Stability of Mn moments and exchange interactions in cobalt substituted Mn₂Sb

Abstract

The magnetic moment distributions in the ferrimagnetic (FI) and antiferromagnetic (AF) phases of Co substituted Mn 2 Sb (Mn 1.9 Co 0.1 Sb) have been determined using both polarized and unpolarized neutron diffraction. In Mn 1.9 Co 0.1 Sb a transition from a ferrimagnetic to an antiferromagnetic state takes place on cooling through T ms = 138 K. The antiferromagnetic structure has propagation vector (00 12 ), and contains (001) layers of Mn atoms with ferromagnetically coupled Mn moments aligned perpendicular to [001]. The two crystallographically distinct Mn atoms have moments 3.98 and 1.71 μ B at 4 K and are oppositely aligned within the unit cell. At 200 K the moments determined from polarized neutron scattering are 3.86 and 1.84 μ B . In both the AF and FI phases the magnetization associated with the high moment (Mn2) site is nearly spherically symmetric; that around the Mn1 site has predominantly t 2g character which is stronger in the AF than in the FI phase. At T ms the only bonds whose lengths change significantly are those between Mn and Sb establishing the 125 • Mn1-Sb-Mn2 interlayer exchange path as the dominant exchange interaction determining the type of long range magnetic order.

Magnetic and Electronic Structures of Cobalt or Copper Substituted Mn₂Sb

“…This result indicates that the Co atom prefers the site Mn(I) to the site Mn(II) in a magnetic state. This is consistent with the report by Brown et al 15) They showed that the Co atom occupies the site Mn(I) in Mn 1.8 Co 0.2 Sb from an analysis of the neutron diffraction experiment.…”

“…15) Our results indicate that the optimization of the ratio c/a is crucial to determine the most stable magnetic state and that the optimization of the atomic positions of the sites Mn(II) and Sb is also crucial.…”

“…This is consistent with the neutron diffraction experiment. 15) In the case of Cu, the Cu atom prefers the site Mn(II) to the site Mn(I) in all magnetic states. To confirm this calculated result, we hope for neutron diffraction measurements on Cu substituted Mn 2 Sb.…”

“…4,15) Thus, we estimate DOS at the Fermi energy and £ for CoMnSb and MnCuSb, and shows results in Table 3. Here the £ can be derived from D(E F ) using…”

Site Preference and Stabilization of Antiferromagnetism in M-Substituted Mn_2&minus;<i>_x</i>M<i>_x</i>Sb (M = Ti, Cr, Co, or Cu)

“…9 shows the magnetic moments calculated for Mn(I) and Mn(II) for the AF and FR states in Mn 2¹x M x Sb (M = Cr or Co, x = 0.25, 0.5, and 1.0). Note that the some experimental data 1,16,20,21) are included in Fig. 9.…”