Unconventional magnetization in the multiphase superconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>PdB</mml:mi> <mml:msub> <mml:mi mathvariant="normal">i</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mm

Unconventional superconductors have specific signatures in their magnetic properties, such as intrinsic magnetization at interfaces and around defects and fractional and multiquanta vortices, with much attention focused on heavy fermion and high- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>T</a:mi> <a:mi mathvariant="normal">c</a:mi> </a:msub> </a:math> superconductors. Here, we report the observation of highly anomalous magnetization in β- <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>PdB</c:mi> <c:msub> <c:mi mathvariant="normal">i</c:mi> <c:mn>2</c:mn> </c:msub> </c:mrow> </c:math> , a layered superconductor previously shown to exhibit a magnetic-field-induced transition from <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>s</e:mi> </e:math> -wave to nodal <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mi>p</f:mi> </f:math> -wave superconductivity at a transition field <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mrow> <g:msup> <g:mrow> <g:mi>H</g:mi> </g:mrow> <g:mo>*</g:mo> </g:msup> <g:mo>∼</g:mo> <g:mn>0.1</g:mn> <g:mspace width="4pt"/> <g:mi>T</g:mi> <g:mspace width="4pt"/> <g:mrow> <g:mo>(</g:mo> <g:msub> <g:mi>H</g:mi> <g:mrow> <g:mi mathvariant="normal">C</g:mi> <g:mn>1</g:mn> </g:mrow> </g:msub> <g:mo>&lt;</g:mo> <g:msup> <g:mrow> <g:mi>H</g:mi> </g:mrow> <g:mo>*</g:mo> </g:msup> <g:mo>&lt;</g:mo> <g:msub> <g:mi>H</g:mi> <g:mrow> <g:mi mathvariant="normal">C</g:mi> <g:mn>2</g:mn> </g:mrow> </g:msub> <g:mo>)</g:mo> </g:mrow> </g:mrow> </g:math> . This transition is driven by the coupling between spin-polarized electronic bands and the in-plane magnetic field. In the unconventional phase (above <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:msup> <l:mrow> <l:mi>H</l:mi> </l:mrow> <l:mo>*</l:mo> </l:msup> </l:math> ) we observe three striking features: strictly linear and nonhysteretic dc magnetization, a sharp drop in the ac susceptibility when the field is applied parallel to the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:mi mathvariant="italic">ab</m:mi> </m:mrow> </m:math> plane, and a pronounced anisotropy in the magnetic response between parallel and perpendicular field orientations. We show that these features are directly correlated with the expected transition to the nodal <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:mi>p</o:mi> </o:math> -wave state and propose that the unusual magnetization behavior can be explained by a transition from a conventional vortex lattice in the low-field <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mi>s</p:mi> </p:math> -wave phase to a domain structure corresponding to spatial phase separation into superconducting ( <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mi>p</q:mi> </q:math> -wave) and normal domains above <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"> <r:msup> <r:mrow> <r:mi>H</r:mi> </r:mrow> <r:mo>*</r:mo> </r:msup> </r:math> . Our work identifies experimental signatures of unconventional multiphase superconductivity, offering an insight into the magnetic-field response of nodal states.