J. Hauschild

Perpendicular magnetization and dipolar antiferromagnetism in double layer nanostripe arrays of Fe(110) on W(110)

Fe(110) nanostripe arrays, consisting of alternating monolayer and double layer stripes, have been grown by step flow on vicinal W(110) substrates. The magnetic easy axis switches from in-plane in the monolayer to perpendicular in the double layer stripes. The data strongly suggest that magnetostatic interactions induce antiferromagnetic order in the double layer nanostripe array. It can be switched into a ferromagnetic arrangement by low external fields.

Magnetism and growth in pseudomorphic Fe films on W(100)

Magnetism and growth of pseudomorphic Fe(100) films grown on a W (100) substrate have been investigated using spin polarized low energy electron diffraction (SPLEED). Different growth modes of the films at different substrate temperatures Tp can be inferred from the temperature dependence of the magnetic order. The Curie- temperature Tc increases monotonously with coverage θ in the temperature range 120≤Tc≤350K for 1.4≤ θ≤2.5 ML, with a tendency to saturation at the completion of the bilayer, for films grown at 300 K and for annealed films. We found a critical temperature Tc=220±5 K and critical behavior of the magnetic order for the completed bilayer independent of preparation conditions. The temperature dependence of the exchange asymmetry Aex(T) is different for different incident beam parameters at temperatures well below Tc. In the vicinity of Tc, Aex(T) follows a power law for films θ≤2 ML, Aex (T) ∼ (Tc−T)β′, with an effective exponent β′=0.22±0.01 independent of θ.

CRITICAL PHENOMENA IN THE TWO-DIMENSIONAL XY MAGNET FE(100) ON W(100)

We experimentally investigated the magnetic phase transition of the in‐plane magnetized double‐layer Fe on W(100). This epitaxial system approximates the theoretical two‐dimensional (2D) XY model to a large extent because of its pseudomorphic growth and structural stability. We measured the magnetization of W(100)/Fe in the vicinity of the Curie temperatureT C using the diffraction of spin polarized electrons and the magnetization of W(100)/Fe/Ag in a wider temperature interval using conversion electron Mossbauer spectroscopy. The temperature dependence of the spontaneous magnetization follows a power law with an exponent β=0.22±0.03 in the temperature regime 0.3≤T/T C ≤0.99. The susceptibility χ(T≳T C ) can be fitted alternatively by a power law with an unusually large exponent γ≊5 or by an exponential law χ∝exp(b/√T−T C ), as predicted for the 2D XY model, with b=1.6.

Magnetism of nanowires of Fe(1 1 0) on W(1 1 0)

Abstract Ferromagnetic nanowires of Fe have been fabricated by molecular-beam epitaxy on a vicinal W(110) single-crystal surface with steps along the [0 0 1] direction. The magnetic properties were investigated by Kerr magnetometry. The magnetic easy axis is in the substrate plane and perpendicular to the steps. The remanent magnetization disappears near T c in a temperature range much narrower than predicted by standard theory of finite-sized systems. Above T c , the magnetization can be saturated in saturation fields H s which are small compared to two-dimensional systems.

Coincidence of susceptibility maximum and Tc

Abstract Magnetic order M(H, T) was determined as a function of temperature and external field for the monolayer Fe on W (110) using spin polarized low energy electron diffraction (SPLEED). The differential susceptibility χ = ∂M / ∂H has a maximum at T c ∗ = 222.65 K . A power-law fit M ( H = 0) ∝ ( T − T ′ c ) β results in T′ c /T c ∗ = 0.997 , whereas M ( H = 0) vanishes at T ∗ /T c ∗ = 1.003 .

SPLEED with external magnetic fields

Abstract The magnetic properties of submonolayers of epitaxial Fe films grown on W(110) are studied using spin-polarized low-energy electron diffraction (SPLEED). Exchange asymmetries A ex of the specular reflected beam were determined as a function of temperature and external field ( H c fell from H c ⩾ 250 Oe at 115 K below 1.5 Oe for T ⩾ 0.95 T c . Spontaneous magnetic order as determined by an extrapolation, M(H a 0) , equals the remanent magnetic order M ( H = 0).