The coexistence of superconductivity and magnetic order in the rutheno-cuprates compounds like RuSr₂GdCu₂O₈ (Ru-1212) and their properties has been extensively studied [1] -[4] . Motivated by the discovery of high-T_c su- perconductivity in cuprates and the colossal magneto resistance effects in manganites, the research was initially focused on 3d transition-metal compounds [5] . However, as it has become increasingly clear that interesting physical phenomena of similar origin also happen in 4d and 5d electron systems, they have been getting a fair amount of attention recently. Among the 4d or 5d transition-metal compounds, ruthenium oxides probably have attracted most attention because of the discovery of superconductivity in Sr₂RuO₄ compound [6] and the poten- tial of unique perovskite ferromagnetic metal SrRuO₃ compound [7] for thin-film applications such as tunneling magneto-resistance or ferroelectric random access memory. These ruthenites also show diverse physical proper- ties depending on the composition or crystal structures. For example, when Sr ion is replaced by Ca ion in the above-mentioned ruthenates, the metallic and magnetic properties are significantly suppressed [8] [9] . From all these studies, it becomes evident that the preparation method plays a very important role, particularly for ob- taining the different physical properties [10] . The research into electrical properties of these compounds requires very pure materials in order to optimize the particular properties of the prepared materials. In this paper, we pro- vide information about the structural, electrical and magnetic properties of the prepared samples using the stoichiometric composition of (Ca_1−xSr_x) RuO₃ system (CSRO) for x = 0.0, 0.07, 0.10, 0.15 and 1.0.

The XRD patterns of (Ca_1−xSr_x) RuO₃ system are shown in the Figure 1. From those spectra, samples with x = 0.07, 0.10 and 0.15 show a solubility up to x = 0.15. Meanwhile, for x = 0.0 and x = 1.0, we observed a single orthorhombic phase identified as CaRuO₃ PDF (70-2790) when x = 0, and SrRuO₃ PDF (70-2791), when x = 1.0 [13] [14] . The samples with x = 0.07 - 0.15 (that have not been reported before in the literature) show very weak reflections of a tetragonal secondary phase (identified as RuO₂ PDF (43-1027)) [15] . In the same referred samples, the Ca ion content variation shows shifts in the peaks. Then, with the calculated lattice parameters a, b, c, and the unit cell volume (V) of each of the compounds considering the following Miller index (h k l): (4 0 0), (0 4 0) and (0 0 4), which are shown in the following Table 1, can be observed that little peaks shift.

Finally, the net lattice parameters of (Ca_1−xSr_x) RuO₃, x = 0.0, 0.07, 0.10, 0.15 and 1.0 system vary with the inclusion of the Sr-ion content and Ru ion coordination. Since the ionic radius of Ca²⁺ ion (Ca²⁺ = 1.34 Å) is lower than the ionic radius of Sr²⁺ ion (Sr²⁺ = 1.44 Å) [16] , we conclude that the Ca ions are substituted by Sr ions with the observed unit cell variation in the volume (V) of each of the compounds, see Table 1. For the behavior of the lattice parameters, the solid solution has a substitution mechanism, where the Sr²⁺ ions substitute Ca²⁺ ions till x = 0.15. With respect to the examined diffractograms, it is worth to mention that the samples with x = 0.0 and x = 1.0 present a single orthorhombic phase identified as CaRuO₃ and SrRuO₃, respectively. Is other synthesis way to obtained this compounds reported in the literature, PDF (70-2790) and PDF (70-2791), with low temperature reaction. In contrast, the samples in the x = 0.07 - 0.15 range present reflections of a secondary phase identified as RuO₃ [16] . That’s way the idea that the anions contributed to the formation of the mechanism of the solid solution.

The next step was the characterization of the samples achieved by SEM. The observed morphology is presented in Figure 2, shows considerable variations in sizes, very few secondary phases and shapes of particles. The grain size varies between 77 to 266 nm. The presented micrographs in the mentioned Figure 2 were taken on the surface of the representative pellets of the CSRO samples with a magnification of 50 KX. Also, in some regions we observe semi-fusion that can be attributed to the ruthenium content. We can observe the secondary phase in the other gray color.

Figure 3 shows the observed resistance of the sintered materials in relation to the temperature. All the samples of Ca_1−xSr_xRuO₃, x = 0.0, 0.07, 0.10, 0.15 and 1.0 system show a metallic behavior. The observed resistance in CaRuO₃ compound (2.009 × 10⁻² Ω) is much higher than that of SrRuO₃ compound (9.367 × 10⁻³ Ω). The

CaRuO₃ compound does not exhibit ferromagnetism and its magnetic properties are still under discussion [17] together with long-range magnetic order. Moreover, as seen with the resistance curve, it does not present any anomaly in the measured range of temperature. The SrRuO₃ compound shows long-range magnetic ordering. The slope changes of 7 to 155 K, which is called Kondo effect. The temperature at which the pronounced break occurs agrees with the reported one, where T_curie (150 K) is related to spin scattering [18] .

In the Ca_1−xSr_xRuO₃ samples within the range of 0.07 ≤ x ≤ 0.15, the short-range ferromagnetic interactions appear. This indicates that the ferromagnetism has been suppressed through the process of substitution of Sr²⁺ ions by Ca²⁺ ions. For the compounds with large Ca²⁺ ions doping (x ≥ 0.7), no clear phase transition is discerned, and

only some irreversibility is observed in the magnetization curves of these materials. The disappearance of the long-range magnetic order is commonly related to the distortion of the RuO₆ octahedra associated with the partial or total replacement of Sr²⁺ ions by Ca²⁺ ions, and the corresponding narrowing of the 4d bandwidth [19] . The samples mentioned before show variations in each one of the profiles. This is because each one has a different chemical composition. Therefore, we can even observe that the resistance of the samples is due to the partial or total composition of Ca²⁺ ions. Since the substitution of Ca²⁺ ions for Sr²⁺ ions introduces and induces the local distortion in the vicinity of calcium ions [20] changing the Ru-O-Ru bond angle and the bandwidth, which weakens the ferromagnetism.

However, for Ca_1−xSr_xRuO₃ (0.07 ≤ x ≤ 0.15) samples, the electrical resistance decreases with the incorporation of Sr²⁺ ions (2.1 × 10⁻³ Ω), giving less resistance than that of SrRuO₃ (9.3 × 10⁻³ Ω). With the sample preparation described above, we did not find any superconducting phase. We observe the same behaviors that were reported for other similar compounds [7] [13] [20] - [22] .

The magnetization at 10 K for x = 0.07 and 0.15 samples are based on the application of a magnetic field of 100 Oe, as shown in Figure 4. The values T_c obtained for different samples are at a temperature of ~164 K, which is very close to those reported in the literature [6] . These samples exhibit such behavior because they have two

phases CaRuO₃ (1 − x) + (SrRuO₃) (x), not one, which explains why both samples have the same transition FM to temperature at T_c―164 K.

Finally, as shown in Figure 5, we measured the magnetic moment (emu) vs. the magnetic field (Oe) for the x = 0.07 sample. This sample has a magnetization applied by a high field at 10 K, whereas at 300 K, it does not present magnetization. A narrow hysteresis involves a small amount of energy dissipated repeatedly, reversing the magnetization. This material could be useful in transformers and other devices for alternating current, where a zero hysteresis would be optimal.

In this work, we obtained nano-crystalline samples of CSRO system by solid-state reaction in air at room temperature, in which a solubility up to x = 0.15 was observed. The SEM micrographs exhibit an almost-spherical grain size distribution from 77 to 266 nm. We also observed that the compounds of the CSRO system exhibit metallic behavior. However, for x = 0.07 and 0.15, the samples exhibit a FM transition to temperature T_c at ~164 K, indicating that the transition temperature decreases with increasing Sr ions concentration. Finally, we found that the x = 0.07 sample has a magnetization at temperature of 10 K, whereas at 300 K the sample does not present a hysteresis behavior.

This work was partially supported by CONACYT-80380, UNAM-IN109308.