Phase transition of geometrically frustrated TbNiAl in a magnetic field

The phase transitions of the geometrically frustrated antiferromagnet TbNiAl in a magnetic field are studied by means of neutron powder diffraction, ac susceptibility, and muon spin relaxation (μSR) measurements. Neutron powder diffraction reveals that, in addition to antiferromagnetic order, ferromagnetic order is induced in a field as low as B∼0.02 T. At higher fields, ferromagnetic and antiferromagnetic order coexist in different domains in the sample, and the domain balance depends on both magnetic field and temperature. Antiferromagnetic Bragg reflections are observed below a Néel temperature of TN =47 K which is independent of the field. Ferromagnetic Bragg peaks are observed below a field-dependent Curie temperature which increases from TC =52 K at B=0.2 T to TC =70 K at B=5 T. Both phase transitions are concurrently observed in ac susceptibility and μSR measurements.