Tuning Magnetism of [MnSb₄]^9– Cluster in Yb₁₄MnSb₁₁ through Chemical Substitutions on Yb Sites: Appearance and Disappearance of Spin Reorientation

Abstract

Single crystals of Yb14-xRExMnSb11 (0 < x < 0.6, RE = Pr, Nd, Sm, and Gd) were synthesized by Sn flux. The compounds are iso-structural with Ca14AlSb11 (I41/acd), and their compositions were determined by wavelength-dispersive spectroscopy. Yb14MnSb11 is described as a partially screened d-metal Kondo system with the isolated [MnSb4](9-) tetrahedral cluster having a d(5) + hole configuration that results in four unpaired electrons measured in the ferromagnetically ordered phase. All of the Yb atoms in Yb14MnSb11 are present as Yb(2+), and the additional RE in Yb14-xRExMnSb11 is trivalent, contributing one additional electron to the structure and altering the magnetic properties. All compounds show ferromagnetic ordering in the range of 39-52 K attributed to the [MnSb4](9-) magnetic moment. Temperature-dependent DC magnetization measurements of Yb14-xPrxMnSb11 (0.44 ≤ x ≤ 0.56) show a sharp downturn right below the ferromagnetic transition temperature. Single-crystal neutron diffraction shows that this downturn is caused by a spin reorientation of the [MnSb4](9-) magnetic moments from the ab-plane to c-axis. The spin reorientation behavior, caused by large anisotropy, is also observed for similar x values of RE = Nd but not for RE = Sm or Gd at any value of x. In Pr-, Nd-, and Sm-substituted crystals, the saturation moments are consistent with ∼4 unpaired electrons attributed to [MnSb4](9-), indicating that local moments of Pr, Nd, and Sm do not contribute to the ferromagnetic order. In the case of RE = Pr, this is confirmed by neutron diffraction. In contrast, the magnetic measurements of RE = Gd show that the moments of Gd ferromagnetically order with the moments of [MnSb4](9-), and reduced screening of moments on Mn(2+) is evident. The sensitive variation of magnetic behavior is attributed to the various RE substitutions resulting in different interactions of the 4f-orbitals with the 3d-orbitals of Mn in the [MnSb4](9-) cluster conducted through 5p-orbitals of Sb.

The remarkable crystal chemistry of the Ca14AlSb11 structure type, magnetic and thermoelectric properties

“…Site preferences are observed in the occupancy of the cation sites when doping or alloying on the A position. 31,[59][60][61][62][63][64][65][66] The tendency is for smaller atoms to prefer the A1 and A3 sites, and for larger atoms to prefer the A2 and A4 sites. This can be understood through the Hirshfeld surface analysis of chemical bonding.…”

“…[75][76][77] More recently, the solid solutions of the A site have focused on RE (rare earth) substitutions. 31,[59][60][61][62][63][64][65][66]78 As mentioned above, the rare earth elements in the 3+ oxidation state (RE) show site preferences that depend upon size. The identity of the 3+ rare earth element affects the sublimation temperature and melting point with the lighter rare earths providing higher melting points and lower vapor pressures.…”

“…19,28,29 However, the introduction of rare earth elements and transition elements are able to change the properties. 30,31 As transition metals or rare earth ions may have unpaired electrons, Zintl compounds consisting of such elements can be magnetic such as ferro-, ferri-or antiferromagnetic. At the same time, these compounds can be semimetallic or metallic.…”

Single crystal growth and magnetic properties of the mixed valent Yb containing Zintl phase, Yb14MgSb11

“…8,9 Studies of Yb14MnSb11 with small amounts of 3+ rare earth element substitution have been investigated, resulting in reduction of the carrier concentration, and thus improvement of zT. [10][11][12][13][14] A limit of 0.7 > x has been found for these Yb14- It was speculated that Yb14MgSb11 would contain only Yb 2+ , similar to Yb14MnSb11, and that the lack of d electrons and changes to the size of the unit cell along with the changes in the tetrahedral site geometry might be responsible for its lowered carrier concentration. 5,15 However, it is possible that mixed valence of Yb, similar to that observed in Yb14ZnSb11, could contribute to the lowered carrier concentration.…”

Excitations and magnetization density distribution in the dilute ferromagnetic semiconductorYb14MnSb11

“…This serves to further explain the strong influence of substitution at these sites on the magnetic properties of Yb 14 MnSb 11 and isostructural compounds. 29,30 Measuring the magnetic excitation spectrum should provide valuable insight into the substitution effects observed in this and isostructural compounds.…”