Spin-cycloid instability as the origin of weak ferromagnetism in the disordered perovskiteBi0.8La0.2Fe0.5Mn0.5O

Abstract

Powder neutron diffraction and magnetometry studies have been conducted to investigate the crystallographic and magnetic structure of Bi0.8La0.2Fe0.5Mn0. 5O3. The compound stabilizes in the Imma orthorhombic crystal symmetry in the measured temperature range of 5 to 380 K, with a transition to antiferromagnetic order at TN≈240 K. The spin cycloid present for BiFeO3 is found to be absent with 50% Mn3+ cation substitution, leading to G-type antiferromagnetic order with an enhanced out-of-plane canted ferromagnetic component, evident from measurable weak-ferromagnetic hysteresis. Structural modifications do not solely explain this behavior, indicating that modified electron exchange interactions must be taken into account. A classical spin simulation was developed to investigate the effect of random substitution in a disordered pseudocubic perovskite. The calculations took into account the nearest-neighbor, next-nearestneighbor, and Dzyaloshinskii-Moriya interactions, along with the local spin anisotropy. Using this framework to extend the established Hamiltonian model for BiFeO3, we show that only certain types of perturbations at a magnetic defect and the surrounding molecular fields trigger a simultaneous collapse of cycloidal order and the emergence of the long-range weak-ferromagnetic component. By adopting values for the Mn molecular fields appropriate for REMnO3 (RE= rare earth), simulations of BiMn0.5Fe0.5O3 exhibit the key magnetic properties of our experimental observations. Powder neutron diffraction and magnetometry studies have been conducted to investigate the crystallographic and magnetic structure of Bi 0.8 La 0.2 Fe 0.5 Mn 0.5 O 3 . The compound stabilizes in the I mma orthorhombic crystal symmetry in the measured temperature range of 5 to 380 K, with a transition to antiferromagnetic order at T N ≈ 240 K. The spin cycloid present for BiFeO 3 is found to be absent with 50% Mn 3+ cation substitution, leading to G-type antiferromagnetic order with an enhanced out-of-plane canted ferromagnetic component, evident from measurable weak-ferromagnetic hysteresis. Structural modifications do not solely explain this behavior, indicating that modified electron exchange interactions must be taken into account. A classical spin simulation was developed to investigate the effect of random substitution in a disordered pseudocubic perovskite. The calculations took into account the nearest-neighbor, next-nearest-neighbor, and Dzyaloshinskii-Moriya interactions, along with the local spin anisotropy. Using this framework to extend the established Hamiltonian model for BiFeO 3 , we show that only certain types of perturbations at a magnetic defect and the surrounding molecular fields trigger a simultaneous collapse of cycloidal order and the emergence of the long-range weak-ferromagnetic component. By adopting values for the Mn molecular fields appropriate for REMnO 3 (RE = rare earth), simulations of BiMn 0.5 Fe 0.5 O 3 exhibit the key magnetic properties of our experimental observations.

Compliments of confinements: substitution and dimension induced magnetic origin and band-bending mediated photocatalytic enhancements in Bi1−xDyxFeO3 particulate and fiber nanostructures

“…40 In a broad context, the origin of enhancement in the magnetic properties of BFO could be either due to the formation of AFM/FM core/shell-like structures or the suppression of its cycloidal spin structure, which essentially leads to a net magnetization due to the manifestation of 'canted' spins. 41 Therefore, temperature dependent magnetization studies were carried out to investigate the possible origin of the observed magnetism in these BDFO x nanostructures. gradual increment and a drastic decrement of ZFC magnetic moments (M ZFC ) with decreasing temperature from 300 K to 5 K.…”

Study of the B-site ion behaviour in the multiferroic perovskite bismuth iron chromium oxide

“…On the other hand, past Monte Carlo classical spin simulations have explored the effect of large scale random chemical disorder indicating a high population of anti-site defects in a ferrimagnet ultimately prohibiting long-range ferrimagnetism, and giving almost zero global magnetization, except for small local spin-canting effects. 40 From these results, it seems reasonable that the difficulty in synthesizing O-phase in the bulk is related to the low energy associated with (partially) disordered BFCO structures. Evidently, obtaining chemical ordering in bulk samples of BFCO is experimentally difficult.…”

The magnetic interfacial properties of an exchange biased nanocrystalline Ni80Fe20/α-Fe2O3 bilayer studied by polarized neutron reflectometry and Monte Carlo simulation

“…Monte Carlo simulations were performed for a 10 monolayer FM/AF bilayer with a polycrystalline microstructure, using the custom-written FullMonty software. 39) Single SF dynamics using a Glauber heat-bath were used to model the thermal evolution of the structure. 40) The model used is an adaptation of the model originally presented in Ref.…”