摘要:

We have studied the nuclear magnetic resonance of163Dy in ferromagnetic Dy1−xGdxAl2alloys (0?x?0.99). The observed behaviour of the resonance frequencies of the various resonances observed is anomalous and does not follow simple molecular field arguments. Quadrupolar splitting measurements suggest that within a given Dy environment of 0, 1, 2, 3 or 4 Gd nearest neighbours the Dy moment is independent of concentration of Gd. These results lead us to believe that the easy axis of magnetization rotates gradually from (100) to (111) in these compounds and that we in fact sense the Dy moment through nuclei in the domain wall edge. From enhancement factor measurements we conclude that the Dy single ion anisotropy is very small and that the predominate term, establishing domain wall stiffness, is the Dy‐Dy interaction anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.326988

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Ternary Er2Co17‐ and Sm2Co17‐based alloys in which Co is replaced by Ni or Cr have been studied to ascertain the effect of alloying on their magnetic properties. The systems are single phase for 0?x?7 in the case of Er2Co17−xNixand for 0?x?2 for the Cr‐substituted ternaries. Directions of magnetization, saturation magnetizations (Ms), anisotropy fields and intrinsic coercive forces (IHC) are reported for 300 and 78 K along with the measured Curie temperatures (Tc). All systems were found to be uniaxial except Er2Co13.6Ni3.4which has planar anisotropy. Replacement of Co by Ni or Cr results in a decrease in Msand Tc.IHCvalues for Er2Co17−xNixare small at room temperature but increased to ∼4 kOe at 78 K. TheIHCvalues for Cr‐containing ternaries rise dramatically between 300 and 78 K, from ∼0 to ∼15 kOe for Er2Co15Cr2as an example. Anisotropy fields are significantly increased by Cr substituting, reaching in the case of Sm2Co15Cr2∼400 kOe at 78 K. Ni is considerably less effective than Cr in enhancing HAin these ternaries. At low concentrations Ni decreases anisotropy presumably because it produces shrinkage in the c‐spacing and brings the dumbbell cobalts closer together.

ISSN:0021-8979    

DOI:10.1063/1.326989

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Magnetic behavior of ThCo5, Th1−xYxCo5and Th1−xYxCo4Fe has been determined over the temperature range 4 K to the Curie temperature in applied fields up to 120 kOe. Crystal parameters, saturation magnetization and anisotropy fields are presented for ThCo5, for Th1−xYxCo5with x=0.1, 0.2, 0.4, 0.6 and 0.8 and for Th1−xYxCo4Fe with x=0.2, 0.4, 0.6 and 0.8. ThCo5is observed to be exceptionally hard, not achieving saturation at 120 kOe. Co in this compound exhibits an anomalously low moment, ∼1.13 &mgr;B(as determined at 120 kOe). The Co moment rapidly increases as Y replaces Th in ThCo5, achieving for x=0.2 a value of 1.5 &mgr;B, the same as in YCo5. The anisotropy field (HA) for Th1−xYxCo5ternaries at 4.2 K rises from 175 to 203 kOe as x increases from 0 to 0.2 and subsequently falls to 175 kOe for Th.2Y.8Co5. HAincreases by 41 kOe between ThCo5and ThCo4Fe. In contrast with the behavior of (Th, Y)Co5ternaries progressive replacement of Th by Y in ThCo4Fe leads to a monatomic decline in HA. Changes of HAby alloying is ascribed to (a) preferential site occupancy or (b) band modification effects and often these cannot be separated. Present results indicate that these two effects are comparable in magnitude.

ISSN:0021-8979    

DOI:10.1063/1.326990

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have investigated the magnetic and superconducting properties of TmRh4B4(which becomes superconducting at 9.6 K) by means of ac and dc magnetic susceptibility and specific heat measurements. At 10.7 K, an ac susceptibility peak similar to those found in spin glasses has been observed. In addition, a pronounced specific heat peak has been observed at 11.4 K. The susceptibility peak is essentially unaffected by substitution of 1&percent; Lu or Er for the Tm, but it diminishes when much larger amounts of Er are substituted. The physical origin of this anomalous peak will be discussed.

ISSN:0021-8979    

DOI:10.1063/1.326991

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Intermetallic compounds of rare‐earth and transition metals present the possibility of using the large magnetic moment of the first with the high Curie temperature of the second. We first discuss the nature of the coupling between the spin of the rare‐earth and transition metal. We assume that it happens within the d band coming from the 5d and 3d levels and describe it using the Van Vleck model for ferromagnetism. We then consider the particular case of Cobalt compounds where Cobalt can be magnetic or not depending of the rare‐earth metal. We describe the appearance of magnetism as a collective metamagnetism due to the position of the Fermi level in these compounds in a steep decrease of the density of states. Calculation of the density of states confirms this hypothesis.

ISSN:0021-8979    

DOI:10.1063/1.326992

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Susceptibility measurements using a SQUID magnetometer on CexLa1−xAl3where x=.01, .02, 0.1, 0.2, 1.0 over a temperature range from 1.5 K to 20 K are reported. (AIP)

ISSN:0021-8979    

DOI:10.1063/1.326993

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In permanent magnet applications such as electric motors, high reverse magnet fields are experienced by the magnet and a critical design parameter is the onset of the ’’knee’’ of the hysteresis loop. The associated field, H*, marks the onset of irreversible demagnetization. This is particularly important for mischmetal‐based magnets which exhibit lower coercivity than SmCo5magnets. This paper reports measurements of the demagnetization of sintered MMl−xSmxCo5magnets for 0.02 ?x? 0.43 over the temperature range: 175 K ?T? 425 K. The compositions were formed by alloying ’’natural’’ and Ce‐free mischmetal with varying percentages of samarium and then blending with a ’’sintering aid’’. The temperature dependence of H* can be described by H* (T2) = H* (T1) (1 − 0.004 (T2−T1)), where the temperature coefficient −4×10−3K−1is independent of the composition and coercivity within the limits investigated.

ISSN:0021-8979    

DOI:10.1063/1.326994

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A rare earth–cobalt permanent magnet with improved mechanical strength has been developed. Sm1−uCeu(Co1−x−yCuxTmy)zwith Tm=Fe or a combination of Fe with other transition metals were prepared by powder‐metallurgical means. Mechanical strength was evaluated by flexural strength testing for sintered permanent magnet rods. The compositional dependence on flexural strength &sgr;fas well as the influence of the different parameters, as for instance particle size and sintering temperature, were investigated. For z ≳ 5, &sgr;fincreases with increasing z and other substitution parameters u, x and y. For instance, fine grained magnet of Sm0.8Ce0.2(Co0.785Cu0.15Fe0.05Cr0.015)7.6shows &sgr;fof 290 MPa, iHc of 360 kA/m and Br of 0.85 T.

ISSN:0021-8979    

DOI:10.1063/1.326995

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Permanent magnets made from SmCo5exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04&percent; per degree between −100 and +200°C. For special applications in precision instruments such as gyros and accelerometers it is desirable to reduce considerably the temperature coefficient of magnetization. Earlier studies have indicated that good temperature‐compensated magnets may be prepared by replacing a part of Sm in SmCo5with other heavy rare earth atoms such as Gd, Dy, Ho and Er. In the present study a number of compositions of the type SmxRl−xCo5[R = Gd, Dy, Ho, Er, Tm, Yb, and Ti], (SmGd) Co5−yFeyand Sm0.6(R′Gd)0.4Co5[R′=Dy, Ho, Er] were prepared and examined by a number of techniques. X‐ray diffraction patterns indicated the formation of essentially single phases in many of these compositions. Saturation magnetization, remanance, coercive force, anisotropy field and energy product of these materials at room temperature are reported. Magnetization measurements were performed in the temperature range −100 to +200°C and the values of &agr; (reversible temperature coefficient of magnetization) were determined. As an illustration, for a material of composition Er0.2Sm0.8Co5.2we observed the following results: 4&pgr;Ms=11.6 kG, Br=11.1 kG, Hci=8.6 kOe and (BH)max= 17 MGOe at room temperature. The values of &agr; observed are 0.025 between 150–225 K, 0.008 between 225–300 K and −0.009 between 300 and 375 K. Results for other compositions and their systematic trends are discussed.

ISSN:0021-8979    

DOI:10.1063/1.326996

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The coercive field of rare earth compounds of the general formula R(Col−xCux)5, with R=Pr and Nd, has been investigated both experimentally and theoretically. Homogeneous single‐phase specimens with compositions from x=0 to 0.6 were prepared and measured. Compounds with x?0.3 have coercive fields greater than 5 kOe at low temperatures, both in bulk single crystal and in powder form. The coercive field increases steeply with decreasing temperature, and the temperature dependence is stronger for larger x. The spin structure and energy of domain walls in R(Col−xCux)5have been calculated using a discrete spin configuration model, and are found to be more sensitive to short‐range fluctuations of the exchange interaction than of the anisotropy. Short‐range exchange fluctuations can account for pinning fields of the same order as the measured coercive fields. The exchange fluctuations may arise from fluctuations in the distribution of the non‐magnetic Cu atoms in the compounds.

ISSN:0021-8979    

DOI:10.1063/1.326997

出版商:AIP    

年代:1979

数据来源: AIP