Magnetocaloric effect and the influence of pressure on magnetic properties of La-excess pseudo-binary alloys La1+δ(Fe0.85Si0.15)13

Abstract

The La-excess alloys La1+δ(Fe0.85Si0.15)13 (δ = 0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature TC. The maximum entropy change −ΔSm was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, respectively. The estimated relative cooling power for ΔH = 70 kOe was 418 J/kg. The alloys show a typical NaZn13-type cubic structure, featuring a doping-induced magnetovolume effect with the increase in TC. Under the applied pressure up to 2 GPa, the TC as deduced from resistance measurements decreased linearly, ΔTC = 113 (for δ = 0.06) and 111 K (for δ = 0.09), together with a corresponding decrease of resistivity, Δρ = 6.1 μΩ m at room temperature for both samples. At a low pressure, the effect of spontaneous magnetostriction on TC caused by applying the pressure appeared to have a similar magnitude to that of the negative magnetovolume effect caused by La-excess doping. In comparison with other stoichiometric La(Fe1−xSix)13 compounds, the pressure in our case was shown to have a smaller influence on TC.

Moment‐Volume Coupling in La(Fe1−xSix)13

“…From literature reports we can in accordance with our own experimental results unambiguously exclude speromagnetism (or non‐collinear spin states) in FM LaFe 11.6 Si 1.4 and similar compounds with low Si content, because at low temperatures (1.8–2 K) magnetic saturation is achieved very fast in M ( H ) curves (at fields of the order of 2 T or lower) . Moreover, our in‐field Mössbauer spectra (not shown here) on the LaFe 11.6 Si 1.4 compound at 4.3 K in a field of 5 T indicate Fe‐spin alignment along the applied‐field direction, i.e., collinear spins, in strong contrast to amorphous Fe‐Zr and Fe‐Y alloys which show non‐collinear spins under similar experimental conditions.…”

Magnetocaloric Effects of La_0.8R_0.2(Fe_0.88Si_0.12)₁₃ (R = Y, Ho and Yb) Compounds in Low Applied Magnetic Field

“…Here the RCP is defined as RCP = «¹¦S m « max © ¤T FWHM . 14,18,19) The obtained RCP-s are 69, 102, 52, 28, and 90 J/kg for R = Y, Sm, 13) Tb, 13) Yb and Ho respectively. It is worth to note that at 13.5 kOe these values are quite large in comparison with that of other compounds available until now.…”

“…Apart from the higher price, the rare-earth based LaFe 13 compounds have certain advantages, as they often possess first order phase transition near T c and their MCE are large even in low field. The available studies report on the fabrication of residual La samples, 14) ribbons-fabricated samples, 11) and on replacements of La in part by the other rare-earth elements such as Ce, Sm and Tb. 12,13) In our previous studies we show that higher values of ¹¦S m and relative cooling proficiency (RCP) could be achieved at low applied field of ¦H = 13.5 kOe in Sm and Tb doped compounds.…”

Saturated Magnetization in Sm and Tb Doped La(Fe0.88Si0.12)13

“…The itinerant electron metamagnetism, its relation to pressure and the magneto-volume effect, which are typical for La(Fe1xMx)13 compounds, are discussed in details by this same group of authors in ref. [8]. Here we are concerned with the saturation of magnetic moments in higher applied magnetic field (above 1.5T) to re-detect the effective field variation that can change RCP values.…”