Magnetic x-ray-scattering study of Tb

Abstract

The temperature and energy dependence of the magnetic scattering in the ferromagnetic spiral phase of Tb has been studied between 220 and 235 K by high-resolution x-ray-scattering techniques using synchrotron radiation. In order to see the magnetic scattering it was necessary to exploit the resonant enhancement of the magnetic x-ray cross section by tuning the incident photon energy to the Tb Lyly edge. A lower bound for this enhancement is of order 20. The magnetic modulation wave vector r decreases continuously with decreasing temperature over most of the range between the Neel and Curie points, in agreement with prior neutron-diffraction measurements. However, no evidence was found for any lock-in behavior above T"as has been observed in other rare earths. A very strong hysteresis eKect is present in Tb below T~, with the value of the modulation wave vector apparently depending on the rate of cooling from the paramagnetic regime. In addition, the radial linewidth of the magnetic satellite at (002)+ is not resolution-limited and increases as T~T + while that of the charge peak at (002) remains constant. No conclusive evidence was found for scattering at higher harmonics.

Resonant magnetic x-ray studies of magnetic ordering in dysprosium layers

“…Magnetic resonant scattering, 28 which is induced by electric multipole transitions, can enhance the scattered magnetic intensity by several orders of magnitude, depending on the selected absorption edge. In the case of metallic heavy rare earths, 8,14,[16][17][18][19]22,28 the resonant enhancement can reach a factor of 50 to 100. Dipole transitions at the L 2,3 edges probe the spin polarization of the electronic vacant d states, while quadrupole transitions probe the strong spin polarization of the 4 f levels.…”

“…Second, the intensity ratio between the -and the -channel at the (0,0,2Ϫ2) is given by (1/sin ) 2 ϭ4.2 2 Ϸ17.6 ͑Table I͒, in good agreement with the observed value. 18 Moreover, the resonance at E D is slightly above the edge. The case of the quadrupole transition is more complex.…”

“…The x-ray source is a linear hybrid undulator with a 48 mm period. It delivers photon beams with a brilliance around 7ϫ10 18 ph/s/mm 2 /mrad 2 /0.1% bw around 8 keV at 100 mA. The optics comprise a double Si͑111͒ crystal monochromator.…”

“…Indeed, the x-ray resonance is, by nature, element sensitive, and the magnetic x-ray resonant scattering cross section contains polarization-dependent terms that distinguish the different electronic orbitals that contribute to the magnetization. This method has been used by several groups to study bulk rare-earth metals ͓Ho, 14,15 Er, 8,16 Tm, 17 Tb, 18 and Dy͔, 19 as well as alloys ͓Ho 0.5 Tb 0.5 , 20 Ho 0.5 Er 0.5 , 21 Dy 0.6 Lu 0.4 ͔. 22 Further references about studies of rare-earth systems can be found in Ref.…”

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

“…Large wavelength magnetic modulation in (0 0 1)Tb films [7,8] Bulk hcp Tb presents the same sequence of magnetic phases as the bulk Dy but with significant differences [19][20][21]: (i) the Néel temperature is higher, i.e., T N = 230 K, (ii) the helical phase is stable on a very reduced temperature range: the firstorder ferromagnetic transition occurs at T C = 220 K, (iii) the turn angle between magnetic moments of successive basal planes is 21 • just below T N and (iv) because of the shape of the electronic cloud and of the consequent anisotropy, the magnetic moments lie in the basal plane along the b-axis.…”