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 (mu SR) measurements. Neutron powder diffraction reveals that, in addition to antiferromagnetic order, ferromagnetic order is induced in a field as low as B similar to 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 Neel temperature of T-N=47 K which is independent of the field. Ferromagnetic Bragg peaks are observed below a field-dependent Curie temperature which increases from T-C=52 K at B=0.2 T to T-C=70 K at B=5 T. Both phase transitions are concurrently observed in ac susceptibility and mu SR measurements.