Phase boundary between uniaxial and planar ferromagnets in layered perovskite manganite La2−2Sr1+2Mn2O7 (0.313⩽x⩽0.350)

Abstract We have examined magnetizations as a function of temperature and magnetic field in layered perovskite manganites La 2−2 x Sr 1+2 x Mn 2 O 7 single crystals ( x =0.313, 0.315, 0.318, 0.320 and 0.350) in order to determine the phase boundary between two ferromagnets (one is an uniaxial ferromagnet whose easy axis is parallel to the c -axis and the other is a planar ferromagnet whose easy axis is within the ab -plane) and following results are obtained: (i) all the present manganites exhibit magnetic transitions from a ferromagnet to a paramagnet at 76, 107, 116, 120 and 125 K for x =0.313, 0.315, 0.318, 0.320 and 0.350, respectively; (ii) for x =0.318, 0.320 and 0.350, the magnetic structure is a planar ferromagnet below Curie temperature; (iii) for x =0.313 and 0.315, the magnetic structure changes from an uniaxial to a planar ferromagnet at 66 and 85 K, respectively. From the results described above we have constructed the magnetic phase diagram of layered perovskite manganite La 2−2 x Sr 1+2 x Mn 2 O 7 (0.313⩽ x ⩽0.350).