摘要:

TheRTiFe11Nxcompounds have higher Curie temperatures, larger saturation magnetization, and entirely different magnetocrystalline anisotropy behavior as compared with theRTiFe11compounds. In contrast toRTiFe11, thecaxis becomes the easy magnetization direction ofRTiFe11NxwhenR=Nd, Tb, Dy, and Ho, while SmTiFe11Nxhas an easy plane and ErTiFe11Nxpresents a spin reorientation at about 45 K. Theoretical calculations were made to explain those anisotropy behaviors. The calculation results show that the changes in anisotropy behaviors could be attributed to the large positive contribution of nitrogen atoms located at 2binterstitial sites to the second‐order crystal‐field coefficientA20.

ISSN:0021-8979    

DOI:10.1063/1.349861

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The spin‐polarized electronic structures of Gd18Co82and Gd32Co68amorphous alloys are calculated self‐consistently in order to study their magnetic properties. The calculated electronic‐state densities of the Gd and Codstates do not have well‐resolved peaks; this is a characteristic of amorphous alloys. The magnetic moments of Co and Gd are 1.51 and 7.16 &mgr;Bin Gd18Co82, and 1.38 and 7.14 &mgr;Bin Gd32Co68, respectively. These values show good agreement with experimental data. The exchange splitting of Codstates in Gd32Co68is smaller than in Gd18Co82, while the density of states at the Fermi level in the former is higher than that in the latter.

ISSN:0021-8979    

DOI:10.1063/1.349862

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The compounds UTAl (T=Fe,Co,Ni,Ru,Rh,Ir,Pt) crystallize in the hexagonal ZrNiAl structure. Measurements suggest that the 5felectrons in these compounds are itinerant [V. Sechovsky and L. Havela, inFerromagneticMaterials, edited by E. P. Wohlfarth and K. H. J. Buschow (North‐Holland, Amsterdam, 1988), Vol. 4, p. 309]. From self‐consistent linear muffin‐tin orbital energy‐band calculations for the compounds the transition to magnetism across the series is explained in terms of the calculated Stoner products. Inclusion of spin‐orbit interaction leads to an induced orbital moment in URhAl, consistent with the experimental observation that the magnetic properties of these compounds are highly anisotropic [V. Sechovsky and L. Havela, inFerromagneticMaterials, edited by E. P. Wohlfarth and K. H. J. Buschow (North‐Holland, Amsterdam, 1988), Vol. 4, p. 309].

ISSN:0021-8979    

DOI:10.1063/1.349863

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Self‐consistent spin‐polarized energy‐band calculations are reported for theRCo2compounds (R=Tb–Yb). By changing the magnitude of the 4fspin in GdCo2from zero to seven and back to zero, hysteresis was obtained with both low‐ and high‐moment conduction‐electron states being obtained for spin less than 4. For the real compounds, when the calculations were started with no moment on the Co, low‐conduction‐electron moments were obtained for DyCo2–YbCo2. However, when the calculations were started with large moments on the Co the total conduction‐electron moments were calculated to be 1.75 &mgr;B/f.u. for all of the compounds. It is suggested that the conduction‐electron‐state densities in all of the compounds are similar to those in YCo2and LuCo2and that the conduction‐band system is essentially metamagnetic.

ISSN:0021-8979    

DOI:10.1063/1.349864

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

For the hexagonal ferromagnet UNi2, an unusual 5fform factor for uranium has been observed, indicating a large orbital contribution to the total moment. We report on self‐consistent electronic structure calculations for the hexagonal Laves phase (C14) compound UNi2, taking both spin and orbital contributions to the total moment into account. In a constrained calculation, where the spin moment is chosen to agree with experiment, very good agreement with the experimental form factor is obtained. In the analysis of the form factor both the 6dand the 5felectrons are taken into account giving improved agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.349865

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A strong anisotropy is induced in melt‐spun and hot‐pressed Nd‐Fe‐B ribbons by a specific heat treatment such as a slow heating up to 1000 °C. The present study clarifies the origin of the induced anisotropy through microstructural observations. The following grain growth of Nd2Fe14B grains during heating has been observed: (I) As‐quenched Nd2Fe14B grains grow coarser at the roll side of the ribbons at around 750 °C, and at the front of the coarse‐grain region a Nd‐rich region is formed. (II) A rapid grain growth of some of the coarse grains (excessive grain growth) occurs at an interface of the two regions at around 800 °C. The grains which have theircaxes parallel to the ribbon thickness direction grow at a faster rate along a band of the Nd‐rich region. Such preferential grain growth in stacked ribbons results in the enhancement of magnetization in the press direction.

ISSN:0021-8979    

DOI:10.1063/1.349866

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of ball milling on the magnetic properties of the Pr15Fe80B5alloy, whose as‐cast structure was composed of matrix phase Pr2Fe14B and Pr‐rich and &agr;‐Fe phases, has been investigated by measuringiHc, thermomagnetic curves, and x‐ray diffraction (XRD) patterns. By ball milling using a planetary ball mill up to 96 h,iHcdecreased with the amorphization of the matrix and Pr‐rich phases. However, subsequent heat treatments gave rise to the marked increase ofiHc. The alloy, after 48 h of ball milling and subsequent 600 °C annealing possessediHcof 17.4 kOe,Brof 5.8 kG, and (BH)maxof 6.5 MGOe. This alloy showed sharp diffraction peaks of Pr2Fe14B phase, while the &agr;‐Fe phase peak, which persisted through the ball milling process, almost disappeared. The highiHcof the Pr‐Fe‐B alloy, subjected to optimum milling and subsequent annealing, was attributed to a very fine Pr2Fe14B phase precipitation from the amorphous state and to the effective solution of the &agr;‐Fe phase into the matrix phase. Also, a small addition of Cu to the Pr15Fe80B5alloy was found to increase the coercivity. Further, the alloy milled for 12 h and annealed at 600 °C for 1 h showediHcof 19.7 kOe,Brof 7.0 kG, and (BH)maxof 10.2 MGOe.

ISSN:0021-8979    

DOI:10.1063/1.349867

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Nd‐Fe‐B powder produced by conventional methods is pyrophoric, and exhibits poor corrosion resistance. Magnets made from powder are also susceptible to corrosion. Conventional methods of production are complicated, potentially hazardous, and relatively expensive. A novel, low cost, less hazardous method of producing powder and magnets with high corrosion resistance and Curie point is discussed. Nd‐Fe‐B alloys are milled in water, vacuum dried, and passivated at a suitable temperature in a nitrogen or carbon dioxide medium. During passivation, a protective layer, comprised of nitride and/or carbide phases, is formed in the surface region of the powder particles. This powder is not pyrophoric, and may be stored in a laboratory air environment for an extended period of time with no loss in magnetic properties. Compacted and sintered magnets produced from this powder are also highly corrosion resistant, and exhibit a higher Curie point compared to conventionally produced magnets. A description of the novel technology, and a discussion of the properties of Nd‐Fe‐B‐C/N powder and magnets is given.

ISSN:0021-8979    

DOI:10.1063/1.349868

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Melt‐spun ribbons of Nd‐Fe‐Co‐B‐C system alloys were prepared by the single roller rapid‐quenching method. The effects of composition, substrate surface velocity, and heat treatment on the magnetic properties were studied. A maximum energy product of 140.5 kJ/m3was obtained for Nd11Fe72Co8(B0.5C0.5)9alloy ribbon prepared at a substrate surface velocity of 17.1 m/s. The amorphous Nd11Fe72Co8(B0.5C0.5)9ribbons prepared at a substrate surface velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 600 °C for 30 min. Then the value of (BH)maxwas 138.5 kJ/m3. The value of (BH)maxfor a Nd11Fe72Co8(B0.5C0.5)9bonded magnet prepared by using the ribbons heated at 600 °C was 90.4 kJ/m3.

ISSN:0021-8979    

DOI:10.1063/1.349869

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High‐performance R2Fe14BNx‐type magnets (R=Nd and/or Pr/Dy) were successfully prepared by sintering. The optimum magnetic properties are coercivityiHc: 680–1440 kA/m;Hc: 500–1000 kA/m;Br: 1.0–1.3 T; and (BH)m: 180–250 kJ/m3depending on the composition and processing parameters, especially the proper sintering conditions, including nitrogen intake at 1040 to 1050 °C. The magnets thus obtained haveTcvalues of 335 to 370 °C depending on the nitrogen content, which should be <6 at. % for thermal stability. The anisotropy field increases from 6.2 to 8 T with addition of nitrogen, and magnetization measured at 2 T increases by 18%. The weight loss after immersion in a 5% HCl solution for 30 min is 25% less for nitrogenated magnets than for those without nitrogen, due to the replacement of the Nd‐rich phase at grain boundaries by more corrosion‐ resistant nitrides.

ISSN:0021-8979    

DOI:10.1063/1.349870

出版商:AIP    

年代:1991

数据来源: AIP