Multiferroic nature of charge-ordered rare earth manganites

Abstract

The present study of the charge-ordered manganites shows that many of the chargeordered rare earth manganites are multiferroics showing magnetocapacitance. They also show exhibit certain other features. Thus, the broad maximum in the dielectric constant around T CO or T N becomes more prominent in the presence of the magnetic field in certain cases. The magnitude and sign of the magnetocapacitance effect depends on the frequency of measurement. It is generally better to employ a relatively high frequency, well above 10k Hz to obtain reliable data.We have also studied the dielectric properties of a few other charge-ordered rare earth manganites, La 0.25 Nd 0.25 Ca 0.5 MnO 3 being one of them. This material exhibits a re-entrant 4 ferromagnetic transition at a temperature lower than the charge-ordered transition. The chargeordered transition is around 240 K and the ferromagnetic transition is at 150 K [15]. Interestingly, we find maxima in the dielectric constant at both T CO and T N , the one at T CO being is more prominent (figure 4).It is important to note some of the important characteristics of the charge-ordered manganites studied by us in order to fully understand their ferroic properties. The most important feature is that all these manganites exhibit electronic phase separation at low temperatures (T < T CO ) [10]. They exhibit a decrease in resistivity on application of large magnetic fields (>4 T) [16,17]. Application of electric fields also causes a significant decrease in the resistivity of the manganites [17,18]. On the application of electric fields, the manganites show magnetic response [19]. Such electric field-induced magnetization may also be taken as evidence for coupling between the electric and magnetic order parameters in the manganites. It is likely that grain boundaries between the different electronic phases have a role in determining the dielectric behaviour. The importance of grain boundaries in giving rise to high dielectric constants has indeed been recognized [20,21]. In spite of the complexity of their electronic structure, the present study shows that the charge-ordered rare earth manganites possess multiferroic and magnetoelectric properties. Clearly, charge-ordering provides a novel route to multiferroic properties specially in the case of the manganites. Acknowledgement:

Structural Determination and Imaging of Charge Ordering and Oxygen Vacancies of the Multifunctional Oxides REBaMn2O6‐χ (RE = Gd, Tb)

“…Charge order (CO) structures have been experimentally evidenced by several techniques in REBaMn 2 O 6 perovskites and different CO models have been proposed from powder neutron diffraction, electron diffraction and resonant X‐ray and Raman scattering experiments . Of particular interest is that multiferroic properties have been ascribed to some manganites due to coupling between magnetic and charge ordering.…”

Charge transfer and a magnetic crossover in hexagonalBaRu1−xMnxO3perovskites

“…5,6 Manganese oxide perovskites ͑manganites͒ have been extensively studied due to the observation of colossal magnetoresistances, charge order, and electronic phase segregation. [7][8][9][10] Mn and Ru can be substituted for each other in these types of oxide and several series have been investigated such as CaMn 1−x Ru x O 3 , 11 SrMn 1−x Ru x O 3 , 12,13 and Ln y A 1−y Mn 1−x Ru x O 3 ͑Ln= lanthanide; A = Ca, Sr͒. [14][15][16][17] Ru doping is found to induce ferromagnetism and metallicity and suppresses the charge ordered state of manganites.…”

The structural and magnetic ordering in La0.5−Nd Ca0.5MnO3 (0.1≤x≤0.5) manganites

“…The difference between the ZFC and FC states essentially arises from application of magnetic field in crystallographically different structures. Magnetic field dependent dielectric studies carried out in charge ordered systems exhibit significant influence of magnetic field on the dielectric behavior, suggesting that the distortions are influenced by the magnetic field [43]. The peak temperature in M(T) identified as T CO shows aminimum at x ¼ 0:3 composition, coinciding with the minimum observed in the ðD JT Þ distortion parameter.…”