The Preparation Of MnCo(Ni)Ge Based Alloy Ribbons And Research On The Regulation Of Magnetic Transition And Related Magnetocaloric Effect

Magnetic refrigeration technology is a new kind of cooling technology which is praised as the most likely to replace the traditional gas compression refrigeration, the key is to search a refrigeration agent with a large magnetocaloric effect(MCE). Fisrt order magnetic phase transfomation alloys obtain much of attention due to the large MCE and other magnetic function properties. Mn-based alloys have been investigated widely because of low cost and various magnetic properties in many kinds of magnetic phase transfomation alloys. Contrast to the bulks, ribbons do not need or just need a short annealing time to form phase,at the same time the magnetic properties are excellent, so in this paper we focus on the study of the preparation of Mn Co(Ni)Ge based alloy ribbons, the regulation of magnetic transfomation and related MCE,then we also do some research on magnetic transfomation and MCE as well as magnetic resisitance properties of Mn1.9Co0.1Sb alloy.The main results are as follows:1. The magnetic transfomation and magnetocaloric effect in melt-spun and annealed Mn0.89Cu0.11 Co Ge ribbons.Stoichiometric Mn Co Ge alloy is a collinear ferromagnet with the orthorhombic Ti Ni Si-type crystal structure at room temperature, the Curie temperature TC=345 K,it will suffer a structure transformation from low-temperature orthorhombic Ti Ni Si-type structure to high-temperature hexagonal Ni2In-type structure at Tt=650 K. In the past few years, persons have used a variety of methods such as substitution of transition metal element, absence of transition element to regulate to realized the coincidence between magnetic and structural transfomation. We have noticed that most people do the research on bulks, the study on ribbons is very less until now. In this section we substituting Cu for Mn atoms in Mn Co Ge to reduce the temperature of structure transformation. The Mn0.89Cu0.11 Co Ge ribbons were prepared by arc-melting and melt-spinning technology, we found that both melt-spun and annealed ribbons are hexagonal Ni2In-type structure at room temperature. A second-order magnetic transfomation was achieved at 242 and 234 K respectively in both ribbons, and the largest magnetic entropy change(ΔSM) were 0.95 and 0.85 J/kg K respectively under the field change of 10 k Oe.2. The regulation of magnetic transition and related magnetocaloric effect in melt-spun and annealed Mn1-x Cux Co Ge ribbonsThe magnetic and structure transfomation did not take place simultaneously in Mn1-x Cux Co Ge ribbons, the reason maybe due to the excess Cu-substitution. Therefore,we reduce the amount of Cu and fabricate a series of Mn1-x Cux Co Ge(x=0.02,0.04,0.06)ribbons. A coupled magnetostructure transfomation is achieved in the annealed Mn1-x Cux Co Ge(x=0.02,0.04) at 286 and 260 K respectively, so we obtain giant low field ΔSM, the peak value of were 7.2 and8.4 J/kg K respectively under the field change of 10 k Oe.3. The regulation of magnetic transition and related magnetocaloric effect in annealed Mn Ni1-x Fex Ge ribbonsIn this part, we study the effect of the substitution of Fe on the magnetic and structure transfomation and MCE in Mn Ni1-x Fex Ge(x=0.15, 0.18) ribbons. The ribbons reveal complicated magnetization process with the variation of temperature and magnetic field. The antiferromagnetic-ferromagnetic conversion and competition are observed in the Ti Ni Si-type phase in these ribbons. The required field to complete the conversion decrease with increasing temperature. When completing conversion, the coupled magnetostructural transformation from the ferromagnetic Ti Ni Si-type to paramagnetic Ni2In-type state with large ΔSM near room temperature is achieved for these ribbons, in addition, large ΔSM peak value of 4.7 and 9.1 Jkg-1K-1 are obtained around 287 and 270 K for 0.15 and 0.18 sample under the field change of 3 T.4. Giant magnetocaloric and magnetoresistance effects in ferromagnetic Mn1.9Co0.1Sb alloyStoichiometric Mn2 Sb alloy is a ferrimagnet with tetragonal Cu2Sb-type crystal structure. We study the effect of the substitution of Co on the MCE and magnetoresistance in Mn1.9Co0.1Sb alloy. The Co-introduction results in the appearance of antiferromagnetic state at low temperature region. Therefore, the first order magnetic transition occurs between antiferromagnetic and ferrimagnetic state which can be induced by temperature or magnetic field in Mn1.9Co0.1Sb alloy.Accordingly, a ΔSM as high as 5 Jkg-1K-1and a large magnetoresistance of 46% under the field change of 10 and 50 k Oe are achieved.