College Park, Maryland      June 6 - 10 , 2004

TP52: Crystal structure and magnetic properties of (Zr,Mn)Coδ+2 compounds.

E. Sherstobitova, A.P. Vokhmyanin (Institute of Metal Physics Ural Branch or RAS.)

The binary Laves-phase compounds ZrCo2 and ZrMn2 are Pauly paramagnetic. The spontaneous magnetization was observed in nonstoichiometric ZrCo2+x-(Zr1-yCoy)Co2 compounds with x>0.8 and the Tc of them reached up 160 K. Curie temperature (Tc) of the ternary Zr1-xMnxCoδ+2 compounds is about 600 K and the magnetization is 100 emu/g at room temperature. It is of interest to look into the reasons of an occurrence of magnetism in that compounds. For that using the X-ray and neutron powder diffraction we studied the crystal and magnetic structure of Zr1-xMnxCo2 and Zr1-xMnxCo2.45 system compounds. Assuming a substitution of Zr-atoms by Mn-atoms, one can consider former system as stochiometric, and the latter as nonstochiometric. We found that Zr0.8Mn0.2Co2 compound crystallized in the MgCu2 type cubic structure, (Fd3m space group). The Zr- and Mn-atoms randomly occupy the 8(a) position and Co atoms occupy 16(d)-one. On the X-ray diagram of Zr0.64Mn0.36Co2 compound the peaks can be well described in assumption that space group is Fd3m too. However, neutron diagram includes additional peaks (for example, (002)), it can be described in assumption of AuBe5 type structure (space group F-43m). In case of Zr0.64Mn0.36Co2.45 compound additional peaks appear on both neutron and X-ray diagrams and they are well described in according to AuBe5 type. For this nonstoichiometric compound Zr- and Mn-atoms distributions are similar as in stoichiometric Zr0.64Mn0.36Co2 compound, and the Co-atoms occupy 16(e) position fully and 4(a) and 4(c) partly. All the compounds are ferromagnetic. An appearance of the ferromagnetism in Zr1-xMnxCoδ+2 alloys can be considered, within the scope of a model of the itinerant electrons, which was before suggested for an explanation of a magnetic behavior of the ZrCo2+x alloys.

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