The effect of histerezis on magnetocaloric properties at magnetostructural transitions

In this thesis, the ferrimagnetic pnictide Mn 2 Sb alloy, which are doped with Cr, Co, Fe elements and their combinations (Cr-Co, Cr-Fe, Co-Fe ) to partially replace Mn element. So that, the first order antiferromagnetic-ferrim agnetic (AF-FI) phase transition were observed in these alloys. In and Ga elements were used to refine the impurity phase MnSb in some alloys. We characterize these alloys using X-ra y diffraction, magnetization measurements and magnetocaloric measuremets. In the results, all alloys were showed two different crystal structure in XRD patterns. The one of them is ferrimagnetic tetragonal Mn 2 Sb which has P 4 /nmm space group and the other one is ferromagnetic hexagonal MnSb from P 63 /mmc space group. The added Cr, Co, Fe and their combinations binds stronger to Mn at the Mn(I) site causing a decrease in the length of the c -axis. So, alloys show the first order AF-FI phase transition at a certain temperature. In Cr doped Mn 2 Sb, the impurity phase, MnSb was refined by In content and also alloy showed the same effect wit h adding Ga content instead of In. Additionally, when the Cr content increased in alloy, impurity phase continued to refine and the first order AF-FI phase transition rose up to roo m temperature. Co doped Mn 2 Sb alloy showed the magnetic-glass behaviour and when the In content was added the alloy, this behaviour became clear in magnetic measurement s. This behaviour disappeared in Mn 2 − x Co x Sb including Ga content. In Fe doped Mn 2 Sb, the impurity phase MnSb was observed excessively. Cr-Co doped Mn 2 Sb has a first order AF-FI phase transition and with increasing Cr content in alloy, the phase transition sh ifted a room temperature. In some alloys, the adiabatic temperature measurements wer e performed and we observed the inverse magnetocaloric effect in these alloys (about 2 K). Additionally, the reversibility of alloys are quite well in adiabatic tempera ture change. KEYWORDS : Magnetocaloric effect (MCE), Mn-Base alloys, Pnictides, First order AF-FI phase transition.