The Ni_4−xCo_xNb₂O₉ phase diagram: from magnetization reversal to linear magnetoelectricity

Abstract

Ni4Nb2O9 and Co4Nb2O9 have two different structures derived from corundum which show different magnetic and electrical properties. The ferrimagnetism (FIM) associated with magnetization reversal (MR) of the former and the...

Compositional Complexity as a Design Principle for Stabilizing Magnetization Reversal in Corundum-Derived A4Nb2O9 Phases

“…More surprisingly, magnetization reversal occurs in a large part of the FIM area (hatched area of Figure a). In the binary (Ni/Co and Ni/Zn) systems, MR is only obtained in between Ni 4 Nb 2 O 9 and Ni 3.83 Co 0.17 Nb 2 O 9 and from Ni 4 Nb 2 O 9 to Ni 3.5 Zn 0.5 Nb 2 O 9 . , In contrast, mixing Ni, Co, and Zn in compounds crystallizing in the orthorhombic structure extends the MR zone toward the center of the diagram. Moving through the compositional space, the compensation temperature ( T comp in Figure b) does not change like T N : it follows the same tendency when keeping Zn constant but opposite at fixed Ni or Co (Figure ).…”

“…In the Ni 4 Nb 2 O 9 structure, nickel can be substituted by different cations, but the limits of the Pbcn ortho structure occur at different substitution levels depending on the foreign cation. In the Ni/Co series, 25,26 . The Zn 2+ cationic radius (0.74 Å) is close to that of Co 2+ (0.745 Å), while both are larger than Ni 2+ (0.69 Å).…”

“…In the Ni 4 Nb 2 O 9 structure, nickel can be substituted by different cations, but the limits of the Pbcn ortho structure occur at different substitution levels depending on the foreign cation. In the Ni/Co series, , the lattice volume increases as the Co amount increases and the structure changes at a threshold composition Ni 1.8 Co 2.2 Nb 2 O 9 . Along the Ni/Zn series, , the tendency is similar, but the change of structure appears at a lower substitution level (Ni 2.75 Zn 1.25 Nb 2 O 9 ).…”

“…Beside this structural aspect, various properties are reported depending on the nature of the substituting element and the degree of substitution. ,,− ,− In the orthorhombic structure, starting from Ni 4 Nb 2 O 9 , the magnetic ordering temperature ( T N ) decreases with an increasing Co amount. The compensation temperature ( T comp ) decreases faster, with MR disappearing for substitutions as low as 5% Co, i.e., Ni 3.8 Co 0.2 Nb 2 O 9 .…”

Magnetic anisotropy, magnetization reversal and switching in Ni4Nb2O9 single crystals

“…Among FIM with MR, polycrystalline samples of Ni 4 Nb 2 O 9 , characterized by T N = 77 K and T comp = 33 K [12,13], have recently shown a reproducible M reversal induced by external magnetic field (H) or temperature (T) changes around T comp [14]. Moreover, both T N and T comp have successfully been tuned by substituting Ni by either Co [15] or Zn [16]. The effect of substitution by Zn has also been studied theoretically to comprehend the phenomena underlying these changes [17].…”