Photomagnetism (photomagnetic effect) is the effect in which a material acquires (and in some cases loses) its ferromagnetic properties in response to light. The current model for this phenomenon is a light-induced electron transfer, accompanied by the reversal of the spin direction of an electron. This leads to an increase in spin concentration, causing the magnetic transition.[1] Currently the effect is only observed to persist (for any significant time) at very low temperature. But at temperatures such as 5K, the effect may persist for several days.[1]
The energy diagram of the transitions between the ground state and the magnetic state. Solid arrows represent absorption of photons and dashed arrows represent non radiative processes
The magnetisation and demagnetisation (where not demagnetised thermally) occur through intermediate states [2] as shown (right). The magnetising and demagnetising wavelengths provide the energy for the system to reach the intermediate states which then relaxe non-radiatively to one of the two states (the intermediate state for magnetisation and demagnetisation are different and so the photon flux is not wasted by relaxation to the same state from which the system was just excited). A direct transition from the ground state to the magnetic state and, more importantly, vice versa is a forbidden transition, and this leads to the magnetised state being metastable and persisting for a long period at low temperatures.
Prussian blue analoguesedit
One of the most promising groups of molecular photomagnetic materials are Co-Fe Prussian blue analogues (i.e. compounds with the same structure and similar chemical make up to Prussian blue.) A Prussian blue analogue has a chemical formula M1-2xCo1+x[Fe(CN)6]•zH2O where x and z are variables (z may be zero) and M is an alkali metal. Prussian blue analogues have a face centre cubic structure.
It is essential that the structure be non-stoichiometric.[3] In this case the iron molecules are randomly replaced by water (6 molecules of water per replaced iron). This non-stoichiometry is essential to the photomagnetism of Prussian blue analogues as regions which contain an iron vacancy are more stable in the non-magnetic state and regions without a vacancy are more stable in the magnetic state. By illumination by the correct frequency one or another of these regions can be locally changed to its more stable state from the bulk state, triggering the phase change of the entire molecule. The reverse phase change can be accomplished by exciting the other type of region by the appropriate frequency.
Ohkoshi, Shin-ichi; Tokoro, Hiroko (2012). "Photomagnetism in Cyano-Bridged Bimetal Assemblies". Accounts of Chemical Research. 45 (10): 1749–1758. doi:10.1021/ar300068k. ISSN 0001-4842. PMID 22869535.
Han, Jie; Meng, Ji-Ben (2009). "Progress in synthesis, photochromism and photomagnetism of biindenylidenedione derivatives". Journal of Photochemistry and Photobiology C: Photochemistry Reviews. 10 (3): 141–147. doi:10.1016/j.jphotochemrev.2009.10.001. ISSN 1389-5567.
April 27, 2024
photomagnetism, confused, with, photoelectric, effect, photomagnetic, effect, effect, which, material, acquires, some, cases, loses, ferromagnetic, properties, response, light, current, model, this, phenomenon, light, induced, electron, transfer, accompanied, . Not to be confused with Photoelectric effect Photomagnetism photomagnetic effect is the effect in which a material acquires and in some cases loses its ferromagnetic properties in response to light The current model for this phenomenon is a light induced electron transfer accompanied by the reversal of the spin direction of an electron This leads to an increase in spin concentration causing the magnetic transition 1 Currently the effect is only observed to persist for any significant time at very low temperature But at temperatures such as 5K the effect may persist for several days 1 The energy diagram of the transitions between the ground state and the magnetic state Solid arrows represent absorption of photons and dashed arrows represent non radiative processes Contents 1 Mechanism 2 Prussian blue analogues 3 See also 4 References 5 Further readingMechanism editThe magnetisation and demagnetisation where not demagnetised thermally occur through intermediate states 2 as shown right The magnetising and demagnetising wavelengths provide the energy for the system to reach the intermediate states which then relaxe non radiatively to one of the two states the intermediate state for magnetisation and demagnetisation are different and so the photon flux is not wasted by relaxation to the same state from which the system was just excited A direct transition from the ground state to the magnetic state and more importantly vice versa is a forbidden transition and this leads to the magnetised state being metastable and persisting for a long period at low temperatures Prussian blue analogues editOne of the most promising groups of molecular photomagnetic materials are Co Fe Prussian blue analogues i e compounds with the same structure and similar chemical make up to Prussian blue A Prussian blue analogue has a chemical formula M1 2xCo1 x Fe CN 6 zH2O where x and z are variables z may be zero and M is an alkali metal Prussian blue analogues have a face centre cubic structure It is essential that the structure be non stoichiometric 3 In this case the iron molecules are randomly replaced by water 6 molecules of water per replaced iron This non stoichiometry is essential to the photomagnetism of Prussian blue analogues as regions which contain an iron vacancy are more stable in the non magnetic state and regions without a vacancy are more stable in the magnetic state By illumination by the correct frequency one or another of these regions can be locally changed to its more stable state from the bulk state triggering the phase change of the entire molecule The reverse phase change can be accomplished by exciting the other type of region by the appropriate frequency See also editPhotomagnetic effect PhotochromismReferences edit a b Pejakovic Dusan A Manson Jamie L Miller Joel S Epstein Arthur J 2000 Photoinduced Magnetism Dynamics and Cluster Glass Behavior of a Molecule Based Magnet Physical Review Letters 85 9 1994 1997 Bibcode 2000PhRvL 85 1994P doi 10 1103 PhysRevLett 85 1994 ISSN 0031 9007 PMID 10970666 Gutlich P 2001 Photoswitchable coordination compounds Coordination Chemistry Reviews 219 221 839 879 doi 10 1016 S0010 8545 01 00381 2 ISSN 0010 8545 Kawamoto Tohru Asai Yoshihiro Abe Shuji 2001 Novel Mechanism of Photoinduced Reversible Phase Transitions in Molecule Based Magnets Physical Review Letters 86 2 348 351 arXiv cond mat 0006076 Bibcode 2001PhRvL 86 348K doi 10 1103 PhysRevLett 86 348 ISSN 0031 9007 PMID 11177828 S2CID 24426936 Further reading editOhkoshi Shin ichi Tokoro Hiroko 2012 Photomagnetism in Cyano Bridged Bimetal Assemblies Accounts of Chemical Research 45 10 1749 1758 doi 10 1021 ar300068k ISSN 0001 4842 PMID 22869535 Han Jie Meng Ji Ben 2009 Progress in synthesis photochromism and photomagnetism of biindenylidenedione derivatives Journal of Photochemistry and Photobiology C Photochemistry Reviews 10 3 141 147 doi 10 1016 j jphotochemrev 2009 10 001 ISSN 1389 5567 Retrieved from https en wikipedia org w index php title Photomagnetism amp oldid 1208525633, wikipedia, wiki, book, books, library,
