Possible ground states and parallel magnetic-field-driven phase transitions of collinear antiferromagnets

Abstract

Understanding the nature of all possible ground states and especially magnetic-field-driven phase transitions of antiferromagnets represents a major step towards unravelling the real nature of interesting phenomena such as superconductivity, multiferroicity or magnetoresistance in condensed-matter science. Here a consistent mean-field calculation endowed with antiferromagnetic (AFM) exchange interaction (J), easy axis anisotropy (γ), uniaxial single-ion anisotropy (D) and Zeeman coupling to a magnetic field parallel to the AFM easy axis consistently unifies the AFM state, spin-flop (SFO) and spin-flip transitions. We reveal some mathematically allowed exotic spin states and fluctuations depending on the relative coupling strength of (J, γ and D). We build the three-dimensional (J, γ and D) and two-dimensional (γ and D) phase diagrams clearly displaying the equilibrium phase conditions and discuss the origins of various magnetic states as well as their transitions in different couplings. Besides the traditional first-order type one, we unambiguously confirm an existence of a second-order type SFO transition. This study provides an integrated theoretical model for the magnetic states of collinear antiferromagnets with two interpenetrating sublattices and offers a practical approach as an alternative to the estimation of magnetic exchange parameters (J, γ and D), and the results may shed light on nontrivial magnetism-related properties of bulks, thin films and nanostructures of correlated electron systems.

Spin mapping of intralayer antiferromagnetism and field-induced spin reorientation in monolayer CrTe2

“…Including the substrate in our calculations would slightly increase the spin-flop field to 49.1 T with H E = 71.0 meV/Cr and H A = 2.16 meV/Cr (Supplementary Tables S1 , S2 ). This field is nearly two orders of magnitude larger than the observed threshold field of spin contrast reversal (~0.2 T), suggesting a different spin-flop picture 31 .…”

Spin-flop phase transition in the orthorhombic antiferromagnetic topological semimetal Cu0.95MnAs

“…No hysteresis is observed in Fig.2(a), as is the case for most AFM materials with spin-flop transitions. For years the spin-flop transition had been considered to be a first-order transition, with the absence of the magnetic hysteresis attributed to low magnetic anisotropy, but its nature is now under debate [27]. No saturation is observed up to 7 T for Cu 0.95 MnAs, which indicates that the system remains in the spin-flop state without saturation up to 7 T. This is consistent with the fact that the maximum magnetic moment at 2 K and 7 T is just 0.04 µ B /f.u., much smaller than the saturation moment of Mn 2+ .…”

Ground and Applied-Field-Driven Magnetic States of Antiferromagnets

“…Additionally, a rotating FM phase was also predicted for a SFO antiferromagnet [147,156]. However, this kind of unusual magnetic phase has never been observed experimentally, which renders the validity of the phase undecided [93].…”

“…For the traditional spin-flop (SFO) transition, typically a first-order (FO) type in character, and limited to a collinear antiferromagnet below the Néel transition temperature, the AFM sublattice spins suddenly rotate 90 • so that they are perpendicular to the original AFM easy axis while applying a magnetic field (B) along the AFM easy axis, and when the applied magnetic-field reaches a critical value (B SFO ). For the so-called spin-flip (SFI) transition [92,93], as the field strength further increases (B > B SFO ), the flopped spins gradually tilt toward the field direction until they are completely aligned at a sufficiently high magnetic field (B SFI ). These magnetic-field driven phase transitions are schematically shown in Figure 3.…”