Spin-reorientational transitions in low-doped Nd_1 xCa_xMnO₃manganites: the evidence of an inhomogeneous magnetic state

Abstract

A study of crystal structure, elastic, and magnetic properties of low-doped Nd 1−x Ca x MnO 3 (x 0.15) perovskites has been carried out. The ferromagnetic component is shown to increase under hole doping and, simultaneously, the temperature of the orbital order-disorder phase transition decreases. The mechanism of the concentrational transition from a weak ferromagnetic state (x = 0) to a ferromagnetic one (x > 0.15) is discussed using a two-phase model, according to which the samples consist of weak ferromagnetic and ferromagnetic phases exchange coupled at their boundary. It is found that interaction between different magnetic phases leads to spin reorientation which takes place for 0.06 x 0.1 compounds around T eff ∼ 9 K. In the temperature range from 5 to 20 K, metamagnetic behaviour is revealed for the Nd 0.92 Ca 0.08 MnO 2.98 sample. H versus T as well as T versus x magnetic phase diagrams, which are characterized by the missing of a canted phase, are proposed. The appearance of orientational transitions is explained on the basis of a magnetic analogue of the Jahn-Teller effect taking into account that the magnetic moments of Nd ions are ordered parallel to the moments of Mn ions in the ferromagnetic phase, and opposite to the direction of the weak ferromagnetic vector at T > T eff in the weak ferromagnetic phase.

Magnetization reversal in the Cr-doped manganite Bi0.3Ca0.7Mn0.75Cr0.25O3

“…For MR occuring in LnCrO 3 , it is attributed to the polarization of the paramagnetic (PM) moments of the Ln ions which align opposite to the canted Cr moments [24]. Besides of MR observed in the studied BCMCO, this phenomenon was also found previously in different manganites, such as (Dy,Ca)MnO 3 [25], Gd 0.67 Ca 0.33 MnO 3 [26], La 1−x Gd x MnO 3 [27], NdMnO 3+ı [28], Nd 1−x Ca x MnO y [29], and (Nd,Ca)(Mn,Cr)O 3 [30]. The MR phenomenon in these compounds was interpreted as a manifestation of a ferrimagnetic-like behavior due to the interplay of two magnetic antiferromagnetically coupled sublattices (rareearth sublattice and Mn sublattice).…”

Magnetic structure in the segregated phases Nd0.93MnO2.96

“…In relation to this point we note that one should reconsider explanations in terms of a weak ferromagnet [40][41][42] in which Nd ions are polarized in the direction opposite to that of the Mn 3+ magnetic moments because of the strong f-d interactions for NdMnO 3 . Related to our studied sample Troyanchuck et al [42] recently suggest that an interpretation based on a coexistence of AFM and FM phases as for Nd 1 [13] show additional evidence that Nd and Mn net magnetization are parallel along a large range of temperature ruling out the competition between Nd and Mn sub-lattices as the origin of the negative magnetization observed in NdMnO 3.11 and related systems [12,13,43].…”

Micro-Raman and magnetization studies of Nd1-xCaxMnO3phase transitions

“…A canted antiferromagnetic ground state, was observed for x < 0.1, and a ferromagnetic insulator ground-state was detected for 0.1 < x < 0.15 [18]. Also, in low-doped Nd 1-x Ca x MnO 3 (x < 0.15) phase separation was inferred [19].…”