Stabilization by Si Substitution of the Pseudobinary Compound Gd₂(Co_3–xSi_x) with Magnetocaloric Properties around Room Temperature

Abstract

We report the discovery of a new solid solution Gd2(Co3-xSix) with 0.29 < x < 0.50 in the Gd-Co-Si ternary system. Members of this solid solution crystallize with the La2Ni3-type structure and correspond to the stabilization of "Gd2Co3" through silicon substitution. The structure of the member Gd2(Co2.53(3)Si0.47) was determined by X-ray diffraction on a single crystal. It crystallizes with the space group Cmce and cell parameters a = 5.3833(4), b = 9.5535(6), and c = 7.1233(5) Å. Co/Si mixing is observed on two crystallographic positions. All compounds studied in the solid solution present a ferrimagnetic order with a strong composition-dependent Curie temperature TC with 280 K < TC < 338 K. The magnetocaloric effect, which amounts to around 1.7 J K(-1) kg(-1) for ΔH = 2 T, is interestingly tunable around room temperature over a temperature span of 60 K through only 4-5% of composition change.

R2Co3-xSix (R = Pr, Nd, Sm, Gd) and R2Ni3-xSix (R = Gd-Er), new series of La2Ni3-type phases

“…We observe R2Co3-xSix as the major phase with only small quantities of secondary phases spread homogeneously throughout the sample. The only exception to this is the Gd2Co3-xSix system where the target phase crystallizes in small amounts from the melt on cooling which confirms the previous results [11]. The EDX data for all the R2Co3-xSix systems show only slight deviations between the nominal and measured compositions (table 1) with the exception of the R = Sm.…”

“…Gd2Co3-xSix is the only exception among the systems studied where the target phase was obtained for all investigated annealing temperatures. It was found to exhibit an increase in the Si content with increasing annealing temperature as explored in our previous publication on the Gd2Co3-xSix system [11]. A summary of the unit cell parameters and annealing temperatures for all rare-earths is presented in table 1 and the unit cell parameters are plotted against rare earth radius in figure 3.…”

“…In general, higher Si contents were found to stabilize the RTSi phase while lower concentrations stabilized the RT2 phase with some small Si substitution (5-6 at%) on the transition element site as indicated in figure 1. It has already been documented that the annealing temperature can influence the final Si concentration in the main phase Gd2Co3-xSix [11]. However, due to the long annealing times for all the Co samples (except R = Gd) the effect of annealing temperature was not investigated further here.…”

“…Magnetocaloric materials which exhibit a second order ferromagnetic transition around the target application temperature are of great interest due to the easily reversible transition with little to no hysteresis, and the speed of the purely magnetic transition. To this end, significant work has been focused on the Gd-Co-Si system due to the high number of ferromagnetic phases with high transition temperatures that can be found therein [11][12][13][14][15]. During our study of this ternary system a new pseudo binary phase with the general formula Gd2(Co3-xSix) has been discovered and its structural and magnetic properties investigated [11].…”

“…To this end, significant work has been focused on the Gd-Co-Si system due to the high number of ferromagnetic phases with high transition temperatures that can be found therein [11][12][13][14][15]. During our study of this ternary system a new pseudo binary phase with the general formula Gd2(Co3-xSix) has been discovered and its structural and magnetic properties investigated [11]. The phases with 0.29 < x < 0.50 crystallize in the orthorhombic La2Ni3-type structure (Cmce space group) with unit cell parameters a = 5.3833(4) Å, b = 9.5535(6) Å, and c = 7.1233(5) Å for x = 0.47 and have a tuneable Curie temperature around room temperature that is dependent on the Si concentration.…”