Single magnetic chirality in the magnetoelectric NdFe3(B11O3)4

Physical review. B, Condensed matter (Impact Factor: 3.77). 01/2010; 81(9). DOI: 10.1103/PhysRevB.81.094429
Source: arXiv

ABSTRACT We have performed an extensive study of single crystals of the magnetoelectric NdFe3(B11O3)4 by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below TN≈30K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at TIC≈13.5K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3(B11O3)4 is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.

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    ABSTRACT: The magnetic field dependences of birefringence in a $NdFe_3(BO_3)_4$ single crystal have been measured in the case where the direction of light propagation coincides with the trigonal crystal axis $C_3$ ($k\|C_3$), and the external magnetic field is oriented along the second-order axis $C_2$ ($H\|C_2$). In the temperature range, in which an incommensurate phase exists with the formation of a long-period antiferromagnetic helix, the strongly pronounced jumps in the field dependence of birefringence are revealed and identified as a firstorder spin-orientation phase transition. The phase transition was accompanied by a hysteresis in the field dependences of birefringence. The $H-T$ phase diagram for a $NdFe_3(BO_3)_4$ single crystal has been plotted in the case where the magnetic field is oriented along the crystal axis $C_2$ ($H\|C_2$).

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