Double perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">Ba</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>NaOs</mml:mi> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn

Of all the oxides of osmium, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi mathvariant="normal">Ba</a:mi> <a:mn>2</a:mn> </a:msub> <a:mi>NaOs</a:mi> <a:msub> <a:mi mathvariant="normal">O</a:mi> <a:mn>6</a:mn> </a:msub> </a:mrow> </a:math> is the only one with a substantial ferromagnetic moment. A fresh theoretical study of the double perovskite is accomplished using a different magnetic symmetry, which embraces all relevant published structural information, and an atomic model of a Kramers doublet formed by the single osmium <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>d</d:mi> </d:math> electron. It possesses symmetry demanded by the Wyckoff position assigned to Os in a canted ferromagnet. Whereupon, magnetic moments in the paramagnetic and magnetically ordered states of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:msub> <e:mi mathvariant="normal">Ba</e:mi> <e:mn>2</e:mn> </e:msub> <e:mi>NaOs</e:mi> <e:msub> <e:mi mathvariant="normal">O</e:mi> <e:mn>6</e:mn> </e:msub> </e:mrow> </e:math> are unified. Analytic x-ray magnetic dichroic signals (XMCD) at osmium <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:msub> <h:mi mathvariant="normal">L</h:mi> <h:mn>2</h:mn> </h:msub> </h:math> and <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:msub> <j:mi mathvariant="normal">L</j:mi> <j:mn>3</j:mn> </j:msub> </j:math> absorption edges are presented, and shown to agree with hitherto unexplained recent measurements [Agrestini ].