In-plane Spin Reorientation Transition Research Articles

Spin reorientation transition induced by surface reconstruction in epitaxial Fe/Co bilayers

Surface reconstruction is a common physical phenomenon, driving the atoms near the surface to form a different spacing or symmetry from the bulk atoms to minimize the free enthalpy of the system. The formation of an asymmetric (7 × 2) reconstruction was observed on (112)-oriented Fe surface, which may be related to the anisotropic strain distribution induced by lattice mismatch. The influence of reconstruction on in-plane magnetic anisotropy has been studied in epitaxial Fe/Co bilayers grown by molecular beam epitaxy. The evolutions of Co layer thickness-dependent magnetic anisotropy for reconstructed and unreconstructed configurations were investigated by magneto-optic Kerr effect technique. The most significant difference caused by reconstruction took place when tCo = 3 nm, showing a reconstruction-dependent in-plane spin reorientation transition with a rotation of 90°, which can be attributed to the dramatically enhanced magnetic interface anisotropy of Fe/Co bilayers.

Metadynamics study of the temperature dependence of magnetic anisotropy and spin-reorientation transitions in ultrathin films

We employ metadynamics simulations to calculate the free energy landscape of thin ferromagnetic films and perform a systematic study of the temperature dependence of magnetic anisotropy and of the spin-reorientation transitions. By using a simple spin model we recover the well-known power-law behavior of the magnetic anisotropy energy against magnetization and present a rather detailed analysis of the spin-reorientation transitions in ultrathin films. Based on tensorial exchange interactions and anisotropy parameters derived from first-principles calculations we perform simulations for Fe double layers deposited on Au(001) and W(110). In case of Fe$_2$W(110) our simulations display an out-of-plane to in-plane spin-reorientation transition in agreement with experiments.

Magnetic properties of (Ga,Mn)As (110) epitaxial films

Magnetic properties of (Ga,Mn)As films epitaxied on GaAs (110) substrates have been investigated. Both magnetic and magnetotransport measurements indicate dominant in-plane magnetic anisotropies for as-grown and annealed samples. Moreover, obvious in-plane spin reorientation transition upon the change of temperature has been observed for the as-grown samples, which disappears after annealing. The above phenomena are shown to be correlated with the competition between the cubic and the uniaxial magnetic anisotropic fields. The relative strengths of these two terms are quantitatively obtained by the planar Hall measurements and can be tuned by annealing. For all the annealed (Ga,Mn)As (110) films, a dominant [−110] uniaxial magnetic easy axis is found and the mechanism is discussed. Our work provides useful information for understanding the origin of magnetic anisotropies in (Ga,Mn)As films.

Thickness-induced spin-reorientation originated from competing magnetic shape anisotropies

Engineering the surface morphology of magnetic film is one of the important methods to tune the magnetic anisotropy of ultrathin magnetic material. However, the influence of competing shape effects on magnetic anisotropy of ultrathin film is still not clearly demonstrated. Here, we investigated the magnetic anisotropy of obliquely deposited Fe films on vicinal Si(111) substrate by using in-situ and ex-situ surface magneto-optical Kerr effect (MOKE). Thickness-induced in-plane spin-reorientation transition, i.e. magnetization easy axis gradually rotates away from the step direction, was observed. MOKE measurements and micromagnetic simulation demonstrate this spin-reorientation transition process largely originated from the competition between step-induced magnetic shape anisotropy and oblique-deposition-induced magnetic shape anisotropy. Our study indicates the possibility of tuning magnetic spin order orientation by the competing magnetic shape anisotropies.

Tunable in-plane spin orientation in Fe/Si (557) film by step-induced competing magnetic anisotropies**Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403 and 2016YFA0300701) and the National Natural Sciences Foundation of China (Grant Nos. 51427801, 11374350, 11274360, and 11274361).

Although the spin-reorientation transition from out-of-plane to in-plane in Fe/Si film is widely reported, the tuning of in-plane spin orientation is not yet well developed. Here, we report the thickness-, temperature- and Cu-adsorption- induced in-plane spin-reorientation transition processes in Fe/Si (557) film, which can be attributed to the coexistence of two competing step-induced uniaxial magnetic anisotropies, i.e., surface magnetic anisotropy with magnetization easy axis perpendicular to the step and volume magnetic anisotropy with magnetization easy axis parallel to the step. For Fe film thickness smaller than 32 monolayer (ML), the magnitudes of two effects under various temperatures are extracted from the thickness dependence of uniaxial magnetic anisotropy. For Fe film thickness larger than 32 ML, the deviation of experimental results from fitting results is understood by the strain-relief-induced reduction of volume magnetic anisotropy. Additionally, the surface and volume magnetic anisotropies are both greatly reduced after covering Cu capping layer on Fe/Si (557) film while no significant influence of NaCl capping layer on step-induced magnetic anisotropies is observed. The experimental results reported here provide various practical methods for manipulating in-plane spin orientation of Fe/Si films and improve the understanding of step-induced magnetic anisotropies.

In-plane spin reorientation transition in Co/Py bilayers grown epitaxially on vicinal Cu(001)

Co/Py bilayers were grown epitaxially onto a vicinal Cu(001) substrate with the atomic steps parallel to the [110] crystalline axis. We show that the magnetization in vicinal Cu/Co/Py/Cu(001) undergoes an in-plane spin reorientation transition (SRT) from perpendicular to parallel direction of the steps as the Co film thickness increases. By performing Rotation Magneto-Optic Kerr Effect (ROTMOKE) measurement as a function of both the Py and the Co film thicknesses, we show that the observed in-plane SRT results from a competition between the step-induced uniaxial anisotropies in the Py and Co films that favor the Py and Co magnetizations perpendicular and parallel to the atomic steps, respectively. Step decoration experiment further shows that the uniaxial anisotropy originates from the step edges of the vicinal surface.

Multiple in-plane spin reorientation transitions inFe/CoObilayers grown on vicinalMgO(001)

Step-induced antiferromagnetic (AFM) uniaxial anisotropy and its effects on the exchange coupling have been systematically investigated in the epitaxial $\mathrm{Fe}/\mathrm{CoO}$ bilayers on a $\mathrm{MgO}(001)$ vicinal surface. X-ray magnetic linear dichroism measurements proved that the atomic steps induced a strong in-plane AFM uniaxial anisotropy in the CoO film. We found that the thermal activation induced in-plane 90\ifmmode^\circ\else\textdegree\fi{} switching of CoO AFM in-plane spins. The competition among the step-induced AFM anisotropy, the interface exchange coupling, and thermal activation generate a novel multiple in-plane spin reorientation transition of the Fe magnetization, which can further provide new insights on the exchange coupling in FM/AFM systems.

Soft perpendicular magnetization and spin reorientation transition of Fe films on NiAl(001)

Ultrathin Fe films were deposited on NiAl(001) for studies of their magnetic properties and crystalline structures. Thickness-driven perpendicular to in-plane spin reorientation transition was observed at a thickness of ∼4 monolayers (MLs) at room temperature without structural variation. At less than the critical thickness, the Fe film’s easy axis is perpendicular to the surface plane with a small coercive field (Hc ≈ 1 Oe), which was much smaller than that of other systems with perpendicular anisotropy. The Fe/NiAl(001) system revealed an extremely soft perpendicular magnetization. At more than the critical thickness, the easy axis lays in the surface plane. The magnetic anisotropy terms were calculated and discussed through a phenomenological model. The weaker surface anisotropy might be attributed to the reconstructed NiAl(001) surface.

Noncollinear spin reorientation transition in S = 1 ferromagnetic thin films

An in-plane spin reorientation transition in thin ferromagnetic films is discussed in terms of the thermodynamics of inhomogeneous low-dimensional systems based on a Néel sublattices concept while using a spin 1 Heisenberg Hamiltonian. The model allows us to investigate in a straightforward manner the layer-dependent phenomena. In this context, we propose a model of noncollinear magnetization structure based on the appropriate distribution of the anisotropy parameters inside the Fe films on W(110). The spin reorientation transition originates at the Fe/W(110) interface and proceeds via noncollinear magnetization structure toward the surface with increasing film thickness in accordance with the experimental findings. The temperature-driven spin reorientation transition in freestanding Fe films and in Fe/W(110) systems is also discussed in detail.

Electron Beam Tuning of the Magnetic Anisotropy in Co/Cu(110) Films

The 90° in-plane spin reorientation transition caused by residual gas adsorption in the Co/Cu(110) system has been investigated using Mott electron polarimetry. The system displays a 3-D growth mode, forming islands with a preferential axis of elongation along the [1-10] direction. The adsorption of CO at the step edges is found to change the net anisotropy of the system and bring about the change in the relaxed magnetization direction. By carefully limiting the duration of electron beam exposure, it has been shown that this spin rotation can also be observed using Mott polarimetry, where it manifests itself as variations in the secondary electron spin polarization. Extended exposure of the switched film to an electron beam can reverse the easy axis direction, allowing local tuning of the magnetic anisotropy in this system.

In-plane spin reorientation transition in Fe/NiO bilayers on Ag(1,1,10)

Magnetic properties of Fe/NiO bilayers grown on a (1,1,10) vicinal surface of Ag(001) were studied by magneto-optical Kerr effect (MOKE) and x-ray magnetic linear dichroism (XMLD). The orientation of the antiferromagnetically (AFM) aligned spins of NiO films shows an in-plane spin-reorientation transition (SRT) from parallel to perpendicular to the steps with increasing NiO thickness. Two in-plane SRTs of Fe moments are found in dependence of the NiO thickness. The first SRT of the Fe magnetization from parallel to perpendicular to the steps is observed at NiO thickness where antiferromagnetic order is found, the second at the NiO thickness of the SRT in the NiO film. Also, the in-plane SRT of Fe spins driven by a temperature increase is observed. The perpendicular coupling between the Fe and NiO spins is proven. The induced uniaxial anisotropy energy is estimated to be 0.12 erg/cm${}^{2}$.

Spin reorientation transition and phase diagram in an He+ ion irradiated ultrathin Pt/Co(0.5 nm)/Pt film

A rich thermal magnetic phase diagram has been determined by magneto-optical Kerr magnetometry and microscopy in a He+ ion irradiated ultrathin Pt/Co(0.5 nm)/Pt film. The components of the net magnetization and the evolution and disappearance of the ribbonlike magnetic domain pattern have been studied in the perpendicular to in-plane spin reorientation transition temperature region. As observed in a dipolar frustrated ferromagnet, the ribbon pattern blurs progressively with increasing the temperature as due to efficient spatial fluctuations. We emphasize the limitation of present theories for interpreting such a type of dynamic transition.

Noncollinear Magnetization Structure at the Thickness-Driven Spin-Reorientation Transition in Epitaxial Fe Films on W(110)

An in-plane spin-reorientation transition occurring during the growth of epitaxial Fe films on W(110) was studied in situ by using the nuclear resonant scattering of synchrotron radiation. The spin-reorientation transition originates at the Fe/W(110) interface and proceeds via a noncollinear spin structure resembling a planar domain wall that propagates towards the surface with increasing film thickness.

In-plane spin reorientation transition in a two-dimensional ferromagnetic/antiferromagnetic system studied using Monte Carlo simulations

We investigated the in-plane spin reorientation transition (SRT) in a two-dimensional ferromagnetic/antiferromagnetic system by using Monte Carlo simulation based on the Heisenberg model. The temperature-driven SRT in the ferromagnetic layer is studied for the case of that the antiferromagnetic layer has an uniaxial in-plane or fourfold in-plane anisotropy. For the case of an uniaxial in-plane anisotropy in the antiferromagnetic layer, the ferromagnetic layer spin processes a $90\ifmmode^\circ\else\textdegree\fi{}$ in-plane SRT from perpendicular to parallel direction of the anisotropy. For the case of a fourfold in-plane anisotropy in the antiferromagnetic layer, the ferromagnetic layer spin processes a $45\ifmmode^\circ\else\textdegree\fi{}$ in-plane SRT. We also studied the Curie temperature of the ferromagnetic layer and find a significant reduction in the Curie temperature as the Curie temperature is close to the SRT temperature.

Analysis of x-ray linear dichroism spectra for NiO thin films grown on vicinal Ag(001)

Antiferromagnetic (AFM) NiO thin films are grown epitaxially on vicinal Ag(118) substrate and investigated by x-ray linear dichroism (XLD). We find that the NiO AFM spins exhibit an in-plane spin-reorientation transition from parallel to perpendicular to the step edge direction with increasing the NiO film thickness. In addition to the conventional ${L}_{2}$ absorption edge, XLD effect at the $\text{Ni}\text{ }{L}_{3}$ absorption edge is also measured and analyzed. The results identify a small energy shift of the ${L}_{3}$ peak. Temperature-dependent measurement confirms that the observed XLD effect in this system at the normal incidence of the x rays originates entirely from the NiO magnetic ordering.

Epitaxial growth and magnetic properties of Fe nanowedge islands on Mo(1 1 0)

Fe films with a nominal thickness ⩾2Å grown on Mo(110) at 500⩽T⩽750K self-assemble into nanowedge islands supported on a pseudomorphic Fe wetting layer. We discuss mechanisms that contribute to the island growth and distribution. Fe adatoms migrate towards the islands under the influence of the strain induced in the substrate around each island and subsequently enter the island through a vertical climb mechanism. We demonstrate that the magnetic properties of these nanostructures are governed by their shape and do not display the in-plane spin reorientation transition found in the morphologically similar Fe/W(110) system.

Investigation of magnetic structure evolution in the substitutional solid solution Sc x Lu (1-x) MnO 3

The hexagonal series AMnO3 (A = Lu, Sc) (space group: P63cm) is an excellent model system for the investigation of magnetic frustration as the magnetic sublattice is made up of edge sharing triangles with nearest neighbour antiferromagnetic exchange. At low temperatures the Mn3+ moments form a 120° long range ordered state. In LuMnO3 (TN=91 K) the magnetic moments are in the ab-plane and perpendicular to the hexagonal axis, whereas ScMnO3 (TN=130 K) undergoes an in-plane spin-reorientation transition below T=70 K. Powder neutron diffraction experiments for the substitutional solid solution ScxLu(1-x)MnO3 (0.0≤x≤1.0) show the evolution of the spin-reorientation as a function of x.

Stranski-Krastanov layers of Fe on W(1 1 0): A combined MOKE, LEED, SAM and stress measurement investigation

The Stranski-Krastanov growth of Fe on W(1 1 0) at 700 K leads to the formation of three-dimensional (3D) Fe islands on a first Fe layer that covers the W substrate pseudomorphically, as confirmed by scanning Auger microscopy (SAM) and low-energy electron diffraction (LEED). In situ stress measurements reveal the reduction of film stress as a dominant driving force for the coalescence of Fe into islands. An in-plane reorientation of the easy axis of magnetization from 〈−1 1 0〉 for layer-by-layer grown films at 300 K to 〈0 0 1〉 in the 3D islands is found by magneto-optical Kerr effect (MOKE) experiments. This in-plane spin reorientation transition is attributed to the crossing of a critical Fe thickness of order 100 Å in the Fe islands.