Exchange interactions and Curie temperatures of Mn₂CoZ compounds

Abstract

The generalized Heusler compounds Mn(2)CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) with the Hg(2)CuTi structure are of great interest due to their half-metallic ferrimagnetism. The complex magnetic interactions between the constituents are studied by means of first principles calculations of the Heisenberg exchange coupling parameters, and Curie temperatures are calculated from those. Due to the direct Mn-Mn exchange interaction in Mn(2)CoZ, the Curie temperature decreases, although the total moment increases when the valence electron number Z is increased. The exchange interactions are dominated by a strong direct exchange between Co and its nearest neighbor Mn on the B site, which is nearly constant. The coupling between the nearest neighbor Mn atoms scales with the magnetic moment of the Mn atom on the C site. Calculations with different lattice parameters suggest a negative pressure dependence of the Curie temperature, which follows from the decreasing magnetic moments. Curie temperatures of more than 800 K are predicted for Mn(2)CoAl (890 K), Mn(2)CoGa (886 K), and Mn(2)CoIn (845 K).

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

“…The latter contribution is more important to the indirect exchange mediated mechanism. It is generally accepted that the indirect exchange interaction mediated by the (sp)-electrons of the Z-element gives rise to FM order, while the competing superexchange interaction mediated by the same electrons leads to AFM coupling of the Mn-spin moments in the Mn-based Heusler alloys [76,[78][79][80][81][82][83] (although, as stated above, the shorter distance between Mn on its original sublattice and Mn on the Ga sublattice may have AFM contributions from direct magnetic exchange interactions). It should be noted that the Anderson (s − d)-impurity model for the formation of localized magnetic moments in a metal includes a hybridization term of strength V k , allowing one to promote electrons between the s-and d-states, as well as a local Coulomb term to avoid the double occupancy of the d-electron states [77].…”

Half-metallic antiferromagnetism in Cr2+xSe (0≤x≤Galanakis1, Özdoğan2, Şaşıoğlu3 2012Phys. Rev. B221100View full textAdd to dashboardCite

“…53 But the long-range exchange constants present the expected general characteristics for the half metals; i.e., they are heavily damped due to the half-metallic gap and above three lattice constants all exchange parameters are nearly zero. 36,[54][55][56][57] The Cr B atoms in the Cr 2 Se case have a vanishing exchange constant when they are the closest possible. The interaction becomes strongly magnetic for a Cr B atom and its neighbors in the second shell and then vanishes as expected for half metals.…”

Electronic, magnetic, and structural properties of the ferrimagnet Mn2CoSn

“…Similar problems were recently reported for Mn 2 CoIn and Mn 2 CoSn. 43 Meinert et al had to reduce the lattice parameters in order to find a ground state. In the present study, it was possible to stabilize the ferrimagnetic ground state at 6.05Å and slightly above and the half-metallic ground state below 6.04Å.…”