Insight into the negative magnetization and anomalous exchange-bias in DyFe5Al7 through neutron depolarization and neutron diffraction studies

We have provided the mesoscopic and microscopic understandings of polarity reversal of the magnetization or negative magnetization (NM) below T (COMP) = 93 K in an exotic magnetic material containing three magnetic sublattices, viz., DyFe5Al7 crystallizing in ThMn12 structure, using neutron depolarization and neutron diffraction techniques. A full recovery of the neutron beam polarization at the T (COMP) in a neutron depolarization experiment reveals a total compensation of magnetization inside the magnetic domains in the sample. The temperature-dependent neutron diffraction study under zero magnetic field has provided temperature dependencies of antiparallelly coupled Dy (M (Dy(2a))) and Fe (M (Fe(8f)) and M (Fe(8j))) sublattice magnetic moments along [100] direction. The dominance of |M (Dy(2a))| over total Fe moment,| M-Fe(total)| = | 4*M-Fe(8f)| +| M-Fe(8j)| COMP leads to the NM in the compound. The magnetization versus magnetic field curves below the T (COMP) indicate the presence of field-induced spin reorientation in the compound. The magnetic field required for spin reorientation (H (SR)) is maximum at the lowest temperature and it decreases to zero as the temperature is increased to T (COMP). Interestingly, the compound shows a finite exchange-bias (H (EB)) below the T (COMP) only, as evident from the field-cooled hysteresis loops, while at T > T (COMP), H (EB) is almost zero. The cooling-field (H (COOL)) dependent study of H (EB) shows a slope change at H (COOL) & SIM; H (SR) indicating a correlation of exchange-bias with spin-reorientation in the compound. This study, apart from revealing microscopic understanding of magnetic behavior of an exotic three magnetic sublattice system, provides a correlation among exchange-bias, magnetic compensation, and spin-reorientation phenomena.