Magnetic coupling inCoCr2O4andMnCr2

Abstract

We present a first principles LSDA+ U study of the magnetic coupling constants in the spinel magnets CoCr 2 O 4 and MnCr 2 O 4 . Our calculated coupling constants highlight the possible importance of AA interactions in spinel systems with magnetic ions on both A and B sites. Furthermore, we show that a careful analysis of the dependence of the magnetic coupling constants on the LSDA+ U parameters provides valuable insights in the underlying coupling mechanisms and allows to obtain a quantitative estimate of the magnetic coupling constants. We discuss in detail the capabilities and possible pitfalls of the LSDA+ U method in determining magnetic coupling constants in complex transition metal oxides.

Effect of Spin Dilution on the Magnetic State of Delafossite CuFeO2 with an S = 5/2 Antiferromagnetic Triangular Sublattice

“…This decrease for the low FM and AFM interactions is a result of the mean field approximation breaking down as Fe composition decreases and next-nearest-neighbor interactions become less, and tend to suppress the magnetic order in CuFe 1−x Sc x O 2 system with increasing x content. The magnitude of J BB is similar to previous studies of Fe-O-Fe exchange in structurally similar spinels with edge-sharing octahedra of Fe [3,37,38]. A ZFC splitting occurs in the x = 0.25 sample below 4 K, which is consistent with splittings seen in low Al content samples studied by Okuda et al [39].…”

“…At temperatures above the long-range ordering temperature, positive deviations from the ideal Curie-Weiss line reflect the presence of compensated antiferromagnetic short-range interactions, while negative deviations reflect uncompensated behavior (ferromagnetism or ferrimagnetism). Consistent with its magnetic frustration, CuFeO 2 displays short-range antiferromagnetic interactions well above its Néel temperature [37]. While Curie-Weiss analysis shows that the dominant long-range interactions in CuFe 1−x Sc x O 2 are antiferromagnetic, the scaled Curie plot reveals the presence of short-range uncompensated behavior in all of the Sc-substituted samples which is likely a result of chemical disorder, which is in a good agreement with results reported by N. Terada et al [31].…”

A First Principle Calculation of Full-Heusler Alloy Co2TiAl: LSDA+U Method

“…It can be seen that the bandwidth of the d bands for the Co site is indeed smaller than for the Ti site as shown in Figures 2(a) and 2(b). The d states on the Co sites are more localized and one can expect a larger on-site Coulomb interaction than that on the Ti site, which is in agreement with U Ti < U Co [22]. However, the half-metallicity is retained till some value of U as shown in Figure 2.…”

Pressure-induced phase transitions in the CdCr2Se4 spinel

“…We note also that we have intentionally excluded the FeCr 2 O 4 , CoCr 2 O 4 , and MgCr 2 O 4 compounds from the plot in Fig. 10(b), because (a) the next-nearest neighbor magnetic exchange interactions of Cr-oxospinels with magnetic A cations are not available [79][80][81] , and (b) the K value of MgCr 2 O 4 determined by the magnetic susceptibility data (but not with the Baltzer model) 12 is significantly different than that of sulphides and selenides, hindering any direct comparison. Hence, we propose that the volume change at the cubic-tetragonal transition observed in several sulphide and selenide ACr 2 X 4 spinels with non-magnetic A cations (A 2+ = Cd, Hg; X 2-= S, Se) arises due to the strong enhancement of the next-nearest neighbor magnetic exchange interactions K upon sufficient compression.…”