Magnetic Hardening of Mechanically Alloyed Pr 2 Co 7
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Magnetic Hardening of Mechanically Alloyed Pr2 Co7
L. Bessais1 , R. Fersi1,2 , M. Cabi´e3 and N. Mliki2 . 1 CMTR,
ICMPE, UMR7182, CNRS − UPEC, 2-8 rue Henri Dunant F-94320 Thiais, France,
2 LMOP,
Faculty of Science of Tunis, University of Tunis El Manar, Tunisia,
3 CP2M,
University Paul Cezanne, F-13397 Marseille, France
ABSTRACT The Pr2 Co7 alloys are known to crystallize in two polymorphic forms: a hexagonal of the Ce2 Ni7 type structure and a rhombohedral of the Gd2 Co7 one. They were synthesized by mechanical milling and subsequent annealing in high vacuum. In this work, we focus on the structural study of these phases using X-ray diffraction and transmission electron microscopy. Also, we present the evolution of magnetic properties of these compounds vs the annealing temperature. The coercivity increases with annealing temperature reaching a maximum for TA = 800 ◦ C. The highest is equal to 18 kOe at 293 K and 23 kOe at 10 K. The high magnetic properties observed in these nanostructured Pr2 Co7 intermetallic alloys have their origin in its relatively high uniaxial magnetocrystalline anisotropy field, and in the homogeneous nanostructure developed by mechanical milling process and subsequent annealing. This high coercivity is attributed to the high anisotropy field of the Pr2 Co7 phase and its nanoscale grain size. This leads to the formation of a magnetically hard Pr2 Co7 phase.
INTRODUCTION The study of magnetic properties of rare earth (R) - 3d transition metals (M) intermetallic compounds has attracted great interest from both fundamental and application point of view. This interest is explained by the rich and exceptional properties of these alloys, which arise from the presence in the same compounds of the outer well delocalized 3d electrons, well localized and anisotropic 4f electronic shell [1]. This combination of R and M elements can give rise to materials exhibiting high Curie temperature, given by the strong exchange interaction between 3d electrons of M metals, and a strong anisotropy provided by the rare earth 4f electrons. Among the family in intermettallics, R2 Co7 have attracted interest due to their potential application as permanent magnets. They exhibit excellent magnetic properties such as high Curie temperature TC , large magnetocrystalline anisotropy HA , and important saturation magnetization MS [2,3]. It is therefore attractive to reinvestigate the high-energy milling route and perform a controlled nanocrystallization treatment to favor the nanostructure responsible for improved high coercivity and remanence. Moreover, mechanical alloying yields a large amount of homogeneous sample. The
subsequent annealing offers the possibility to refine the nanostructure by a judicious choice of the annealing temperature combined to an adequate duration [4]. The reduction of the size of the objects prepared by various physico-chemical processes revealed very peculiar and fascinating magnetic or electronic properties. In the present work, we discuss the structural and magnetic properties of P
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