Coercivity Analysis in Sm(CoFeCuZr)z Magnets with Abnormal Temperature Behavior

Abstract

A comprehensive characterization of sintered magnets with composition Sm(Co bal Fe 0.06 Cu x Zr 0.03 ) z , where 0.088 x 0.128 and 5.8 z 7.2, was undertaken with the objective of clarifying the coercivity mechanisms. For the range of compositions evaluated in this study Cu has a small effect on microstructure, while z has a more pronounced effect. The abnormal coercivity behavior as function of temperature takes place preferentially in samples with low Cu and low z. The microstructure of the samples is composed by cells of rombohedral Sm 2 (Co,Fe) 17 phase, a cell boundary hexagonal Sm(Co,Cu) 5 phase and lamellae of the crystallographically coherent Zr rich platelet phase. Magnetic viscosity studies show that the activation length L a (7-20 nm) has a dimension very similar to the width of the cell boundary phase (10 nm) and is also compatible with the cell size (10-90 nm). Through the Barbier plot, it is found a law of the type S V H c 0.71 , for Sm(CoFeCuZr) z samples with coercivity between 0.09 and 4.2 T. Initial magnetization curves and the angular dependence of the coercivity are used to discuss coercivity mechanisms.

Thermodynamic and experimental study on phase stability in nanocrystalline alloys

“…In view of that the Sm 2 Co 17 -type magnet materials are expected to be able to operate continuously at high temperatures (up to about 800 K [41]), it is very important to study the phase stability and phase transformation behavior in nanocrystalline Sm 2 Co 17 alloy at a high temperature. In our experiment, we examined the high-temperature phase stability in nanocrystalline Sm 2 Co 17 alloy at 773 K and 873 K, respectively.…”

Kinetical analysis of the heat treatment procedure in SmCo5 and other rare-earth transition-metal sintered magnets

“…This effect is observed for all main types of rare-earth transitionmetal magnets like SmCo 5 [1][2][3][4][5][6][7][8], Sm(CoCuFeZr) z [8][9][10][11][12] and NdFeB [13][14][15], but the reason of the coercivity increase remains not plentifully clarified [3,4,11].…”

“…In this situation, there are islands of Sm 2 (Co, Cu) 17 phase separated by a paramagnetic Sm(Co, Cu) 5 . Then, these magnets would be better classified as nanocrystalline nucleation-controlled magnets [11,37].…”

“…Indeed, recent studies have provided evidence in favor of the nucleation controlled hypothesis [11,37].…”

“…(9). This is compatible with the microstructure of the Sm(CoCuFeZr) z magnets, because the 2:17 grains are nanometric ∼100-200 nm [11,12]. This small distance should favor attaining high coercivities after the continuous cooling heat treatment.…”