Cascade of magnetic phase transitions and large topological Hall effect in the noncentrosymmetric antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Eu</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:

The interplay between symmetry breaking, spin-orbit coupling, and magnetic frustration in noncentrosymmetric antiferromagnets has emerged as a fertile ground for discovering intertwined topological and quantum phenomena. Here, we report a cascade of magnetic phase transitions and a large topological Hall response in the newly discovered noncentrosymmetric antiferromagnetic (AFM) material <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi>Eu</a:mi> <a:mn>2</a:mn> </a:msub> <a:msub> <a:mi>Pd</a:mi> <a:mn>3</a:mn> </a:msub> <a:msub> <a:mi>Bi</a:mi> <a:mn>4</a:mn> </a:msub> </a:mrow> </a:math> with a Neél temperature <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mi>T</b:mi> <b:mi>N</b:mi> </b:msub> <b:mo>=</b:mo> <b:mn>7.6</b:mn> <b:mspace width="0.16em"/> <b:mi mathvariant="normal">K</b:mi> </b:mrow> </b:math> . Under magnetic fields ( <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>H</e:mi> </e:math> ) parallel to the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mi>c</f:mi> </f:math> axis, two successive phase transitions at critical fields <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>H</g:mi> <g:mn>1</g:mn> </g:msub> </g:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:msub> <h:mi>H</h:mi> <h:mn>2</h:mn> </h:msub> </h:math> are observed in magnetization at temperatures below <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:msub> <i:mi>T</i:mi> <i:mi>N</i:mi> </i:msub> </i:math> , which are attributed to the occurrences of sequential field-induced spin states. A pronounced topological Hall effect signal emerges exclusively within an intermediate field window <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mrow> <j:msub> <j:mi>H</j:mi> <j:mn>1</j:mn> </j:msub> <j:mo>&lt;</j:mo> <j:mi>H</j:mi> <j:mo>&lt;</j:mo> <j:msub> <j:mi>H</j:mi> <j:mn>2</j:mn> </j:msub> </j:mrow> </j:math> , signifying the formation of topological spin textures. The field-temperature phase diagram mapped via specific heat and magnetoelectric transport measurements incorporates five phase regimes: The paramagnetic state, a high-field polarized state, and three AFM states with distinct spin configurations. Our results identify <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mrow> <k:msub> <k:mi>Eu</k:mi> <k:mn>2</k:mn> </k:msub> <k:msub> <k:mi>Pd</k:mi> <k:mn>3</k:mn> </k:msub> <k:msub> <k:mi>Bi</k:mi> <k:mn>4</k:mn> </k:msub> </k:mrow> </k:math> as a good candidate for scrutinizing sophisticated interplays between magnetic structure and nontrivial band topology.