Magnetic anisotropy and related matters. Studied by neutron diffraction

P. Aarosin Hansen

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    Abstract

    Single crystals of Tb-Tm alloys, Nd and MnSi were investigated by neutron diffractometry. Four Tb-Tm alloys with a Tm content of 12%, 40%, 55% and 65% were investigated in the temperature range of 4.2-300 K. All these alloys order magnetically to a basal plane spiral below the Néel temperature. Below the Curie temperature the magnetic ordering of the Tb-12% Tm alloy is ferromagnetic with
    the moments in the basal plane, while the other alloys have a ferromagnetic component along the c-axis and a spiral component in the basal plane below T_. The Tb-55% Tm and che Tb-65% Tm alloys have an intermediate mixed phase, where the c-axis component is modulated along the c-axis (CAM-strueture). In contrast to all other heavy rare earth alloys studied so far, these neutron diffraction studies show unambiguously that Tb-Tm alloys have an inhomogeneous phase, where the spins associated with the Tb-ions lie in the basal plane, while the spins associated with the Tm-ions order along the c-axis.
    The magnetic structure of Nd was investigated between 4.2 K and the ordering temperature 20 K. It is shown that the magnetic structure can be understood with the assumption of single ion anisotropy and that the measured magnetic intensities are not in agreement with the magnetic model proposed by Moon et al. (1964). The critical exponent 6 is in agreement with the c-expansion. NnSi is shown to be an example of a magnetic material with magnetism of nearly itinerant character. The magnetic structure is a spiral structure below the ordering temperature (26.7 K) . The screw axis is the (111) direction and the modulation vector is very short (0.036 A ). In a magnetic field the structure transform into a cone structure at 1 kGauss and above 6 kGauss it is ferromagnetic.
    Original languageEnglish
    Place of PublicationRoskilde, Denmark
    PublisherRisø National Laboratory
    Number of pages78
    ISBN (Print)87-550-0485-7
    Publication statusPublished - 1977
    SeriesDenmark. Forskningscenter Risoe. Risoe-R
    Number360
    ISSN0106-2840

    Keywords

    • Risø-R-360
    • Risø-360
    • Risø report 360

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