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Organic photoresponsive materials, which change their physical properties upon irradiation with light, are attracting tremendous scientific attention, as they offer a flexible and sustainable platform for developing various optoelectronic devices. In this work, photoinduced magnetization switching in two carbazole‐functionalized organic molecules, (9H‐carbazol‐9‐yl)(4‐chlorophenyl)methanone (ClPhCz) and (9H‐carbazol‐9‐yl)(2,4‐dichlorophenyl)methanone (DClPhCz) is reported for the first time. It was found that stabilization of the triplet excited state in those molecules is long enough for a net change in magnetic moment to be detected with a SQUID magnetometer. The change in magnetic moment upon excitation with a blue light laser was larger in ClPhCz, remaining high upon repeating the photoirradiation. In contrast, DClPhCz exhibited a smaller magnetic response, which gradually decreased upon repeating the experiment. [ABSTRACT FROM AUTHOR]

Abstract Understanding the feasibility to couple semiconducting and magnetic properties in metal halide perovskites through interface design opens new opportunities for creating the next generation spin‐related optoelectronics. In this work, a fundamentally new phenomenon of optically induced magnetization achieved by coupling photoexcited orbital magnetic dipoles with magnetic spins at perovskite/ferromagnetic interface is discovered. The depth‐sensitive polarized neutron reflectometry combined with in situ photoexcitation setup, constitutes key evidence of this novel effect. It is demonstrated that a circularly polarized photoexcitation induces a stable magnetization signal within the depth up to 7.5 nm into the surface of high‐quality perovskite (MAPbBr3) film underneath a ferromagnetic cobalt layer at room temperature. In contrast, a linearly polarized light does not induce any detectable magnetization in the MAPbBr3. The observation reveals that photoexcited orbital magnetic dipoles at the surface of perovskite are coupled with the spins of the ferromagnetic atoms at the interface, leading to an optically induced magnetization within the perovskite’s surface. The finding demonstrates that perovskite semiconductor can be bridged with magnetism through optically controllable method at room temperature in this heterojunction design. This provides the new concept of utilizing spin and orbital degrees of freedom in new‐generation spin‐related optoelectronic devices.

Understanding the feasibility to couple semiconducting and magnetic properties in metal halide perovskites through interface design opens new opportunities for creating the next generation spin‐related optoelectronics. In this work, a fundamentally new phenomenon of optically induced magnetization achieved by coupling photoexcited orbital magnetic dipoles with magnetic spins at perovskite/ferromagnetic interface is discovered. The depth‐sensitive polarized neutron reflectometry combined with in situ photoexcitation setup, constitutes key evidence of this novel effect. It is demonstrated that a circularly polarized photoexcitation induces a stable magnetization signal within the depth up to 7.5 nm into the surface of high‐quality perovskite (MAPbBr3) film underneath a ferromagnetic cobalt layer at room temperature. In contrast, a linearly polarized light does not induce any detectable magnetization in the MAPbBr3. The observation reveals that photoexcited orbital magnetic dipoles at the surface of perovskite are coupled with the spins of the ferromagnetic atoms at the interface, leading to an optically induced magnetization within the perovskite's surface. The finding demonstrates that perovskite semiconductor can be bridged with magnetism through optically controllable method at room temperature in this heterojunction design. This provides the new concept of utilizing spin and orbital degrees of freedom in new‐generation spin‐related optoelectronic devices. [ABSTRACT FROM AUTHOR]

Time‐resolved magneto‐optical Kerr effect measurement is carried out to determine ultrafast hysteresis behavior during a photo‐induced demagnetization/remagnetization process for Co/Pt ferromagnetic multilayers. Due to the stroboscopic measurement scheme, hysteresis curve measured by a pump–probe technique exhibits an irreversible behavior, repeatedly reset to a metastable hysteresis state at each stroboscopic measurement, observed as the reduction of the coercivity. It is demonstrated that the stroboscopically measured hysteresis and the coercivity could be a stable parameter in describing the ultrafast photo‐induced spin dynamics for both reversible and irreversible behaviors. Moreover, it is found that an unusual coercivity behavior exists together with a nontrivial magnetization change under external fields comparable to the coercivity of the sample. [ABSTRACT FROM AUTHOR]

We study the enhancement of the magnetic transition temperature Tc due to incident light in ferromagnetic semiconductors such as EuS. The photoexcited carriers mediate an extra ferromagnetic interaction due to the coupling with the localized magnetic moments increasing the Tc. The Hamiltonian consists of a Heisenberg model for the localized moments and an interaction term between the photoexcited carriers and the localized moments. The model predicts a small enhancement of the transition temperature, about a fraction of a degree K, in semi-quantitative agreement with the experiments. [ABSTRACT FROM AUTHOR]

Abstract: We report a detailed study of a double-exchange model proposed for the molecule-based magnets. The model is applied to a two-dimensional periodic complex made of a transition metal and an organic molecule in which the electronic structure is described by effective d orbitals of the transition metal ion at infinite Hund''s coupling limit and the lowest unoccupied molecular orbital of the organic molecule, . Depending on the average electron density of the organic molecules and various superexchange couplings between metal ions'' core spins, magnetic states of the complex are investigated. Performing Monte Carlo calculations on a model Hamiltonian for various electron densities of the organic molecule, the average magnetization and critical magnetic ordering temperatures are determined. [Copyright &y& Elsevier]

Abstract: An intermediate in photoinduced magnetization process for the photomagnetic high-spin molecule [MoIV(CN)2(CN-CuL)6]8+ is studied with quantum chemistry calculations of the density functional theory and the ab initio multireference configuration interaction methods. It is found that the intramolecular electronic transfer from MoIV to CuII leads one trigonal-bipyamid coordinated CuII to be changed to the tetrahedral coordinated CuI with the light irradiation. The calculated magnetic properties show that the paramagnetic system [MoIV(CN)2(CN-CuIIL)6]8+ with six isolated spin 1/2 Cu ions is changed to ferromagnetic coupling high-spin system [MoV(CN)2(CN-CuIIL)5(CN-CuIL)]8+. These calculations will help to understand photoinduced magnetization phenomenon and provide a clue for the synthesization of new reversible photoinduced magnetic compounds. [Copyright &y& Elsevier]

Abstract: In this review, recent studies on photoinduced magnetization in molecular compounds are introduced. The magnetic materials presented here range from Prussian blue analogues to purely organic radicals. Various photomagnetic phenomena observed in those materials are briefly described. These are, for example, photoinduced magnetization, photoinduced demagnetization, photoinduced spin cluster, photoinduced magnetic-pole inversion, photoinduced spin flipping, light-induced excited spin state trapping, photoinduced valence tautomerism, etc. It is thought that these can be used for future high-density photo-recording media and optical switches in molecular devices. [Copyright &y& Elsevier]

Photoinduced magnetization of the cyano-bridged 3d–4f hetero-bimetallic assembly Nd (DMF)4(H2O)3(μ-CN)Fe(CN)5⋅H2O (1) (DMF=N,N-dimethylformamide) is described in this paper. The χMT values are enhanced by about 45% after UV light illumination in the temperature range of 5–50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing molecule-based magnetic materials. [ABSTRACT FROM AUTHOR]

This paper reviews the most recent progress in the studies of photocarrier-induced magnetism, phototunable magnetization reversal, as well as photoenhanced magnetization in the magnetic alloy semiconductor heterostructure (In,Mn)As/(Ga,Al)Sb and the GaAs–Fe granular structure. Emphases are given to point out that the interplay between the nonmagnetic constituents and magnetic constitutes can be mediated by carrier spins. [ABSTRACT FROM AUTHOR]

Abstract: We study magnetic ordering in non-equilibrium processes in temperature cycling where first the photoinduced saturated magnetic ordered state is prepared, and then the system is warmed up to a certain temperature (say ) and it is cooled down to the initial temperature. Using a generalized model which describes both spin-crossover transition and magnetic transition, we show that depending on the value of , the critical temperature of magnetization and its saturated value change, which reproduces qualitatively the experimental results of magnetic ordering. It is found that the properties of dilution of magnetic sites affect the magnetic ordering. [Copyright &y& Elsevier]

The current investigation in magnetism in 2D materials offers new opportunities for studying spintronics at low dimensions. Here, reversible photoinduced room temperature magnetization in 2D Bi 2 WO 6 nanosheets is reported for the first time. Compared with the original state, the ultraviolet (UV)-illuminated Bi 2 WO 6 nanosheets show a yellow-green color change and significantly enhanced magnetic signals (saturated magnetization (M s ) increased from 0.002 to 0.12 emu g -1 ). X-ray photoelectron spectroscopy (XPS) results show unexpected W reduction (W 6+ to W 5+ /W4+) and Bi oxidation (Bi 3+ to Bi 5+ ) upon UV illumination for the Bi 2 WO 6 nanosheets, indicating a photoexcited Bi to W charge transfer. Density functional theory (DFT) calculations indicate spontaneous spin polarization of the Bi 2 WO 6 nanosheets in the excited metastable state. Meanwhile, thicker Bi 2 WO 6 nanoplates or nanoparticles show no enhanced magnetic signals upon UV illumination. UV illumination of the thin Bi 2 WO 6 nanosheets can induce the formation of internal electric field (polarization), leading to structural deformation/lattice distortion (photostriction). The photoexcited electrons are trapped in the WO 6 layers while the photogenerated holes are trapped in the Bi 2 O 2 layers, leading to spin polarization and enhance the magnetization. The research may bring some new insights in tuning the magnetic properties of 2D nanostructures., (© 2020 Wiley-VCH GmbH.)

Abstract: An analytic expression is given for the inverse Faraday effect, i.e., for the magnetization occuring in a transparent medium exposed to a circularly polarized high-frequency electromagnetic wave. Using a microscopic approach based on the Drude approximation of a free-electron gas, the magnetization of the medium due to the inverse Faraday effect is identified as the result of microscopic solenoidal currents generated by the electromagnetic wave. In contrast to the better known phenomenological derivation, this microscopic treatment provides important information on the frequency dependence of the inverse Faraday effect. [Copyright &y& Elsevier]