Magnetization curves have been measured in the temperature range from 4.2 to 300 K along the [100], [110],and [001]directions of a Dy(Fe~, Ti) single crystal in fields up to 7 T. The magnetic moment is along [100] below 58 K and parallel to the c axis above 200 K. Between the two spinreorientation transitions (first order at 58 K, second order at 200 K) there is a canted spin structure where the net magnetization lies in a (010) plane and is inclined at an angle to the c axis, Three first-order magnetization processes are observed as a function of applied field below 150 K. All the data are used to derive a set of five crystal-field coefficients at the single rare-earth site of the ThMn]2 structure: Aro= 32 3 «o A4o= l2 4 «o A44=118 Kao A6o=2 56 «o A64=0. 64 Kao . Spin reorientation observed in the other members of the R(Fe"Ti)(R:rare earth) series, except those in Tb(Fe] l Ti), are explained by the same crystal-field coe%cients.

Form factor analysis in rareearth intermetallics: Evidence for 5d polarization and higherorder exchange terms

Magnetic properties of the series of ThMn,,-structure intermetallic compounds R(Fe,,Ti) have been determined for rare earths from Nd to Lu plus Y. The highest Curie temperature (607 K) is for R = Gd, and R-Fe exchange interactions are much stronger for light rare earths than for heavy ones. The temperature dependence of the iron sublattice magnetisation and anisotropy are determined for the Y and Lu compounds. Spin reorientation transitions are found as a function of temperature for the rare earths with a negative second-order Stevens coefficient cu,(Nd, Tb, Dy), and a set of crystal-field parameters is derived to account for the transitions in a consistent way. A sharp increase in magnetisation observed for Sm(Fe,,Ti) below 130 K in a field of about 10 T applied perpendicular to the easy direction indicates that J-mixing may be important for Sm3'. Compared with R2Fe,4B, the iron anisotropy in R(Fe,,Ti) is greater, and the rare-earth anisotropy is much weaker at low temperature, with the opposite sign for the rare-earth crystal-field coefficient Azo. The average iron moment is 1.7 pB in R(Fe,,Ti) at 4.2 K; Mossbauer spectra are analysed to yield the average moments on each site. Limits set by the intrinsic magnetic properties on the performance of magnets made from these families of alloys are discussed.

Magnetisation processes have been investigated for model multilayer systems where antiferromagnetic interactions couple adjacent ferromagnetic layers. In this first study, only coherent rotations of the magnetisation of each layer are taken into account. Depending on the direction of the applied magnetic field, the initial moment configuration and the magneto-crystalline anisotropy, various first-or second-order magnetic transitions may be observed.The cases of cubic and uniaxial anisotropy bilayer systems are treated in detail. Spin-flop and spin-flip transitions are calculated to occur for both symmetries when starting from antiferromagnetic configurations that are parallel to the field axis. In the cubic case, various other transitions have been found. In particular, first-order transitions between symmetric and non-symmetric states have been calculated, involving asymmetric behaviour of the magnetisation vectors of adjacent layers. Such transitions give rise to a transverse magnetisation. All the critical transition fields have been calculated as a function of the anisotropy and are reported in the various phase diagrams.Hysteresis loops have also been calculated. They generally consist of an upper and a lower part shifted symmetrically about the origin as in the case of bulk antiferromagnets.The influence of the number of layers has been investigated in some particular cases. It is shown that in most instances when the number of layers n becomes very large (i.e. when boundary effects disappear), the multilayer behaves like a bilayer but with different transition-field values. For small numbers of layers, whether or not the magnetism is compensated (n even or odd) has a very strong effect on the magnetisation processes.