Effect of Subsidiary Phase on the Magnetic and Transport Properties of Sr1.6La1.4Mn2O7

Abstract

Temperature and field dependent magnetic and transport measurements on a polycrystalline sample of Sr 1.6 La 1.4 Mn 2 O 7 reveal distinct magnetic peaks above the ferromagnetic ordering temperature T C % 90 K. The magnetic moment of the subsidiary phases identified as perovskitic impurities by a relation between the volume fraction and the corresponding magnetic moment does not couple with that of Sr 1.6 La 1.4 Mn 2 O 7 in the high temperature range. This is evidenced by the presence of two slopes, dM/dH, in the M(H) curves and two different field dependences, H and H 2 , in the r(H) curves. On the other hand, a simple slope, dM/dH, in the low temperature regime hints at an exchange coupling between the magnetic moments of the two phases.

Metal-Insulator Transition Induced by Short Range Magnetic Ordering in Mono-layered Manganite

“…As shown in Figure 5(b), the shape of the MR curves defined as {ρ H − ρ 0 }/ρ 0 is slightly different from below and above T MI ≈ 160 K. The MR decreases almost linearly with H at 190 K but exponentially at 5 K as reported in other CMR materials. 24 It should be mentioned that the occurrence of a hysteretic behavior in the paramagnetic state is unusual, where the MR typically varies with H 2 . 24 This is a strong evidence for the existence of non-paramagnetic state above T MI .…”

“…24 It should be mentioned that the occurrence of a hysteretic behavior in the paramagnetic state is unusual, where the MR typically varies with H 2 . 24 This is a strong evidence for the existence of non-paramagnetic state above T MI . This hysteretic behavior found in both temperature ranges above and below T MI is mainly attributed to the fieldinduced alignment of antiferromagnetically coupled magnetic moments.…”

“…25 It is worthy to remark that a magnetic signal due to negligible amount of perovskite phase included in the bi-layered manganite, which is not detected by X-ray diffraction, is clearly resolved using a SQUID magnetometer. 24 However, we have not seen any other magnetic signals in the entire temperature range besides the weak FM transition near 130 K. Second, the perovskite phase La 1-x Sr x MnO 3 that considers as the most likely impurity shows the onset of FM ordering typically in the higher temperature range above 200 K. 24 Finally, the M-I transition cannot be induced by the impurity or inter-grown phases alone because a minimal volume fraction to connect percolation path is at least about 20%. 26 Another important feature to be addressed is that neither weak FM ordering nor M-I transition has been observed in single crystal of the mono-layered manganite.…”