Magnetic Anisotropy Of La0 Research Articles

Evolution of magnetic anisotropy in La0.67Sr0.33MnO3 thin films due to the appearance of out-of-plane magnetization at low temperature

We have observed quadrupolar angle-dependent anisotropic magnetoresistance (AMR) at low temperature in La0.67Sr0.33MnO3 (LSMO) films grown on SrTiO3 substrate, where the magnetic field was applied while rotating the direction of the applied magnetic field from out-of-plane (OP) to in-plane. At room temperature, the easy axis is in-plane and has a two-fold magnetic anisotropy. As the temperature decreases, it changes to a quadrupolar anisotropy. Along with the AMR, we have measured the magnetoresistance (MR) in the OP direction at various temperatures. Like the AMR, we found the appearance of a new magnetic configuration in the OP direction at low temperatures. We suggest that one of the important origins of the new OP magnetism, which appears at temperature much lower than the Curie temperature (Tc), is the d3z2−r2 orbital at the interface between the LSMO films and SrTiO3 substrate. It has been reported that despite the tensile strain imposed by the SrTiO3 substrate, the d3z2−r2 orbital exists at the interface and causes the OP magnetism. We demonstrate by a polarized x-ray resonant scattering that there is a higher density of d3z2−r2 orbitals at the interface than in the region away from the interface. As other references have proposed, we suggest the orbital reconstructions and the orbital reconstruction-driven magnetic reorientation at the interface as the origin of the appearance of the OP magnetism present in the AMR and MR results.

Enhanced low-field positive magnetoresistance and magnetic anisotropy in La0.7Sr0.3MnO3 films grown on (001) Si

Strong anisotropy is observed in the magnetization and magnetoresistance (MR) of a series of La0.7Sr0.3MnO3 (LSMO) films grown on (001) oriented Si using pulsed sputtering plasma. Magnetic anisotropy (MA) of LSMO films is in the order of 106 erg/cm3, comparable to or larger than that of the other heterostructures. Analysis using the Stoner-Wohlfarth model and the density functional theory (DFT) indicates that the crystalline and induced anisotropies are almost compensating with each other, and observed MA is of the same order of shape anisotropy. The rise in MA with the LSMO thickness is attributed to the shape anisotropy and interfacial spin reordering. These LSMO films exhibit positive and negative MR, even though the LSMO is well known for colossal negative MR. The 12.4 nm thick LSMO film shows a maximum ∼7 % in-plane low-field positive MR, which increases to ∼12 % for 20.0 nm thick LSMO, but the variation of out-of-plane positive MR is ∼ ± 0.8 %. The maximum in-plane positive MR occurs at ∼ ± 0.2 kG (switching field), which corresponds to the coercive field. In contrast, the out-of-plane positive MR switching field is relatively higher, ∼ ± 5 kG, 25 times larger than the in-plane switching field. The anisotropy in positive MR and its switching field is due to the strong MA, modulated by the charge transfer-induced interfacial exchange coupling strength, confirmed using the DFT. The MA and anisotropy in MR with the dual sign of MR are intriguing phenomena; their tunability could pave the way for advanced technology in magnetic devices.

Temperature-dependent out-of-plane anisotropy in compressively strained La0.67Sr0.33MnO3 thin films

We studied the temperature and strain dependence of the perpendicular magnetic anisotropy in La0.67Sr0.33MnO3 thin films by performing temperature- and angle-dependent magnetotransport measurements. Three films of similar thickness (14 u.c., 14 u.c. and 15 u.c.) but with different out-of-plane crystallographic strain (1.9%, 0.9% and -0.7%) are studied. The films are grown on LaAlO3 and SrTiO3 substrates by pulsed laser deposition. We observe a clear increase in the out-of-plane magnetic anisotropy with increasing out-of-plane strain in the angle-dependent magnetotransport measurements which is present up to 80 K for the highest (1.9%) strained sample. The deformation of the unit cell, as discussed in earlier reports, point to the magnetocrystalline anisotropy as the main driver altering the magnetic easy axis direction. Our results highlight the utility of the effective magnetocrystalline anisotropy as a tool to control the desired anisotropy in crystalline thin films of La0.67Sr0.33MnO3.

Vertical strain tuning and perpendicular magnetic anisotropy in La0.5Ca0.5MnO3 vertically aligned nanostructured thin films by the application of high magnetic fields

Epitaxial La0.5Ca0.5MnO3 (LCMO) thin films with vertically aligned nanostructures (VANs) have been achieved with the application of high magnetic fields in pulsed laser deposition processing. More interestingly, the microstructures, vertical strain, and perpendicular magnetic anisotropy (PMA) in the LCMO VAN films can be systematically manipulated by changing the applied high magnetic field strength. With increasing the high magnetic field, an increase in growth rate and a decrease in nanocolumn dimension are observed in the LCMO VAN films, which can be attributed to the enhanced suppression effect on adatom mobility and surface diffusion. Different from the LCMO planar-structured films, the intrinsic stress behaviors associated with vertical interfaces and grain boundaries instead of substrate strain in the LCMO VAN films are dominant in vertical strain evolution, indicating an out-of-plane compressive state, which is highly correlated with the growth rate and nanocolumn dimension. A core-shell model based on phase separation is proposed to understand the nanoscale size effect on magnetic properties in the LCMO VAN films. A tunable and enhanced PMA effect in the LCMO VAN films is also demonstrated. The results suggest that the application of a high magnetic field in pulsed laser deposition processing is a practicable route to achieve tunable VANs, and manipulate physical properties in manganite films.

Continuous tunable lateral magnetic anisotropy in La0.67Ca0.33MnO3/SrRuO3 superlattices by stacking period-modulation

Effective control of magnetic anisotropy is important for developing spintronic devices. In this work, we performed a case study of stacking periods (N)-mediated reorientation of lateral magnetic anisotropy in ultrathin La0.67Ca0.33MnO3/SrRuO3 superlattices. As N increases from 1 to 15, the magnetic easy-axis switches from the orthorhombic [010] to [100]-axis. The maximum anisotropy constant of the superlattice (SL) (N = 15) reaches −1.83 × 105 erg/cm3. X-ray absorption spectroscopy and x-ray linear dichroism further suggest that the observed changes in lateral magnetic anisotropy are driven by in-plane orbital polarization. For SLs with small N, anisotropic strain-induced orbital polarization along the b-axis can result in the [010]-oriented magnetic easy axis. For SLs with large N, the dimension crossover from 2-dimension to 3-dimension could enhance the hybridization of Ru t2g and Mn dx2−y2 orbitals, which can compete with the strain effect and switch the magnetic easy axis to [100]. Our results suggest a potential strategy for engineering magnetic anisotropy through the cooperation of strain engineering and interfacial orbital engineering.

Control of ferromagnetism and magnetic anisotropy via tunable electron correlation and spin-orbital coupling in La0.67Ca0.33MnO3/Ca(Ir,Ru)O3 superlattices

Electron-electron (e-e) correlation and spin-orbit coupling (SOC) are two essential control parameters that determine the physical properties of transition-metal-oxide-based thin films and heterostructures. Here, by harnessing these two parameters, we report the systematic control of both ferromagnetism and in-plane magnetic anisotropy in La0.67Ca0.33MnO3/CaIr1-xRuxO3 (LCMO/CIRO) superlattices grown on NdGaO3 substrates. In these all-oxide epitaxial systems, we demonstrate that the e-e correlation and the SOC depend strongly on the chemical composition of CIRO layers. By simply increasing the Ru doping level x, we can significantly suppress the degradation of ferromagnetism in ultrathin LCMO layers and enhance the TC by ∼90 K. Moreover, we observe a clear reorientation of the magnetic easy axis from orthorhombic [010] to [100] as x decreased to 0, which may originate from the enhanced SOC. Our work provides an insight for utilizing the 4d/5d transition-metal-oxides to tune the functionality of magnetic heterostructures.

Room temperature biaxial magnetic anisotropy in La0.67Sr0.33MnO3 thin films on SrTiO3 buffered MgO (001) substrates for spintronic applications

Spintronics exploits the magnetoresistance effects to store or sense the magnetic information. Since the magnetoresistance strictly depends on the magnetic anisotropy of a system, it is fundamental to set a defined anisotropy to the system. Here, we investigate half-metallic La0.67Sr0.33MnO3 thin films by means of vectorial Magneto-Optical Kerr Magnetometry and found that they exhibit pure biaxial magnetic anisotropy at room temperature if grown onto a MgO (001) substrate with a thin SrTiO3 buffer. In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions that may be detrimental for specific applications. The detailed study of the angular evolution of the magnetization reversal pathways and critical fields (coercivity and switching) discloses the origin of the magnetic anisotropy, which is magnetocrystalline in nature and shows fourfold symmetry at any temperature.

Thickness and angular dependent magnetic anisotropy of La0.67Sr0.33MnO3 thin films by Vectorial Magneto Optical Kerr Magnetometry

We investigate the in-plane magnetic anisotropy in La0.67Sr0.33MnO3 thin films grown on SrTiO3 (001) substrate using angular dependent room temperature Vectorial Magneto-Optical Kerr Magnetometry. The experimental data reveals that the magnetic anisotropy symmetry landscape significantly changes depending upon the strain and thickness. At low film thickness (12 and 25 nm) the dominant uniaxial anisotropy is due to interface effects, step edges due to mis-cut angle of SrTiO3 substrate. At intermediate thickness, the magnetic anisotropy presents a competition between magnetocrystalline (biaxial) and substrate step induced (uniaxial) anisotropy. Depending upon their relative strengths, a profound biaxial or uniaxial or mixed anisotropy is favoured. Above the critical thickness, magnetocrystalline anisotropy dominates all other effects and shows a biaxial anisotropy.

Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders

The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a function of temperature by the modified singular point detection technique. In this method singularities indicating the anisotropy field were determined analyzing ac susceptibility data. The observed relationship between temperature dependence of anisotropy constant and temperature dependence of magnetization was used to deduce the origin of magnetic anisotropy in the nanopowders. It was shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by the two-ion (dipolar or pseudodipolar) and single-ion mechanisms.

Substrate-induced magnetic anisotropy in La0.7Sr0.3MnO3 epitaxial thin films grown onto (110) and (11̄8) SrTiO3 substrates

We show a detailed magneto-optical Kerr study at room temperature of well characterized epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto (110) and (11̄8) SrTiO3 substrates. The films present a well-defined uniaxial (two-fold) magnetic anisotropy ascribed to substrate-induced anisotropy. In particular, the in-plane uniaxial anisotropy in the(110)-oriented LSMO films originates from the existence of elongated in-plane [001]-oriented structures. Similar elongated structures, parallel to the [110] crystallographic direction, are found for LSMO films grown on (11̄8) STO surfaces. In all films, such a uniaxial magnetic anisotropy is characterized by an easy axis lying along the elongated structures. Furthermore, the vectorial-resolved hysteresis loops as a function of the in-plane applied field direction are interpreted in terms of rotation and propagation and nucleation of magnetic domains processes. Our results demonstrate the tailoring of magnetic anisotropy by exploiting the substrate-induced anisotropy in epitaxial thin films.

Magnetic anisotropy of La0.75Sm0.25Mn2Si2 compound

The magnetic anisotropy of theLa0.75Sm0.25Mn2Si2 compound, whichhas a layered ThCr2Si2-type crystal structure, has been studied using a quasi-single-crystalline sample. It wasfound that the compound possesses a strong uniaxial magnetic anisotropy in bothmagnetically ordered and paramagnetic states. The magnetic anisotropy of the compoundis mainly due to the Mn sublattice anisotropy. In the ferromagnetic state at 180 K,the magnetization process is characterized by the magnetic anisotropy constantK1 = 6 × 106 erg cm−3. In the paramagnetic state, a considerable anisotropy of paramagnetic Curie temperatureΔθp ≈ 35 Kand an appreciable difference between values of the effective magnetic moment measured along thec-axis and in thebasal plane, Δμeff≈0.4 μB per formula unit, has been observed. The natural layered structure of the compound andpartial unquenching of the Mn orbital momentum have been considered as possible reasonsfor the observed strong magnetic anisotropy.

Effect of three-dimensional strain states on magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

Magnetic anisotropy of La0.8Ca0.2MnO3 (LCMO) epitaxial thin films grown on (001) SrTiO3 and LaAlO3 a substrates exhibits strong correlation with substrate-induced strain states as determined by normal and grazing incidence x-ray diffraction. In a 250 Å thick LCMO (001)T film grown on SrTiO3 substrate, an in-plane biaxial magnetic anisotropy is observed, and it is accompanied by a substrate-induced in-plane biaxial tensile strain. In contrast, the observed magnetic easy axis for a 250 Å (110)T film grown on LaAlO3 substrate is perpendicular to the film plane, and the corresponding in-plane strain is biaxial compressive. In both cases the magnetic easy axes are along the crystallographic directions under tensile strain, indicating the presence of a positive magnetostriction. In thicker films (∼4000 Å) grown on both substrates that are nearly strain relaxed, the magnetic easy axis lies in the film plane along the [110] direction of the (001) substrate.

Effect of three-dimensional strain states on magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

Effect of three-dimensional strain states on magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

Magnetic anisotropy of doped manganite thin films and crystals

Magnetic anisotropy of La0.7Sr0.3MnO3 thin films and single crystals has been measured using vibrating sample and torque magnetometry. The magnetic anisotropy of thin films is dominated by strain anisotropy due to the lattice mismatch between the film and SrTiO3 substrate. The two and fourfold symmetries in the (110) and (001) films, respectively, can only be explained by stress anisotropy contributions (Kstress∼8.4×104 ergs/cm3). Magnetic anisotropy of La0.7Sr0.3MnO3 single crystals, subject to no external stress, reveals a uniaxial anisotropy in the (100) plane of K1∼1.8×104 ergs/cm3 that can be attributed to magnetocrystalline effects.

The Effects of Strain on The Magnetic Anisotropy of Doped Manganite Thin Films

ABSTRACTWe show the importance of the role of strain in doped manganite perovskite materials by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropy effects in the magnetic anisotropy of these films. In order to measure magnetic anisotropy in the plane of the films, remnant magnetization was measured as a function of in-plane angle. The (110) La0.7Sr0.3MnO3 films reveal a twofold symmetry while the (100) films have fourfold symmetry. Temperature dependence of the magnetic anisotropy of La0.7Sr0.3MnO3 films reveals decreasing anisotropy as the Curie temperature is approached.