Strained activated half-metallicity, giant magnetic anisoptropy, superior <i>T</i> _<i>C</i>, and high figure of merit in Cd₂FeReO₆

Abstract Ordered double perovskite oxides (DPO) have received significant interest due to their unique aspects including numerous magnetic ordering, half-metallic phase, and large Curie temperature. This work presents the results of various traits of the Cd 2 FeReO 6 DPO employing density functional theory (DFT). It is found that the energy gap opens for a critical U of 4.5/3.4 eV and 4.6/3.0 eV on the Fe 3 d /Re 5 d states within GGA+ U and GGA+ U + SOC methods, respectively. Moreover, Fe/Re ion displays a m s of 4.10/−1.06 μ B /f.u. owing S = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfrac> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:mfrac> </mml:math> /1 as they lie in a high/low spin +3(3 d 5 )/+5(5 d 2 ) state holding charge distributions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↑</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↓</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↑</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↓</mml:mo> </mml:math> / <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↑</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↓</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↑</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>↓</mml:mo> </mml:math> . Moreover, Fe/Re shows m orb . of 0.048/0.39 μ B indicating half-filled 3 d 5 /less-than-half-filled 5 d 2 orbitals. Remarkably, the system exhibits a high T C of 473 K and a giant magnetic anisotropy energy (MAE) of 3.91 meV keeping MAE constant of 2.79 × 10 7 erg cm −3 with [001] the easy magnetic axis. Interestingly, the spin-majority channel (N ↑ ) demonstrates a very high figure of merit of 0.98 at ambient conditions (300 K). Conversely, the spin-minority channel (N ↓ ) discloses a low ZT of 0.16. Strikingly, the system becomes HM for a compressive strain of −1% attributing a large E g of 2.45 eV in the N ↑ , which is adequately large enough to support a long mean free path for spin and to limit spin-flipping occurrences as well as provide exceptional spin-filtering performance. Additionally, it is observed that MAE and T C enhanced to 80%/69% and 7%/12% under the influence of +4%/−4% strain due to an increase in the structural distortions as compared to the unstrained one, thereby improving the systems capability for applications in magnetic memory devices. Moreover, ZT remains almost invariant for the whole considered strain range in the N ↑ , while its value increases/decreases to 0.75/0.001 for +4%/−4% strain in the N ↓ . This indicates that the system holds a significant potential for use in TE applications particularly in recovering waste heat.