Magnetic Phase Diagram in Layered Perovskite Manganite La_(2-2x)Sr_(1+2x)Mn_2O_7 (0.313 ≤ x ≤ 0.350)

摘要

We have measured the magnetization as a function of temperature and magnetic field in layered perovskite manganites of La_(2-2x)Sr_(1+2x)Mn_2O_7 single crystals (x=0.313, 0.315, 0.320, 0.350) in order to know their magnetic structures. All the present manganites exhibit magnetic transitions from ferromagnetic to paramagnetic at 76K, 107K, 120K and 125K for x=0.313, 0.315, 0.320 and 0.350, respectively. For x=0.350 and 0.320, the magnetic structure is a planar ferromagnetism whose easy axis is in the ab-plane at all temperatures below the Curie temperature. On the other hand, for x=0.315 and 0.313, the magnetic structure is an uniaxial ferromagnetism whose easy axis is along the c-axis below 85K and 66K, respectively, and a planar ferromagnetism above the temperature. From the results described above, we made the detailed magnetic phase diagram of layered perovskite manganite La_(2-2x)Sr_(1+2x)Mn_2O_7 (0.313 ≤ x ≤ 0.350).