Electron Spin Resonance in the Double-Perovskite Oxide Antiferromagnet Ba$$_2$$CoWO$$_6$$

Abstract We report electron spin resonance studies of double perovskite Ba $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> CoWO $$_6$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>6</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> single crystals. Above $$T_\textrm{N} = 14$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>N</mml:mtext> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:math> K, we observe a paramagnetic resonance with $$g_\textrm{eff}\simeq 3.66$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>g</mml:mi> <mml:mtext>eff</mml:mtext> </mml:msub> <mml:mo>≃</mml:mo> <mml:mn>3.66</mml:mn> </mml:mrow> </mml:math> . Upon cooling, this mode transforms into a broad antiferromagnetic resonance (AFMR) with a zero-field energy gap of about 200 GHz. The AFMR becomes barely detectable at low magnetic fields, indicating unusually strong decay processes. We argue that symmetry-allowed anisotropic spin–spin interactions are a possible reason for the pronounced spin-wave damping. Linear spin-wave theory calculations support this scenario.