Evidence of cluster-glass and Griffiths-like phases in partially ordered La₂FeMnO₆ double perovskite

Abstract

The double perovskite La 2 FeMnO 6 is ideally expected to be a ferrimagnet with a low saturation moment of 1 µ B / f.u. Inhomogeneity in the Fe/Mn sites, along with other lattice disorders, can modify the exchange interactions in the material and result in a net saturation moment of more than 1 µ B / f.u. Here, the origin of complicated magnetic behavior is examined of a pure phase La 2 FeMnO 6 sample prepared by the sol-gel method. XRD analysis established that the material crystallizes in the orthorhombic Pbnm symmetry. The comprehensive analysis of x-ray photoelectron spectroscopy, x-ray near edge structure, and magnetic measurements acknowledge an antiferromagnetic coupling between Fe 3+ and Mn 3+ cations, thereby, resulting in the ferrimagnetic ground state for La 2 FeMnO 6 . The magnetic hysteresis loop obtained at 5 K shows a large coercivity of ∼820 Oe and a saturation moment of 1.6 µ B / f.u., hinting at partial B-site ordering in La 2 FeMnO 6 . The ac susceptibility and dc magnetization measurements indicate the existence of magnetic glassy states (of cluster-glass type) with two distinct dynamical freezing points at ∼27 and 92 K, along with a Griffiths-like phase in the material. The experimental results are discussed taking several possible exchange interactions among Fe 3+ and Mn 3+ ions in the system into consideration. The magnetic complexity of this system makes it attractive for fundamental research and technological applications.

Effect of Heat Treatment on Structural, Magnetic and Electrical Properties of La2FeMnO6

“…The fitting results for the oxidation states for each sample are shown in Figure 3a-d. All states of La 2 FeMnO 6 at different calcination temperatures agree well with previous reports [3,[11][12][13][14][15].…”

“…The two main modes (ω 1 and ω 2 ) and the high-frequency mode (ω 3 ) are identified as the characteristic Raman phonon modes of La 2 FeMnO 6 [3,4,11,12]. According to previous reports [3,4,11,12] the ω 1 phonon mode is related to the bending of (Fe/Mn)O 6 octahedra with A1g symmetry, the ω 2 phonon mode corresponds to the stretching of (Fe/Mn)O 6 octahedra with B1g symmetry, and the ω 3 phonon mode is ascribed to second-order processes which are attributed to the strong spin-lattice interactions [11,18]. No additional mode was detected in the Raman spectra indicating a high-purity La 2 FeMnO 6 phase.…”

Magnetoelastic Coupling and Cryogenic Magnetocaloric Effect in Two-Site Disordered GdSrCoFeO6 Double Perovskite

“…The obtained values of the lattice parameters a = 5.4003(1) Å, b = 7.6300(3) Å, c = 5.4094(2) Å, and V = 222.89(3) Å 3 , the average bond length ⟨(Co/Fe) − O⟩ = 1.927(4) Å and ⟨Gd/Sr − O⟩ = 2.592(9) Å, and the average bond angle ⟨(Co/ Fe) − O − (Co/Fe)⟩ = 165.1(4)°agree with those obtained for other DP with an orthorhombic structure. 21,43,44 Comparatively, the GdSrCoFeO 6 disordered structure is less distorted because the Gd ionic radius is smaller compared to Pr and La ions (r Gd = 1.05 Å < r Pr = 1.13 Å < r La = 1.16 Å), for example, and despite A-site sharing with Sr (with a larger radius, r Sr = 1.26 Å), a cell volume reduction is caused through bond lengths decreasing, whereas the bond angles increase. To better visualize this, the octahedral tilting can be calculated and c-lattice parameters increase by +0.0004(1) and +0.0006(7) Å, respectively.…”

Study on the decisive factor for metal–insulator transitions in a LaVO3 Mott–Hubbard insulator

“…The Rietveld analysis was performed in the orthorhombic space group Pbnm by considering the structural parameters previously reported for La 2 FeMnO 6 as the initial mode. 28 The refinement was performed until convergence was achieved. Acceptable fittings between the experimental data and the proposed models are obtained with R p ∼5% for all the data confirming the formation of all three samples in the Pbnm crystal structure.…”