S. F. Cheng

Magnetic and structural properties of SmTiFe11-xCox alloys

Abstract SmTiFe11-xCox (0⩽x⩽11) alloys were synthesized and studied by X-ray, SEM, EDXS and magnetometry at fields up to 90 kOe in the temperature range of 4.2–1100 K. It is established that almost single-phase materials exhibiting a ThMn12 type structure can be formed only for x

Magnetic properties of LaCo13-based systems

Four polycomponent systems based on LaCo13 have been studied: La(Co1−xFex)13, La(Co1−xAlx)13, La(Co1−x−yFexAly)13, and La0.7Nd0.3(Co0.7Fe0.3)13. These 1:13 systems were studied because of their potential for permanent magnet fabrication. LaCo13 has a high 3d metal content, the highest for any known rare‐earth intermetallic, a 13 kG saturation induction, and a high Tc (1318 K). Unfortunately, it is cubic and lacks anisotropy. The substituted systems were examined as a portion of a program to find LaCo13‐based systems of applications significance. Replacement of Co in LaCo13 by Fe and/or Al leads to a rapid decline in Tc for all systems studied. Replacement of Co by Al results in a decline in moment, whereas replacement by Fe leads to a rise in moment to 2.39μB/3d atom for La(Co0.4Fe0.6)13, as compared to 2.46μB/3d atom for Fe0.7Co0.3. Analysis of the magnetic data shows that vacancies occur in both half‐bands for LaCo13 (4.8 spin up and 3.24 spin down) but in only one half‐band in La(Co1−xAlx)13 for x≥0.2....

Magnetic behavior of heavy rare earth RTiFe11-xCox alloys☆

Abstract A series of novel alloys of the composition RTiFe11-xCox (R= Gd, Dy, Ho, Er, 0.5Er0.5Sm; 0 ≤ x ≤ 11) have been synthesized and investigated magnetically over the temperature range of 77–1100 K. The alloys exhibited the tetragonal ThMn12 structure and were almost single-phase materials for lower cobalt contents. In the range, 0 ≤ x ≤ 3, a very small amount of Fe-Co-Ti phase was present, primarily along the grain boundaries. At higher Co contents, a considerable amount of an extraneous phase of the Th2Ni17 structure was observed. The RTiFe11-xCox alloys possess saturation magnetization (σs) in the range 58–120 emu/g at 295 K. σs decreases with decreasing temperature, exhibiting an antiferromagnetic coupling of rare earth and transition metals. At 77 K, σs is in the range 39–110 emu/g. A characteristic maximum in σs is found for x ≈ 3. For the alloys we studied the easy magnetization direction appears to be axial at 295 K at both the Fe and Co ends. The Curie temperatures (Tc) of the alloys are fairly high and range from 495 K (ErTiFe11) to 1119 K (GdTiFe2Co9). In all these materials Tc is considerably enhanced by Co substitution.

Effect of Al substitution on the magnetic properties of RCo5 (R=rare earth)

Magnetic and structural characteristics of RCo5−xAlx have been established for R=Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Tm. All systems have the CaCu5 structure. Al and Co are randomly distributed over the Co‐sublattice sites. Al‐substitution decreases μCo and Tc and significantly alters magnetic anisotropy. Analysis of the magnetic anisotropy data shows that the Sm anisotropy in SmCo4Al is only 32% of that in SmCo5. In terms of the point charge model this requires that Al carry a positive charge. This is consistent with inferences drawn from the decreased Co moment accompanying Al substitution, which implies electron transfer from Al to Co. At room temperature, RCo4Al systems are uniaxial for R=Y, La, Ce, Pr, Sm, and Er, whereas for R=Nd and Dy the magnetization is at an angle with respect to the unique c axis. PrCo4Al, NdCo4Al, DyCo4Al, and TmCo4Al exhibit changes in anisotropy at about 165, 295, 420, and 84 K, respectively.

Magnetic properties of RCo4M (R=Y, Nd and Ho; M=B, Al and Ga)

Magnetic and crystallographic measurements have been made for the compounds RCo4M (R=Y, Nd, and Ho; M=B, Al, and Ga) to intercompare the magnetic properties of RCo4B, RCo4M (M=Al and Ga) and RCo5. The compounds RCo4B crystallize in the CeCo4B type structure, while RCo4M (M=Al and Ga) in the CaCu5 type. The following main conclusions have been obtained: (1) the Curie temperature and the averaged Co‐moment of RCo4M (R=Y, Nd, and Ho; M=B, Al, and Ga) are lower and smaller than those of RCo5, respectively, and 6i‐site Co‐moment in RCo4B is smaller than the 2c‐site Co‐moment by the influence of the neighboring B‐layer; (2) magnetocrystalline anisotropy of R‐sublattice of RCo4B is stronger than that of RCo5, while that of RCo4Al is remarkably weaker than that of RCo5; (3) the Co‐sublattice anisotropy constants of YCo4M (M=B and Al) are 20% or less of that of YCo5; and (4) JR‐Co and JCo‐Co, which are the exchange parameters of the atomic pairs in NdCo4M (M=B and Al), have been estimated to be JR‐Co/k ≂ 7 K and J...

Magnetic and crystallographic properties of NdCo4M (M=B, Al, and Ga)

The magnetic and crystallographic properties have been investigated for NdCo4M (M=B, Al, and Ga). The temperature dependencies of lattice parameters have been determined between 80 and 730 K by x‐ray diffraction. NdCo4B crystallizes in the CeCo4B‐type structure, whereas NdCo4M (M=Al and Ga) exhibits a CaCu5‐type structure. Magnetic properties of NdCo4B show a clear difference from those of its Al and Ga counterparts. All these compounds exhibit planar anisotropy in the low‐temperature regime, and the spin‐reorientation temperature is found to be ∼280 K for NdCo4Al and NdCo4Ga, whereas NdCo4B is planar up to its Curie temperature. Thermal expansion curves of c axes show an anomalous contraction for NdCo4B and expansion for NdCo4Al and NdCo4Ga only in the temperature region of planar anisotropy.

Phase analysis and magnetic properties of RTiFe11−xCox (R=Y,Gd) (x=0–11)

Both as‐cast and 1000 °C annealed RTiFe11 samples are nearly single phase with a small amount of Fe2Ti. Small amounts of Co additions do not change the microstructure, but the minor phase changed to a Fe,Co,Ti solid solution. At high Co concentration, as‐cast samples are multiphase [1‐12, 2‐17, (Fe,Co,Ti)] and high‐temperature (∼1200 °C) annealing is needed in order to produce a single‐phase microstructure. Results of x‐ray analysis and magnetic measurements show that YTiFe11, YTiCo11, GdTiFe11, and GdTiCo11 are uniaxial and their anisotropy fields at room temperature are 22, 18, 33, and 25 kOe, respectively. Therefore, Fe and Co sublattices are uniaxial with Fe sublattice anisotropy stronger than that of Co. In the intermediate range of composition, there is a conical‐planar region for both Y and Gd systems and spin reorientations with temperature were observed. In general, the anisotropy behavior of the RTiFe11−xCox systems (R=Y,Gd) is similar but opposite to their counterpart of R2Fe17−xCox. This is du...

Phase analysis and microstructural characterization of SmTiFe11−xCox (x = 0,8,11) and DyTiCo11 by transmission electron microscopy☆

Abstract We have examined alloys of composition SmTiFe 11− x Co x (x = 0,8,11) and DyTiCo 11 via transmission electron microscopy. Results indicate the sample without Co to be composed primarily of the body centered tetragonal 1–12 phase with a small amount of α-Fe and Fe 2 Ti present. With increasing Co content, the frequency of occurence of the 2–17 phase increases. In Sm containing samples, this phase is rhombohedral, while for Dy samples, the hexagonal phase was also found. Correspondingly, we observed an increase in the amount of transition metal-Ti solid solution as the Co concentration increases. In addition, there are orientation relationships between the 1–12 and both 2–17 phases. This is consistent with a coordinate transformation matrix based on the 1–5 structure. Both the 1–12 and 2–17 phases were found to contain antiphase boundaries in annealed samples containing Sm. The 1–12 phase alone contained antiphase boundaries in the DyTiCo 11 sample. These and other results are discussed.

Magnetic properties of R-Fe-B and R-Fe-Co-Al-B magnets (R=Pr and Nd)

Etude des effets de substitutions de Fe par Co et Al dans les aimants frittes PrFeB et de traitements thermiques sur leurs proprietes magnetiques

Magnetic and structural characteristics of the Pr2(Co,Fe)7B3 system

Pr2Co7−xFexB3(0≤x≤7) alloys have been synthesized and studied at temperatures from 4 to 1100 K at fields up to 90 kOe. The structure and magnetic properties vary significantly with increasing Fe content. The material exhibits the Ce2Co7B3 structure for 0≤x≤0.5. For 0.5≤x≤3 the alloy is comprised of a main phase of hexagonal structure. A change in magnetocrystalline anisotropy occurs around x=3.5; all alloys of x≤3 exhibit conical anisotropy at both 295 and 77 K, and axial anisotropy for x≥3.5. Tc increases from 328 to 890 K when x varies from 0 to 3, then decreased to 564 K when x further increased to 7. The saturation magnetization, Ms, increases monotonically with increasing Fe content. A sintered magnet with a Br of 6.1 kG, a Hci of 10.6 kOe, and a BHmax of 9.1 MGOe were obtained using Pr2Co2Fe5B3.