Emerging magnetic phase in the orthoferrite HoFeO3 detected by spin Hall magnetoresistance and spin Seebeck effect

The orthoferrite <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>HoFeO</a:mi><a:mn>3</a:mn></a:msub></a:math> exhibits a complex interplay of magnetic interactions between the antiferromagnetically ordered <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msup><b:mrow><b:mi>Fe</b:mi></b:mrow><b:mrow><b:mn>3</b:mn><b:mo>+</b:mo></b:mrow></b:msup></b:math> spins and the rare-earth <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msup><c:mrow><c:mi>Ho</c:mi></c:mrow><c:mrow><c:mn>3</c:mn><c:mo>+</c:mo></c:mrow></c:msup></c:math> ions. In this work, we combine superconducting quantum interference device (SQUID) magnetometry studies with electrical spin transport measurements of the spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) on a <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>HoFeO</d:mi><d:mn>3</d:mn></d:msub></d:math> single crystal interfaced by a thin Pt layer. Our measurements show that the increase in Ho magnetic susceptibility below the Morin-like spin reorientation transition at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mn>58</e:mn><e:mspace width="0.16em"/><e:mi mathvariant="normal">K</e:mi></e:mrow></e:math> affects the magnetic anisotropy of the Fe sublattice and induces a tilting of the easy axis. Below the ordering temperature of Ho at <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mn>4</h:mn><h:mspace width="0.16em"/><h:mi mathvariant="normal">K</h:mi></h:mrow></h:math>, we observe a rapid increase in the SSE signal associated with the emergence of low-energy magnon modes with the onset of Ho-Ho exchange. These findings demonstrate that spin transport techniques can sensitively probe rare-earth–induced modifications of anisotropy and spin dynamics in complex oxides, opening pathways to electrically access low-energy <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mn>4</k:mn><k:mrow><k:mi>f</k:mi></k:mrow></k:math> excitations.