Large Magnetic Moment Research Articles

Phase Switch Driven by the Hidden Half-Ice, Half-Fire State in a Ferrimagnet.

The notion of "half fire, half ice" was recently introduced to describe an exotic macroscopic ground-state degeneracy emerging in a ferrimagnet under the critical magnetic field, in which the "hot" spins are fully disordered on the sublattice with smaller magnetic moments and the "cold" spins are fully ordered on the sublattice with larger magnetic moments. Here, we further point out that this state has a twin named "half ice, half fire" in which the hot and cold spins switch positions. The new state is an excited state-thus hidden in the ground-state phase diagram-and is robust with respect to the interactions that destroy the half-fire, half-ice state. We demonstrate with exact results how this hidden state can drive phase switching at desirable finite temperature, even for the one-dimensional Ising model where phase transition at finite temperature is forbidden. We suggest that our findings may open a new door to the understanding and controlling of phase competition and transition in unconventional frustrated systems.

Large cryogenic magnetocaloric effect in transition metal-based double dinitrates

Exploring paramagnetic salts with weak magnetic interactions and large saturation magnetic moments is of great significance in the field of cryogenic magnetic refrigeration. In this article, the first-principles calculation is performed to predict the magnetocaloric effect (MCE) of La-transition metal-based double nitrate hydrated salts. Through the comparison of the calculation results, La2Mn3(NO3)12·24H2O (LMnN) is chosen for further research on cryogenic magnetic refrigeration. The magnetic measurements reveal a weak antiferromagnetic interaction and large saturation magnetic moment of 4.95 μB of LMnN, which are consistent with theoretical calculation results. In addition, the maximum magnetic entropy change of LMnN is calculated to be 26.61 J kg−1 K−1 under a magnetic field change of 7 T at 2.5 K, which is greater than that of another double nitrate hydrated salts La2Co3(NO3)12·24H2O (LCoN). Excellent MCE verifies the rationality of first-principles calculation and suggests that LMnN is a promising hydrated paramagnetic salt for cryogenic magnetic refrigeration.

2D Magnetic MXenes (M11-xM2x)3C2 (M1 = V, Cr; M2 = Mn, Cr): The Stability, Ordering, and Magnetic Properties.

Since their discovery in 2011, the MXene family of two-dimensional (2D) materials has attracted much interest due to its unique properties, leading to practical applications. Recently, special attention has been paid to magnetic MXenes. However, despite the great diversity of the chemical composition of MXenes, which opens up prospects for obtaining magnetic 2D materials, only a few MXenes with intrinsic magnetism have been synthesized to date. The main reason for this is the phase instability of both MXenes and their parent MAX phases. Here, we use the first-principles calculations and the cluster expansion (CE) method to analyze the thermodynamic stability of second-order MXenes (M11-x M2x)3C2 and their parent MAX phases with two transition metals (M1 = V, Cr; M2 = Mn, Cr). Our analysis allows us to identify the most stable MXene structures with possible magnetism. In the stable structures found, the electronic and magnetic properties were calculated. The effect of surface functionalization with fluorine and oxygen on the properties of the MXenes was also studied. It was found that the most promising for synthesis is (V1/3Mn2/3)3C2, which is ferromagnetic with a large magnetic moment per cell, both in bare form and with functionalization of its surface with fluorine.

Unexpected Magnetic Moments in Manganese-Doped (CdSe)13 Nanoclusters: Role of Ligands.

This study explores the enhancementin magnetic and photoluminescence properties of Mn2+-doped (CdSe)13 nanoclusters, significantly influenced by the introduction of paramagnetic centers through doping, facilitated by optimized precursor chemistry and precisely controlled surface ligand interactions. Using a cost-effective and scalable synthesis approach with elemental Se and NaBH4 (Se-NaBH4) in n-octylamine, we tailored bonding configurations (Cd-O, Cd-N, and Cd-Se) on the surface of nanoclusters, as confirmed by EXAFS analysis. These bonding configurations allowed for tunable Mn2+-doping with tetrahedral coordination, further stabilized by hydrogen-bonded acetate ligands, as evidenced by 13C NMR and IR spectroscopy. Mulliken charge analysis indicates that the charge redistribution on Se2- suggests electron transfer between surface ligands and the nanocluster, contributing to spin fluctuations. These tailored configurations markedly increased the nanoclusters' magnetic susceptibility and photoluminescence efficiency. The resulting nanoclusters demonstrated a clear concentration-dependent response in emission lifetimes and intensities upon exposure to magnetic field effects (MFE) and spin-spin coupling, alongside a large magnetic moment exceeding 40 μB at 180 K. These findings highlight the potential of these nanoclusters for magneto-optical devices and spintronic applications, showcasing their tunable magnetic properties and exciton dynamics.

Unexpected Magnetic Moments in Manganese‐Doped (CdSe)13 Nanoclusters: Role of Ligands

This study explores the enhancement in magnetic and photoluminescence properties of Mn2+‐doped (CdSe)13 nanoclusters, significantly influenced by the introduction of paramagnetic centers through doping, facilitated by optimized precursor chemistry and precisely controlled surface ligand interactions. Using a cost‐effective and scalable synthesis approach with elemental Se and NaBH4 (Se‐NaBH4) in n‐octylamine, we tailored bonding configurations (Cd‐O, Cd‐N, and Cd‐Se) on the surface of nanoclusters, as confirmed by EXAFS analysis. These bonding configurations allowed for tunable Mn2+‐doping with tetrahedral coordination, further stabilized by hydrogen‐bonded acetate ligands, as evidenced by 13C NMR and IR spectroscopy. Mulliken charge analysis indicates that the charge redistribution on Se2‐ suggests electron transfer between surface ligands and the nanocluster, contributing to spin fluctuations. These tailored configurations markedly increased the nanoclusters' magnetic susceptibility and photoluminescence efficiency. The resulting nanoclusters demonstrated a clear concentration‐dependent response in emission lifetimes and intensities upon exposure to magnetic field effects (MFE) and spin‐spin coupling, alongside a large magnetic moment exceeding 40 μB at 180K. These findings highlight the potential of these nanoclusters for magneto‐optical devices and spintronic applications, showcasing their tunable magnetic properties and exciton dynamics.

Study on High-Voltage Cathode Li-Ni-Mn Spinel Oxides with Low-Temperature Magnetism

Lithium-ion rechargeable batteries have been attracting researcher’s interest, because they are candidate to address environmental issues, especially for application to electric vehicles and stationary energy storage systems. The battery operating voltage is one of the factor affecting the energy density of battery cell, and therefore positive electrode with high operating voltage is very attracting. A typical high-voltage cathode material, LiNi0.5Mn1.5O4 is an end member of LiNixMn2-xO4 solid solution compounds (0.00<x<0.50). From the previous study, it is known that LiNi0.5Mn1.5O4 spinel is a ferri-magnetic material with large magnetic moment and high transition temperature. In this work, the compounds of LiNixMn2-xO4 (0.40<x<0.50) are studied with both low-temperature magnetism and electrochemical charge-discharging. Additionally, the correlation between electrochemical and magnetic properties is also discussed.LiNixMn2-xO4 (0.40<x<0.50) were prepared by gelation of nitrate/citrate solution, thermal decomposition at 500 ℃ and annealing under various conditions (temperature and atmosphere). Under the preparation condition at relatively low temperature (700 ℃) in oxygen atmosphere, they were single phase of cubic spinel with fine particles. The lattice parameters monotonously decreased, as x increased. The charge-discharge profiles have twin plateaus around 4.7 V, to Ni2+/Ni3+ and Ni3+/Ni4+ redox signals, with a small signal at ~4.0 V. The capacity at >4.5 V formers increased with x and that at <4.5 V was reduced. From the magnetic evaluation, the saturation magnetization at 2 K (Ms) increased with x, and simultaneously, the ferri-magnetic/paramagnetic transition temperature (Tc), evaluated from temperature dependence of the saturation magnetization, shifted higher. These results exhibited the following relation-ships (presented in Fig. 1); the capacity at >4.5 V was almost proportional to Ms, and the operating voltage was proportional to Tc. However, it was found that the magnetic response under weak magnetic field was not usual (shown in Fig. 2) and it implied two-step phase transition around Tc. The anomaly was thought to be attributed to magnetic in-homogeneity, which is very sensitive to the specimen characters. The analysis of experimental results of specimens prepared under different conditions are being carried out and then presented and discussed at the conference. Figure 1

Non-stoichimometric square sheets in RSe2−x (x ∼ 1/6) (R = Gd and Tb)

The application of optimal electron count has proven effective in predicting the existence of complex structural topologies containing electron-rich polyanionic networks, including linear and zig-zag chains, square planar structures, and simple cubic lattices of main group elements. In this study, we report the successful synthesis of a new family of magnetic compounds, RSe2−x (x ∼ 1/6) (R = Gd and Tb), using KCl flux. The resulting crystal structure of RSe2−x is tetragonal, exhibiting PbFCl-type symmetry with space group P4/nmm. Chemical composition analysis consistently reveals x ∼ 1/6, indicating chalcogen-deficient square sheets. This observation suggests that RSe2−x adheres to the 14-electron rule, as the total valence electrons per RSe2−x (x ∼ 1/6) is 14 e−. In GdSe2−x (x ∼ 1/6), the magnetic susceptibility measurement displays a lambda-shaped peak around 8 K, indicating an antiferromagnetic-type transition. However, the positive Curie–Weiss temperature (θCW) suggests the presence of an additional ferromagnetic interaction, which may result from the large magnetic moment of the Gd atoms. In contrast, TbSe2−x (x ∼ 1/6) exhibits antiferromagnetic ordering. Chemical bonding analysis also indicates that the strong Se–Se antibonding in the square net may be related to Se deficiency. Our work shed light on ellucidating the interplay between chemical rule, defects, and magnetism.

Porous Metal Phosphonate Frameworks: Construction and Physical Properties.

ConspectusPorous metal phosphonate frameworks (PMPFs) as a subclass of metal-organic frameworks (MOFs) have promising applications in the fields of gas adsorption and separation, ion exchange and storage, catalysis, sensing, etc. Compared to the typical carboxylate-based MOFs, PMPFs exhibit higher thermal and water stability due to the strong coordination ability of the phosphonate ligands. Despite their robust frameworks, PMPFs account for less than 0.51% of the porous MOFs reported so far. This is because metal phosphonates are highly susceptible to the formation of dense layered or pillared-layered structures, and they precipitate easily and are difficult to crystallize. There is a tendency to use phosphonate ligands containing multiple phosphonate groups and large organic spacers to prevent the formation of dense structures and generate open frameworks with permanent porosity. Thus, many PMPFs are composed of chains or clusters of inorganic metal phosphonates interconnected by organic spacers. Using this feature, a wide range of metal ions and organic components can be selected, and their physical properties can be modulated. However, limited by the small number of PMPFs, there are still relatively few studies on the physical properties of PMPFs, some of which merely remain in the description of the phenomena and lack in-depth elaboration of the structure-property relationship. In this Account, we review the strategies for constructing PMPFs and their physical properties, primarily based on our own research. The construction strategies are categorized according to the number (n = 1-4) of phosphonate groups in the ligand. The physical properties include proton conduction, electrical conduction, magnetism, and photoluminescence properties. Proton conductivity of PMPFs can be enhanced by increasing the proton carrier concentration and mobility. The former can be achieved by adding acidic groups such as -POH and/or introducing acidic guests in the hydrophilic channels. The latter can be attained by introducing conjugate acid-base pairs or elevating the temperature. Semiconducting PMPFs, on the other hand, can be obtained by constructing highly conjugated networks of coordination bonds or introducing large conjugated organic linkers π-π stacked in the lattice. In the case of magnetic PMPFs, long-range magnetic ordering occurs at very low temperatures due to very weak magnetic exchange couplings propagated via O-P-O and/or O(P) units. However, lanthanide compounds may be interesting candidates for single-molecule magnets because of the strong single-ion magnetic anisotropy arising from the spin-orbit coupling and large magnetic moments of lanthanide ions. The luminescent properties of PMPFs depend on the metal ions and/or organic ligands. Emissive PMPFs containing lanthanides and/or uranyl ions are promising for sensing and photonic applications. We conclude with an outlook on the opportunities and challenges for the future development of this promising field.

Band gap correction via GGA[formula omitted]mBJ function and strained modulated physical properties of 2D-like DyOBr oxybromide

Two-dimensional (2D) oxyhalides offer unique and fascinating properties due to long-range magnetic ordering in a low dimensional limit. These have potential applications in spintronics and low-dimensional data storage devices. Herein, we demonstrate the biaxial ([110]) strain impact on the electronic and magnetic properties of thermodynamically stable 2D like DyOBr oxybromide based on the first-principles calculations including Hubbard parameter (U) and U+mBJ (modified-Becke-Johnson) methods as well as spin–orbit coupling (SOC) effects. Our calculations predict that an unstrained system exhibits an anti-ferromagnetic (AFM) insulating state with a direct wide energy band gap (Eg) of 5.404 eV within GGA+U+mBJ scheme and the estimated Neel temperature (TN) using the Ising model is 13 K, which is in excellent agreement with the experimentally observed values of 5.41 eV and 9.5 K, respectively. Moreover, it is revealed that Dy ions displayed a large partial spin magnetic moment (ms) of 4.969 μB/f.u. (per formula unit) with S = 2.5 as they lie in ＋ 3 state having the electronic configuration of [fx(x2−3y2)+fy(3x2−y2)]↑2↓1, [fxz2+fyz2]↑2↓1, [fz(x2−y2)]↑1↓0, [fxyz]↑1↓0, and [fz3]↑1↓0. Interestingly, the system displays a large magnetic anisotropy energy of 4.31 meV/atom with a magnetic easy axis of [100] (a-axis), which enhances its utilization in magnetic memory devices. Further, it is established that the AFM insulating behavior of the structure remains robust against biaxial ([110]) strain for the considered range of ±5%. However, a well-ordered shift in conduction band edge (CBE) position to higher and lower energy values is predicted for compressive and tensile strains, respectively. Strikingly, it is found that the TN increases to 265% for ＋5% strain.

GdWN3 is a nitride perovskite

Nitride perovskites ABN3 are an emerging and highly underexplored class of materials that are of interest due to their intriguing calculated ferroelectric, optoelectronic, and other functional properties. Incorporating novel A-site cations is one strategy to tune and expand such properties; for example, Gd3+ is compelling due to its large magnetic moment, potentially leading to multiferroic behavior. However, the theoretically predicted ground state of GdWN3 was a non-perovskite monoclinic structure. Here, we experimentally show that GdWN3−y crystallizes in a perovskite structure. High-throughput combinatorial sputtering with activated nitrogen is employed to synthesize thin films of Gd2−xWxN3−yOy with oxygen content y &amp;lt; 0.05. Ex situ annealing crystallizes a polycrystalline perovskite phase in a narrow composition window near x = 1. LeBail fits of synchrotron grazing incidence wide angle x-ray scattering data are consistent with a perovskite ground-state structure. Refined density functional theory calculations that included antiferromagnetic configurations confirm that the ground-state structure of GdWN3 is a distorted Pnma perovskite with antiferromagnetic ordering, in contrast to prior predictions. Initial property measurements find that GdWN3−y is paramagnetic down to T = 2 K with antiferromagnetic correlations and that the absorption onset depends on cation stoichiometry. This work provides an important path toward both the rapid expansion of the emerging family of nitride perovskites and understanding their potential multiferroic properties.

High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets

To realize room temperature ferromagnetic (FM) semiconductors is still a challenge in spintronics. Many antiferromagnetic (AFM) insulators and semiconductors with high Neel temperature TN are obtained in experiments, such as LaFeO3, BiFeO3, etc. High concentrations of magnetic impurities can be doped into these AFM materials, but AFM state with very tiny net magnetic moments was obtained in experiments because the magnetic impurities were equally doped into the spin up and down sublattices of the AFM materials. Here, we propose that the effective magnetic field provided by a FM substrate could guarantee the spin-dependent doping in AFM materials, where the doped magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM) materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM insulator LaFeO3 with FM substrate of Fe metal by the density functional theory (DFT) calculations. It is shown that the doped magnetic Mn impurities prefer to occupy one sublattice of the AFM insulator and introduce large magnetic moments in La(Fe, Mn)O3. For the AFM insulator LaFeO3 with high TN = 740 K, several FIM semiconductors with high Curie temperature TC > 300 K and the band gap less than 2 eV are obtained by DFT calculations when 1/8 or 1/4 Fe atoms in LaFeO3 are replaced by the other 3d, 4d transition metal elements. The large magneto-optical Kerr effect (MOKE) is obtained in these LaFeO3-based FIM semiconductors. In addition, the FIM semiconductors with high TC are also obtained by spin-dependent doping in some other AFM materials with high TN, including BiFeO3, SrTcO3, CaTcO3, etc. Our theoretical results propose a way to obtain high TC FIM semiconductors by spin-dependent doping in high TN AFM insulators and semiconductors.

Cooperative Binding and Chirogenesis in an Expanded Perylene Bisimide Cyclophane.

The encapsulation of more than one guest molecule into a synthetic cavity is a highly desirable yet a highly challenging task to achieve for neutral supramolecular hosts in organic media. Herein, we report a neutral perylene bisimide cyclophane, which has a tailored chiral cavity with an interchromophoric distance of 11.2 Å, capable of binding two aromatic guests in a π-stacked fashion. Detailed host-guest binding studies with a series of aromatic guests revealed that the encapsulation of the second guest in this cyclophane is notably more favored than the first one. Accordingly, for the encapsulation of the coronene dimer, a cooperativity factor (α) as high as 485 was observed, which is remarkably high for neutral host-guest systems. Furthermore, a successful chirality transfer, from the chiral host to encapsulated coronenes, resulted in a chiral charge-transfer (CT) complex and the rare observation of circularly polarized emission originating from the CT state for a noncovalent donor-acceptor assembly in solution. The involvement of the CT state also afforded an enhancement in the luminescence dissymmetry factor (glum) value due to its relatively large magnetic transition dipole moment. The 1:2 binding pattern and chirality-transfer were unambiguously verified by single-crystal X-ray diffraction analysis of the host-guest superstructures.

Spin-flavor precession phase effects in supernova

We study the phase effects driven by neutrino magnetic moment for Majorana neutrinos in a core collapse supernova. A neutrino with a large magnetic moment is emitted in a superposition of energy eigenstates from the neutrinosphere. These energy eigenstates can interfere to create a phase effect at a partially adiabatic spin flavor precession (SFP) resonance. We examine the dependence of the SFP phase effect on the size of the neutrino magnetic moment as well as its variation with the post-bounce time. In particular, at late post-bounce times the SFP resonance becomes wider and eventually overlaps with the Mikheev–Smirnov–Wolfenstein (MSW) resonance. At this point Landau–Zener criteria for adiabaticity can no longer be applied to individual resonances, but we show that SFP phase effect is still present after the overlap. We also discuss the observability of the SFP phase effect at Deep Underground Neutrino Experiment (DUNE). Our analysis reveals that at low energies event rates do not fluctuate despite the presence of a sizable SFP phase effect. We find larger event rate fluctuations at high energies, but these fluctuations are also erased in the energy spectra of the observed charged leptons. A more refined treatment of electron fraction and the inclusion of neutrino–neutrino interactions may change our conclusions for observability in future studies.

Comparative electronic structure, magnetic and optical properties of cubic perovskite BaXO3 (X=Ti, Sn) with self-defects: A first-principles calculation

In this work, a comparative analysis of the electronic structures and various optical properties of perovskite BaTiO3 and BaSnO3 with self-defects was estimated via DFT calculations. Although both materials are categorized as semiconductors, they exhibit significant differences in band gap values. BaTiO3 possesses a band gap of 1.75 eV, whereas BaSnO3 has a substantially lower band gap of only 0.43 eV. Despite both BaTiO3 and BaSnO3 being nonmagnetic materials, defects can lead to nonzero magnetic moments. For BaTiO3, oxygen vacancies and Ti interstitial strongly induce a magnetic moment of 0.35 μB/f.u. and 0.57 μB/f.u., respectively. In contrast, BaSnO3 shows large magnetic moments of 0.50 μB/f.u. for Ba and Sn interstitials and 0.47 μB/f.u. for O interstitial. We expected that our findings would promote the application of BaTiO3 and BaSnO3 materials not only as semiconductors but also as extensions for ferromagnetic semiconductor materials.

The unique geometries and magnetic anisotropy energy of FenPt (n = 3–13) clusters: A first-principles investigation

Enthusiasm for exploring magnetic anisotropy energy (MAE) and spin–orbit coupling (SOC) effects in magnetic studies of transition metal alloy clusters remains high. In this paper, the first-principle method was used to investigate the global minimum energy structure of FenPt (n = 3–13) clusters and their interesting magnetic properties. Comparative structural analyses show that FenPt (n = 3–13) clusters have unique structures, and their relative stability analyses indicate that the increase in the number of atoms influences the geometrical arrangement of the clusters. The exploration of magnetic properties has focused on two areas. First, FenPt (n = 3–13) is found to have a large magnetic moment, while the magnetic moment increment surprisingly varies in the same way in different cases with and without the inclusion of SOC effects. Second, the calculations show that FenPt (n = 3, 4, 9, 13) has MAE, ranging from 1.420-2.687 meV/atom. The SOC matrix results show the interaction of Pt dx2-y2 and Pt dxy, and the interaction of Pt dz2 and Pt dyz, exhibit an indispensable force in determining the MAE.

Searching for new two-dimensional spintronic materials: Doping-induced magnetism in graphene-like SrS monolayer

In this work, doping approach is explored to induce feature-rich electronic and magnetic properties in graphene-like SrS monolayer and make it prospective spintronic two-dimensional (2D) candidate. For such goal, 3d transition metals (V, Cr, Mn, and Fe) and halogens (F, Cl, Br, and I) are selected as dopants at Sr and S sublattice, respectively. Pristine SrS single layer shows good dynamical and thermal stability. Its indirect-gap semiconductor nature is also asserted with energy gap of 2.87/3.81 eV obtained by PBE/HSE06 functional, generated by the separation in energy between S-3p and Sr-4d orbitals. The magnetic semiconducting with total magnetic moment of 2.00 μB is obtained by creating a single Sr vacancy, meanwhile S single vacancy preserves the non-magnetic nature. The monolayer is significantly magnetized by doping with transition metals, where large total magnetic moments of 3.00, 4.00, and 5.00 μB are obtained for the V-, Cr/Fe-, and Mn-doped SrS monolayer, respectively. In these cases, impurities play a key role on producing magnetic properties and generating the magnetic semiconductor nature. This feature-rich nature is also induced by doping with F atom, where a total magnetic moment of 1.00 μB is obtained that is originated mainly from Sr atoms closest to the doping site. Besides, Cl doping leads to the emergence of the half-metallicity. Importantly, the magnetization becomes significantly weaker according to increase the atomic number of halogen dopants, such that the non-magnetic nature is preserved by doping with I atom. This feature is attributed to the increase of the electronic hybridization. Results presented herein introduce the doped SrS monolayer as promising 2D spintronic materials, exhibiting novel properties that are not found in the pristine counterpart.

Magnetism in the axion insulator candidate Eu5In2Sb6

Eu5In2Sb6 is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu5In2Sb6 single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu5In2Sb6 results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the a axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-q structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics. Published by the American Physical Society 2024

Geometrically frustrated Gd2Ti2O7 oxide: A comprehensive exploration of structural, magnetic, and magnetocaloric properties for cryogenic magnetic cooling applications

The magnetocaloric effect (MCE) has been extensively studied in various magnetic solids, aiming to both facilitate practical applications in magnetic cooling and deepen our understanding these materials’ intrinsic properties. This study presents a systematic investigation of Gd2Ti2O7 oxide, characterized by a geometrically frustrated magnetic structure, focusing on its structural and magnetic characteristics through experimental analysis and theoretical calculations. Emphasis is placed on its magnetic phase transition (MPT) and magnetocaloric properties, scrutinizing temperatures as low as 0.4 K and magnetic fields up to 16 T. The results reveal that Gd2Ti2O7 oxide possesses a crystalline cubic pyrochlore-type structure with an antiferromagnetic (AFM) semiconductor ground state. The material undergoes a first-order MPT in low field and low-temperature regimes, transitioning to a second-order MPT above 2 K up to 16 T. Evaluation of magnetocaloric parameters, including maximum magnetic entropy change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, indicates moderate values under low magnetic field changes, while significantly large values are achievable under high magnetic field changes. This finding suggests that potential cryogenic magnetocaloric materials (MCMs) with optimal performance should exhibit low MPT temperatures induced by magnetic frustration and possess a ground state with a sufficiently large magnetic moment induced by low magnetic fields, thus avoiding excessively strong AFM coupling. This study lays the groundwork for future cryogenic MCM design and provides valuable insights into the intrinsic properties of geometrically frustrated magnetic materials.

Surface ferromagnetism of lead-free ferroelectric bismuth sodium titanate materials

The role of complex surface defect on the magnetic at the (110) surface of bismuth sodium titanate (Bi0.5Na0.5TiO3) was discussed based on the first-principles calculation. The first-principle calculations for various types of surface defects exhibited the existence of magnetic moments for selected chemical and position defects. Specifically, Na and Bi vacancies induced large magnetic moments of 0.52 µB/f.u and 0.50 µB/f.u, respectively, which were larger than that of Ti vacancies of 0.01 µB/f.u. Interestingly, oxygen vacancies did not induce local magnetic moments. Furthermore, significant magnetic moments of 0.50 µB/f.u and 0.49 µB/f.u were obtained for Na and Bi interstitial defects, while the local magnetic moments were slightly achieved around 0.03 µB/f.u and 0.04 µB/f.u for Ti and O interstitial defects, respectively. Anti-site defects between Bi and Na at A-site in perovskite ABO3 structure exhibited magnetic moments of 0.55 µB/f.u for Na anti-site at Bi-site and 0.39 µB/f.u for Bi anti-site at Na-site. Interestingly, anti-site defects between the A-site and B-site in perovskite ABO3 structure resulted in larger magnetic moments, with values of 0.57 µB/f.u and 0.53 µB/f.u obtained for Ti anti-site defects at the Bi-site and Na-site, respectively. Additionally, magnetic moments of 0.50 µB/f.u and 0.54 µB/f.u were achieved for Bi and Na anti-site defects at the Ti-site, respectively. We expected that our work further contributed to the understanding of the role of surface defects in the magnetism of Bi0.5Na0.5TiO3 materials in integrating ferromagnetic properties into lead-free ferroelectric materials for smart electronic device applications.

Effects of La-Mn co-substitution on the structure and magnetic properties of M-type strontium hexaferrite

Research into enhancing the magnetic properties of permanent ferrite using ion substitution techniques has continued, particularly concerning replacing commercially available La-Co co-substitution ferrite with larger magnetic anisotropy and lower prices. Mn ions with larger magnetic moments have become one of the options. In this work, Sr1-xLaxFe11.6-xMnxO19 (0 ≤ x ≤ 0.5) with equal substitution of La-Mn was synthesized by the conventional ceramic route. X-ray diffraction analyses indicated that the upper limit of La-Mn concentration was 0.4. The lattice constant a increases and c decreases with increasing La-Mn concentrations. With the increase of La-Mn concentrations, Ms reaches the highest value of 80.52 emu/g (x = 0.2) at 300 K. As evidenced by Raman spectroscopy, the substitution sites of Mn ions in the ferrite lattice altered with the substitution concentration, and the substitution tendency was 4f2 > 12 k + 2a > 4f1. In addition, La-Mn substitution affects the inherent magnetic properties such as HA and Tc of the samples, which has a reference for further improvement of permanent ferrites.