Field-induced metamagnetic transitions and two-dimensional excitations in ludwigite Co4.76Al1.24(O2BO3)2
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Universidade Federal de Minas Gerais
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This paper presents an extensive study of the structural, magnetic, and thermodynamic properties of the heterometallic ludwigite Co4.76 Al 1.24 (O2 BO3 ) 2 . This material orders ferrimagnetically at 57 K. Despite the fact that, in Co4.76 Al 1.24 (O2 BO3 ) 2 , one quarter of the Co ions of the parent compound Co3 O2 BO3 is replaced by nonmagnetic Al 3+ ions, the TC of the former (57 K) is larger than that of the latter (42 K). We obtain the phase diagram of Co4.76 Al 1.24 (O2 BO3 ) 2 in an external magnetic field. We find a line of second-order phase transitions
where the system presents a metamagnetic transition (from 57 to 25 K). This line ends at a tricritical point at 25 K and 4.3 T, below which the transition to the paramagnetic phase is first order (from 25 to 3 K). In the magnetic phase at low temperatures specific heat measurements in zero and finite magnetic fields show that the low-energy excitations are magnetic (magnons) and elastic (phonons) excitations with two-dimensional character. These measurements also reveal the magnetocaloric properties of this material.
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Antiferromagnetismo, Transições de fases
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Heterometallic ludwigite, Phase transitions, Antiferromagnetism
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https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.214419