Kinetic-arrest-induced phase coexistence and metastability in(Mn,Fe)2(P,Si)

Abstract

Neutron diffraction, Mössbauer spectroscopy, magnetometry, and in-field x-ray diffraction are employed to investigate the magnetoelastic phase transition in hexagonal (Mn,Fe) 2 (P,Si) compounds. (Mn,Fe) 2 (P,Si) compounds undergo for certain compositions a second-order paramagnetic (PM) to a spin-density-wave (SDW) phase transition before further transforming into a ferromagnetic (FM) phase via a first-order phase transition. The SDW-FM transition can be kinetically arrested, causing the coexistence of FM and untransformed SDW phases at low temperatures. Our in-field x-ray diffraction and magnetic relaxation measurements clearly reveal the metastability of the untransformed SDW phase. This unusual magnetic configuration originates from the strong magnetoelastic coupling and the mixed magnetism in hexagonal (Mn,Fe) 2 (P,Si) compounds.

Short-range magnetic correlations and spin dynamics in the paramagnetic regime of(Mn,Fe)2(P,Si)

“…The detected AFM order is consistent with the susceptibility measurements [see the inset of Fig. 2 (a)] and previous neutron diffraction experiments [21]. Intensive temperature-dependent neutron diffraction measurements [21] clearly reveal that some (Mn,Fe) 2 (P,Si) compounds undergo a PM to AFM phase transition before further transforming into a FM phase upon cooling.…”

“…With a further decrease in temperature, the peak intensity significantly increases and the peak position shifts to larger Q values. This reveals the enhancement of AFM order and variations in the propagation vector of the incommensurate AFM structure [21]. The detected AFM order is consistent with the susceptibility measurements [see the inset of Fig.…”

“…The absence of thermal hysteresis implies that this PM-AFM transition is second order. It should be noted that the AFM intermediate phase has only been found in certain (Mn,Fe) 2 (P,Si) compositions [21]. The formation of the AFM phase is due to the competing magnetic configurations and strong magnetoelastic coupling in (Mn,Fe) 2 (P,Si) compounds, as revealed by recent theoretical [22] and experimental [21] studies.…”

“…The forward scattering becomes more pronounced when the sample is cooled from 500 to 350 K, which is due to the development of magnetic correlations. However, AFM order [21,24] appears at 275 K, as suggested by the weak peak at Q ≈ 0.36Å −1 . With a further decrease in temperature, the peak intensity significantly increases and the peak position shifts to larger Q values.…”

Kinetic Spinodal Instabilities in the Mott Transition inV2O3: Evidence from Hysteresis Scaling and Dissipative Phase Ordering

“…But many real systems do spontaneously fall out of equilibrium in a window of thermal hysteresis around the abrupt phase transition (APT) [2]. The accompanying nonergodic behaviorarrested kinetics [3, 4], spatial inhomogeneity [5,6] and phase coexistence [7][8][9], and rate dependence [10-12]-is well documented.Within the mean field (MF) picture, this metastable phase is predicted to abruptly terminate at the spinodals, the two values of field or temperature where the barrier against nucleation vanishes [2,7,[13][14][15][16][17][18]. The analogy between the MF spinodals and the critical point in the power law divergence of susceptibility [2,13,[18][19][20] and their being fixed points under renormalization group transformation [17,21] has long been discussed [2,18,22].…”