| Functional materials in the modern social development play a more and more important role,and have been widely studied.In recent years,was found,Due to the huge development potential and the application prospect in the aerospace?defense?medical?civil and other aspects,ferromagnetic shape memory alloys as a new kind of functional materials has been one of the hot topics in the condensed matter physics.Recently researchers observed zero field exchange bias effect in high Mn content NiMnIn alloy,meanwhile,a kind of spin wave magnetic resistance characteristics and peculiar thermoelectric transport properties,respectively,are observed in Mn2NiGa of Mn2Ni based alloys at room temperature.These new phenomena and new effect made Mn2Ni-based alloys become the new research focus of ferromagnetic shape memory alloy.Take this as an opportunity,a series of pure phase Mn50Ni50-xAlx alloys are prepared by arc smelting and melt spinning techniques.The structure and phase transformation of the alloys are analysed by X-ray diffraction method(XRD)and differential scanning calorimeter(DSC).A physical property measurement system(PPMS)is used to test various magnetic thermal properties of the alloys.We discussed the structure,magnetism,zero field exchange bias effect,spin glass behavior,and other physical properties of the Mn50Ni50-xAlx ferromagnetic shape memory alloys.Through the survey and analysis,the preliminary conclusions are as follows:1.Using arc smelting,especially combined with fast quenching cooling melt spinning techniques,a series of pure phase high A1 content Mn50Ni50-xAlx alloys(13?x?22)is prepared.The austenitic phase of samples is body centered cubic(BCC)B2 structure;the lattice constant of samples decreases with increasing Al content,and this may be associated with the increase of covalent bond in the alloys.A large exchange bias is observed in Mn50Ni50-xAlx alloys after zero-field cooling from an unmagnetized state,and the value of exchange bias field HE is as large as 2326 Oe.High field part initial magnetization curve of sample is outside of magnetic hysteresis,showing that the irreversible pinning-depinning effect exists within the sample.For studying the intrinsic physical mechanism of zero field exchange bias effect,the ZFC/FC curve,training effect,ac susceptibility ?-T curve and memory effect curve of the samples were obtained.Based on the experimental results and data analysis,it is confirmed that the low temperature magnetic phase of the samples are super spin glass phase(SSG).Zero field cooling SSG state under the action of the initial magnetization in strong magnetic field,has been translated into a unidirectional anisotropic superferromagnetism(SFM)phase,and make sample magnetic hysteresis loop shift to the the opposite direction of the initial magnetization field.Through the M-T curve measurement,we confirmed the Curie temperature of SFM phase is about 10 K.The strong magnetic field can stabilize SFM phase,while the thermal disturbance destroys SFM phase.2.We also study exchange bias effect,super spin glass behavior and the connection between them in the Mn50Ni50-xAlx series alloy.Super spin glass phase(SSG)in strong magnetic field action is translated into super ferromagnetic phase(SFM),and external measurement field strength can control the ratio of AFM to SFM phase content in samples,the strength of the phase interface pinning action is related to the ratio between the two phase contents,and then HE and HC changes with measurement field H regularly.3.About the Mn50Ni50-xAlx series alloy,when x ? 15,ferromagnetism increase with the increase of the Al content,this may be derived from more Mn(A)and Mn(B)forming the ferromagnetic phase;when x>17,ferromagnetism began to decrease with the increase of the A1 content,but hysteresis and coercive force are enhanced,which reflects the degree of disorder atomic occupation in the alloys.T=300 k,x? 15,sample began to appear hysteresis phenomenon,ferromagnetism is obvious,but magnetic moment weakened. |
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