Tuning of multi-magnetic phase and exchange bias effect by antisite disorder in Ca-doped La₂CoMnO₆ double perovskites

Abstract

The exchange bias effect at the magnetic interfaces and multi-magnetic phases strongly depends on the antisite disorder (ASD) driven spin configuration in the double perovskite systems. The percentage of ASD in double perovskites is extensively accepted as a key for designing diverse new nanospintronics with tailored functionalities. In this regards, we have investigated such ASD driven phenomena in Ca2+ doped bulk and polycrystalline La2−x Ca x CoMnO6 (0 ⩽ x ⩽ 1) series of samples. The structural and Raman studies provide evidence of an increase in the disorder due to the increment of Ca concentration in the parent compound (x = 0). The enhancement of disorder in the doped system induces various magnetic orderings, magnetic frustration and cluster glass-like behavior, which have been confirmed from AC and DC magnetic studies and neutron diffraction studies. As a result, significantly large exchange bias effects, namely zero-field cooled (spontaneous) and field-cooled (conventional) exchange bias, are found. These results reveal the tuning of ASD by doping, which plays an active role in the spin configuration at the magnetic interfaces.

The spontaneous exchange bias effect in La2-xCaxCoMnO6 series

“…A previous investigation of the SEB effect in La 2−x Ca x CoMnO 6 polycrystals prepared by the sol-gel method [26] showed H EB values remarkably different from ours, further demonstrating the severe sample-dependence in this system. Moreover, in contrast to our work, increasing H EB for 0 ≤ x ≤ 0.5 samples followed by a decrease for x > 0.5 was observed, although the x = 0.75 concentration was not investigated.…”

“…According to the arguments proposed in Ref. [26], the H EB of our series should decrease for 0 ≤ x ≤ 0.5, in contrast to the results. Thus, for our La 2−x Ca x CoMnO 6 samples, we ascribe the increase of H EB directly to the changes in the AFM/FM interfaces.…”

“…The controversy occurs because the Co and Mn scattering factors are very similar for XRD performed with Cu-K α radiation. Different groups have reported such compounds as belonging to one of these space groups or even a mixture of both [18,24,25,26,27,28]. The Co-and Mn-based perovskites are known to be very sensitive to the synthesis route [6,29,30], and the La 2−x Ca x CoMnO 6 seems to be a clear manifestation of this.…”

Structural transitions and spontaneous exchange bias in La2-xBaxCoMnO6 series

“…Fig. 3(f) shows that the H EB is maxima for x = 0.5, in resemblance with La 2−x Sr x CoMnO 6 and La 2−x Ca x CoMnO 6 series growth by the sol-gel method [12,22]. The evolution of H EB for these Sr-and Ca-based systems was ascribed to changes in the ASD at Co/Mn site, which destroys the long-range magnetic order and gives rise to a metamagnetic state at low temperatures.…”

Maxwell–Wagner Polarization and Mixed Ferromagnetic and Antiferromagnetic State in Eu2CoMnO6

“…The ongoing research on multifunctional materials drives people toward double perovskite (DP) oxides, i.e., A 2 BB'O 6 (A = rareearth/alkaline cation and B/B' = transition-metal cations). [1][2][3][4][5][6] The recent studies on various rare-earth-based DP with B sites occupied by Co and Mn, that is R 2 CoMnO 6 (R = La to Lu), have received extensive attention owing to their various exciting functional properties, namely, electrical and optical properties, [7,8] defect-induced modulation of physical properties, [9] tunable magnetization steps, [10] magnetocaloric effect and pyro-current, [11,12] magnetoresistance, [13] exchange bias, [14][15][16] magnetocaloric and magnetodielectric effects, [17,18] Griffiths-like and non-Griffithslike clustered phase, [19][20][21] spin-phonon coupling (SPC), [22] Hopkinson effect, [23] multiferroicity, [24] etc. The slight change in rare-earth size in the R 2 CoMnO 6 family instigates significant variations in the Co─O─Mn bond length and angle, thus modifying magnetic and electronic ground states via modification of superexchange (SE) interactions.…”