Strain development during the phase transition of La(Fe,Mn,Si)13Hz

Abstract

We use powder X-ray diffraction to evaluate the temperature dependence of the crystalline properties during the magnetic phase transition of La(Fe,Mn,Si)13Hz as a function of the Fe/Mn/Si ratio. Both the paramagnetic and ferromagnetic phases were observed as peak overlaps in the patterns around the Curie temperature (TC) occurring continuously in a temperature range of about 5 K around TC. Using the Williamson-Hall method, we evaluate the strain developing in the crystallites during the transition and find that it is associated with the growth of the paramagnetic phase as the transition occurs. Based on our measurements and microstructure analyses, we propose that cracking during the phase transition is due to or aggravated by the small content of a La-rich phase.

Mechanical properties of the magnetocaloric intermetallic LaFe11.2Si1.8 alloy at different length scales

“…Taking into account the brittleness of the whole alloy such pre-existing cracks definitely represent potential weak links for the initiation of catastrophic fracture. Preferable cracking around the La-rich grains was directly observed during cyclic magnetocaloric transition in [9]. The nature of these pre-existing cracks is unclear.…”

“…The base La(Fe, Si) 13 alloy system shows an overall mechanically brittle behavior and a large difference in volume ΔV of the para-and ferromagnetic phases of up to 1.5 vol% with decreasing Si content [7]. This volume change induces cracks and mechanical degradation of the material over several induced MCE cycles [6,8,9,10], especially in La(Fe, Si) 13 alloys with a first order phase transition.…”

Noncollinear spin structure in Fe3+xCo3−xTWang1, Balamurugan2, Pahari3 et al. 2019Phys. Rev. Materials5030View full textAdd to dashboardCite

“…The corresponding errors of 1-2 nm (Table I) were calculated from the dispersion of the results of different peaks. Our Williamson-Hall analysis reveals a very small microstrain of only about 0.1%, which has little effect on the estimated crystallite size [47]. The crystallite sizes do not exhibit any obvious temperature dependence, suggesting that the microstructures are stable over the temperature range of the measurements.…”

Coupling Phenomena in Magnetocaloric Materials

“…Local orbitalm oments m l for the magnetization alongt he [100]axis and anisotropy oft he local orbital moments Dm l = m l,100 Àm l,001 in different layers for Ni (orange) and Mn (red) atoms in the bilayer system. asymmetric with cooling and heating, [74] and is much more pronounced for the expandingcell. Thee xertion of pressure or strain on as ample is not limited to an active external or internal force as with the strain fields that occur during the magnetovolume transition.…”

“…As this only happens for the transition with expanding cell volume [e.g., the cooling transition in La(Fe,Si) 13 ], and the reverse transition is unaffected, an asymmetry in the progress of the heating and cooling transition is observed . Consequently, the development of strain in the sample is also asymmetric with cooling and heating, and is much more pronounced for the expanding cell.…”