3 μB per Co). No geometric origin for this factor of 1/3 could be found. Hysteresis was observed around the first spin-flop transition, indicating the presence of spin canting or magnetic domains under an applied field. The first successful fabrication of CoMoO4 thin films was achieved via RF magnetron sputtering, yielding β phase films which remain in the β phase upon cooling. The β-CoMoO4 thin films demonstrated antiferromagnetic ordering below 10 K. While two spin-flop transitions are seen in the β phase films (with a hysteresis around the first), spin saturation is not reached in fields up to 6 T, suggesting the existence of a third spin reorientation at higher field. A magnetic phase diagram was also constructed for the β-CoMoO4 film, which demonstrated the same three low-temperature magnetic phases, though with lower critical fields and transition temperatures. Comparisons with isostructural Ni and Mn molybdates showed that the key differences in the α and β phases arise from the different coordination of the Mo tetramers, indicating differences in magnetic properties in both phases arise from variations in the inter-tetramer exchange coupling.

Complex magnetic interactions and critical behavior analysis in quaternary CoFeV0.8Mn0.2Si Heusler alloy

We investigate the magnetic behavior and critical exponents of quaternary CoFeV0.8Mn0.2Si Heusler alloy to understand the interactions across the Curie temperature (TC). The Rietveld refinement of the x-ray diffraction pattern with the space group F4¯3m confirms a single-phase cubic Y-type crystal structure. The magnetic susceptibility χ(T) data show a ferromagnetic nature with a second-order phase transition from paramagnetic to ferromagnetic at 446±1 K. The saturation magnetization at 5 K is found to be 2.2 μB/f.u., which is close to the Slater–Pauling rule and indicates its half-metallic nature. The values of asymptotic critical exponents (β, γ, and δ) and the TC are extracted through detailed analytical analysis including the modified Arrott plot, the Kouvel–Fisher (K–F) method, and the Widom scaling relation. Interestingly, the estimated values of β=0.369 and γ=1.445 closely approximate the theoretical values of the 3D Heisenberg model across the TC and validate the second-order thermodynamic phase transition. The obtained exponents lead to the collapse of renormalized isotherms, represented by the relationship between the magnetization (m) and the applied magnetic field (h), into two distinct branches above and below the TC, which validates the reliability of the analysis. Furthermore, these exponents suggest that the spin interaction follows a decay pattern of J(r)∼r−4.99, indicating a short-range magnetic ordering, akin to the itinerant-electron 3D Heisenberg model.

Magnetic properties and cryogenic magnetocaloric effect of pyrochlore structure RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds

Magnetic refrigeration technology is regarded as one of the ideal solutions for cryogenic refrigeration, while magnetocaloric materials are the crucial ones. A series of polycrystalline RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds were prepared by a simple one-step solid-phase reaction method in the atmosphere. The crystal structure, magnetic properties, and magnetocaloric effect (MCE) of these compounds were systematically investigated. Crystallographic research indicates that these compounds crystallized in a pyrochlore structure. Meanwhile, magnetic measurements illustrate that this class of pyrochlore oxides is highly frustrated magnetic materials and exhibits complex magnetic behavior. In addition, under the field change of 0–1 T, the values of the maximum magnetic entropy change (−ΔSMmax) and the refrigeration capacity are calculated to be 0.9 and 5.8 J/kg for Gd2Ti2O7, 9.0 and 32.9 J/kg for Tb2Ti2O7, 9.9 and 29.9 J/kg for Ho2Ti2O7, respectively. Therefore, RE2Ti2O7 (RE = Tb and Ho) pyrochlores exhibit excellent MCEs under low magnetic fields, providing candidate materials for the application of cryogenic magnetic refrigeration technology.

Synthesis, crystal structure, and physical properties of the Eu(ii)-based selenide semiconductor: EuHfSe3

A novel Eu(ii)-containing chalcogenide, EuHfSe3, has been synthesized with a structure that is found to exhibit intriguing and complex low-temperature magnetic behavior.

Spin-phonon coupling driven magnetodielectric effect in low-dimensional complex magnetic BaGdFeO4 system

In this report, we have investigated the detailed magnetodielectric properties associated with spin-phonon coupling in the BaGdFeO4 polycrystalline compound, X-ray diffraction study confirms the orthorhombic crystal structure with a space group of Pnma. The DC magnetization measurements indicate the complex magnetic behavior with multiple magnetic transitions at TN1 = 62 K and TN2 = 31 K. In the field-dependent magnetization study, field-induced metamagnetic transitions and their temperature dependence have been attributed to the competing magnetic interactions of two magnetic sub-lattices with rare-earth (Gd3+) and Fe3+ magnetic spins. Dielectric measurements have revealed the correlation of observed dielectric anomalies with the magnetic transitions. The frequency-independent and magnetic field-dependent dielectric anomalies, along with the corresponding magnetic transitions, thus corroborate the subtle magnetodielectric coupling studied by temperature-dependent magnetodielectric measurements. We discuss possible origins for the magnetodielectric behavior in terms of weak spin-phonon interactions, as confirmed by the temperature-dependent Raman spectra measurements.

Complex magnetic behaviour and photocatalytic response in narrowed band gap NiO nanoparticles synthesized by novel Lepidagathis ananthapuramensis leaf extract

The present work focussed on the detailed investigation on structural, morphological, optical, photocatalytic, and magnetic properties of NiO nanoparticles (NPs) derived by a novel Lepidagathis ananthapuramensis leaf extract. The structural information using X-ray powder diffraction and Raman spectroscopy method indicates a single phase NiO hexagonal crystal structure for the sample calcined at ≥ 600 °C. Field emission scanning electron microscopy and high-resolution transmission electron microscopy studies noticed the various morphologies. UV–Visible, photoluminescence, and X-ray photoelectron spectroscopy confirmed the presence of both Ni2+ and Ni3+ ions with the narrowed band gap. Thorough magnetic studies indicate the existence of antiferromagnetic, ferromagnetic and superparamagnetic nature of NiO NPs. The photocatalytic activity of NiO NPs for the photocatalytic degradation of methylene blue dye in the presence of sunlight showed considerable results. This study can help us to deliver the wide range of properties which can be utilised in the field of magnetism and photocatalysis.

An abrupt spin reorientation transition and complex magnetic behavior in Dy0.7Nd0.3FeO3 single crystal

Discovery of novel functional materials is the cornerstone of spintronics and other emerging technologies. We report an abrupt spin reorientation transition from Γ4(Gx, Ay, Fz) to Γ2(Fx, Cy, Gz) in Dy0.7Nd0.3FeO3 single crystal that combines the Morin transition characteristics of DyFeO3 and the Γ2 spin configuration of NdFeO3. The Γ2 transition along a-axis has two critical temperatures corresponding to the rotation of Dy3+/Nd3+ spins and the spin reorientation of Fe3+ sublattice, respectively. At 5 kOe, the Γ4–Γ2 transition becomes a continuous one beginning at 27.3 K and the Γ4 spin configuration re-emerges at 7.8 K unexpectedly. The b-axis exhibits non-zero magnetization and Nd-related transition that disappear at 10 kOe at TSR due to a structural phase transition. The anomalous change in the mode frequencies and linewidth near the transition temperature observed in Raman spectroscopy reveals clear evidence of spin–phonon coupling in Dy0.7Nd0.3FeO3 single crystal.

Low-temperature magnetic and magnetocaloric properties of orthorhombic DyNiSn

In this work, magnetic and magnetocaloric properties of antiferromagnetic (AFM) DyNiSn compounds which shows complex magnetic behavior at low-temperatures are investigated. Performed magnetic and specific heat measurements showed that except transition to the antiferromagnetic state at TN = 7.7(1) K, there are two more changes in the magnetic structure at T1 = 5.6(1) K = and T2 = 2.6(1) K. The magnetocaloric properties of the DyNiSn were determined indirectly from magnetic and specific heat measurements. DyNiSn shows normal and inverse magnetocaloric effect peaks at ∼9 K and ∼5 K, respectively. The maximum values of the magnetic entropy change (ΔSm), relative cooling power (RCP), and temperature averaged entropy change (TEC(5)) evaluated from magnetic measurements and for magnetic field change of 5 T are −8.0(1) Jkg−1K−1, 130(9) Jkg−1, and 8.7(1) Jkg−1K−1, respectively.

Unusual magnetic properties of (Sr, Mn)-substituted BiFeO3 near the polar/antipolar phase boundary

Investigations of the crystal structure and magnetic properties of the Bi0.85Sr0.15Fe1-xMnxO3 (0.1 ≤ x ≤ 0.5) ferromanganites were carried out. The materials maintain the single-phase polar R3c structure of the pure bismuth ferrite up to x = 0.35 (a further increase in the Mn content stabilizes the antipolar Pnam phase), thus exhibiting the coexistence of spontaneous polarization and magnetic order over a wide range of Mn concentrations, sufficient to influence the cycloidal antiferromagnetic arrangement typical of the parent compound and contribute to the canted antiferromagnetic phase formation (at room temperature). A complex magnetic behaviour with irregular changes in remanent magnetization and coercive field suggesting the temperature-driven modification of the canted antiferromagnetic structure near the polar/antipolar phase boundary has also been found.

Coexistence of tetragonal and cubic phase induced complex magnetic behaviour in CoMn2O4 nanoparticles

CoMn2O4, known for its extensive range of applications, has been subject to limited investigations regarding its structure dependent magnetic properties. Here, we have examined the structure dependent magnetic properties of CoMn2O4 nanoparticles synthesized through a facile coprecipitation technique and are characterized using x-ray diffractometer, x-ray photoelectron spectroscopy (XPS), RAMAN spectroscopy, transmission electron microscopy and magnetic measurements. Rietveld refinement of the x-ray diffraction pattern reveals the coexistence of 91.84% of tetragonal and 8.16% of cubic phase. The cation distribution for tetragonal and cubic phases are (Co0.94Mn0.06)[Co0.06Mn1.94]O4 and (Co0.04Mn0.96)[Co0.96Mn1.04]O4, respectively. While Raman spectra and selected area electron diffraction pattern confirm the spinel structure, both +2 and +3 oxidation states for Co and Mn confirmed by XPS further corroborate the cation distribution. Magnetic measurement shows two magnetic transitions, Tc1 at 165 K and Tc2 at 93 K corresponding to paramagnetic to a lower magnetically ordered ferrimagnetic state followed by a higher magnetically ordered ferrimagnetic state, respectively. While Tc1 is attributed to the cubic phase having inverse spinel structure, Tc2 corresponds to the tetragonal phase with normal spinel. In contrast to general temperature dependent H C observed in ferrimagnetic material, an unusual temperature dependent H C with high spontaneous exchange bias of 2.971 kOe and conventional exchange bias of 3.316 kOe at 50 K are observed. Interestingly, a high vertical magnetization shift (VMS) of 2.5 emu g−1 is observed at 5 K, attributed to the Yafet–Kittel spin structure of Mn3+ in the octahedral site. Such unusual results are discussed on the basis of competition between the non-collinear triangular spin canting configuration of Mn3+ cations of octahedral sites and collinear spins of tetrahedral site. The observed VMS has the potential to revolutionize the future of ultrahigh density magnetic recording technology.

Exploring complex magnetic behavior induced by Mn in LaNiO3 perovskite

Exploring complex magnetic behavior induced by Mn in LaNiO3 perovskite

Disorder induced cluster spin glass like state in MnFeSb

Hexagonal MnSb is a ferromagnet with Curie temperature and saturation magnetization values of 587 K and 110 emu/g, respectively. In this paper, the origin of the complex magnetic behavior of a single phase MnFe0.20Sb prepared using solid-state reaction method is examined. A thorough investigation of temperature dependent magnetization and magnetic relaxation measurements reveals the presence of a glassy like phase below 15 K. AC susceptibility measurements revealed the existence of a cluster glass-like state with a freezing temperature of 18 K. The presence of competing magnetic interactions and random occupation of Fe atoms at 2d site leads the system to exhibit a cluster glass state. Furthermore, resistivity measurements indicate that the material exhibits a Kondo-like behavior below 30 K and can be attributed to the interaction of conduction electrons with localized Mn moments.

Indirect magnetic signals in Weyl semimetals mediated by a single Fermi arc

Recently, abundant transport phenomena characterizing the surface states of Weyl semimetals (WSMs) have been reported. To generate these phenomena, electrons have to complete a closed intersurface orbit. Due to the unavoidable impurities in real materials, this orbit could be destroyed by the impurity scattering, which limits the detection of the surface states in WSMs. Here, we investigate the RKKY interaction between magnetic impurities, solely mediated by a single surface band, in semi-infinite WSMs. It is found that peculiar oscillations and slowly decaying laws of the RKKY interaction can act as the signals to capture the dispersive nature of the surface states of WSMs. The underlying physics is attributed to two effects: the band-edge effect and the bending effect of the surface band, which can control the RKKY interaction individually or compete with each other to produce more complex magnetic behaviors. In addition, the band-edge effect together with the finite Fermi energy would result in another interesting oscillation with battering pattern. All the results are significantly different from that in previous literatures where surface states have to couple with bulk states (or other surface states of different spins) to generate nonzero magnetic interaction. Compared to the previous models of surface states, the model here is more practical and is helpful for the deeper understanding of the surface magnetic properties in WSMs.

An Outlook into the Magnetic and Magnetocaloric Properties of Cr1.3Fe0.7O3

Herein, the magnetic and magnetocaloric properties of Cr1.3Fe0.7O3 particles are presented. The structural and oxidation states of the samples are confirmed from the X‐ray diffraction and X‐ray photoemission spectroscopy measurements. In addition, the thermomagnetization experiments reveal the coexistence of two spin reorientation, Morin transition, as well as Néel temperature below 300 K. Such complex magnetic behavior of the system can be ascribed to the metal–ligand–metal interaction caused both by Cr3+ and Fe3+ magnetic ions. The maximum magnetic entropy change estimated from the isothermal magnetization measurements is 0.056 J kg−1 K−1 at 41 K for an external magnetic‐field change of 70 kOe.