Reentrant spin-flop transition in nanomagnets

Abstract

Antiferromagnetic chains with an odd number of spins are known to undergo a transition from an antiparallel to a spin-flop configuration when subjected to an increasing magnetic field. We show that in the presence of an anisotropy favoring alignment perpendicular to the field, the spin-flop state appears for both weak and strong field, the antiparallel state appearing for intermediate fields.Both transitions are second order, the configuration varying continuously with the field intensity. Such re-entrant transition is robust with respect to quantum fluctuations and it might be observed in different types of nanomagnets.

Quantum effects in nanosystems: Good reasons to use phase-space Weyl symbols

“…The second application illustrates how a typical nanosystem can be conveniently treated: thanks to the phase-space approach it was indeed possible to compute the counterintuitive results reported in Ref. 46.…”

“…Such a parity effect is due to the Zeeman energy gain of one unbalanced spin which wins against the spin-flop configuration up to a transition field h + (N, µ). Furthermore, it is intuitive that for easy-plane anisotropy at zero-field the spins lie in the easy-plane and the AP configuration sets in one only beyond a finite field h − (N, µ): hence, by increasing the field there are two boundaries enclosing the AP phase, i.e., a re-entrant transition 46,47 , as shown in Fig. 2.…”

“…The numerical iterative procedure has been applied in order find the quantum renormalized upper and lower critical fields h + (µ, S) and h − (µ, S) for different spin values 50 reported in Ref. 46. At variance with the naïve expectation, after the result of Section IV, that quantum fluctuation acted to weaken the ordered phase, quite unexpectedly it happens that in this finite-size system they turn out to stabilize the AP phase, i.e.…”