Search

Magnetic exchange interactions in Mn3O4 spinel systems are complicated due to the presence of magnetic frustration between one tetrahedral and two octahedral sites, and the strongly correlated Jahn–Teller crystal distortion due to the singly occupied eg band of Mn3+ cations at the octahedral site. In general, the tetrahedral–octahedral exchange interaction is the most dominant interaction among the other two interactions which enforces the octahedral and tetrahedral spins to align parallel to themselves. Doping of Cr3+ ions (with the empty eg band) at the octahedral sites of Mn3O4 reduces the Jahn–Teller distortion and the magnetic moment in the system and hence it affects the magnetic anisotropy, magnetic exchange interaction, and magnetic frustration. In this manuscript, we have investigated the variations in these properties of the Mn2.7Cr0.3O4 and Mn1.5Cr1.5O4 systems and compared them to those of the documented parent Mn3O4 to unveil the evolution of these cross interactions. The neutron diffraction results disclose the noncollinear magnetic structure of Mn2.7Cr0.3O4, while Mn1.5Cr1.5O4 shows a collinear magnetic structure [G. D. Dwivedi, C. W. Wang, S. M. Kumawat and H. Chou, Appl. Phys. Lett., 2020, 116, 182406]. A comparative study of the magnetic structure and exchange interactions (calculated using the TB2J method) of the low doping Mn2.7Cr0.3O4 reveals that the exchange interaction between the nearest octahedral–octahedral cations is the most prominent due to the ionic size effect, which is contrary to the general understanding of spinel systems. However, the exchange interactions in the high doping cubic Mn1.5Cr1.5O4 switched back to the dominant AFM interaction between tetrahedral–octahedral ions due to the smaller moment of Cr ions. [ABSTRACT FROM AUTHOR]

We perform isothermal Brownian-type molecular dynamics simulations to obtain the velocity autocorrelation function and its time Fourier-transformed power spectral density for the metallic cluster Ag17Cu2. The temperature dependences of these dynamical quantities from T = 0 to 1500 K were examined and across this temperature range the cluster melting temperature Tm, which we define to be the principal maximum position of the specific heat is determined. The instantaneous normal mode analysis is then used to dissect the cluster dynamics by calculating the vibrational instantaneous normal mode density of states and hence its frequency integrated value Ij which is an ensemble average of all vibrational projection operators for the jth atom in the cluster. In addition to comparing the results with simulation data, we look more closely at the entities Ij of all atoms using the point group symmetry and diagnose their temperature variations. We find that Ij exhibit features that may be used to deduce Tm, which turns out to agree very well with those inferred from the power spectral density and specific heat. [ABSTRACT FROM AUTHOR]