Magnetic behavior of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5</mml:mn> <mml:msup> <mml:mi>d</mml:mi> <mml:mn>1</mml:mn> </mml:msup> </mml:mrow> </mml:math> Re-based double perovskite <mml:math xmlns:mml="http

The subtle interplay between spin-orbit coupling, exchange interactions, and cation ordering can lead to exotic magnetic states in transition-metal ions. We report a comprehensive study of the Re-based ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>5</a:mn> <a:msup> <a:mi>d</a:mi> <a:mn>1</a:mn> </a:msup> </a:mrow> </a:math> ) ordered double perovskite oxide <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mi>Sr</b:mi> <b:mn>2</b:mn> </b:msub> <b:msub> <b:mi>ZnReO</b:mi> <b:mn>6</b:mn> </b:msub> </b:mrow> </b:math> combining synchrotron x-ray diffraction (XRD), magnetic susceptibility, muon spin relaxation ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>μ</c:mi> <c:mi>SR</c:mi> </c:mrow> </c:math> ) measurements, and density functional theory (DFT) calculations. XRD reveals that <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi>Sr</d:mi> <d:mn>2</d:mn> </d:msub> <d:msub> <d:mi>ZnReO</d:mi> <d:mn>6</d:mn> </d:msub> </d:mrow> </d:math> crystallizes in the monoclinic structure (space group <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mi>P</e:mi> <e:msub> <e:mn>2</e:mn> <e:mn>1</e:mn> </e:msub> <e:mo>/</e:mo> <e:mi>n</e:mi> </e:mrow> </e:math> ) at low temperature. Magnetic susceptibility data indicate a transition below <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mo>∼</f:mo> <f:mn>13</f:mn> <f:mspace width="0.16em"/> <f:mi mathvariant="normal">K</f:mi> </f:mrow> </f:math> , with <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mi>M</i:mi> <i:mo>–</i:mo> <i:mi>H</i:mi> </i:mrow> </i:math> loops showing ferromagnetic-like hysteresis and an unusually high coercive field of 23 kOe at 2 K. Zero-field <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mrow> <j:mi>μ</j:mi> <j:mi>SR</j:mi> </j:mrow> </j:math> measurements detect static and spatially disordered internal fields below <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mrow> <k:msub> <k:mi>T</k:mi> <k:mi>M</k:mi> </k:msub> <k:mo>≃</k:mo> </k:mrow> </k:math> 12 K, consistent with a canted antiferromagnetic ground state determined by detailed DFT and force-theorem in Hubbard-I calculations. The reduced high-temperature effective moment ( <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mrow> <l:mo>∼</l:mo> <l:mn>0.76</l:mn> <l:mspace width="4pt"/> <l:msub> <l:mi>µ</l:mi> <l:mi>B</l:mi> </l:msub> </l:mrow> </l:math> ) and very small static moment ( <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"> <n:mrow> <n:mo>≲</n:mo> <n:mn>0.2</n:mn> <n:mspace width="4pt"/> <n:msub> <n:mi>µ</n:mi> <n:mi>B</n:mi> </n:msub> </n:mrow> </n:math> ) derived from <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mrow> <p:mi>μ</p:mi> <p:mi>SR</p:mi> </p:mrow> </p:math> analysis and local-field simulations indicate a decisive role of spin-orbit coupling. Through a combined experimental and computational approach we unambiguously determine the canted antiferromagnetic order in <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mrow> <q:msub> <q:mi>Sr</q:mi> <q:mn>2</q:mn> </q:msub> <q:msub> <q:mi>ZnReO</q:mi> <q:mn>6</q:mn> </q:msub> </q:mrow> </q:math> , showing that a very small ordered moment coexists with an exceptionally large coercivity. These results underscore the crucial role of spin-orbit coupling and orbital ordering, providing new insights into magnetism in <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"> <r:mrow> <r:mn>5</r:mn> <r:msup> <r:mi>d</r:mi> <r:mn>1</r:mn> </r:msup> </r:mrow> </r:math> double perovskites.