Miho Itoi

Control of charge transfer phase transition and ferromagnetism by photoisomerization of spiropyran for an organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)3] (SP = spiropyran, dto = C2O2S2).

Iron mixed-valence complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)](dto = C(2)O(2)S(2)), shows a spin entropy-driven phase transition called charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) around 120 K and a ferromagnetic transition at 7 K. These phase transitions remarkably depend on the hexagonal ring size in the two-dimensional honeycomb network structure of [Fe(II)Fe(III)(dto)(3)](-)(infinity). In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photoirradiation, we have synthesized a photosensitive organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)(3)](SP = spiropyran), and investigated the photoinduced effect on the magnetic properties. Upon UV irradiation at 350 nm, a broad absorption band between 500 and 600 nm appears and continuously increases with the photoirradiation time, which implies that the UV irradiation changes the structure of spiropyran from the closed form to the open one in solid state. The photochromism in spiropyran changes the ferromagnetic transition temperature from 5 to 22 K and the coercive force from 1400 to 6000 Oe at 2 K. In this process, the concerted phenomenon coupled with the charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) and the photoisomerization of spiropyran is realized.

Pressure Effect on Charge-Transfer Phase Transition in a Mixed-Valence Iron Complex, (n-C3H7)4N[FeIIFeIII(dto)3] (dto = C2O2S2)

We have investigated the hydrostatic pressure effect on the charge-transfer phase transition between Fe II and Fe III in a mixed-valence iron complex, ( n -C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ] (dto...

Search on Multi-Functional Properties of Spin-Crossover System

We have investigated the spin-crossover behavior for one-dimensional complexes [Fe(trz) 3 (RSO 3 ) 2 (trz= triazole) and two-dimensional mixed-valence complexes (C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](dto=C 2 O 2 S 2 ). For the case of [Fe(4-NH 2 trz) 3 ](RSO 3 ) 2 , we have controlled Tc and the thermal hysteresis width of spin transition by using the isomerization of counter anion or the fastener effect between the alkyl chains of counter anions C n H 2n+1 SO 3 − . Moreover, we have synthesized a [Fe(Htrz) 3 ] film by using an ion-exchange film having SO 3 − , which shows the spin transition around room temperature. For the case of (C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](n=3,4), we have found a charge transfer phase transition between Fe II and Fe III around 120 K.

Origin of charge transfer phase transition and ferromagnetism in (CnH2n+1)4N[FeIIFeIII (dto)3] (dto=C2O2S2)

Mixed-valence complex (n-C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ] (dto=C 2 O 2 S 2 ) shows a new-type of phase transition coupled with spin and charge around 120 K, where the charge transfer between the Fe and Fe III sites occurs reversibly, and shows the ferromagnetic transition at 6.5 K. We have investigated the transport and magnetic properties for the single crystal of (n-C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ]. Both of the intra- and interlayer resistivity showed an anomalous drop due to the charge transfer phase transition. The anisotropy of the magnetization implied that the spins in the ferromagnetic ordered state were aligned parallel to the layer of [Fe II Fe III (dto) 3 ]∞.

Pressure Effect on Ferromagnetic Transition and Charge-Transfer Phase Transition in a Mixed-Valence Iron Complex (n-C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ](dto=C 2 O 2 S 2 )

Iron mixed-valence complex (n-C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ] (dto=C 2 O 2 S 2 ) exhibits not only the ferromagnetic transition at 6.5 K but also the charge-transfer phase transition between Fe II and Fe III around 120 K. In order to elucidate the mechanism of the charge-transfer phase transition, we measured the magnetic susceptibility under external pressure. Under hydrostatic pressure up to 0.9 Gpa, the critical temperature of the charge-transfer transition strongly depends on external pressure, while the Curie temperature remains unchanged. Under uniaxial stress of 0.6 GPa, on the other hands, the Curie temperature increases up to 15 K, while the charge-transfer temperature remains unchanged. After releasing uniaxial stress, the zero field magnetization at ambient pressure has two peaks at 7 K and 15 K, which implies two kinds of ferromagnetic spin configuration coexist, i.e. Fe III (S=5/2), Fe II (S=0) and Fe III (S=1/2), Fe II (s=2). The coexistence of two kinds of ferromagnetic spin configuration was also observed for (n-C 4 H 9 ) 4 N[Fe II Fe III (dto) 3 ] at ambient pressure. mixed-valence spin crossover charge transfer pressure effect

New-type Phase Transition Coupled with Spin and Charge in Iron Mixed-Valence System

We have investigated the physical properties of (n-C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](dto = C 2 O 2 S 2 ) by means of 57 Fe Mössbauer spectroscopy, magnetic susceptibility, and ESR. From the analysis of 57 Fe Mössbauer spectra and ESR signal, we have discovered a new type of first order phase transition around 120 K for (n-C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ](n = 3, 4), where the charge transfer transition between Fe II and Fe III occurs reversibly. In the higher temperature phase, the Fe III ( S = 1/2) and Fe II ( S = 2) sites are coordinated by six S atoms and six O atoms, respectively. In the lower temperature phase, on the other hand, the Fe III ( S = 5/2) and Fe II ( S = 0) sites are coordinated by six O atoms and six S atoms, respectively. Moreover, we have found the ferromagnetic phase transition in this system. The ferromagnetic order is induced by the charge transfer interaction between the Fe III ( S = 5/2) and Fe II ( S = 0) sites. spin crossover ferromagnetism charge transfer phase transition mixed valence