In-plane Remanent Magnetization Research Articles

Magnetotransport, spin reorientation, and anomalous ferrimagnetic-to-antiferromagnetic phase transition in epitaxial Mn2Sb alloy thin films

High-quality ferrimagnetic Mn2Sb epitaxial thin films have been successfully grown on SrTiO3 (001) single-crystal substrates via systematically optimizing the growth parameters using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that a spin reorientation transition occurs in the 260–150 K region where the direction of spins rotates from out-of-plane to in-plane upon cooling, resulting in the ferrimagnetic(II) phase, followed by a giant magnetoresistance associated anomalous ferrimagnetic(II)-to-canted antiferromagnetic (c-AFM) phase transition in the 150–115 K region, resulting in the c-AFM ground state, both of which are completely absent and have yet not been previously observed in Mn2Sb bulk and thin films. Temperature-dependent X-ray diffraction measurements reveal that the low-temperature c-AFM phase originates from the contraction of the out-of-plane lattice constant c, which would increase the exchange interaction between neighbouring magnetic sublattices and thus stabilize the c-AFM phase. DFT calculations reveal that substrate clamping is the cause of the unique c-axis contraction in Mn2Sb films. For the 24-nm films, there is almost no out-of-plane magnetization in the ground state, but exists a weak in-plane remanent magnetization (∼0.4 μB/f.u.) and anomalous Hall effects, implying spin canting within the ab plane. With decreasing film thickness from 64 to 8 nm, the out-of-plane saturation magnetization at 10 K increases by approximately 10 times, and for the 8-nm film, its saturation magnetization (4.8 μB/f.u.) is 2.8 times larger than that of Mn2Sb bulk (∼1.74 μB/f.u.), both of which are attributed to the interfacial strain effect. Our work demonstrates that Mn2Sb films grown on perovskite oxide substrates show anomalous spin-charge-lattice coupling phenomena, which may inspire more study of its basic properties and potential device applications.

Field-Free Magnetization Switching Induced by Bulk Spin–Orbit Torque in a (111)-Oriented CoPt Single Layer with In-Plane Remanent Magnetization

Field-Free Magnetization Switching Induced by Bulk Spin–Orbit Torque in a (111)-Oriented CoPt Single Layer with In-Plane Remanent Magnetization

Bulk-Like Dynamic Magnetic Properties of Nickel Ferrite Epitaxial Thin Films Grown on SrTiO3(001) Substrates

Nickel ferrite (NiFe 2 O 4 , NFO) films were grown at high temperatures on SrTiO 3 (001) substrates using laser molecular beam epitaxy. A spinel lattice structure, with lattice parameters close to those of bulk NFO, was confirmed by electron and X-ray diffraction. Vibrating sample magnetometer measurements show an in-plane remanent magnetization, relatively narrow (~50 Oe) hysteresis loops, and fourfold symmetry. Soft X-ray magnetic dichroism measurements indicate an inverse spinel structure. X-band ferromagnetic resonance (FMR) measurements show a line width as low as 45-50 Oe, which corresponds to the value for bulk NFO crystals. The angular dependence of FMR on a 110 nm thick NFO film indicates cubic anisotropy close to that of bulk crystals and a substrate-induced stress anisotropy field of about 0.4 kG.

Electric-field tuning of magnetism in spin gapless semiconductor (SGS)-like CoFeMnSi thin film

The experimental demonstration of the controllable or tunable magnetism of Heusler compounds, which theoretically exhibit the feature of spin gapless semiconductor, has drawn wide interest due to their promises for spintronic device concepts. Here, we realized the spin gapless semiconductor-like characteristic of Heusler alloy CoFeMnSi thin film deposited on [Pb(Mg1/3Nb2/3)O3]0.7[PbTiO3]0.3 ferroelectric single-crystal substrates, and demonstrated that its magnetism can be tuned through applying an electric-field or performing the electric pre-polarization. The transport properties reveal that the electric conductivity of CoFeMnSi is small and almost independent of temperature. The in-plane remanent magnetization Mr can be tuned up to 17% by applying a relatively small in situ electric-field of 4.2 kV/cm. The controlled coercivity of CoFeMnSi is observed with the electric pre-polarization, which might suggest a non-volatile magnetic switching for the controllable magnetic properties.

Magnetic anisotropy in epitaxial Mn5Ge3films

High crystalline quality Mn 5 Ge 3 films with thicknesses ranging 4–200 nm have been grown on Ge(111) substrates by solid phase epitaxy. The basal hexagonal plane of Mn 5 Ge 3 is in epitaxy with the Ge(111) plane. Magnetic properties of the films have been investigated as a function of the film thickness and the magnetization curves have been analyzed using a theory that includes a description of magnetic domains in uniaxial thin films. The results clearly indicate the existence of a critical thickness below which the magnetic stripe phase disappears. We have determined the value of this thickness to lie between 10 and 25 nm from the analysis of experimental magnetization curves and the theoretical fit of the in-plane remanent magnetization. Although analogies can be drawn between the behavior observed in our system and that of hcp Co, we have shown that the critical thickness is considerably smaller in Mn 5 Ge 3 ; this has the potential to open new fields of applications for Mn 5 Ge 3 thin films in magnetic recording and spintronics.

Competition of perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt/Co/α-Cr2O3(0001) thin film

We investigated perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt/Co/α-Cr2O3(0001) thin film grown on an α-Al2O3(0001) substrate. The film exhibits perpendicular magnetic anisotropy below a Co thickness of 1.2 nm at room temperature. Independent of the magnetic easy direction of the Co layer, the perpendicular exchange bias (PEB) appears in a direction perpendicular to the film below 80 K. The maximum unidirectional magnetic anisotropy energy estimated from the exchange bias field is 0.33 erg/cm2, which is higher than the reported PEB strength. The perpendicular exchange bias is accompanied by the in-plane remanent magnetization and an increase in the in-plane coercivity. We speculate that the increases in the in-plane remanent magnetization and the in-plane coercivity are caused by the spin canting of Cr3+ in the α-Cr2O3(0001) layer.

Rotation of the magnetic easy axis in La0.67Sr0.33MnO3 thin film on NdGaO3(112)

The in-plane magnetic anisotropy is studied for pseudocubic {011}pc oriented La0.67Sr0.33MnO3 (LSMO) thin film grown on orthorhombic NdGaO3(NGO)(112)o (the subindices “pc” and “o” indicate the pseudocubic and orthorhombic lattice structure, respectively). The direction of the in-plane remanent magnetization of LSMO thin films with different thicknesses is determined. With increasing film thickness the easy axes rotate and the anisotropy changes from uniaxial to biaxial. This is associated with the increasing symmetry of the LSMO with increasing thickness, starting with a monoclinic LSMO structure at the nonrectangular NGO(112)o surface unit cell of the substrate, developing into an orthorhombic structure at the top part of the thickest films.

Remanent electrical spin injection from Fe into AlGaAs∕GaAs light emitting diodes

We compare surface and edge emission electroluminescence of spin-polarized light emitting diodes with Fe contacts. The edge emission geometry permits transduction of the spin state variable between the electron spin and optical polarization utilizing the in-plane remanent magnetization and low coercive fields of the metal contacts. The spin injection efficiencies are similar for electron spins oriented normal to the surface plane and in plane. The lower circular polarization consistently observed in edge emission at low magnetic fields is attributed to a partial out-of-plane orientation of the heavy hole angular momentum which persists even in wide quantum wells.

Magnetic capping layer induced spin reorientation: Co on Fe/Cu(100)

A spin reorientation phase transformation can occur either by a continuous process, such as spin canting, or by an abrupt spin rotation. We investigate the spin reorientation of ultrathin Fe/Cu(100) films induced by Co capping layers using the magneto-optical Kerr effect. The spin axis reorients from the perpendicular to the in-plane direction when the amount of Co exceeds some critical value. Experimental evidence indicates that this transformation involves the formation of multidomains. In the transition thickness regime, we observed that the perpendicular and the in-plane remanent magnetization are complementary, and attribute this to the presence of an inhomogeneous anisotropy field.

Magnetic anisotropy, magnetic moments and coupling of Cu/Co/Cu/Ni/Cu(001) trilayer

Polar magneto-optic Kerr effect (MOKE) measurements on an epitaxial Cu/Co (23 Å)/Cu (0-49 Å)/Ni (53 Å)/Cu/Si(001) structure reveal that the Ni magnetization is aligned in plane for zero Cu spacer layer thickness and becomes increasingly aligned out of plane with increasing Cu spacer layer thickness, whereas an in-plane remanent magnetization for Co is always observed. Layer selective polarized neutron reflection (PNR) measurements yield almost bulk-like magnetic moments of 1.57±0.08 µB for Co and 0.50±0.04 µB for Ni for a Cu/Co (22 Å)/Cu (10 Å)/Ni (53 Å)/Cu/Si(001) structure at room temperature. A reduced remanence is observed for both the out-of plane magnetization by polar MOKE, and the in-plane magnetization for Co and Ni by PNR. This could suggest either a canted magnetization or multidomain state at remanence.

Direct evidence for complete antiferromagnetic coupling between Co films epitaxially grown on Cu(1 1 1) using Pb as surfactant

Co/Cu films were grown epitaxially on Cu(1 1 1), using Pb as a surfactant. The exchange coupling between Co layers separated by Cu is studied with magnetic circular dichroism in valence band photoemission. Direct evidence for complete antiferromagnetic coupling is observed at 4 monolayer Cu thickness for Co films both with perpendicular and in-plane remanent magnetization from the sign reversal of the dichroic asymmetry.

Spin-resolved inverse photoemission from Fe films epitaxially grown on Ag(100)

Very thin Fe films epitaxially grown on Ag(100) have been studied by means of spin-resolved inverse photoemission spectroscopy. Results for film thicknesses in the range 1–100 bcc Fe monolayers are reported. It is shown that the exchange splitting δ E ex at the H point of the bcc Fe Brillouin zone reaches the bulk value of 1.8 eV for film thicknesses larger than 15 ML; for thinner films, the exchange splitting is reduced. Moreover, it is found that films thinner than 5 ML do not show any in-plane remanent magnetization.

Ultrathin magnetic Fe films on W(001): A spin-polarized inverse photoemission study of Fe electronic structure evolution (abstract)

By using spin-dependent electron spectroscopic techniques, one can explore the relevant problems in 3d metallic ferromagnetism, including temperature effects. Current surface science methods of ultrathin-film preparation and characterization make it possible to study interesting two dimensional magnetic systems. In the present work, ultrathin epitaxially grown Fe films on W(001) have been investigated by spin- and angle-resolved inverse photoemission spectroscopy. The evolution of the electronic structure has been studied for thickness from one monolayer to ‘‘bulklike’’ Fe thin films. In-plane remanent magnetization is observed. In the thick bulklike sample, transitions to majority and minority states near the H point of bcc Fe were identified, in contrast with data from bulk Fe(001).1 The thinner Fe films showed a trend of ‘‘collapsing’’ d bands at H′25. The results suggested a reduced Curie temperature for monolayers thick films. Information obtained for examining the correlation length in the itinerant ferromagnetic systems does not support the local-band picture at finite temperatures.2

Spin- and angle-resolved photoemission from single crystals and epitaxial films using circularly polarized synchrotron radiation

We describe some novel results on the experimental spin-resolved electronic structure of a layered system, consisting of ultrathin films of fcc-Cobalt epitaxially grown onto a Cu(100) single crystal surface. Films more than 2 mono-atomic layers (ML) thick are found to be ferromagnetic at room temperature with an in-plane remanent magnetization. The electronic structure of 5 ML fcc-Co films turns out to be already bulk-like. On the other hand, the excitation with circularly polarized light leads to strong spin-polarization effects from the clean Cu(100) surface. This proves a significant influence of the spin-orbit interaction even in copper, resulting in strongly hybridized electronic energy bands.

Magnetism and epitaxy of Fe/Cr(001) multilayers

Spin-polarized low-energy electron-diffraction measurements show in-plane remanent magnetization of Fe thin films only for thicknesses above two monolayers (2 ML) on Cr(100). This is interpreted as due to a dominant surface-induced perpendicular anisotropy for d( Fe) ⪅ 2 ML. For d( Fe) = 3 ML, the magnetization lies almost fully in the plane of the thin film. Evaporation of Cr on top of the 3 ML Fe film does not destroy the in-plane magnetic order at the interface. Intercalation of a 10 ML Cr slab between two Fe slabs gives rise to antiparallel coupling between the ferromagnetic films. The clean Cr(001) surface, however, shows no in-plane magnetic order.