Magnetic Anisotropy and Spin Reorientation in Nd 2-x Pr x Co 14 B
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MAGNETIC ANISOTROPY AND SPIN REORIENTATION IN Nd 2 -xPrxCol 4 B F. POURARIAN, S. MEMS Department, PA 15213.
G. SANKAR, A. T. PEDZIWIATR , E. B. BOLTICH AND W. E. WALLACE Carnegie-Mellon University, and Mellon Institute, Pittsburgh,
ABSTRACT Nd2_xPrxCOl4B intermetallics crystallize in tetragonal form isostructural to Nd 2 Fel 4 B. Structural and magnetic properties of the polycrystalline maRoom temperature magnetic measurements indicate terials have been determined. that these intermetallics exhibit uniaxial anisotropy throughout the entire composition range. Substitution of praseodymium in Nd2 _xPrxCol 4 B significantMagly enhances the anisotropy field both at 78 K and at room temperature. netization versus temperature plots show spin reorientation TSR 2 at 546 K for Nd2 Co 1 4B and at 668 K for Pr 2 Co
1 4 B.
TSR2 increases linearly with compo-
The 3d sublattice anisotropy which seeks the tetragonal plane sition x. In addition to the above, low appears to dominate above these temperatures. temperature magnetic measurements demonstrate the spin reorientation in Further additions of praseodymium strengthen Nd2 Co 1 4 B and Ndl. 9 Pro. 1 Col 4 B. the axial anisotropy at temperatures down to 4.2 K. Effect of competing crystal field interactions and the consequences of praseodymium substitution that result in considerable increase in anisotropy field in these quaternaries are discussed.
INTRODUCTION It has been established that the outstanding permanent magnet characteristics of the Nd-Fe-B material originate from a large magnetic moment, a reasonable uniaxial anisotropy of the Nd 2 Fel 4 B phase and a significant coercivity [1,2]. One of the disadvantages of these magnets is their relatively Replacement of cobalt for iron leads to an low Curie temperature [3]. increase of T. [3-6]. Generally, the anisotropy in R2 Fel 4 B compounds arises from two contribuThe 3d subtions - the 3d sublattice and 4f sublattice anisotropies [7-9]. lattice favors an easy direction of magnetization parallel to the c-axis, as At room temperature the 4f anisotropy domin Y2 Fel 4 B and Lu 2 Fel 4 B [2,10]. inates over the 3d anisotropy in all cases where the R atoms are magnetic, but the easy direction of magnetization along the c-axis develops only in those compounds in which the R component has a negative second-order Stevens In the case of R2 Co 1 4 B compounds, the 4f sublattice anisotropy coefficient. However, the conribushows qualitatively the same behavior as in R2 Fel 4 B. The 3d sublattice gives rise to a tion of the 3d anisotropy is different. planar anisotropy, such as in the cases of Y2 Co 14 B and La 2 Co 1 4 B [6]. In Nd 2 Fel 4 B-type structures, there are four formula units per unit cell, with six inequivalent Fe sites and two Nd sites in the space group P4 2 /mnm [11]. The inequivalent crystallographic Fe sites are: 16k1 , 16k 2 , 8jl, 8j2, 4 4e and c. Neutron diffraction studies of powdered Nd 2 (Fe,Co) 1 4 B revealed that the cobalt atoms show a preference for occupying 4e sites, while Fe atoms occupy preferentially th
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