Exchange bias in structure-phase separated K0.8Fe2−xNixSe2 (x=0.015) single crystal: Interface evidence

Emergence of exchange bias field in FeS superconductor with cobalt-doping

“…There is a similar situation in the SEM image of K 0.8 Fe 2−x Ni x Se 2 , and its XRD shows there are two phases with different c axis lattice parameters, which exhibit FM and AFM properties, respectively [36]. However, no second phase is revealed in our XRD measurement, since only one c axis lattice parameter is observed.…”

“…The two intersection points of the hysteresis loop on the horizontal line M off (M off is the value of vertical loop offset along the magnetization axis), the coercive fields and exchange bias field are represented by H C1 , H C2 , H C and H E , respectively, where H E and H C are calculated with [38]. Similar phenomenon also appeared in K 0.8 Fe 2−x Ni x Se 2 [36], which mainly originated from the exchange coupling between the FM domain and AFM domain. According to the deviation of the hysteresis loop from the center under the FC condition, the value of H E is calculated as shown in figure 4(g).…”

“…Below the T N , the field-cooling (FC) curve continues to rise, while the zero-field-cooling (ZFC) curve starts to descend. This situation usually occurs in a system where FM and AFM interactions coexist, indicating that there may be FM interaction or component in the sample [36]. When fitting the high temperature part of the reciprocal of the magnetic susceptibility data, it is not completely linear before the transition temperature, which indicates that there may be a FM signal in the sample.…”

“…There may be exchange bias phenomenon or spin glass in a system where antiferromagnetism and ferromagnetism coexist [36]. Exchange bias is an effect that widely exists at the interface of FM/AFM materials.…”

Effects of Co and Mn doping in K0.8Fe2−ySe2revisited

“…On the other hand, Mn substitution only slightly decreases superconducting transition temperatures up to 5.5 at.% [14]. More interestingly, another class of iron chalcogenide superconductors A z Fe 2−y Se 2 (A = K, Cs, Rb, Tl/Rb, Tl/K) [15][16][17][18][19] seems to be even more sensitive to certain dopants [20][21][22]. Previous results on a series of 3d metals-substituted K 0.8 Fe 2−y Se 2 compounds by Tan et al [20] show that the substitution of Fe by Cr, Co, and Zn leads to rapid depression of superconductivity (superconductivity disappeared in K 0.8 Fe 2−y−x M x Se 2 at real doping concentrations x = 0.01, 0.018, 0.005 for Cr, Co, and Zn, respectively) while doping of Mn at a similar level hardly decreases the superconducting transition temperatures.…”