Sublattice Anisotropy Research Articles

Magnetic structure and anisotropy of Ga- and Al-substituted LaCo5 and YCo5 intermetallics.

The crystal and magnetic structures of hexagonal compounds ${\mathrm{LaCo}}_{5}$, ${\mathrm{LaCo}}_{4}$Ga, and ${\mathrm{YCo}}_{4}$Ga (space group ${\mathit{P}}_{6}$/mmm) have been investigated by time-of-flight neutron diffraction at 293 K. The Ga atoms are found to preferentially occupy the 3g site. For ${\mathrm{LaCo}}_{5}$, Co moments at crystallographic sites 2c and 3g of 1.60${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 1.76${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ have been refined and these moments decrease substantially with substitution of one Ga atom for Co. The magnetic anisotropy field has been measured for ${\mathrm{LaCo}}_{5}$, ${\mathrm{LaCo}}_{4}$Ga, ${\mathrm{YCo}}_{4}$Ga, and ${\mathrm{LaCo}}_{4}$Al on oriented powders using the singular point detection technique. The Co sublattice displays an axial anisotropy for all compounds at temperatures from 77 to 293 K. The anisotropy field is decreased by up to 50% with substitution of one Co atom by Ga (Al). The Co moments for ${\mathrm{LaCo}}_{5}$ are in agreement with results of band structure computations. The single-site approximation for the Co sublattice anisotropy is found to be not generally applicable. \textcopyright{} 1996 The American Physical Society.

Magnetocrystalline anisotropy in Re2(FeTi)17, RE = Nd, Y

The magnetic anisotropies of both Nd and FeTi sublattices have been studied in the 2:17 phase. Contrary to that observed in Nd3(FeTi)29 and Nd(FeTi)12 parent structures, no spin reorientation takes place at low temperature in Nd2(FeTi)17, where both Nd and Fe sublattices give a planar anisotropy. However similarly to 1:12 and 3:29 phases a FOMP (A2-type) is observed in Nd2Fe17-xTix for x = 0 and 0.2.

Magnetocrystalline anisotropy in DyFe12-xVx intermetallics and their carbides

The magnetocrystalline anisotropy in DyFe12−xVx−yCy has been studied by torsion magnetometry and ac susceptibility measurements in the temperature range 4.2–293 K. Carbon solution, unlike vanadium, increases both the saturation magnetization and the magnetocrystalline anisotropy. Changes in the Fe sublattice anisotropies are observed.

Crystallographic and magnetic properties of ternary nitrides of the type RCo 10Mo 2N x

The magnetic and crystallographic properties of rare earth-based interstitial nitrides of the type RCo 10Mo 2N x (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) were investigated by means of X-ray diffraction, high-field measurements and a.c. susceptibility measurements. From X-ray diffraction it was derived that the interstitial hole filling remains substantially below one nitrogen atom per formula unit RCo 10Mo 2N x . We determined the easy magnetization direction in these compounds and found that the Co sublattice anisotropy favours an easy moment direction along the c-axis. The rare earth sublattice anisotropy is governed by a positive value of the second-order crystal field parameter. The large uniaxial anisotropy and the atomic disorder favour the occurrence of a thermally activated intrinsic coercivity in some of the nitrides.

Magnetic properties of rare earth compounds of the type RCo 11Ti

We have investigated the magnetic properties of rare earth compounds of the type RCo 11Ti (R = Sm, Gd, Tb, Dy, Ho, Er, Tm and Y) by means of high-field and ac susceptibility measurements. From the experimental values of the saturation magnetisation at 4.2 K we have derived the magnitude of the Co moments in these compounds, which were found to be almost invariant across the series ( μ Co = 1.41 μ B). We have determined the easy magnetisation direction in the various RCo 11Ti compounds and found that the Co sublattice anisotropy favours an easy moment direction along the c-axis, whereas the rare earth sublattice anisotropy is governed by a positive second-order crystal field parameter ( A 2 0 > 0). Spin reorientation phenomena were observed for compounds with R = Dy, Er and Tm.

Structure and magnetocrystalline anisotropy of R2Fe17−xGax compounds with higher Ga concentration

The effect of Ga substitution for Fe in R2Fe17 (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Tm) compounds on the structure and magnetocrystalline anisotropy has been studied by means of x-ray diffraction and magnetization measurements. Both iron sublattice anisotropy and rare earth sublattice anisotropy are found to be modified by the introduction of the gallium atoms. A uniaxial anisotropy is shown in R2Fe17−xGax (for R=Y, Gd, Tb, Dy, Ho, Er, and Tm) compounds with high Ga concentration, whereas a reversal change in the easy magnetization direction is observed in the samples for R=Sm. The contributions to the uniaxial orientation of the magnetization in these compounds result from not only the rare earth sublattice, but also the iron sublattice.

Field-induced transitions of RCo 3 (R = Ho, Er and Tm) in ultrahigh magnetic fields up to 110 T

Magnetization has been measured for HoCo 3, ErCo 3 and TmCo 3 in magnetic fields up to 110 T. These compounds exhibit field-induced transitions originating from the electronic structure of d electrons and the competing anisotropies of the magnetic sublattices.

155Gd Mössbauer effect studies and magnetic properties of GdFe 12− xMo x(N y) compounds

Structural and magnetic properties of the GdFe 12− x Mo x compounds having the ThMn 12 type of structure were studied. Rare-earth nitrides of the composition GdFe 12− x Mo x N y were prepared by the reaction of GdFe 12− x Mo x with nitrogen gas at 475°C. The crystal structure and lattice constants have been determined for all compounds. The lattice expansion of the nitrogenated compounds is mainly along the a-axis, the Curie temperatures are increased by about 110 K. We investigated the effect of interstitial nitrogen on the magnetic properties and the 155Gd Mössbauer spectrum of GdFe 12− x Mo x . Values of the electric field gradient V zz derived from the quadrupole splitting of the spectra were strongly negative, with V zz = −21.3 × 10 21 V m −2 and V zz = − 19.9 × 10 21 V m −2 for x = 1.5 and 3.0, respectively. Nitrogenation is shown to lead to a sign reversal of the 4f as well as of the 3d sublattice anisotropies.

Magnetic properties of (Er 1−xY x) 2Fe 17C 1.5 compounds prepared by melt-spinning

The single-phase compounds of (Er 1−xY x) 2Fe 17C 1.5 (x=0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8 and 1.0) were prepared by melt spinning at the quenching rates of v s=10–20 m/s. X-ray diffraction shows that the melt-spun carbides crystallize in the rhombohedral Th 2Zn 17-type structure. The substitution of Y for Er is found to have a small effect on the unit cell volume v and Curie temperature T c. The saturation magnetization M s at 1.5K increases monotonically and almost linearly with increasing Y concentration from 79.0 emu/g for x = 0 to 168.5 emu/g for x = 1.0, and the Y-concentration dependence of the Fe magnetic moment is approximately constant. Introducing interstitial carbon atoms into the Er 2Fe 17 results in the increase of Er sublattice anisotropy and the presence of spin reoriention. An approximately linear decrease of the spin reoriention temperature with x in (Er 1−xY x) 2Fe 17C 1.5 compounds is observed as a result of the substitution of Er by nonmagnetic Y atoms.

Role of anisotropy on high field transitions in ferrimagnetic free particles

The effects of the magnetic anisotropy of the two sublattices on both the critical field intensities and the order of spin-flop transitions exhibited by a ferrimagnetic crystal free to rotate in a high magnetic field are examined. The analytical expressions of the critical fields and the stability of the system are analysed through power expansion of the equilibrium equations in the neighbourhood of the transition point. The peculiar case of equal sublattice anisotropies is treated.

The Thomas-Fermi limit of crystal-field interaction

Rare-earth permanent magnets are metals, and it is physically unreasonable to treat crystal-field generating charges as point charges. A more realistic description is given by the screened-charge model, where the conduction electrons are treated as linearized Thomas-Fermi gas. The distance dependence Amnα 1/R2m + 1 of the point-charge model is replaced in the screened-charge model by spherical Bessel functions. An explicit description of these functions is given, and it discussed how Thomas-Fermi screening affects the rare-earth sublattice anisotropy of metallic permanent magnets.

Magnetic anisotropy and magnetization processes in 3:29 and 1:12 Nd(FeTi)-based compounds

The temperature behavior of the magnetic anisotropy and magnetization processes in the tetragonal Nd(FeTi)12 and monoclinic Nd3(FeTi)29 have been studied and compared. Both compounds are characterized by the occurrence of temperature-induced spin reorientation transitions, as well as field-induced magnetization processes of different types, which have been interpreted as first-order magnetization process. In both systems the resultant anisotropy of Nd favors the occurrence of an easy magnetization direction out of the principal axes at low temperature. On the contrary the overall Fe sublattice anisotropy favors the tetragonal c-axis in the 1:12 and seems to prefer the monoclinic a-axis in the 3:29 compound.

Neutron study of the magnetic structure change in DyMn 6Ge 6

The hexagonal compound DyMn 6Ge 6 has been studied by neutron diffraction at various temperatures between T N = 420 K and 11 K. The magnetic structure is incommensurate at all temperatures in the ordered regime with q = (0, 0, q z ). The corresponding wavevector component q z decreases strongly on cooling to about T t = 100 K. It remains almost temperature independent ( q z = 0.1631) below T t at which temperature a second set of Fourier components with q = 0 appears. The phase transition at about 100 K is shown to be of second order and marks the transition from a triple flat spiral structure stable at high temperatures to a triple conical structure stable at low temperatures. The origin of the phase transition is the competition between the temperature-dependent Mn and Dy sublattice anisotropies.

A magnetic, neutron diffraction, and Mössbauer spectral study of Nd2Fe15Ga2 and the Tb2Fe17−xGax solid solutions

An x-ray diffraction study of the substitution of gallium in Tb2Fe17 to form the Tb2Fe17−xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a-axis lattice parameter increase linearly with increasing gallium content. The c-axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ∼150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in x. Neutron diffraction studies of Nd2Fe15Ga2 and Tb2Fe17−xGax, with x equal to 5, 6, and 8, indicate that the gallium completely avoids the 9d site, occupies the 6c ‘‘dumbell’’ site only at high values of x and strongly prefers the 18f site at high values of x. The magnetic neutron scattering indicates both that the terbium sublattice magnetization couples antiferromagnetically with the iron sublattice and that there is a change in easy magnetization direction from planar to axial with increasing gallium concentration. This change in easy magnetization direction is explained in terms of a sign reversal of the second-order crystal field parameter, A02, the most important parameter responsible for determining the terbium sublattice anisotropy. The Mössbauer effect spectra indicate a larger room-temperature average hyperfine field at the iron site in the Tb2Fe17−xGax solid solutions than in several related R2Fe17 compounds. The large observed increase in the isomer shift with increasing gallium content results from interatomic charge transfer and intraatomic s-d charge redistribution in the presence of gallium.

Study of the iron contribution to the 3d-sublattice anisotropy in some uniaxial YCoFe structures derived from the CaCu 5 unit cell

The effects of the Fe substitution for Co on the anisotropy of uniaxial structures (YCo 3, Y 2Co 7, Y 5Co 19, YCo 5) all derived from the parent CaCu 5 unit cell were studied. The unique Singular Point Detection (SPD) technique was used to measure temperature and composition dependence of the anisotropy. A characteristic behaviour of both Co and Fe anisotropies was individuated. The overall Fe sublattice anisotropy is always opposite and 2–3 times larger than that of Co. From the temperature behaviour of the anisotropy constant ( K 1), spin reorientation transitions (SRT) were predicted at temperature values which depend on Fe content. ac susceptibility measurements seem to confirm the presence of SRT. The magnetic phase diagrams of mixed Y-Co-Fe compounds were derived.

High field magnetization study of the Gd/sub 2/Fe/sub 17/H/sub x/ system

Insertion of light elements such as H, C or N in the R/sub 2/Fe/sub 17/ series (R=rare-earth) has been found to improve some magnetic properties of most ferromagnetic compounds of the series, thus becoming prospective candidates for metal-bonded permanent magnets. For instance spectacular increases of T/sub c/ and M/sub s/ have been observed upon interstitial insertion. Among the R/sub 2/Fe/sub 17/H/sub x/ series we focused on the Gd compound and we report on high field magnetization measurements that have been carried out on the Gd/sub 2/Fe/sub 17/H/sub x/ system (x=0, 3 and 5). The measurements have been performed up to 200 kOe in continuous field. We present the isothermal magnetization curves measured between 2 K and 300 K on powder samples embedded in a resin then aligned under a magnetic field of about 10 kOe in order to get oriented samples. The magnetic anisotropy constants K/sub 1/ and K/sub 2/ have been determined taking into account the angular distribution of the grain axes. Their thermal variation as a function of hydrogen concentration is presented. Finally, the observed effect of hydrogen on the iron sublattice anisotropy is compared to that observed in other systems such as R/sub 2/Fe/sub 14/BH/sub x/. >

Structural and magnetic properties of rare-earth iron nitride Ce2(Fe1−xCox)17Ny series

The ternary nitrides Ce2(Fe1−xCox)17Ny have been studied to determine the effect of nitrogenation on their crystal structure and magnetic properties. X-ray diffraction results show that the nitrides retain the rhombohedral Th2Zn17 structure of their parent compounds, but with an expansion in the unit cell volume. For x≥0.6, no Th2Zn17-type nitride compounds are formed. The room temperature saturation magnetization of nitrides is greater than that of the parent compounds for low Co concentrations. The 3d sublattice anisotropy is modified upon nitrogenation; the transition from easy plane to easy axis shifts from x≊0.5 in Ce2(Fe1−xCox)17 to x≊0.15 in Ce2(Fe1−xCox)17Ny.

Structural and magnetic properties of rare earth iron nitride series R2(Fe1−xCox)17N3−δ

The structural and magnetic properties of ternary nitride compounds R2(Fe1−xCox)17N3−δ with R=Ce, Pr, and Nd have been studied. X-ray diffraction results show that nitrides are formed in a limited range of x in each series and the rhombohedral Th2Zn17 structure of their parent compounds is retained with an expansion in the unit cell volume. The room temperature saturation magnetization of nitrides is greater than that of the parent compounds for low Co concentrations. The 3d sublattice anisotropy is modified upon nitrogenation. All of the terminal compounds R2Fe17N3−δ have their easy direction of magnetization in the basal plane. However, easy direction of magnetization shifts from planar to axial for x≊0.5 in the R2(Fe1−xCox)17 series with R=Ce and Pr. This planar to axial transition of easy direction of magnetization shifts towards lower x (x≊0.15) in the nitride series R2(Fe1−xCox)17N3−δ for R=Ce, and is not observed for R=Pr and Nd. The results are interpreted in terms of enhancements in competing 3d sublattice (axial) and R sublattice (planar) anisotropies on nitrogenation, with Ce being essentially in the nonmagnetic intermediate valence state.

Phenomenological analysis of the magnetocrystalline anisotropy of the Co sublattice in some rhombohedral and hexagonal intermetallic structures derived from the CaCu5 unit cell

A comparative study of the saturation magnetization, Curie temperature, and magnetocrystalline anisotropy in several rhombohedral and hexagonal Y-Co compounds was done. The considered phases YCo3, Y2Co7, Y5Co19 (rhombohedrals), YCo5+z, and Y2Co17 (hexagonals) are all derived from the hexagonal CaCu5 unit. The variation of the magnetic properties in the different compounds was found to be strongly correlated to the cobalt content. In particular the Co sublattice anisotropy varies linearly with the Co content in the phases, while it seems to be not affected by structural changes (rhombohedral-hexagonal). The highest anisotropy of Co was found in YCo5, every modification of the CaCu5 cell resulting in a weakening of the overall axial anisotropy. An evaluation of the strength of the Co anisotropy in the 2c, 3g, and dumbbell sites was done using a phenomenological model.

Note on the anisotropy fields in tetragonal RFe 10V 2 compounds

The temperature dependence of the anisotropy field in RFe 10V 2 (R  Nd, Sm, Tb, Dy, Ho, Er, Lu and Y) has been studied from cryogenic temperatures up to the corresponding Curie temperatures. It is shown that the R sublattice anisotropy at room temperature is mainly determined by the second-order crystal field contribution, although fourth-order contributions are substantial and gain in weight at lower temperatures. A comparatively large R sublattice contribution is found in SmFe 10V 2, indicating the participation of higher multiplet levels.