A.T. Pedziwiatr

Magnetic properties of RCo4B compounds where R = Y, Pr, Nd, Gd and Er☆

Abstract The magnetic properties of RCo 4 B compounds (R = Y, Pr, Nd, Gd and Er) were studied in the temperature range 4.2–1000 K. The compoun with R = Y, Pr and Nd are ferromagnetically ordered. The reciprocal susceptibility, χ -1 , for R = Pr follows a modified Curie-Weiss law. The compounds with R = Gd and Er show a ferrimagnetic-type ordering. Above the Curie points the χ -1 vs. T curves may be described by a hyperbolic law of Neel-type. The mean molecular field coefficients characterizing the exchange interactions inside and between magnetic sublattices were determined. These are correlated with the mean magnetic contributions of cobalt atoms.

Spin reorientations in R2Fe14-xCoxB systems (R = Pr, Nd and Er)

Abstract The effect of cobalt substitution on spin reorientation phenomena in R 2 Fe 14- x Co x B systems (R = Pr, Nd, Er) was studied by means of bulk magnetometry in the temperature range 4.2–1100 K. It was established that in the Nd-based system the introduction of cobalt resulted not only in a shift of the low temperature spin reorientation (cone to axis) but also triggered, for x ⩾ 10, an appearance of a second spin reorientation (axis to plane) at high temperature. In the Pr-based system, for x ⩾ 9.5, a high temperature spin reorientation (axis to plane) was also observed. Its dependence on Co content was determined. For the Er-based system, an increase of the spin reorientation temperature (plane to axis) was observed as more cobalt was introduced into that system. It was also established that the tetragonal single-phase materials in this system exist only up to x = 5. Temperature-composition diagrams are presented, indicating types of spin arrangements observed in the investigated systems.

Magnetic properties of R2Fe14C (R=Dy or Er)

Abstract The Dy 2 Fe 14 C and Er 2 Fe 14 C compounds crystallize in a tetragonal structure of P4 2 /mnm-type. The compounds are ferrimagnetically ordered. The mean iron moments as well as the Curie temperatures are smaller than the values obtained in corresponding boron compounds. The easy direction of magnetization is along the c -axis for R = Dy and in the basal plane for R = Er.

Structure and magnetism of the Pr2Fe14-xCoxB system☆

Abstract Isostructural, tetragonal materials were synthesized for the entire composition range (x = 0 to 14). They were studied by X-ray and magnetometry methods. Magnetization measurements confirm a ferromagnetic arrangement of 3d and Pr magnetic moments and reveal a sharp increase of the Curie temperature with the increase of Co concentration. Saturation magnetization at 295 and 77 K reaches a slight maximum around x = 1 and gradually decreases for higher Co content. Anisotropy fields initially decrease and afterwards increase very quickly as more Co is introduced to the system. A spin reorientation occurs in alloys with x ⩾ 9.5 at temperature higher than 660 K. It marks a transition between uniaxial anisotropy and planar anisotropy. Spin reorientation temperature becomes lower for materials with higher Co content. A discussion of the Curie temperature change is conducted in terms of preferential substitution of Co into 16k2 sites. The weakening of the exchange interaction between Pr and 3d sublattices, as well as the decreasing Pr-sublattice anisotropy with rising temperature, are considered to be responsible for anisotropy field changes. The interplay between crystal field and exchange field interactions is emphasized. A comparison with the Nd2Fe14-xCoxB system is included.

Magnetic properties of Nd2Fe14−x−yCoxAlyB alloys

Abstract The magnetic properties of Nd2Fe14−x−yCoxAlyB alloys having x⩽3 and y⩽1 are reported. For the composition range x=(2÷3) and y⋍0.5 , materials with high Curie temperatures and anisotropy fields are obtained. The saturation magnetizations of these compounds are somewhat decreased as compared to the value evidenced in Nd2Fe14B. The effect of aluminium on the anisotropy field and coercive force of Nd-Fe-Co-Al-B magnets is analysed.

Magnetic studies of RCo12B6 compounds (R=Y, Ce, Pr, Nd, Sm, Gd and Dy)☆

Abstract Magnetization of the RCo 12 B 6 borides (R=Y, Ce, Pr, Nd, Sm, Gd and Dy), which crystallize in a rhombohedral structure of the SrNi 12 B 6 -type, has been measured in the temperature range 4.2–300 K. All compounds were found to order magnetically with Curie temperatures ranging from 154 to 177 K. Saturation moments at 4.2 K were found to be 6.5, 5.4, 8.4, 8.8, 6.8, 2.1 and 5.9μ B /f.u. for R=Y, Ce, Pr, Nd, Sm, Gd and Dy, respectively. These results imply a ferromagnetic coupling of Co and rare earth moments for light rare earths and an antiferrimagnetic coupling for heavy rare earths in these compounds. A spin-compensation effect is observed in GdCo 12 B 6 alloys at T comp =46 and 72 K, respectively. Results suggest that in CeCo 12 B 6 the Ce ion exists in the quadripositive state. It is clear that RCo 12 B 6 materials are not of interest for permanent magnet applications.

Magnetic properties of Y2Fe14−xMxB compounds where M=Si OR Cu

The results of magnetic measurements performed on Y2Fe14−xMxB compounds, where M=Si or Cu are reported. The compounds crystallize in a tetragonal structure of P42/mnm-type for a silicon content up to x=2.0 and a copper content up to x=1.5. The Curie temperatures increase when substituting Fe by Si or Cu while the saturation magnetizations decrease. The anisotropy fields, HA, diminish linearly when Fe is replaced by Si. In the case of the copper system a more complex composition dependence of HA values is shown, with a maximum at x=1.5. The reciprocal susceptibilities obey a Curie-Weiss behaviour. The magnetic properties of the above compounds are analysed in correlation with the crystalline structure.

Structure and magnetism of the R2Fe14−xCoxB ferrimagnetic systems (R = Dy and Er)

Abstract R2Fe14−xCoxB ferrimagnetic systems (R = Dy and Er) have been synthesized and studied by X-ray and magnetometry methods to determine the lattice parameters, Curie temperatures, saturation magnetizations, anisotropy fields and spin-reorientation temperatures. It has been established that the single phase materials, exhibiting a tetragonal crystal structure, can be formed in the Dy-based system only for x ⩽ 8, while in the Er-based system only for x ⩽ 5. An average increase of the Curie temperature of 58 K per one substituted Fe atom by Co is observed for both systems (x ⩽ 5). A characteristic maximum in composition dependence of the saturation magnetizations at 295 K is found for x ≃ 2, although this is less pronounced than in light rare earth-based Co-substituted systems. The composition dependencies of the anisotropy fields for the Dy-based system at 77 and 295 K show distinct maxima for low Co concentrations and a sharp decrease for higher Co content. The spin-reorientation temperature for the Er-based system is shifted towards higher temperatures by the Co substitution. A brief comparison between ferro- and ferrimagnetic R2Fe14−xCoxB systems is included.

Spin phase diagrams for R2Fe14−xCoxB systems (R = Y,Gd,Pr,Nd,Tb,Er,Tm)

Abstract Magnetization versus temperature measurements and x-ray measurements for magnetically oriented samples have been performed for a series of R 2 Fe 14-x Co x B systems (R = Y,Gd,Pr,Nd,Tb,Er and Tm). Based on these measurements, the temperature-composition diagrams of different spin arrangements appearing in R 2 Fe 14-x Co x B systems have been established. Three distinct types of spin phase diagrams have been found, depending on the sign of the Stevens factor of the rare earth ion involved.

Magnetic properties of Nd2Fe14−xRuxB alloys☆

Abstract Nd 2 Fe 14- x Ru x B alloys (for 0⩽ x ⩽2) crystallize in a tetragonal P4 2 /mnm-type structure. The Curie points as well as spin-reorientation temperatures decrease when iron is substituted by ruthenium. These lowerings are ascribed to the weakening of overall exchange as the lattice shrinks when Fe is replaced by Ru and to antiferromagnetic Fe-Ru coupling. A mictomagnetic-type behavior is also shown. The magnetic properties of the compounds are analyzed and correlated with their composition.