Magnetic Ordering Effects Research Articles

The effect of intrinsic magnetic order on electrochemical water splitting

To reach a long term viable green hydrogen economy, rational design of active oxygen evolution reaction (OER) catalysts is critical. An important hurdle in this reaction originates from the fact that the reactants are singlet molecules, whereas the oxygen molecule has a triplet ground state with parallel spin alignment, implying that magnetic order in the catalyst is essential. Accordingly, multiple experimentalists reported a positive effect of external magnetic fields on OER activity of ferromagnetic catalysts. However, it remains a challenge to investigate the influence of the intrinsic magnetic order on catalytic activity. Here, we tuned the intrinsic magnetic order of epitaxial La0.67Sr0.33MnO3 thin film model catalysts from ferro- to paramagnetic by changing the temperature in situ during water electrolysis. Using this strategy, we show that ferromagnetic ordering below the Curie temperature enhances OER activity. Moreover, we show a slight current density enhancement upon application of an external magnetic field and find that the dependence of magnetic field direction correlates with the magnetic anisotropy in the catalyst film. Our work, thus, suggests that both the intrinsic magnetic order in La0.67Sr0.33MnO3 films and magnetic domain alignment increase their catalytic activity. We observe no long-range magnetic order at the catalytic surface, implying that the OER enhancement is connected to the magnetic order of the bulk catalyst. Combining the effects found with existing literature, we propose a unifying picture for the spin-polarized enhancement in magnetic oxide catalysts.

Two-dimensional heavy fermions in the van der Waals metal CeSiI.

Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions1-6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases7-11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions. Owing to its vdW nature, CeSiI has a quasi-2D electronic structure, and we can control its physical dimension through exfoliation. The emergence of coherenthybridization of f and conduction electrons at low temperature is supported by the temperature evolution of angle-resolved photoemission and scanning tunnelling spectra near the Fermi level andby heat capacity measurements. Electrical transport measurements on few-layer flakes reveal heavy-fermion behaviour and magnetic order down to the ultra-thin regime. Our work establishes CeSiI and related materials as a unique platform for studying dimensionally confined heavy fermions in bulk crystals and employing 2D device fabrication techniques and vdW heterostructures12 to manipulate the interplay between Kondo screening, magnetic order and proximity effects.

Spin States and Spin Order in Perovskite Oxide Oxygen Evolution Electrocatalysts

The ‘power-to-hydrogen’ strategy aims at splitting water into O2 and H2 via the oxygen and hydrogen evolution reactions. The complex four-step oxygen evolution reaction (OER) limits the overall efficiency of hydrogen production. An important reason of the low efficiency is that the production of ground-state (triplet) O2 is a spin-forbidden reaction: in fact, the reactants, OH- or H2O, are diamagnetic, but the final product, O2, is a paramagnetic molecule. Recently, this was well-recognized theoretically1 and the use of spin selective catalysts was described as a possible way to promote the OER.2 . However, it remains complex to understand and exploit intrinsic and extrinsic magnetic features to enhance catalytic performance. Here, we investigate the role of magnetic moments in individual active sites in the catalyst surface layer and the role of spin order in ferromagnetic vs. paramagnetic catalysts, focussing on perovskite oxides.First, we investigated the role of Ni magnetic moment in the the (001), (110) and (111) facet of LaNiO3 electrocatalysts, which we studied using electrochemical measurements, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT+U) calculations.3 The results show a facet-dependent activity, where the (111) overpotential is ~60 mV lower as compared to the other facets. Closer investigation of the (001) and (111) facets reveals a surface transformation to a oxyhydroxide-like NiOO with edge-sharing octahedra,4 and we observed that the transformed surface is thicker for (111) than for (001).3 The detailed DFT+U analysis reveals important distinctions that give rise to the increased activity: the transformed LaNiO3 (111) surface exhibits a better match to the underlying perovskite layer. Moreover, protonation induces reduced Ni3+ with a finite magnetic moment. A moderate Jahn-Teller distortion enables a favorable binding of reaction intermediates. In contrast, the structural mismatch to the underlying LaNiO3(001)-substrate leads to a strong distortion of the transformed layer for this orientation and a weak binding of *O and ultimately to a different potential determining step (PDS), *OH→*O, compared to *O→*OOH for the transformed LaNiO3(111) surface.Second, we experimentally demonstrate the effect of intrinsic magnetic order on the OER on catalytic performance. Thin films of La0.67Sr0.33MnO3 grown by pulsed laser deposition with appropriate magnetic and electronic properties were chosen as well-defined model systems. Using the ferromagnetic to paramagnetic transition at the Curie temperature in these ferromagnetic perovskite oxides, the magnetic order of the catalysts were switched in situ during the OER by changing the temperature. For ferromagnetic films, the decrease in current density with decreasing temperature, induced by the reduction of thermal energy, was suppressed for temperatures below the Curie temperature, indicating that the presence of ferromagnetic ordering below Curie temperature enhances OER activity. This claim is further supported by an enhancement of OER activity for the same ferromagnetic film upon alignment of magnetic domains with an external magnetic field. All in all, our results reveal that the spin state, intrinsic spin order, and extrinsic magnetic fields are decisive for the OER activity. Biz, C., Fianchini, M. & Gracia, J. Strongly Correlated Electrons in Catalysis: Focus on Quantum Exchange. ACS Catal 11, 14249–14261 (2021).Sun, Y. et al. Spin‐Related Electron Transfer and Orbital Interactions in Oxygen Electrocatalysis. Advanced Materials 32, 2003297 (2020).Füngerlings, A. et al. Crystal-facet-dependent surface transformation dictates the oxygen evolution reaction activity in lanthanum nickelate. in preparation (2023).Baeumer, C. et al. Tuning electrochemically driven surface transformation in atomically flat LaNiO3 thin films for enhanced water electrolysis. Nat Mater 20, 674–682 (2021).

Giant segregation transition as origin of liquid metal embrittlement in the Fe-Zn system

A giant Zn segregation transition is revealed using CALPHAD-integrated density-based modeling of segregation into Fe grain boundaries (GBs). The results show that above a threshold of only a few atomic percent Zn in the alloy, a substantial amount of up to 60 at.% Zn can segregate to the GB. We found that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy required for triggering the segregation transition decreases. Direct evidence of the Zn segregation transition is obtained using high-resolution scanning transmission electron microscopy. Base on the model, we trace the origin of the segregation transition back to the low cohesive energy of Zn and a miscibility gap in Fe-Zn GB, arising from the magnetic ordering effect, which is confirmed by ab-initio calculations. We also show that the massive Zn segregation resulting from the segregation transition greatly assists with liquid wetting and reduces the work of separation along the GB. The current predictions suggest that control over Zn segregation, by both alloy design and optimizing the galvanization and welding processes, may offer preventive strategies against liquid metal embrittlement.

Spin-phonon interaction in nanocrystalline Dy3Fe5O12 probed by Raman spectroscopy: Effects of magnetic ordering

Spin-phonon interaction in nanocrystalline Dy3Fe5O12 probed by Raman spectroscopy: Effects of magnetic ordering

Photoemission signature of the competition between magnetic order and Kondo effect in CeCoGe3

The competition between magnetic order and Kondo effect is essential for the rich physics of heavy fermion systems. Nevertheless, how such competition is manifested in the quasiparticle bands in a real periodic lattice remains elusive in spectroscopic experiments. Here we report a high-resolution photoemission study of the antiferromagnetic Kondo lattice system CeCoGe3 with a high TN1 of 21K. Our measurements reveal a weakly dispersive 4f band at the Fermi level near the Z point, arisingfrom moderate Kondo effect. The intensity of this heavy 4f band exhibits a logarithmic increase with lowering temperature and begins to deviate from this Kondo-like behavior below 25 K, just above TN1, and eventually ceases to grow below 12 K. Our work provides direct spectroscopic evidence for the competition between magnetic order and the Kondo effect in a Kondo lattice system with local-moment antiferromagnetism, indicating a distinct scenario for the microscopic coexistence and competition of these phenomena, which might be related to the real-space modulation.

The Study of Interplay of Singlet Superconductivity and Ferromagnetism in Superconducting HoMo6Se8

This article reports the effect of magnetic ordering and superconducting order parameter on superconducting and magnetic transition temperatures of interacting singlet superconductivity and ferromagnetism in HoMo6Se8 material. The basic superconducting parameters were calculated starting with the BCS type model Hamiltonian and using the double time temperature dependent Green function formalisms. Results showed that the superconducting critical temperature decreases with enhancement of superconducting order parameter and vice versa. This is perhaps due to the weakening of the binding energy as the temperature approaches its critical value. On the other hand, the superconducting critical temperature demonstrates attenuation with increasing magnetic order parameters . It was also observed that the enhancement of magnetic transition temperature with the increase of the magnetic order parameter demonstrates variation with the alteration of the superconducting order parameter. Moreover, the calculations revealed that there is a temperature region where both superconductivity and magnetic order coexist. Furthermore, the present theoretical analysis is broadly in agreement with existing experimental findings.

Spin-mediated Mott excitons

Motivated by recent experiments on Mott insulators, in both iridates and ultracold atoms, we theoretically study the effects of magnetic order on the Mott-Hubbard excitons. In particular, we focus on spin-mediated doublon-holon pairing in Hubbard materials. We use several complementary theoretical techniques: Mean-field theory to describe the spin degrees of freedom, the self-consistent Born approximation to characterize individual charge excitations across the Hubbard gap, and the Bethe-Salpeter equation to identify bound states of doublons and holons. The binding energy of the Mott exciton is found to increase with increasing the N\'eel order parameter, whereas the exciton mass decreases. We observe that these trends rely significantly on the retardation of the effective interaction, and require consideration of multiple effects from changing the magnetic order. Our results are consistent with the key qualitative trends observed in recent experiments on iridates. Moreover, the findings could have direct implications on ultracold atom Mott insulators where the Hubbard model is the exact description of the system and the microscopic degrees of freedom can be directly accessed.

Magnetic Amplification at Yb3+ "Designer Defects" in the van der Waals Ferromagnet CrI3.

The two-dimensional (2D) van der Waals ferromagnet CrI3 has been doped with the magnetic optical impurity Yb3+ to yield materials that display sharp multiline Yb3+ photoluminescence (PL) controlled by the magnetism of CrI3. Magneto-PL shows that Yb3+ magnetization is pinned to the magnetization of CrI3. An effective internal field of ∼10 T at Yb3+ is estimated, attributed to strong in-plane Yb3+-Cr3+ superexchange coupling. The anomalously low energy of Yb3+ PL in CrI3 reflects relatively high Yb3+-I- covalency, contributing to Yb3+-Cr3+ superexchange coupling. The Yb3+ PL energy and line width both reveal the effects of spontaneous zero-field CrI3 magnetic ordering within 2D layers below TC, despite the absence of net magnetization in multilayer samples. These results illustrate the use of optical impurities as "designer defects" to introduce unique functionality to 2D magnets.

Large magnetic-field-induced strains in sintered chromium tellurides

Sintered samples of Cr3Te4 and Cr2Te3 are found to show large strains accompanied by large volume changes under a magnetic field. In Cr3Te4, volume increases of ΔV/V = 500–1170 ppm by applying a magnetic field of 9 T are observed over the entire temperature range below 350 K. At room temperature, the ΔV/V value exceeds 1000 ppm, which is considerably larger than the maximum values reported for Cr-based magnets, thus far, and is comparable to the room-temperature value of forced-volume magnetostriction in invar alloys. Cr2Te3 shows a large ΔV/V of 680 ppm when applying a magnetic field of 9 T at 200 K. Both samples display particularly large volume increases around the Curie temperature, where they also show negative thermal expansion due to the microstructural effects, suggesting that the cooperation between anisotropic lattice deformation associated with the magnetic ordering and microstructural effects is essential for the manifestation of the large magnetic-field-induced volume changes.

The effect of magnetic order on the thermal transport properties of the intrinsic two-dimensional magnet 2H-VSe2.

By using first-principles calculations combined with the phonon Boltzmann transport equation, in this work, we systematically investigate the effect of magnetic order on the phonon and thermal transport properties of the intrinsic two dimensional magnet 2H-VSe2. The results show that 2H-VSe2 is dynamically stable in both paramagnetic and ferromagnetic phases, and the obvious discrepancy of characteristic frequencies of Raman-active phonon modes provides a reliable way to identify the magnetic phase. Meanwhile, our calculations also indicate that the magnetic order has a vital effect on the thermal transport properties. Around the Curie temperature (500 K), the thermal conductivity of 2H-VSe2 in the FM phase (16.3 W mK-1) is about four times larger than that in the PM phase (4.3 W mK-1), and such a difference could be maintained even when considering the temperature dependent force constants. By analyzing the phonon mode information and root mean square displacement, we reveal that large atomic interactions and suppressed phonon anharmonicity are the main roots for the enhanced thermal conductivity in the FM phase 2H-VSe2. These results further demonstrate that magnetic materials with a FM phase always host more excellent thermal transport properties than those with a PM phase, and shed light on the great potential applications of thermal switching devices based on 2H-VSe2.

Structure and Physical Properties of the Layered Titanium-Based Pnictide Oxides (EuF)2Ti2Pn2O (Pn = Sb, Bi).

We report two novel titanium-based pnictide oxide compounds (EuF)2Ti2Pn2O (Pn = Sb, Bi), which are synthesized by replacing Sr2+ in (SrF)2Ti2Pn2O [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O. Chem. Mater. 2010, 22, 1503-1508] with Eu2+ using a solid-state reaction. (EuF)2Ti2Sb2O exhibits an obvious anomaly in resistivity and heat capacity at T ∼ 195 K, which may arise from the spin-density wave/charge-density wave instability. Similar features are also observed in BaTi2Pn2O, (SrF)2Ti2Pn2O, and Na2Ti2Pn2O (Pn = As and Sb) [Liu, R. H. Structure and Physical Properties of the Layered Pnictide-Oxides: (SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O. Chem. Mater. 2010, 22, 1503-1508, Ozawa, T. C. Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors. Sci. Technol. Adv. Mater. 2008, 9, 033003, Wang, X. F. Structure and physical properties for a new layered pnictide-oxide: BaTi2As2O. J. Phys.: Condens. Matter. 2010, 22, 075702, and Xu, H. C. Electronic structure of the BaTi2As2O parent compound of the titanium-based oxypnictide superconductor. Phys. Rev. B 2014, 89, 155108]. Magnetic susceptibility measurements indicate an antiferromagnetic transition at T ∼ 2.5 K for (EuF)2Ti2Sb2O. In particular, the electronic specific heat coefficients of both (EuF)2Ti2Sb2O and (EuF)2Ti2Bi2O are significantly enhanced compared to those of (SrF)2Ti2Pn2O, Na2Ti2Pn2O, and BaTi2Pn2O,1,5,6 which may be due to a strong electron correlation effect in this system. Thus, (EuF)2Ti2Pn2O (Pn = Sb, Bi) may provide new platforms for studying density wave, magnetic ordering, and electron correlation effects.

Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R−Au−Si (R=Tb,Ho) quasicrystal approximants

In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth $(R)$ ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center $R$ magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral $R$ magnetic moments are less affected by the cluster-center $R$, while the averaged cluster-center $R$ magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.

Successive magnetic transitions and broad refrigeration temperature span of Gd3Ni6Ga2

Magnetic ordering and magnetocaloric effect of polycrystalline Ce3Ni6Si2-type Gd3Ni6Ga2 (space group Im-3m, N 229, cI44) has been investigated via heat capacity and magnetic measurements. Gd3Ni6Ga2 exhibits ferromagnetic ordering at TC ​= ​104 ​K and a field-sensitive transformation of magnetic ordering at Tm ​= ​38 ​K. At 2 ​K, it is soft ferromagnetic with magnetic moment per Gd of 6.73 μB in 90 ​kOe. Heat capacity measurements in zero magnetic field indicated the Debye temperature around 320 ​K and peak in heat capacity around TC, only. Gd3Ni6Ga2 shows table-like magnetic entropy change of −4.9 ​J/kg⋅K at TC and −3.8 ​J/kg⋅K at Tm in a field change of 50 ​kOe with a wide working temperature range.

Composition-tunable magnetic properties of {Gd, Dy, Ho}6FeTe2, Ho6RuSb2 ternary compounds and Dy6FeSbBi, Dy6FeSbTe and Dy6FeBiTe quasiternary solid solutions

The magnetic ordering and magnetocaloric effect of polycrystalline Fe2P-type Gd6FeTe2, Dy6FeTe2, Ho6FeTe2 and Ho6RuSb2 ternary compounds and Dy6FeSbBi, Dy6FeSbTe and Dy6FeBiTe quasiternary solid solutions (space group P-62m, N 189, hP9) have been investigated using magnetic and heat capacity measurements. Gd6FeTe2 exhibits ferromagnetic ordering with Curie temperature (TC) of 212 K and magnetic entropy change of −4.9 J/kg⋅K in a field change of 50 kOe. Meanwhile, Dy6FeTe2, Ho6RuSb2, Dy6FeSbBi, Dy6FeSbTe and Dy6FeBiTe show high-temperature ferromagnetic ordering (TC) and low-temperature transformation of magnetic ordering (Tm), presenting a table-like magnetocaloric effect in a temperature range from TC to Tm and hard magnet properties at low temperatures. In field of 100 Oe, Ho6FeTe2 exhibits high-temperature antiferromagnetic ordering at TN = 26 K and low-temperature ferromagnetic transition at TC = 6 K with metamagnetic transformation in field lower than 10 kOe. It shows magnetocaloric effect with entropy change of −12.9 J/kg⋅K and −6.2 J/kg⋅K and magnetic enthalpy change of 580 J/kg and 62 J/kg at 22 K and 7 K, respectively, in a field change of 50 kOe.Tuning the magnetocaloric effect and the magnetic ordering via chemical composition is validated in the quasiternary Dy6FeSbBi, Dy6FeSbTe and Dy6FeBiTe solid solutions.

Ambi-chiral anomalous Hall effect in magnetically doped topological insulators

The chirality associated with broken time reversal symmetry in magnetically doped topological insulators has important implications to the quantum transport phenomena. Here we report the anomalous Hall effect studies in Mn- and Cr-doped Bi$_2$Te$_3$ topological insulators with varied thickness and doping content. By tracing the chirality of the Hall loops, we find that the Mn-type anomalous Hall effect with clockwise chirality is strengthened by the reduction of film thickness, which is opposite to that of the Cr-type anomalous Hall effect with counterclockwise chirality. We provide a phenomenological model to explain the evolution of magnetic order and anomalous Hall effect chirality in magnetically doped topological insulators.

Magnetic ordering and magnetocalori effect of GdNiGa4, GdNi0.5Ga1.5 and GdNiGa

The polycrystalline YNiAl4-type GdNiGa4 (space group Cmcm, N 63, oC24), CeCu2-type GdNi0.5Ga1.5 (space group Imma, N 74, oI12) and TiNiSi-type GdNiGa (space group Pnma, N 62, oP12) are prepared by arc melting with following annealing. The magnetic ordering and magnetocaloric effects of these compounds have been investigated using magnetic measurements in fields up to 90 ​kOe GdNiGa4 shows field insensitive antiferromagnetic ordering below TN ​= ​12 ​K, GdNi0.5Ga1.5 demonstrate ferromagnetic ordering below TC ​= ​36 ​K and low-temperature field-sensitive ferro-antiferromagnetic ordering (Tm) in the range of 12–32 ​K, while GdNiGa exhibits ferromagnetic ordering below TC ​= ​28 ​K. The saturation magnetizations at 2 ​K indicate a collinear ferromagnetic ordering of Gd-sublattice in GdNi0.5Ga1.5 and GdNiGa. The transformation of crystal lattice from GdNi0.5Ga1.5 to GdNiGa with ordering of Ni-sublattice leads to a remarkable increasing of magnetic entropy change and magnetocaloric effect. The structural and magnetic features of ternary Gd-Ni-Ga compounds are discussed.

Notable effect of magnetic order on the phonon transport in semi-hydrogenated graphene

Semi-hydrogenated graphene (SHG) is a ferromagnetic semiconductor with a large Curie temperature. Using this simple structure as a platform, we investigate how the coupling between magnetic order and lattice vibration affects the thermal transport by using first-principles calculations and the phonon Boltzmann transport equation. The results show that both paramagnetic and ferromagnetic phases are stable in SHG. The frequency features of the Raman-active phonon modes of the two phases clearly differ, which could serve as a fingerprint by which to identify the different magnetic orders. In addition, the coupling effect plays a critical role in the lattice thermal conductivity. At room temperature, SHG in its paramagnetic phase has a lattice thermal conductivity of about 24.5 W/mK, whereas, in its ferromagnetic phase, it is about 55.7 W/mK, almost twice as large as the paramagnetic case. An analysis of the phonon modes reveals that the enhanced thermal conductivity of ferromagnetic SHG is mainly due to the greater group velocity of the flexural acoustic mode and the attenuation of the anharmonicity of the transverse and longitudinal acoustic modes. These results reveal how magnetic order affects phonon transport in SHG and open the way for potential applications of magnetic monolayer materials as thermal switching devices.

First-principles investigation of uranium mononitride (UN): Effect of magnetic ordering, spin-orbit interactions and exchange correlation functional

Uranium mononitride (UN) is a promising nuclear fuel that combines the advantageous properties of readily used UO 2 and uranium alloys . Various properties of UN have been previously studied using different density functional theory (DFT) methodologies; however, there are still inconsistencies when it comes to the dynamical stability and defect properties of UN. We address these inconsistencies by studying the UN phonons and defect properties using DFT calculations employing two generalized gradient approximation (GGA) exchange-correlation functionals: PBE and AM05, with and without an added on-site Coulomb repulsion term (+U). Furthermore, we investigate the importance of spin-orbit coupling (SOC) when calculating the properties of UN. We use the different methodologies to determine the preference of UN to have antiferromagnetic (AFM) ordering, as seen in experiments, or ferromagnetic (FM) ordering of the uranium spins. We compare the crystallographic properties , density of states, the DFT X-ray photoelectron spectra and phonon dispersions calculated using the different methodologies. We demonstrate that GGA + U reproduces the AFM ordering in UN, but the crystal structure is dynamically unstable. We also show that magnetic ordering is important in finding the lowest energy defective structure, and that SOC has a distinct influence on the energy of the different uranium interstitial defects . Lastly, we discuss the point defect formation energies under U-rich and N-rich conditions, and the stoichiometric formation energies calculated with the different methodologies, providing insight into the observed tendency for forming hypostoichiometric UN.

Emergence of magnetic order and enhanced magnetoelectric coupling in Lu-doped Sm2BaCuO5

The green-phase compound Sm2BaCuO5 has recently drawn significant attention due to the prominent linear magnetoelectric (ME) coupling effect. Herein, we report a successful chemical doping control of magnetic order and ME effect in Lu3+-doped multiferroic Sm2BaCuO5. Upon a small amount of Lu3+ doping, it is suggested that the majority of Cu ions interact through Sm3+ and order at TN1 ∼ 23 K, whereas some Cu2+ interacting through Lu3+ can lead to another transition at T* ∼21 K–16 K upon doping Lu3+ ions from 5% to 20%. More interestingly, this emergent magnetic order is concomitant with a broad valley in the pyroelectric current and dielectric anomaly, providing clear evidence of intrinsic coupling between magnetic and ferroelectric orders. In contrast to the parent phase, significant enhancement of the linear ME coefficient is obtained. Our results unveil the importance of interplay of 4f-3d magnetic interactions in inducing ferroelectricity and offer an alternative route to achieve high performance in ME coupling.