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2D van der Waals (vdW) magnets are the incentive for a new era of spintronics research with unprecedented opportunities. Hitherto, maximum research on vdW magnets is restricted by cryogenic temperature due to the inability to retain long‐range magnetic order at room temperature. The present study demonstrates the emergence of spin dynamics in association with phonon dynamics at room temperature in chemically exfoliated FexGeTe2 (x = 3,4,5) flakes employing a time‐resolved magneto‐optical Kerr effect microscope. The highly intense femtosecond laser pulse is supposed to establish magnetic ordering. This photoinduced magnetization is realized and modulated in the ultrafast demagnetization and GHz frequency precessional dynamics. Furthermore, coherent phonon excitation at optical regime is observed which subsequently triggers THz frequency magnon modes via direct spin‐phonon coupling. This study unfolds an all‐optical route to control optomagnetic properties and the future perspectives of 2D vdW magnets for multidisciplinary applications. [ABSTRACT FROM AUTHOR]

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials. [ABSTRACT FROM AUTHOR]

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of 2D van der Waals (vdW) materials. Herein, the observation of spin‐phonon coupling in the otherwise non‐magnetic TI Bi2Te3 is reported, due to the proximity of FePS3 (an antiferromagnet (AFM), TN ≈ 120 K), in a vdW heterostructure framework. Temperature‐dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity originated from spin‐lattice coupling at the Bi2Te3/FePS3 interface at/below 60 K in the peak position (self‐energy) and linewidth (lifetime) of the characteristic phonon modes of Bi2Te3 (106 and 138 cm−1) in the stacked heterostructure. The Ginzburg‐Landau (GL) formalism, where the respective phonon frequencies of Bi2Te3 couple to phonons of similar frequencies of FePS3 in the AFM phase, is adopted to understand the origin of the hybrid magneto‐elastic modes. At the same time, the reduction of characteristic TN of FePS3 from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe‐S‐Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, inserting hexagonal boron nitride within Bi2Te3/FePS3 stacking regains the anharmonicity in Bi2Te3. Controlling interfacial spin‐phonon coupling in stacked heterostructure can have potential application in surface code spin logic devices. [ABSTRACT FROM AUTHOR]

Phonon blockade is an important quantum effect for revealing the quantum behaviors of mechanical systems. For a nitrogen-vacancy center spin strongly coupled to a mechanical resonator via the second-order magnetic gradient, we show that the qubit driving can lead to the implementation of the two-phonon blockade, while the usual mechanical driving only allows for the appearance of a single-phonon blockade. As a signature, we investigate three-phonon antibunching with a simultaneous two-phonon bunching process by numerically calculating the second-order and third-order correlation functions. We also analyze in detail the influence of the system parameters (including the qubit driving strength, the dephasing rate of the qubit, as well as the thermal phonon number) on the quality of the two-phonon blockade effect. Our work provides an alternative method for extending the concept of a phonon blockade from a single phonon to multiphonon. It is of direct relevance for the engineering of multiphonon quantum coherent devices and thus has potential applications in quantum information processing. [ABSTRACT FROM AUTHOR]

The physics of mutual interaction of phonon quasiparticles with electronic spin degrees of freedom, leading to unusual transport phenomena of spin and heat, has been a subject of continuing interests for decades. Despite its pivotal role in transport processes, the effect of spin-phonon coupling on the phonon system, especially acoustic phonon properties, has so far been elusive. By means of inelastic neutron scattering and first-principles calculations, anomalous scattering spectral intensity from acoustic phonons was identified in the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong spin-lattice correlations that renormalize the polarization of acoustic phonon. In particular, a clear magnetic scattering signature of the measured neutron scattering intensity from acoustic phonons is demonstrated by its momentum transfer and temperature dependences. The anomalous scattering intensity is successfully modeled with a modified magneto-vibrational scattering cross-section, suggesting the presence of spin precession driven by phonon. The renormalization of phonon eigenvector is indicated by the observed "geometry-forbidden" neutron scattering intensity from transverse acoustic phonon. Importantly, the eigenvector renormalization cannot be explained by magnetostriction but instead, it could result from the coupling between phonon and local magnetization of ions.

Abstract 2D magnetic materials offer the opportunity to study and manipulate emergent collective excitations. Among these, spin–phonon coupling is one of the most important interactions correlating charge, spin and lattice vibrations. Understanding and controlling this coupling is important for spintronics applications, control of magnons and phonon by THz radiation, and for strain‐driven magnetoelastic applications. Here, a resonant mode‐selective spin–phonon coupling in several magnetic 2D metal thiophosphates (NiPS3, FePS3, CoPS3 and MnPS3) through multi‐excitation and temperature‐dependent Raman scattering measurements is uncovered. The phonon mode, which is a Raman‐active out‐of‐plane vibrational mode (∼250 cm−1 or 7.5 THz), exhibits an asymmetric Fano lineshape where its asymmetry is proportional to the spin–phonon coupling. The measurements reveal the coupling to be the highest in NiPS3, followed by FePS3 and CoPS3, and least in MnPS3. These differences are attributed to the metal–sulfur interatomic distances, which are the lowest in NiPS3, followed by CoPS3, FePS3 and MnPS3. Finally, the spin–phonon coupling is also observed in exfoliated materials, with a slight reduction between 20 and 30% in the thinnest flakes compared to the bulk crystals.

Phonon blockade is an important quantum effect for revealing the quantum behaviors of mechanical systems. For a nitrogen-vacancy center spin strongly coupled to a mechanical resonator via the second-order magnetic gradient, we show that the qubit driving can lead to the implementation of the two-phonon blockade, while the usual mechanical driving only allows for the appearance of a single-phonon blockade. As a signature, we investigate three-phonon antibunching with a simultaneous two-phonon bunching process by numerically calculating the second-order and third-order correlation functions. We also analyze in detail the influence of the system parameters (including the qubit driving strength, the dephasing rate of the qubit, as well as the thermal phonon number) on the quality of the two-phonon blockade effect. Our work provides an alternative method for extending the concept of a phonon blockade from a single phonon to multiphonon. It is of direct relevance for the engineering of multiphonon quantum coherent devices and thus has potential applications in quantum information processing.

In this study, nanocrystals of antiferromagnetic Cr2O3 are shown via Raman spectroscopy to display peculiar lattice dynamics in terms of phonon softening and the occurrence of an exceptionally strong spin‐phonon coupling. This effect, which is observed to persist well above the onset of the antiferromagnetic ordering temperature, is ascribed to locally correlated spin fluctuations due to the modulation of the magnetic exchange interactions as the chromium atoms oscillate about their equilibrium position. It is found that the spin‐phonon coupling strength is governed by the competing antiferromagnetic and ferromagnetic interactions, where changes in the surface spin configuration can also play a crucial role. Overall, this work proves the size dependence of the interplay between the crystalline and magnetic structures in 3D antiferromagnets varying the surface‐to‐volume ratio and helps establish the fundamentals for a spin‐phonon coupling engineering at the nanoscale via a simple route in a very stable and easy to synthesize material. More importantly, it demonstrates the possibility of coupling phononic excitations with the magnetization dynamics at room temperature, offering a highly prospective nanomaterial for the design of novel magnonic devices. [ABSTRACT FROM AUTHOR]

We report on the far-infrared, temperature-dependent optical properties of a CrI 3 transition metal halide single crystal, a van der Waals ferromagnet (FM) with a Curie temperature of 61 K. In addition to the expected phonon modes determined by the crystalline symmetry, the optical reflectance and transmittance spectra of CrI 3 single crystals show many other excitations as a function of temperature as a consequence of the combination of a strong lattice anharmonicity and spin–phonon coupling. This complex vibrational spectrum highlights the presence of entangled interactions among the different degrees of freedom in CrI 3 . [ABSTRACT FROM AUTHOR]

Layered magnetic metal-organic frameworks (MOFs) are an emerging class of materials that can combine the advantages of both MOFs and 2D magnetic crystals. The recent discovery of large coercivity and long-range magnetic ordering up to 515 K in a layered MOF of general formula MCl2(pyz)2 (M = transition metal, pyz = pyrazine) offers an exciting versatile platform to achieve high-TC magnetism at the 2D limit. In this work, we investigate the exfoliation feasibility down to the monolayer of VCl2(pyz)2 and CrCl2(pyz)2 by means of first-principles calculations. We explore their structural, electronic, magnetic and vibrational properties, as well as the effect of halide substitution. Then, we provide a full analysis of the spin-phonon coupling (SPC) in both 2D derivatives. Our calculations reveal a low SPC and thermal evolution of the magnetic exchange interactions and single-ion anisotropy mainly governed by low-frequency phonon modes. Finally, we provide chemical insights to improve the performance of these magnetic 2D MOFs based on the effective manipulation of the phonon modes that can present a major impact on their magnetic properties. [ABSTRACT FROM AUTHOR]

Understanding defect-phonon interactions in solid-state devices is crucial for improving our current knowledge of quantum platforms. In this work, we develop first-principles calculations for a defect composed of two spin- 1 / 2 particles that interact with phonon modes in a one-dimensional lattice. We follow a bottom-up approach that begins with a dipolar magnetic interaction to ultimately derive the spectral density function and time-local master equation that describes the open dynamics of the defect. We provide theoretical and numerical analysis for the non-Markovian (NM) features of the defect-phonon dynamics induced by a pure dephasing channel acting on the Bell basis. Finally, we analyze two measures of NM based on the canonical rates and Coherence, shedding more light on the role of the spectral density function and temperature; and envisioning experimental realizations. [ABSTRACT FROM AUTHOR]

Hexagonal Lu0.5−xZrxSc0.5FeO3 polycrystalline samples are synthesized by conventional solid‐state reaction. Effects of slight Zr4+ ions substitution on the structural distortion and magnetoelectric properties are investigated. The coexistence of Fe2+ and Fe3+ is checked by X‐ray photoelectron spectroscopy (XPS). X‐ray diffraction (XRD) and Raman spectrum (RS) microstructural analysis reveal that all samples are in the hexagonal structure with the polar space group of P63cm. With x increasing slightly, the tilting of FeO5 bipyramids and the bending of rare‐earth atomic layers are suppressed. The Néel temperature TN of antiferromagnetic (AFM) transition is decreased, whereas the weak ferromagnetic (WFM) order is strengthened. The permittivity εr of the samples is significantly increased. A dielectric anomaly near TN in Lu0.45Zr0.05Sc0.5FeO3 may indicate magnetoelectric coupling. It is attributed to the spin–phonon coupling as is evidenced by the Raman phonon modes. The improvement of dielectricity and magnetoelectric coupling is explained by considering the Dzyaloshinskii–Moriya interaction, structural distortion, and the incremental ratio of Fe2+ ions. These results provide an idea for sensitive control of electric and magnetic properties in related materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pure polycrystalline CeFe 0.5 Cr 0.5 O 3 ceramics were prepared by a modified solid-state method. • A first-order spin-reorientation transition of Fe/Cr ions from Γ 4 to Γ 1 is observed in CeFe 0.5 Cr 0.5 O 3. • The exchange-bias effect is found in CeFe 0.5 Cr 0.5 O 3 ceramics during the spin-reorientation transition. • The coexistence of spin-reorientation transition and exchange-bias effect is helpful to expand the practical application. The polycrystalline CeFe 0.5 Cr 0.5 O 3 ceramics were synthesized by the solid-state method, whose structural and magnetic properties were systematically studied. With the interaction between Ce and Fe/Cr ions, a first-order spin-reorientation transition from Γ 4 to Γ 1 is observed over a wide temperature interval in CeFe 0.5 Cr 0.5 O 3 , which is remarkably sensitive to applied magnetic field. Interestingly, the exchange-bias effect is found in CeFe 0.5 Cr 0.5 O 3 ceramics during the spin-reorientation transition, ascribed to the paramagnetic/antiferromagnetic system presented by the two interacting magnetic sublattices (Ce and Fe/Cr). The coexistence of spin-reorientation transition and exchange-bias effect is promising to expand the practical application of CeFe 0.5 Cr 0.5 O 3 ceramics in multifunctional spintronics. [ABSTRACT FROM AUTHOR]

[Display omitted] A spin-liquid state can be induced by uncompensated interactions in the spin lattice due to disorder or randomness in exchange pathways. Sr 2 CuTeO 6 and Sr 2 CuWO 6 are square-lattice antiferromagnetic double perovskites (A 2 BB′O 6) with dominant nearest-neighbor (Néel-type) and next-nearest neighbor (Columnar-type) magnetic interactions, respectively. Random distribution of these interactions in a system has been theoretically predicted to be a way to induce the spin-liquid state. Here, we have synthesized a spin-liquid candidate Sr 2 CuTe 0.5 W 0.5 O 6 with B′-site mixing of its parent systems (Sr 2 CuTeO 6 and Sr 2 CuWO 6) to explore the phonon properties and their correlations with the liquid-like magnetic interactions. Our measurements reveal the presence of a broad continuum in the Raman spectrum of Sr 2 CuTe 0.5 W 0.5 O 6 , instead of the well-defined spin-wave excitations (magnon) observed in the parent systems. Observation of continuum feature in the Raman spectrum in conjunction with the lack of long-range magnetic order provide the signatures of liquid-like correlations. On the other hand, phonon anomalies are observed below the short-ranged magnetic ordering temperature indicating the onset of spin-phonon coupling. [ABSTRACT FROM AUTHOR]

Mössbauer spectra of FeIII complex salts with urea-related ligands show a broadened line due to magnetic relaxation. The origin of the relaxation is not known, mostly spin–spin type is considered. A study of a large number of compounds can be helpful to show differences in the Mössbauer parameters and to see the infuence of the chemical environment on the relaxation. We have evaluated the Mössbauer spectra of 13 compounds recorded at various temperatures with the Blume–Tjon two-state relaxation model and with the (unrestricted) Afanasev–Gorobchenko model. The latter showed significant differences between some salts, and proved the presence of spin–lattice relaxation.Graphical abstract: Mössbauer spectra of FeIII complex salts with urea-related ligands show a broadened line due to magnetic relaxation. The origin of the relaxation is not known, mostly spin–spin type is considered. A study of a large number of compounds can be helpful to show differences in the Mössbauer parameters and to see the infuence of the chemical environment on the relaxation. We have evaluated the Mössbauer spectra of 13 compounds recorded at various temperatures with the Blume–Tjon two-state relaxation model and with the (unrestricted) Afanasev–Gorobchenko model. The latter showed significant differences between some salts, and proved the presence of spin–lattice relaxation. [ABSTRACT FROM AUTHOR]

• Structural and magnetic properties of polycrystalline Pr 1.8 La 0.2 CoFeO 6 sample have been explored. • Pr 1.8 La 0.2 CoFeO 6 adopts orthorhombic structure with space group Pnma. • XPS study reveals mixed valence state Fe3+/Fe4+ and Co2+/Co3+ ions in the system. • Magnetization data demonstrate Griffiths phase, exchange bias and cluster glass. • Raman study shows signature of spin phonon coupling in the system. The structural and magnetic properties of the double perovskite P r 1.8 L a 0.2 C o F e O 6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism with T N ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (T G ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; H S E B ∼ 1.8 kOe and giant conventional exchange bias, H C E B ∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below T N , clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly. [ABSTRACT FROM AUTHOR]

We report on the spin-phonon coupling in (1-x)Pb(Fe 1/2 Nb 1/2)O 3 – (x)Pb(Co 1/3 Nb 2/3)O 3 (PFCN, x = 0.1–0.5) ceramics by noticing changes in the phonon modes around the magnetic phase transition (T N) in the temperature-dependent Raman spectroscopy. A huge bifurcation was found between M ZFC and M FC curves, revealing the existence of strong magnetic anisotropy in all the ceramics. Variations in T N are due to the coexistence of antiferromagnetic and ferromagnetic interactions through Fe–O–Fe, Co–O–Co, Fe–O–Co canted magnetic moments. The T g is due to the superexchange interaction among Fe/Co–O–Nb–O–Co/Fe paths formed by the local short-range chemical ordering of Fe, Co, and Nb ions. The Raman spectra, recorded over a wide range of temperatures, reveal some anomalies in B–O–B bending and O–B–O stretching modes in the vicinity of T N, corresponding to the spin-phonon coupling in all the ceramics. This evidences the existence of magnetoelectric coupling in all the PFCN ceramics. Room temperature Mössbauer spectra of x = 0.1, 0.3 and 0.5 revealed the paramagnetic nature. Electron paramagnetic resonance (EPR) spectra showed the existence of antiferromagnetic and ferromagnetic orderings in all the ceramics. [ABSTRACT FROM AUTHOR]

The first part of this article attempts to highlight in chronological order some prominent papers that have direct connexion with the Born‐Oppenheimer approximation. This timeline successively points to the role of level crossing, the notions of gauge field and geometrical or Berry phase, early experiments that were accounted for with that concept, and its major role in understanding anomalous transport in solids. The second part analyzes the time evolution of states under the adiabatic approximation when the states are spin degenerate. The geometrical phase thus found entails an electron spin evolution. Then, we examine the case of moleclar dynamics. Starting from the Born‐Oppenheimer approximation, we obtain a spin evolution by replacing the classical nuclear positions by their quantum mechanical counterparts in the terms that describe electrostatic interactions between nuclei and electrons. [ABSTRACT FROM AUTHOR]

Due to the coexistence of spin-orbital coupling (SOC) and electron correlation interactions, double perovskite iridates are considered ideal material to investigate the Mott insulating states and Kitaev interactions. In this work, we studied the spin-orbital coupling (SOC), spin-phonon coupling (SPC), and Kitaev magnetism in antiferromagnetic La 2 ZnIrO 6 single crystal by magnetometer and Raman scattering spectroscopy measurements. Based on the temperature dependence of the magnetization under different magnetic fields, we found that all the initial temperatures of the paramagnetic-ferromagnetic transition were basically concentrated around 8.8 K, while the temperature of ferromagnetic-antiferromagnetic transition continued to decrease from 7 K to 2 K. Anomalous modes of frequency softening at magnetic-order temperature were detected from the polarized Raman scattering spectra, indicating the presence of strong spin-phonon coupling and Kitaev interaction in La 2 ZnIrO 6. [ABSTRACT FROM AUTHOR]

The physics of mutual interaction of phonon quasiparticles with electronic spin degrees of freedom, leading to unusual transport phenomena of spin and heat, has been a subject of continuing interests for decades. Despite its pivotal role in transport processes, the effect of spin-phonon coupling on the phonon system, especially acoustic phonon properties, has so far been elusive. By means of inelastic neutron scattering and firstprinciples calculations, anomalous scattering spectral intensity from acoustic phonons was identified in the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong spin-lattice correlations that renormalize the polarization of acoustic phonon. In particular, a clear magnetic scattering signature of the measured neutron scattering intensity from acoustic phonons is demonstrated by its momentum transfer and temperature dependences. The anomalous scattering intensity is successfully modeled with a modified magneto-vibrational scattering cross-section, suggesting the presence of spin precession driven by phonon. The renormalization of phonon eigenvector is indicated by the observed "geometry-forbidden" neutron scattering intensity from transverse acoustic phonon. Importantly, the eigenvector renormalization cannot be explained by magnetostriction but instead, it could result from the coupling between phonon and local magnetization of ions. [ABSTRACT FROM AUTHOR]

Molecular magnetism, though distinctly a field within chemistry, encompasses much more than synthesis and has strong links with other disciplines across the physical sciences. Research goals in this area are currently dominated by magnetic memory and quantum information processing but extend in other directions toward medical diagnostics and catalysis. This review focuses on two popular subtopics, single-molecule magnetism and molecular spin qubits, outlining their design and study and some of the latest outstanding results in the field. The above topics are complemented by an overview of pertinent electronic structure methods and, in a look towards the future, an overview of the state of the art in measurement and modeling of molecular spin–phonon coupling. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-quality LCMO polycrystalline films were obtained via chemical solution deposition, annealed at different temperatures (700, 800, and 900 °C). • Temperature-dependent Raman spectroscopic studies reveal multiple anomalous phonon energy behaviors, which are associated with strong spin-phonon coupling. • Temperature-dependent Raman spectroscopy uncovered the dynamic interplay of antiferromagnetic (AFM) and ferromagnetic (FM) competition during the phase transition. • Raman spectroscopy uncovered the presence of short-range Mn4+/Co2+ ferromagnetic clusters at room temperature. • Phonon lifetime analysis elucidated the temperature regime in which magnetic phases compete, shedding light on the dynamics of FM superexchange Mn4+-O-Co2+ and AFM interactions resulting from anti-site disorder. We report the dynamic effects of magnetic inhomogeneity on the temperature evolution of the Raman modes in polycrystalline La 2 CoMnO 6 (LCMO) films. The LCMO films were obtained via chemical solution deposition and annealed at different temperatures, 700, 800 and 900 °C. Temperature-dependent Raman spectroscopic studies uncover anomalous phonon energy behaviors, associated with strong spin-phonon couplings revealed even at ambient conditions. This effect, which is observed to occur well above ferromagnetic ordering temperature is ascribed to short-range Mn4+/Co2+ ferromagnetic clusters. Moreover, our study has shown that spin-phonon coupling strength is governed by competing antiferromagnetic (AFM) and ferromagnetic (FM) interactions. These results significantly enhance the understanding of the complex spin-phonon coupling mechanism to provide insights into magnetic inhomogeneity in systems with two or more magnetic sublattices. These findings suggest the presence of similar effects in other double perovskites within the RE 2 CoMnO 6 (RE = rare earths) family, which exhibit analogous magnetic sublattice and order–disorder defects. [ABSTRACT FROM AUTHOR]

Layered magnetic metal-organic frameworks (MOFs) are an emerging class of materials that can combine the advantages of both MOFs and 2D magnetic crystals. The recent discovery of large coercivity and long-range magnetic ordering up to 515 K in a layered MOF of general formula MCl2(pyz)2 (M = transition metal, pyz = pyrazine) offers an exciting versatile platform to achieve high-TC magnetism at the 2D limit. In this work, we investigate the exfoliation feasibility down to the monolayer of VCl2(pyz)2 and CrCl2(pyz)2 by means of first-principles calculations. We explore their structural, electronic, magnetic and vibrational properties, as well as the effect of halide substitution. Then, we provide a full analysis of the spin-phonon coupling (SPC) in both 2D derivatives. Our calculations reveal a low SPC and thermal evolution of the magnetic exchange interactions and single-ion anisotropy mainly governed by low-frequency phonon modes. Finally, we provide chemical insights to improve the performance of these magnetic 2D MOFs based on the effective manipulation of the phonon modes that can present a major impact on their magnetic properties.

The disorder due to anti-site cation distribution is intrinsic to the double perovskites wherein the crystal orientations of the substrate template are predicted to offer different degrees of cation order in thin film form. To demonstrate this effect, epitaxial thin films of half-metallic double perovskite Ca _2 FeMoO _6 (CFMO) were prepared on (100) and (111) oriented LaAlO _3 substrates in vacuum and nitrogen atmospheres. The findings using X-ray absorption near-edge structure, Terahertz (THz) and Raman spectroscopies, in combination with magnetization show that (111) epitaxial template effectively restricts the Fe–Mo anti-site cation disorder. A resultantly enhanced cation order in (111) films induces dramatic transformations in its properties as follows: (i) significantly enhanced ferromagnetic exchange interactions and saturation magnetization, (ii) a significant increase in the Curie temperatures, (iii) a metallic behavior down to much lower temperature (∼75 K) compared to that down to 200 K for (100) film, (iv) an enhanced spin–phonon coupling. The complex THz optical conductivity spectra evaluated in the framework of Drude and Drude–Smith phenomenological models and the temperature-dependent Raman data fitted to the Balkanski model corroborate well to indicate an enhanced cation order in (111) films. While this study establishes a dominant role of crystallographic orientation in the much-desired control of cation order in double perovskites, a demonstration of the same in room temperature half-metallic CFMO system could reinforce its technological utility both as active and passive components in emergent spintronic functionalities.

Understanding defect-phonon interactions in solid-state devices is crucial for improving our current knowledge of quantum platforms. In this work, we develop first-principles calculations for a defect composed of two spin- $1/2$ particles that interact with phonon modes in a one-dimensional lattice. We follow a bottom-up approach that begins with a dipolar magnetic interaction to ultimately derive the spectral density function and time-local master equation that describes the open dynamics of the defect. We provide theoretical and numerical analysis for the non-Markovian (NM) features of the defect-phonon dynamics induced by a pure dephasing channel acting on the Bell basis. Finally, we analyze two measures of NM based on the canonical rates and Coherence, shedding more light on the role of the spectral density function and temperature; and envisioning experimental realizations.

Raman scattering is an excellent method for simultaneously determining the dynamics of lattice, spin, and charge degrees of freedom. Furthermore, polarization selection rules in Raman scattering enable momentum-resolved quasiparticle dynamics. In this review, we highlight the potential of Raman scattering in probing magnetic quasiparticles or excitations in various magnetic materials. We demonstrate how temperature-dependent Raman scattering data can confirm the existence of magnons in long-range ordered magnets and fractionalized excitations in Kitaev spin liquid candidates. To make this review easily understandable to novices, we provide background information on magnons and fractionalized excitations, and explain how they become visible in the Raman scattering process. We also show how to estimate magnetic exchange interactions from the data. For both types of magnetic materials, we discuss the impact of spin-phonon coupling on the lineshape of the phonon modes. In terms of materials, we present magnetic Raman scattering data of antiferromagnetic Sr 2 IrO 4 and La 2 CuO 4 , ferromagnetic CrI 3 monolayers, and Kitaev spin liquid candidates α -RuCl 3 and β -Li 2 IrO 3 . Overall, our review demonstrates the versatility of the Raman scattering technique in probing quasiparticles in magnetic quantum materials. The review aims to inform young experimental researchers about the potential of Raman scattering, thereby motivating them to use this technique in their research., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

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 Nd 2 CoIrO 6 and Sm 2 CoIrO 6 were successfully prepared by conventional solid-state method. Detailed structural analysis revealed that both samples crystallized in monoclinic structure with P2 1 /n (No.-14) space group. X-ray photoelectron spectroscopy analysis confirms the presence of multiple oxidation states of Ir (i.e. Ir 4+ and Ir 5+ ). Both samples show a paramagnetic-ferrimagnetic (T FiM ) 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 Co 2+ and Ir 4+ 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., (© 2024 IOP Publishing Ltd.)

We report the spin dynamic properties of non‐substituted ferrocenium complexes. Ferrocenium shows a field‐induced single‐molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non‐Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system. The analysis of the spin relaxation shows an important participation of quantum tunnelling, Raman, direct and local‐mode mechanisms which depend on temperature and the external field conditions. The calculation of spin‐phonon coupling constants for the vibrational modes shows that the first vibrational mode, despite having a low spin‐phonon constant, is the most efficient process for the spin relaxation at low temperatures. In such conditions, vibrational modes with higher spin‐phonon coupling constants are not populated. Additionally, the vibrational energy of this first mode is in excellent agreement with the experimental fitted value obtained from the local‐mode mechanism. [ABSTRACT FROM AUTHOR]

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single‐molecule magnets (SMMs). Spin‐phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin‐phonon coupling in molecules is challenging. We have found that far‐IR magnetic spectra (FIRMS) of Co(PPh3)2X2 (Co‐X; X=Cl, Br, I) reveal rarely observed spin‐phonon coupling as avoided crossings between magnetic and u‐symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero‐field split (ZFS) levels of the S=3/2 electronic ground state were probed by INS, high‐frequency and ‐field EPR (HFEPR), FIRMS, and frequency‐domain FT terahertz EPR (FD‐FT THz‐EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand‐field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co‐X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin‐phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling. [ABSTRACT FROM AUTHOR]

In this study, we have successfully grown a high-quality single crystal of perovskite TbMnO 3 utilizing an optical floating zone furnace under an air atmosphere. To ensure the crystal purity and orientation, we probed X-ray diffractometer (XRD) and X-ray Laue photographic analysis, respectively. The XRD analysis confirmed that TbMnO 3 ceramics possess a distorted orthorhombic perovskite structure (Pbnm). By analyzing the X-ray absorption and vibrational modes via Raman spectroscopy, we not only confirmed the pure phase of the TbMnO 3 sample but also gained valuable insights. In terms of magnetic properties, we conducted measurements in two different orientations: H || a and H || c. Notably, there were no successive transitions observed along the H ||a direction, but along H ||c, we observed three successive transitions with decreasing temperature at T N = 41 K, T S = 28 K, and T N Tb = 7 K. Below T N (41 K), there is an unusual softening observed in one of the first order phonon modes, indicating a robust connection between spin and phonon interactions. The magnetic phase transition along both axes validates the presence of magnetic anisotropy in the prepared single crystal, as indicated by magnetic susceptibility. The negative θ cw value along the a -axis and the positive θ cw value along the c -axis suggest a competition between antiferromagnetic and ferromagnetic interactions in the ac -plane. • High-quality single crystal of TbMnO 3 has been grown using an optical floating zone furnace. • Material's purity confirmed through XRD, XAS and Raman spectroscopy. • Spin-phonon coupling within the TbMnO 3 single crystal. • Magnetic properties of TbMnO 3 single crystal: presence of magnetic anisotropy. • Anharmonic decay of a phonon into two phonons of lower energy [ABSTRACT FROM AUTHOR]

Spin in semiconductors facilitates magnetically controlled optoelectronic and spintronic devices. In metal halide perovskites (MHPs), doping magnetic ions is proven to be a simple and efficient approach to introducing a spin magnetic momentum. In this work, we present a facile metal ion doping protocol through the vapor-phase metal halide insertion reaction to the chemical vapor deposition (CVD)-grown ultrathin Cs 3 BiBr 6 perovskites. The Fe-doped bismuth halide (Fe:CBBr) perovskites demonstrate that the iron spins are successfully incorporated into the lattice, as revealed by the spin-phonon coupling below the critical temperature T around 50 K observed through temperature-dependent Raman spectroscopy. Furthermore, the phonons exhibit significant softening under an applied magnetic field, possibly originating from magnetostriction and spin exchange interaction. The spin-phonon coupling in Fe:CBBr potentially provides an efficient way to tune the spin and lattice parameters for halide perovskite-based spintronics.c around 50 K observed through temperature-dependent Raman spectroscopy. Furthermore, the phonons exhibit significant softening under an applied magnetic field, possibly originating from magnetostriction and spin exchange interaction. The spin-phonon coupling in Fe:CBBr potentially provides an efficient way to tune the spin and lattice parameters for halide perovskite-based spintronics.

Temperature‐dependent Raman scattering spectra of NiAs‐type MnTe epitaxial films were measured to explore the temperature evolution of phonon modes and especially the spin‐phonon coupling across Néel temperature (TN). A significant deviation from an anharmonic mode below TN strongly supports the existence of spin‐phonon interaction, and its coupling strength is calculated to be approximately −0.16 cm−1 from the E2g phonon. Two‐magnons (2M) scattering is found, which is proposed to closely relate to the nearest neighbor (NN) exchange interaction. These data elucidate the nature of the spin‐phonon coupling in antiferromagnetic (AFM) MnTe and can avail to develop MnTe‐based AFM spintronic devices. [ABSTRACT FROM AUTHOR]

Two series of B-site ordered, double-perovskite A2CoMnO6 and A2NiMnO6 (A = La, Pr, Nd, Sm, Gd) epitaxial films with thickness d ~ 100 nm were grown on SrTiO3(111) substrates via metalorganic aerosol deposition. Polarization and temperature-dependent Raman spectroscopy were carried out in order to determine the spin-phonon coupling constant, λ, and the impact of the A-site cation radius on the phonon properties. The reduction of the A-site cation radius from La3+ down to Gd3+ systematically shifts the Raman modes to lower wavenumbers, and decreases the magnetization-induced softening of the Ag breathing mode, described by the spin-phonon coupling constant, λ, which changes from λ = 1.42 cm−1 (La2CoMnO6) and λ = 1.53 cm−1 (La2NiMnO6) down to λ = 0.58 cm−1 (Gd2CoMnO6) and λ = 0.44 cm−1 (Gd2NiMnO6). A similar effect of the A-cation radius was established for the c-lattice parameter and Curie temperature, TC, in this series of double-perovskite films. Our observations directly demonstrate a strong impact of the lattice structure on the ferromagnetic superexchange interaction in double perovskites. Moreover, the A2CoMnO6 and A2NiMnO6 series exhibit very similar behavior of spin-phonon coupling due to the only moderate difference of Co2+ and Ni2+ cation size.

Large separations between ground and excited magnetic states in single‐molecule magnets (SMMs) are desirable to reduce the likelihood of spin reversal in the molecules. Spin‐phonon coupling is a process leading to magnetic relaxation. Both the reversal and coupling, making SMMs lose magnetic moments, are undesirable. However, direct determination of large magnetic states separations (>45 cm−1) is challenging, and few detailed investigations of the spin‐phonon coupling have been conducted. The magnetic separation in [Co(12‐crown‐4)2](I3)2(12‐crown‐4) (1) is determined and its spin‐phonon coupling is probed by inelastic neutron scattering (INS) and far‐IR spectroscopy. INS, using oriented single crystals, shows a magnetic transition at 49.4(1.0) cm−1. Far‐IR reveals that the magnetic transition and nearby phonons are coupled, a rarely observed phenomenon, with spin‐phonon coupling constants of 1.7–2.5 cm−1. The current work spectroscopically determines the ground–excited magnetic states separation in an SMM and quantifies its spin‐phonon coupling, shedding light on the process causing magnetic relaxation. [ABSTRACT FROM AUTHOR]

The present work reports the frequency dependent dielectric, ac -conductivity study across spin reorientation transition (T SRT) & Raman spectroscopy study across T SRT , Néel temperature (T N , Fe) of polycrystalline SmFeO 3 (SFO). Anomalous variation is observed in phonon mode parameters for SFO across T SRT and T N , Fe indicating the presence of spin-phonon coupling similar to that of other RFeO 3 compounds. Anomalous behavior is also observed in the temperature variation of dielectric constant and ac -conductivity across T SRT and frequency dispersion is observed at lower temperature side of T SRT. [ABSTRACT FROM AUTHOR]

The ferric pseudobrookite is a rare example of uniaxial anisotropic spin-glass insulator, depicting a multiglass behavior and magnetoelectric coupling. Here, we present Raman spectroscopy results in order to elucidate the spin-phonon coupling in Fe 2 TiO 5 for the first time. The experimental data are supported by computational simulations performed in view of density functional theory, which allowed us to assign the main Raman-active modes. Temperature-dependent phonon behavior exhibited anomalous evolution around 55 and 80–200 K, which was explained as successive coupling between lattice and spin configuration arising from spin freezing and short-range magnetic correlation, respectively. Arguments that the magnetoelectric effect in Fe 2 TiO 5 is mediated by spin-phonon coupling are presented. • Fe 2 TiO 5 compound was synthesized by solid state route. • Phonon assignments were provided by DFT calculations. • Temperature-dependent Raman spectra were recorded. • Anomaly in phonon mode was detected below freezing transition. • Magnetoelectric effect may be mediated by spin-phonon coupling. [ABSTRACT FROM AUTHOR]

The local structure of SrFe 12 O 19 nanoparticles was investigated by a combined synchrotron pair distribution function (PDF), Raman and 57Fe-Mössbauer spectroscopic analysis. The PDF and 57Fe-Mössbauer spectroscopy results indicate that SrFe 12 O 19 nanoparticles exist in an M-type hexagonal phase (∼10 nm), with a dynamically disordered trigonal bipyramidal Fe(2) site (2b). We determine that at 300 K, the timescale dynamics of Fe3+ ions near the 2b positions are between 10−15 and 10− s. The Raman spectra show anomalous shifts in all active phonon wavenumbers above T N ≈ 720 K, indicating the presence of spin-phonon coupling. The Fe3+(2b) dynamic regime motion was interpreted by taking into account changes in the electric polarization at T = T N , which discontinuously drops to zero at this temperature. [ABSTRACT FROM AUTHOR]

Abstract We report the presence of ferromagnetic short-range interactions, metamagnetic transitions and spin-phonon coupling on monoclinic polycrystalline Nd 2 CoMnO 6 double perovskite. DC thermomagnetic characterization shows a paramagnetic to ferromagnetic transition at T C1 ∼168 K and further to a cluster glass like magnetic transition at T C2 ∼135 K. Griffiths phase like features are also observed, attributed to the presence of competing magnetic interactions. Step like nature observed in the virgin curves of magnetic isotherms implies the presence of metamagnetic features. Additionally, temperature evolution of Raman spectra signatures spin-phonon coupling extending up to Griffiths like phase region indicating the possibility of magnetoelectric coupling in Nd 2 CoMnO 6. Highlights • Nd 2 CoMnO 6 (NCMO) double perovskite ceramic was prepared by the solid state method with P2 1 /n space group. • Mixed valence cations of Mn and Co induce magnetic super-exchange interactions leading to double magnetic transitions. • Domain wall pinning and magnetocrystalline anisotropy induced metamagnetic phenomena. • Observation of Griffith phase due to competing magnetic interactions. • Evidence of spin-phonon coupling. [ABSTRACT FROM AUTHOR]

An overall comparative study is made of the spin-phonon interactions in several rutile-structure transition-metal difluorides, specifically FeF2, MnF2, NiF2, and CoF2, in terms of recent developments obtained experimentally using inelastic light scattering spectroscopy and theoretically using a modified mean-field approach to estimate spin-pair correlation functions. New experimental data are presented here and interpreted within an extended and comprehensive theoretical treatment to yield estimates for the spin-phonon coupling coefficients and the relative magnitudes of the magneto-optical coupling coefficients. [ABSTRACT FROM AUTHOR]

We report the systematic study of structural and magnetic properties of Nd 1- x Pr x CrO 3 (0.0 ≤ x ≤ 0.30) perovskites. The XPS measurements confirm desired Pr (3+) valence state for the samples. The significant magnetization value with increased antiferromagnetic ordering (T N) and decreased spin-reorientation transition (T SR) is observed with Pr substitution. The enhanced weak ferromagnetism by Pr3+ presence dilutes Nd and Cr interactions, which finally vanishes T SR at maximum substitution. The Griffiths phase is observed in the substituted samples. A noticeable exchange bias (EB) effect is found for all samples. However, for the samples with higher Pr content, where spin-reorientation is suppressed, we observed the sharp increase in the EB field at 5 K (T < T SR). Interestingly, at 100 K (T > T SR), the substitution dependence of the EB field and magnetization link with the changes in the Cr-O bond length. Furthermore, the CrO 6 octahedral Raman modes below T N mark spin-phonon coupling. The evolution of the magnetic phase diagram is given. The study sheds light on tuned spin-reorientation, EB effect, and structural features in Nd 1- x Pr x CrO 3 compounds. • The study of structural and magnetic properties of Nd 1- x Pr x CrO 3 is presented. • The spin-reorientation transition decreases with the Pr substitution. • The Griffiths phase is observed for the first time in Nd-based orthochromite. • The exchange bias field for highest Pr substitution is four times the parent sample at low temperature. • The exchange bias effect correlated to spin-reorientation and structural parameters is observed. [ABSTRACT FROM AUTHOR]

Abstract: We report on the temperature dependent Raman scattering studies of polycrystalline HoCr1 − xFexO3 (x = 0 and 0.5) compounds. No signature of phonon mode related to structural phase transition is evident in the investigated temperature range in both the compounds. The thermal evolution of phonon spectra indicates a deviation of B3g(3) mode from the expected anharmonic behaviour below magnetic ordering temperature TN in HoCrO3 compound. This behaviour is attributed to spin–phonon coupling, which is due to the modulation of super exchange integral by lattice vibration. On the other hand, the anomalous behaviour of Ag mode and its line‐width around magnetic ordering in HoCr0.5Fe0.5O3 compound suggest the spin–phonon coupling. Apart from that, a clear deviation of wavenumber pertinent to B2g(1) mode suggests the possibility to observe ferroelectricity in HoCr0.5Fe0.5O3 compound. We believe that the present results would be helpful in obtaining new materials with multiferroicity near room temperature. [ABSTRACT FROM AUTHOR]

Transport, dielectric, magnetic and Raman studies of polycrystalline double perovskite EuTbCoMnO 6 have been performed. Temperature-dependent resistivity follows the variable range and small polaron hopping mechanism. The temperature-dependent dielectric study shows the usual frequency-dependent step-like behavior. It also shows thermally activated relaxor peak in loss curves with giant dielectric constant near room temperature. The temperature-dependent magnetization demonstrates a second-order phase transition around 113 K. The critical behavior near the magnetic transition has been systematically investigated. The Widom scaling relation and magnetic entropy change calculation have verified the reliability of critical parameters. Maximum magnetic entropy change around the magnetic transition temperature shows the magnetocaloric effect. The estimated values of critical parameters are close to the value of the theoretical mean-field model. Temperature-dependent Raman study shows spin-phonon coupling in the system. The appearance of the magnetocaloric effect and colossal dielectric constant shows that these materials are interesting for real-life applications. • Double perovskites Eu2-xTbxCoMnO6 (x = 0.0 and 1.0) have been investigated. • Resistivity follows the variable-range and small-polaron hopping mechanism. • The temperature-dependent dielectric study shows frequency-dependent steps and thermally activated relaxor peaks. • Inverse DC susceptibility study shows ferromagnetic clustered phase in the paramagnetic matrix. • Temperature-dependent Raman study shows spin-phonon coupling. [ABSTRACT FROM AUTHOR]

The spin-reorientation phenomenon exhibited by rare-earth based ferrite systems generate lot of interest due to its application potential in related fields like spintronic devices. In this work, it was demonstrated that the spin-reorientation temperature (T SR) of SmFeO 3 was tuned towards near room temperature by Cr doping. The SmFe 1- x Cr x O 3 (x = 0.0, 0.1, 0.3 and 0.4) samples were prepared by solid state reaction method and the structural refinements carried out on the x-ray diffraction patterns revealed that the samples were crystallized in orthorhombic structure with Pbnm space group. The magnetic measurements displayed that the samples were all ordered antiferromagnetically and the ordering temperature (T N) shows decreasing trend with increase in Cr doping. Furthermore, T SR was tuned from 472 K to 317 K when the composition was changed from x = 0.0 to x = 0.4. The temperature-dependent Raman spectroscopic studies on x = 0.4 sample revealed the existence of the spin-phonon coupling. In addition, this sample also displayed an interesting negative magnetization and compensation temperature. The details are discussed in this work. • SmFe 1- x Cr x O 3 sample shows systematic changes in T SR and T N with x. • x = 0.4 composition display near room temperature spin-reorientation T SR = 317 K. • Negative magnetization and compensation temperature is observed on x = 0.4 sample. • Evidence for spin-phonon coupling is observed through the Raman spectroscopic studies. [ABSTRACT FROM AUTHOR]