Magnetic study on novel organic ferromagnetic semiconductors

1 . We present clear evidence for ferromagnetic ordering in the magnetization data of（BEDT-TTFVS） febr_4，which was newly synthesized as a semiconducting 1:1 charge-transfer salt. Magnetization dataobtained by a resonant circuit method show a magnetic transition temperature of 1.9±0.3 K，a hysteresis loop below 1.5 K. An additional magnetization jump at 0.2 T was clearly observedbelow 1.9 K，suggesting that the salt shows a canted ferromagnetism.2)We observed magnetic orderings of Fe <3+> dspins in the 1:1 salts of BEDT-TTFVS(O) with fex_4 (X=Br,Cl) ions by magnetization measurements upto 0.5 T in the temperature range down to 0.4 K using a homemade pulsed magnet system combined witha ^3He cryostat. Although temperature dependences of the magnetic susceptibilities above 20k obeyedCurie-Weiss law with positive Weiss temperatures，salts not subjected to ferromagnetic ordering but to antiferromagnetic orderings except for（BEDT-TTFVS） febr_4 . The Neel temperatures, t_n were determined to be 2.4，1.0 and 0.8 K for (BEDT-TTFV0) / febr_4, (BEDT-TTFVO) / fecl_4 / (BELMTTFVS) / fecl_4，respectively. Below t_n，a clear magnetization jump due to the spin-flop was also observed.3)We performed high fieldmagnetization measurements up to 55 T for newly synthesized antiferromagnetic charge-transfer salts（Benzo-TTFVS）_2 febr_4 with t_n =5.8 K and (Benzo-TTFVO)_2 febr_4 with t_n =9.3 K A spin-flop behaviorat 1.8 T and a saturation at 14.8 T were observed in the magnetization curve at 0.5 K for the（Benzo-TTFVS）_2 febr_4 salt. For the (Benzo-TTFV0)_2 febr_4 salt a spin-flop at 6.9 T and a saturationat 36.2 T were observed. We estimate the exchange interaction between d spins and the magneticanisotropy for both salts from the magnetization data。

1)We present clear evidence for ferromagnetic ordering in the magnetization data of (BEDT-TTFVS)・FeBr_4, which was newly synthesized as a semiconducting 1:1 charge-transfer salt. Magnetization data obtained by a resonant circuit method show a magnetic transition temperature of 1.9±0.3 K, and a hysteresis loop below 1.5 K. An additional magnetization jump at 0.2 T was clearly observed below 1.9 K, suggesting that the salt shows a canted ferromagnetism.2)We observed magnetic orderings of Fe^<3+> d spins in the 1:1 salts of BEDT-TTFVS(O) with FeX_4 (X=Br,Cl) ions by magnetization measurements up to 0.5 T in the temperature range down to 0.4 K using a homemade pulsed magnet system combined with a ^3He cryostat. Although temperature dependences of the magnetic susceptibilities above 20 K obeyed a Curie-Weiss law with positive Weiss temperatures, the salts were not subjected to ferromagnetic ordering but to antiferromagnetic orderings except for (BEDT-TTFVS)・FeBr_4. The Neel temperatures, T_N were determined to be 2.4, 1.0 and 0.8 K for (BEDT-TTFV0)・FeBr_4, (BEDT-TTFVO)・FeCl_4 and (BELMTTFVS)・FeCl_4, respectively. Below T_N, a clear magnetization jump due to the spin-flop was also observed.3)We performed high field magnetization measurements up to 55 T for newly synthesized antiferromagnetic charge-transfer salts, (Benzo-TTFVS)_2FeBr_4 with T_N=5.8 K and (Benzo-TTFVO)_2FeBr_4 with T_N=9.3 K A spin-flop behavior at 1.8 T and a saturation at 14.8 T were observed in the magnetization curve at 0.5 K for the (Benzo-TTFVS)_2FeBr_4 salt. For the (Benzo-TTFV0)_2FeBr_4 salt a spin-flop at 6.9 T and a saturation at 36.2 T were observed. We estimate the exchange interaction between d spins and the magnetic anisotropy for both salts from the magnetization data.