Re-entrant spin glass transitions: new insights from acoustic absorption by domain walls

Abstract

Re-entrant spin glass (RSG) transitions in Ni-Mn and Au-Fe have been reassessed by acoustic measurements of the magneto-mechanical damping by domain walls. Stress-induced non-thermally activated domain wall dynamics is progressively replaced by an intense thermally activated relaxational response when the temperature approaches the RSG freezing point. A “frozen” state with negligible motion of domain walls on atomic and mesoscopic scales occurs in the RSG. We propose that RSG freezing has its origin in intrinsic properties of domain walls.

Revisiting neutron studies of reentrant spin glasses: the role of small-angle scattering

“…These two behaviours are connected with the strength of the Dzyaloshinskii-Moryia (DM) anisotropy field (Mirebeau et al, 1992). Note that the domains have also been observed by electron microscopy (Senoussi et al, 1988) and, more recently, acoustic damping measurements (Kustov et al, 2017), confirming the global validity of the MF model, at least in FM RSGs far from the critical region.…”

Field-induced vortex-like textures as a probe of the critical line in reentrant spin glasses

“…Below T F , this process leads to a strong decrease of the susceptibility χ(T ) and to strong irreversibilities of the magnetization M(H). This picture is supported by electron microscopy 23 , neutron depolarisation 15 and recent acoustic absorption measurements 24 , which clearly show that LRMO and µm-sized domains are preserved in the ground state of the weakly frustrated RSG. As the field increases, the domain walls are washed out by low fields, whereas vortices persist up to much higher fields, where their contribution to the SANS can be clearly identified.…”

Magnetic Domain Walls and Macroscopic Magnetization-Related Elastic and Anelastic Effects during Premartensitic Transition in Ni2MnGa

“…The strength of the microeddy current relaxation is [14,15,42]: Δμ=Aμ0μiλsEUIs, where A represents a numerical factor, μi≈μr represents the initial permeability, λs represents the saturation magnetostriction, and IS represents the spontaneous magnetization. Δμ is the highest in the demagnetized state and falls off to zero at saturation [14,15,16].…”

“…Three canonical components of magnetomechanical internal friction (IF) and related modulus softening, known as the ΔE-effect, are considered [14,15,16]: two linear eddy current relaxations, microeddy and macroeddy, and the non-linear hysteretic term. The non-linear term and the fourth, recently discovered category, low-temperature relaxation due to the thermal freezing of DWs during re-entrant spin glass transition [16], are unrelated to the subject of the present study.…”

“…Three canonical components of magnetomechanical internal friction (IF) and related modulus softening, known as the ΔE-effect, are considered [14,15,16]: two linear eddy current relaxations, microeddy and macroeddy, and the non-linear hysteretic term. The non-linear term and the fourth, recently discovered category, low-temperature relaxation due to the thermal freezing of DWs during re-entrant spin glass transition [16], are unrelated to the subject of the present study. The microeddy current relaxation is traditionally ascribed to the short-range (less or much less than the average domain size) reversible displacements of individual DWs, whereas the macroeddy one exists in partially macroscopically magnetized samples, and operates at a scale of the penetration depth of the electromagnetic wave, averaging over many domains [14,15,17].…”