## 3 Results and Discussion
The powder sample shows a small _H\({}_{C}\)_ in all the temperature range, smoothly increasing at low temperatures (Figure 4). Figure 3: Magnetization loops at different temperatures for (Fe\({}_{0.69}\)Co\({}_{0.31}\))B\({}_{0.4}\) dispersed (**a**) and powder (**b**) particles. The insets correspond to the low field magnetization detail. It is noticeable that _M(H)_ does not saturate even at the maximum applied field, with a linear behavior at high magnetic fields, suggesting the existence of two contributions to the magnetization: \(M(H)=M_{irr}+M_{rev}\). The first term (\(M_{irr}\)) is related to the blocked regime, which saturates at low field; whereas the second one (\(M_{rev}\)) is related to a paramagnetic contribution to the magnetization. The saturation magnetization, \(M_{S}\), of each curve is determined by subtracting the linear contribution of the magnetization at high field or, similarly, by extrapolating the magnetization at \(H\) = 0 from the high field linear behavior. From the magnetization curves of the non-interacting system, the increase of \(M_{S}\) when the temperature decreases is evident, whereas \(M_{S}\) of the powder sample remains quasi-constant with a value equal to the lowest saturation magnetization measured for the non-interacting sample. \(M_{S}\) as a function of temperature (5-350 K) curves for the dispersed and powder samples of (Fe\({}_{0.69}\)Co\({}_{0.31}\))B\({}_{0.4}\) are plotted particles in Figure 5. The saturation magnetization of  
Figure 4: Coercive field _vs._ temperature for (Fe\({}_{0.69}\)Co\({}_{0.31}\))B\({}_{0.4}\) samples. The lines are only a guide for the eye. Figure 5: Saturation magnetization (\(M_{S}\)) _vs._ temperature for dispersed (non-interacting) and powder (with strong interparticle interactions) (Fe\({}_{0.69}\)Co\({}_{0.31}\))B\({}_{0.4}\) particles, and the bulk (Fe\({}_{0.7}\)Co\({}_{0.3}\))\({}_{0.8}\)B\({}_{0.2}\) and Fe\({}_{0.7}\)Co\({}_{0.3}\) samples. The lines are only a guide for the eye. the non-interacting particles presents a peculiar characteristic, showing three regions of different behaviors. In the range of temperature of 300-350 K, \(M_{S}\sim\) 100 emu/g\({}_{\rm FeCo}\); in the second region (80 K \(<T<\) 280 K) we observed a plateau of \(M_{S}\sim\) 175 emu/g\({}_{\rm FeCo}\); and in the last one (5 K \(<T<\) 70 K) the saturation magnetization reaches \(\sim\)280 emu/g\({}_{\rm FeCo}\). The low temperature value of \(M_{S}\) is larger than the calculated value for the Fe-Co bulk alloy at this composition (\(\sim\)240 emu/g). In order to characterize the magnetic properties of the alloy at this composition (\(x=0.69\)) and compare it with our particles, bulk samples of (Fe\({}_{0.7}\)Co\({}_{0.3}\))\({}_{0.8}\)B\({}_{0.2}\) and Fe\({}_{0.7}\)Co\({}_{0.3}\) composition were prepared in an arc furnace. The relative boron/FeCo ratio in this sample is the maximum boron amount that the amorphous alloy can incorporate when synthesized by this method (at the eutectic point) [27]. \(M(H)\) was measured at different temperatures for these bulk samples, obtaining \(M_{S}\) approximately constant in the range of 5 K \(<T<\) 300 K with a value of \(M_{S}\sim\) 240 emu/g\({}_{\rm FeCo}\) (see Figure 5) close to the pure Fe-Co alloy saturation value. The \(M_{S}\) values obtained for both samples indicate that the boron content does not affect the magnetization of the system. The saturation magnetization of the bulk alloy when compared with the non-interacting nanoparticles (the dispersed sample) shows that the last one presents a very different temperature dependence, confirming that the changes in \(M_{S}\) (\(T\)) observed in the particles did not originate in the intrinsic ferromagnetic order of the alloy. Consequently, the magnetization observed in the dispersed sample may evidence the existence of three different internal magnetic orders of the particle's spins. At high temperatures, a _core-shell_ magnetic structure of the particles is expected, _i.e._, a core ferromagnetically ordered, whereas the shell spins in a paramagnetic state.