C.J.M. Denissen

Interface mixing in Fe/Co multilayers

Abstract Ion beam sputtered Fe/Co multilayers were studied by means of magnetostriction measurements and conversion electron Mossbauer spectroscopy. With decreasing period of modulation the magnetostriction constant of the total multilayer increases. This effect can be attributed to the presence of Fe-Co interdiffusion layers having a large positive magnetostriction. Assuming a linear concentration gradient between the individual Fe and Co layers an interdiffusion layer thickness of about 10 A can be calculated from the magnetostriction data. The Mossbauer spectra of the Fe/Co multilayers showed an increasing asymmetrical broadening with decreasing modulation wavelength. An atomic layer model was applied to explain the observed spectra again assuming a linear concentration gradient. A good fit can be obtained assuming an interdiffusion layer consisting of 5–6 atomic planes, i.e. having a thickness of 10–12 A. Both techniques proved to be good tools for studying interface effects in Fe/Co multilayers quantitatively.

Magnetic, Electrical, and Specific-Heat Properties of UPdSn and UAuSn

Abstract UPdSn orders antiferromagnetically below 40 K and undergoes another magnetic phase transition at about 27 K, which is connected with a re-arrangement of the antiferromagnetic structure. The magnetic properties of UPdSn are strongly anisotropic with the c-axis as the hard-magnetization direction. For UAuSn, the maximum at 36 K in the χ(T) curve may also indicate the onset of antiferromagnetism. However, the very broad anomaly in the specific heat, the poorly resolved 119Sn Mossbauer spectra and the magnetic history phenomena at lower temperatures do not point to long-range magnetic order. The possibility of a frozen non-periodic arrangement of U magnetic moments is discussed in connection with atomic disorder within the Au-Sn sublattice. The distinction between the electron properties of UAuSn and UPdSn is reflected in the different values of the γ coefficient of the low-temperature specific heat, which is remarkably small for UPdSn (5 mJ/mol K2) in contrast to UAuSn (80 mJ/mol K2). A possible localization of the 5f states in UPdSn is envisaged.

Magnetic properties of Er2Fe14−xMnxC

Abstract The magnetic properties of the compounds Er 2 Fe 14− x Mn x have been determined by means of X-ray diffraction, magnetic measurement and 57 Fe Mossbauer spectroscopy. Magnetization measurements made in fields up to 38 T showed that the saturation moment exhibits a minimum at a Mn concentration corresponding to about x =2, due to the antiparallel coupling between the R and 3d sublattice magnetizations the latter becoming strongly reduced with increasing Mn concentration. The reduction of the 3d-sublattice magnetization is accompnied by a corresponding reduction in the 57 FE hyperfine fields and by a lowering of the Curie temperature and the spin orientation temperature. Most of the compounds investigated have a break in the magnetization curves measured at 4.2 K which is interpreted as the onset of decoupling between the antiparallel rare earth and 3d sublattices. A mean field analysis was used to derive the intersublattice molecular field coefficient n RT .

Structure and 57Fe Mössbauer effect in R2Fe14C compounds

The crystal structure of the ternary compound Lu2Fe14C was determined and shown to be isotypic with Nd2Fe14B. 57Fe Mossbauer spectra were taken of the compounds Lu2Fe14C and Gd2Fe14C at 300 K and 10 K. Analysis of the spectra showed that the average iron moment in R2Fe14C is approximately the same as in R2Fe14B. The Mossbauer spectra were decomposed into six subspectra according to the six different iron sites in R2Fe14C. There are considerable differences in the sizes of the iron moments associated with the six iron sites.

57Fe Mössbauer study of RFe12−xTx compounds (T = V, Cr, Mo)

Abstract The 57 Fe Mossbauer spectra of various compounds of the type RFe 12− x T x (T = V, Cr, Mo) have been measured. They were analysed in terms of the different nearest neighbour coordinations of the Fe atoms, arising from a statistical occupation of the T atoms on exclusively the 8(i) site in the tetragonal ThMn 12 type of structure. An assignment of the hyperfine fields to the 3 crystallographic sites 8(i), 8(j) and 8(f) has been made on the basis of the results of recent band structure calculations.

Spin reorientation in Nd2Fe14C

Abstract The temperature dependences of the magnetization and the 57 Fe hyperfine interaction were studied in the tetragonal compound Nd 2 Fe 14 C, which is isotypic with Nd 2 Fe 14 B. The compound Nd 2 Fe 14 C is ferromagnetic with T c = 535 K. Below T c , at about 140 K, a spin reorientation occurs, the corresponding easy magnetization direction deviating from that found at room temperature.