Magnetic properties of the zigzag ladder compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>SrTb</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:

We report on the properties of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>SrTb</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>4</a:mn></a:msub></a:mrow></a:math>, a frustrated zigzag ladder antiferromagnet, studied by single crystal neutron diffraction (with polarized neutrons in zero field and unpolarized neutrons in an applied magnetic field), as well as by neutron spectroscopy on a polycrystalline sample. The neutron scattering results are supported by single-crystal magnetization and heat capacity measurements. In zero field, neutron diffraction data show no transition to a magnetically ordered state down to the lowest experimentally available temperature of 35 mK, and the material remains magnetically disordered down to this temperature. Polarized neutron diffraction measurements reveal the presence of a diffuse scattering signal suggesting only very weak spin-spin correlations in the ground state. For <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>H</c:mi><c:mo>∥</c:mo><c:mi>c</c:mi></c:mrow></c:math> (the easy magnetization direction), we followed the magnetization process using neutron diffraction measurements and observed the appearance of field-induced magnetic Bragg peaks with integer <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>h</d:mi></d:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mi>k</e:mi></e:math> indices in the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mo>(</f:mo><f:mi>h</f:mi><f:mi>k</f:mi><f:mn>0</f:mn><f:mo>)</f:mo></f:mrow></f:math> scattering plane. No magnetic peaks with a nonzero propagation vector were detected. The observed in-field data fit well to a simple two-sublattice model with magnetic moments aligned along the field direction but being significantly different in magnitude for the two inequivalent <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:msup><g:mrow><g:mi>Tb</g:mi></g:mrow><g:mrow><g:mn>3</g:mn><g:mo>+</g:mo></g:mrow></g:msup></g:math> sites in the unit cell. Overall, the collected data point to a nonmagnetic ground state in <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:msub><h:mi>SrTb</h:mi><h:mn>2</h:mn></h:msub><h:msub><h:mi mathvariant="normal">O</h:mi><h:mn>4</h:mn></h:msub></h:mrow></h:math> despite the presence of strong interactions.