Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting

Abstract

Spin-reorientation phase transitions that involve the rotation of a crystal's magnetisation have been well characterised in distorted perovskite oxides such as the orthoferrites. In these systems spin reorientation occurs due to competing rare earth and transition metal anisotropies coupled via f − d exchange. Here, we demonstrate an alternative paradigm for spin reorientation in distorted perovskites. We show that the R2CuMnMn4O12 (R = Y or Dy) triple A-site columnar ordered quadruple perovskites have three ordered magnetic phases and up to two spin reorientation phase transitions. Unlike the spin reorientation phenomena in other distorted perovskites, these transitions are independent of rare earth magnetism, but are instead driven by an instability towards antiferromagnetic spin canting likely originating in frustrated Heisenberg exchange interactions, and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.

Magnetic phase diagram of rare-earth orthorhombic perovskite oxides

“…A study by Vibhakar et al [42] on triple A-site columnar-ordered quadruple perovskites has shown that the mechanism behind SR in these structures is the competition between DMI and SIA, which is similar to the mechanism that we found to be at play in RM O 3 's SR.…”

Effects of magnetic dilution in the ferrimagnetic columnar ordered Sm2MnMnMn4−xTixO12Vibhakar1, Khalyavin2, Manuel3 et al. 2020Phys. Rev. BSelf Cite6000View full textAdd to dashboardCite

“…The refined magnetic structure is consistent with the collinear ferrimagnetic phase found in Tm 2 MnMnMn 4 O 12 [17] and R 2 CuMnMn 4 O 12 [18]. Moment orientations of m||[x, 0, 0], m||[x, x, 0], or m||[x, y, 0] correspond to different magnetic symmetries described by the three distinct order-parameter directions of the + 5 irrep (see Tables III, IV, and V of Appendix A); however, these three cases cannot be differentiated by our neutron-diffraction data due to powder averaging in the tetragonal crystal symmetry.…”

“…The prevalence of spin fluctuations is emerging in the wider family of A-site columnar ordered quadruple perovskites that support competing exchange pathways. For example, in R 2 CuMnMn 4 O 12 (R = Y or Dy), B-site Mn 3+ moments appear to saturate at 3 4 of their theoretical value, and only on cooling through a low-temperature phase transition, proposed to originate in the softening of low-energy magnons, do they recover their full moment [18].…”

“…The weakness of A-A d-d exchange has recently been demonstrated in (NaDy)MnMnTi 4 O 12 [16], where in the absence of A-B and B-B interactions (B = Ti 4+ ), antiferromagnetic order develops on the A-site sublattices only below 12 K. To the contrary in Tm 2 MnMnMn 4 O 12 , the presence of both A-B and B-B exchange stabilizes ferrimagnetic order below 74 K, with a ferromagnetic B-site sublattice that is in direct contradiction to the C-type antiferromagnetic B-site sublattice theoretically predicted by B-B exchange alone-a state that is instead thought to arise as a result of A-B exchange dominating over both A-A and B-B exchange [17]. Indeed, it was shown that when A-B exchange is weakened by substituting Cu 2+ for Mn 3+ on the A sites (R 2 CuMnMn 4 O 12 , R = Dy and Y), antiferromagnetic spin canting is introduced onto the B-site sublattice [18]. Hence it has become clear that the A-site columnar ordered quadruple perovskite manganites present a flexible framework in which novel frustrated geometries of A-A, A-B, and B-B exchange interactions may be tuned through chemical substitution to give rise to unconventional magnetic states.…”

Direct Observation of Fe‐Ge Ordering in Fe5−xGeTe2 Crystals and Resultant Helimagnetism

“…Spin reorientation should occur via competition between DMI and other energy terms such as Heisenberg exchange interaction, magneto‐crystalline anisotropy, and magnetostatic energy. [ 39–41 ] It is natural to see the transition from the helimagnetic spin alignment to the commensurate state due to the competitions. Since all those energies are T dependent, quantitative study for each energy parameter is required to manifest exact origin of the large‐range cusp.…”