Electronic and magnetic phase diagram of polycrystalline Gd 1−x Ca x MnO 3 manganites

Experimental and theoretical demonstration of negative magnetization induced by particle size reduction in nano-form Gd$_{1-x}$Ca$_x$MnO$_3$

“…We note that the magnetic behaviors in our samples of x = 0.4, 0.5, and 0.6 are in agreement with those reported in Ref. 28. Now, the system at x = 0.4, based on the phase diagram in Ref.…”

“…Now, the system at x = 0.4, based on the phase diagram in Ref. 28 and Fig. 4, is primarily ferromagnetic with small domains that are antiferromagnetic.…”

“…With the Gd ions remaining paramagnetic down to low temperatures, the Mn-Mn interaction leads to different ordered states in Gd 1−x Ca x MnO 3 depending on the relative percentage of Mn 3+ and Mn 4+ ions. The phase diagram of Gd 1−x Ca x MnO 3 , obtained from magnetoresistive measurements, report ferromagnetic insulating phase for x < 0.5, which transforms into charge ordered (CO) state with AFM interactions for x ≥ 0.5 18,28 . In the low-doped region (0 < x < 0.5), the ferromagnetically ordered Mn-spins force the Gd-spins to align opposite to its direction, i.e., opposite to H ext , due to a weak negative exchange interaction between them 18 ; thus, a ferrimagnet results at very low temperatures.…”

“…With decreasing temperature, as the contribution of the magnetic moment of paramagnetic Gd ions keeps on increasing in the direction opposite to the external magnetic field, the net moment decreases and can become negative. At higher doping concentrations (x > 0.5), the AFM domains become larger in extent and percolate the sample causing the total magnetization to increase steadily with decreasing temperature 28 .…”

“…Although the phenomenon of negative magnetization has been studied in manganite compounds in bulk form 11,18,28,29 and in thin-film form 30 , the role of particle size in nano-form manganites has not been investigated. In the nano systems surface effects in nanoparticles can alter the magnetic behavior.…”