Uniaxial Magnetic Anisotropy Research Articles

Tailoring magnetic properties of CoFeB films via tungsten buffer and capping layers

Controlling the interface between W and CoFeB-based buffer or capping layers at an appropriate temperature is essential for modifying the strength of magnetic anisotropy. In this work, we systematically explore the impact of W buffer and capping layers on the structural, topological, and magnetic anisotropy properties of W (5 nm)/CoFeB(10 nm) and CoFeB(10 nm)/W(3 nm) bilayers sputtered at room temperature (RT) and annealed at an optimal annealing temperature (TA) of 400 °C. Our findings demonstrate that the bilayer films’ uniaxial magnetic anisotropy (UMA) with out-of-plane coercivity (Hc⊥) is highly influenced by the W buffer, capping layers, and TA. Specifically, the Hc⊥ of the CoFeB layer with the buffer and capping layers annealed at 400 °C samples exceed several times the coercivity of those unannealed. CoFeB buffered with W and annealed at 400 °C shows larger Hc⊥, two-fold UMA, and higher in-plane UMA energy density (Keff) than the CoFeB/W bilayers, which can be attributed to the W buffer layer inducing the crystallization of CoFeB during annealing. The W buffer, capping layers, and the TA for W and CoFeB-based bilayer samples significantly alter the surface morphology, grain sizes, and surface roughness. The XRD analysis reveals nano-crystallites embedded in the larger grains of the 400 °C annealed samples. Hence, this work offers a promising approach to achieving high thermal stability of UMA in W and CoFeB-based spintronic applications.

Influence of an ultrathin Mn ‘spy layer’ on the static and dynamic magnetic coupling within FePt/NiFe bilayers

Abstract We explore whether insertion of an ultrathin Mn ‘spy layer’ within a magnetic hard/soft bilayer can enable depth-sensitive element-specific measurements of the static and dynamic magnetization, while avoiding significant disruption of the original magnetic state. MgO(110)/FePt(100 Å)/NiFe(200 Å)/Mn(t Mn Å)/NiFe(200 Å) samples with Mn thicknesses of t Mn = 0, 5, and 10 Å were fabricated by magnetron sputtering and studied by element-selective x-ray magnetic circular dichroism (XMCD), vector network analyzer ferromagnetic resonance (VNA-FMR), and x-ray detected ferromagnetic resonance (XFMR). For t Mn = 5 Å, the magnetic reversal properties remain broadly similar to t Mn = 0 Å. For t Mn = 10 Å, the two NiFe layers decouple with XMCD hysteresis loops at the Mn edge showing two switching events that suggest the presence of two distinct Mn-containing regions. While the Mn moments within each region have ferromagnetic order, their relative alignment is antiparallel at high field. Analysis of the magnetic data and additional scanning transmission electron microscopy measurements point to the presence of a Mn layer at the lower NiFe/Mn interface, and the formation of a NiFeMn alloy at the upper Mn/NiFe interface. The Mn moments of the former region lie antiparallel to those of the underlying NiFe layer. The VNA-FMR data suggests that for t Mn = 5 and 10 Å, the interfacial exchange coupling at the FePt/NiFe is suppressed and the in-plane uniaxial magnetic anisotropy of the NiFe is increased, perhaps due to migration of Mn towards the buried interface. The above findings show that Mn is a problematic magnetic spy, and that a Mn thickness of less than 5 Å would be required.

Low-Energy Magnetic States of Tb Adatom on Graphene.

Electronic structure and magnetic interactions of a Tb adatom on graphene are investigated from first principles using combination of density functional theory and multiconfigurational quantum chemistry techniques including spin-orbit coupling. We determine that the six-fold symmetry hollow site is the preferred adsorption site and we investigate electronic spectrum for different adatom oxidation states including Tb3+, Tb2+,Tb1+, and Tb0. For all charge states, the Tb 4f8configuration is retained with other adatom valence electrons being distributed over 5dxy, 5dx2+y2, and 6s/5d0single-electron orbitals. We find strong intra-site adatom exchange coupling that ensures that the 5d6sspins are parallel to the 4fspin. For Tb3+, the energy levels can be described by theJ= 6 multiplet split by the graphene crystal field. For other oxidation states, the interaction of 4felectrons with spin and orbital degrees of freedom of 6s5delectrons in the presence of spin-orbit coupling results in the low-energy spectrum composed closely lying effective multiplets that are split by the graphene crystal field. Stable magnetic moment is predicted for Tb3+and Tb2+adatoms due to uniaxial magnetic anisotropy and effective anisotropy barrier around 440 cm-1controlled by the temperature assisted quantum tunneling of magnetization through the third excited doublet. On the other hand, in-plane magnetic anisotropy is found for Tb1+and Tb0adatoms. Our results indicate that the occupation of the 6s5dorbitals can dramatically affect the magnetic anisotropy and magnetic moment stability of rare earth adatoms.

Enhancing the Thermal Stability of Skyrmion in Magnetic Nanowires for Nanoscale Data Storage.

Magnetic skyrmion random switching and structural stability are critical limitations for storage data applications. Enhancing skyrmions' magnetic properties could improve their thermal structural stability. Hence, micromagnetic calculation was carried out to explore the thermal nucleation and stability of skyrmions in magnetic nanodevices. Different magnetic properties such as uniaxial magnetic anisotropy energy (Ku), saturation magnetization (Ms) and Dzyaloshinskii-Moriya interaction (DMI) were used to assess the thermal stability of skyrmions in magnetic nanowires. For some values of Ms and Ku, the results verified that the skyrmion structure is stable at temperatures above 800 K, which is higher than room temperature. Additionally, manipulating the nanowire geometry was found to have a substantial effect on the thermal structural stability of the skyrmion in storage nanodevices. Increasing the nanowire dimensions, such as length or width, enhanced skyrmions' structural stability against temperature fluctuations in nanodevices. Furthermore, the random nucleation of the skyrmions due to the device temperature was examined. It was shown that random skyrmion nucleation occurs at temperature values greater than 700 K. These findings make skyrmion devices suitable for storage applications.

Analysis of Magnetization Dynamics in NiFe Thin Films with Growth-Induced Magnetic Anisotropies

We have used angled magnetron sputter deposition with and without sample rotation to control the magnetic anisotropy in 20 nm NiFe films. Ferromagnetic resonance spectroscopy, with data analysis using a Bayesian approach, is used to extract material parameters relating to the magnetic anisotropy. When the sample is rotated during growth, only shape anisotropy is present, but when the sample is held fixed, a strong uniaxial anisotropy emerges with in-plane easy axis along the azimuthal direction of the incident atom flux. When the film is deposited in two steps, with an in-plane rotation of 90 degrees between steps, the two orthogonal induced in-plane easy-axes effectively cancel. The analysis approach enables precise and accurate determination of material parameters from ferromagnetic resonance measurements; this demonstrates the ability to precisely control both the direction and strength of uniaxial magnetic anisotropy, which is important in magnetic thin-film device applications.

Observation of Néel-type magnetic skyrmion in a layered non-centrosymmetric itinerant ferromagnet CrTe1.38

Magnetic skyrmions are nanoscale vortex-like magnetization textures that hold great promise for next-generation memory and spintronic devices. While extensive research has focused on discovering such localized spin textures in bulk magnets and multilayers with heavy metals, there is a growing interest in finding them in two-dimensional (2D) magnetic materials. In this research work, we report two distinct phases of the 2D CrxTey family: non-centrosymmetric CrTe1.38 and centrosymmetric CrTe0.96, with a Curie temperature of around 200 and 300 K, respectively. Detailed magnetic study indicates a prominent out-of-plane magnetic anisotropy in CrTe1.38. In contrast, CrTe0.96 exhibits a weak uniaxial magnetic anisotropy. Lorentz transmission electron microscopy shows that the spontaneous ferromagnetic ground state of CrTe1.38 consists of Néel skyrmions, whereas CrTe0.96 exhibits Bloch domain walls, consistent with their crystalline symmetries. This research expands the quasi-2D CrxTey family and opens up new avenues for exploring non-trivial spin structures and their potential applications in spintronic devices.

Effects of interfacial oxygen diffusion on the magnetic properties and thermal stability of Pd/CoFeB/Pd/Ta heterostructure

We investigated the effects of annealing temperatures (TA) on a Pd (5 nm)/CoFeB (10 nm)/Pd (3 nm)/Ta (10 nm) multilayer structure. The as-deposited sample showed an amorphous state with in-plane uniaxial magnetic anisotropy (UMA), resulting in low coercivity and moderate Gilbert damping constant (α) values. Increasing TA led to crystallization, forming bcc-CoFe (110) crystals, which increased in-plane coercivity and introduced isotropic magnetic anisotropy, slightly reducing the α. The two-fold UMA persists up to 600 °C, and the thermal stability of the in-plane magnetic anisotropy remains intact even TA = 700 °C. The TA significantly influenced the magnetic properties such as in-plane saturation magnetization (Ms//), in-plane and out-of-plane coercivities (Hc// and Hc⊥), and in-plane effective magnetic anisotropy energy density (Keff). Above 600 °C, Keff decreased, indicating a transition towards uniaxial perpendicular magnetic anisotropy. Interfacial oxidation and diffusion from the Ta capping layer to the Pd/CoFeB/Pd interfaces were observed, influencing chemical bonding states. Annealing at 700 °C, reduced oxygen within TaOx through a redox reaction involving Ta crystallization, forming TaB, PdO, and BOx states. Ferromagnetic resonance spectra analysis indicated variations in resonance field (Hr) due to local chemical environments. The α reduction, reaching a minimum at 300 °C annealing, was attributed to reduced structural disorder from inhomogeneities. Tailoring magnetic anisotropy and spin dynamic properties in Pd/CoFeB/Pd/Ta structures through TA-controlled oxygen diffusion/oxidation highlights their potential for SOT, DMI, and magnetic skyrmion-based spintronic devices.

In-plane hard magnetic BaFe12O19 thin films grown on a-plane Al2O3 112¯0 substrates

Ferrimagnetic barium hexaferrite (BaFe12O19) thin films of varying thicknesses were grown on a-plane Al2O3 112̅0 substrates at elevated temperatures using pulsed laser deposition. X-ray diffraction measurements, Raman spectroscopy, and atomic force microscopy analyses were used to investigate the BaFe12O19 film growth and structure. The results indicate that the formation of an α-Fe2O3 ‘bridge layer’ promotes the growth of a BaFe12O19 phase showing an in-plane uniaxial magnetic anisotropy with an easy-axis of magnetization along the [ 0001 ] hexagonal c-axis direction. The crystallographic relationship between the existing phases is given by BaFe12O19 101̅0 //α-Fe2O3 112̅0 //Al2O3 112̅0. As the thickness increases, the fraction of the BaFe12O19 phase increases further. This is accompanied by a change in grain morphology turning from a columnar to a more elongated shape, where the short axis of the BaFe12O19 grains points along the [ 0001 ] easy axis direction.

Modification of magnetoelectric properties of thin film composite multiferroics of Fe10Ni90/PVDF type with using nanostructured Fe10Ni90 layer

In this work, we study the effectiveness of using nanostructuring of a magnetostrictive Fe10Ni90 layer in a film composite multiferroic of the [Fe10Ni90/Cu]p/Fe10Ni90/PVDF type in order to obtain the maximum magnetoelectric effect (ME) while maintaining the high magnetosensitivity characteristic of thin Fe10Ni90 films. In this case, such nanostructuring parameters as the number of periods p and the thickness LFeNi of the Fe–Ni sublayers were varied. The analysis of the dependences of the ME coefficient αE on the indicated parameters carried out in this work made it possible to identify the optimal configuration of the multiferroic. Thus, the work shows that in the non-resonant mode the highest ME coupling coefficient (αE = 4.2 V/cm∙Oe) is achieved for a structure with p = 4 and LFeNi = 200 nm in a saturation field of ∼50 Oe, and a close to linear change in αE is realized in the field range 6–15 Oe. At the same time, this structure retains a low coercive field Hc ∼ 4–5 Oe and pronounced uniaxial magnetic anisotropy in the film plane. These facts indicate the absence in the magnetic component of the multiferroic structure of an undesirable “supercritical” magnetic state, which appears in unstructured Fe10Ni90 films with equivalent thicknesses of the ferromagnetic layer and sharply worsens its magnetosensitivity. Thus, in the case of a homogeneous magnetic layer, the thickness of which is equivalent to the total thickness of the magnetic phase of a nanostructured multiferroic (1000 nm), a significantly lower value of αE = 1.6 V/cm∙Oe is achieved. The totality of the data obtained indicates the validity of using the nanostructuring method when optimizing the properties of film composite multiferroics. A detailed analysis of the dependences αE(p) and αE (LFeNi) together with the results of computer modeling made it possible to determine the main factors influencing the value of αE. In particular, it is shown that an increase in αE is primarily caused by an increase in the total volume of the magnetostrictive phase in the composite, as well as a weakening of the damping effect of the substrate, which occurs with an increase in the number of periods and the thickness of individual sublayers in the structure.

Adjusting microwave sensing frequency through aspect ratio variation and bending repetitions in Permalloy ellipses

The Ferromagnetic Resonance (FMR) phenomenon, marked by the selective absorption of microwave radiation by magnetic materials in the presence of a magnetic field, plays a pivotal role in the development of radar absorbing materials, high speed magnetic storage, and magnetic sensors. This process is integral for technologies requiring precise control over microwave absorption frequencies. We explored how variations in resonance fields can be effectively modulated by adjusting both the shape and stress anisotropies of magnetic materials on a flexible substrate. Utilizing polyethylene-naphthalate (PEN) as the substrate and Permalloy (Ni79Fe21, noted for its positive magnetostriction coefficient) as the magnetic component, we demonstrated that modifications in the aspect ratio and bending repetitions can significantly alter the resonance field. The results, consistent with Kittel’s equation and the predictions of a uniaxial magnetic anisotropy model, underscore the potential for flexible substrates in enhancing the sensitivity and versatility of RF-based magnetic devices.

FePd2Te2: An Anisotropic Two-Dimensional Ferromagnet with One-Dimensional Fe Chains.

Two-dimensional (2D) magnets have attracted significant attention in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with 1D Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter size could be grown. Density functional theory calculations, mechanical exfoliation, and atomic force microscopy on these crystals reveal that they are 2D materials that can be thinned down to ∼5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with TC ∼ 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and the anomalous Hall effect demonstrate that ferromagnetism could be maintained in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right angle bent in the cleavage plane and creates an intriguing spin texture. Besides, a large electronic specific heat coefficient of up to γ ∼ 32.4 mJ mol-1 K-2 suggests FePd2Te2 is a strongly correlated metal. Our results show that FePd2Te2 is a correlated anisotropic 2D magnet that may attract multidisciplinary research interests.

Occupation distribution analysis of Co in La-Co substituted M-type hexaferrite and its significant effect on magnetic properties

In recent years, La-Co co-substituted M-type strontium hexaferrite (La-Co SrM) has gained significant attention due to its improved permanent magnet performance and elevated operating temperature. However, the occupation of Co ions within the lattice of La-Co SrM has sparked considerable debate over the past two decades. To address this, neutron powder diffraction and Raman spectroscopy were employed in this study to analyze Co occupancy in La-Co SrM single crystal and polycrystalline samples. Results consistently reveal a preference for most Co ions to occupy the spin-down tetrahedral 4f1 site, which enhances the net magnetic moment and uniaxial magnetic anisotropy. Differences in Co ion distribution between single crystals (octahedral 12k and 2a sites) and polycrystalline powders (bipyramidal 2b sites) are attributed to sample preparation conditions, often overlooked in previous discussions. Therefore, precise regulation of Co occupancy, particularly maximizing the occupation of the 4f1 site, proves pivotal in enhancing magnetic properties.

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Effect of post-annealing on magnetic anisotropy in La–Co co-substituted M-type strontium ferrite

We investigated the effect of post-annealing on the magnetic anisotropy in La–Co co-substituted magnetoplubite-type strontium ferrite, a matrix phase of commercial high-performance ferrite magnets. Post-annealing was found to be effective in controlling the distribution of substituted Co2+. The Co2+ distribution obtained by lower-temperature annealing shows higher magnetic anisotropy, suggesting that uniaxial magnetic anisotropy is enhanced only when Co2+ occupies the most stable occupied site, i.e., the 4f1 site in the tetrahedral coordination. Furthermore, the slower the cooling rate, the higher the anisotropy. The temperature-dependent Co2+ distribution predicted from the reported density functional theory calculations was compared with the actual anisotropy after annealing, yielding +2.3 meV/ion as the Co2+ anisotropy constant at the tetrahedrally coordinated site and −1.2 meV/ion as that at the octahedrally coordinated sites. Careful selection of heat treatment conditions leads to efficient use of cobalt, an element with supply risks.

Effect of growth conditions on magnetization reversal and magnetic anisotropy in Co2Fe0.5Ti0.5Si quaternary Heusler alloy thin films

Ferromagnetic resonance and magneto-optic Kerr effect (MOKE) techniques are employed to unravel the nature of ‘in-plane’ (IP) magnetic anisotropy and magnetization reversal (MR) processes in magnetron-sputtered 100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films, deposited (and subsequently annealed) at different substrate temperatures (Ts) ranging from 200 °C to 550 °C. By varying TS, the CFTS films are produced with different amounts of anti-site (AS) atomic disorder. Irrespective of the degree of AS disorder, the IP uniaxial magnetic anisotropy (UMA) is prevalent in all the CFTS films. The TS450 and TS500 films, deposited at T S = 450 °C and 500 °C, stand out as they have (i) the least AS disorder, (ii) lowest value (α = 0.0055) of the Gilbert damping constant, (iii) high saturation magnetization ( ≅770 G ) at 300 K, (iv) UMA energy density as high as ≅1.6×104erg/cc at 120 K dropping to ≅1.0×104erg/cc at 300 K, (v) spin-wave stiffness ( D ) at T = 0 K, D0≅175 meVÅ2 and, as in other CFTS films, the electron–magnon interaction is primarily responsible for the thermal renormalization of D . Furthermore, in the TS450 and TS500 films, MOKE hysteresis loops at various angles ( ψH ) that the field makes with the easy axis in the film plane, reveals two mutually exclusive UMAs, UMA1≫UMA2 , with easy axes perpendicular to each other. By contrast, only a single UMA is observed in all the remaining films. When ψH=0∘ , MOKE domain images reveal that, consistent with the uniaxial nature of magnetic anisotropy, an abrupt reversal of magnetization is accompanied by the formation of 180° domains. When ψH = 90°, due to the presence of two UMAs in TS450 and TS500 films, following the field reversal, first the reverse domains nucleate and then grow at the expense of the fundamental domains through field-induced domain wall motion.

Enhanced magnetic anisotropy and its thermal stability in obliquely deposited Co-Film on the nanopatterned substrate

The deliberate manipulation of magnetic anisotropy through controlled adjustments to surface and interface morphology has become important due to its potential applications in spintronics and magnetic memory devices. In the present work, oblique angle deposition (OAD) at 65° to the surface normal on a rippled substrate, keeping nanopatterns on the SiO2 substrate perpendicular to the OAD projection, has been used to induce in-plane uniaxial magnetic anisotropy (UMA) and its thermal stability in cobalt (Co) thin film. Prior to film preparation, the patterned substrate of wavelength 68 ± 4 nm and amplitude 3.4 ± 0.2 nm was prepared separately using a low-energy ion beam erosion (IBE) process. Grazing incidence small-angle X-ray scattering (GISAXS) and magneto-optical Kerr effect (MOKE) techniques have been used for film characterization. While GISAXS provided information about film structure and morphology, MOKE provided information about magnetic properties, thus making it possible to correlate the temperature-dependent evolution of morphology with that of UMA in the film. A clear anisotropy in the growth of Co film is found to result in strong UMA. Unlike previous studies, which typically observe a reduction in UMA strength with thermal annealing, the present work demonstrates a 31 % increase in UMA strength after annealing up to 200 °C, underscoring the importance of oblique angle deposition on nano-rippled substrates for achieving high UMA and ensuring its thermal stability up to moderate temperatures. The appearance of large UMA and its unusual temperature dependence is understood in terms of the shadowing effects and column coalescence, resulting in more robust shape anisotropy. This work provides insights into morphological anisotropy, elucidating the interplay of shadowing effects, shape anisotropy, and dipolar interactions within interacting column and ripple structures. This method gives rise to morphology-induced anisotropy, which can also be applied to other ferromagnetic films to enhance the magnetic anisotropy and ensure thermal stability.

Uniaxial Magnetization and Electrocatalytic Performance for Hydrogen Evolution on Electrodeposited Ni Nanowire Array Electrodes with Ultra-High Aspect Ratio.

Ni nanowire array electrodes with an extremely large surface area were made through an electrochemical reduction process utilizing an anodized alumina template with a pore length of 320 µm, pore diameter of 100 nm, and pore aspect ratio of 3200. The electrodeposited Ni nanowire arrays were preferentially oriented in the (111) plane regardless of the deposition potential and exhibited uniaxial magnetic anisotropy with easy magnetization in the axial direction. With respect to the magnetic properties, the squareness and coercivity of the electrodeposited Ni nanowire arrays improved up to 0.8 and 550 Oe, respectively. It was also confirmed that the magnetization reversal was suppressed by increasing the aspect ratio and the hard magnetic performance was improved. The electrocatalytic performance for hydrogen evolution on the electrodeposited Ni nanowire arrays was also investigated and the hydrogen overvoltage was reduced down to ~0.1 V, which was almost 0.2 V lower than that on the electrodeposited Ni films. Additionally, the current density for hydrogen evolution at -1.0 V and -1.5 V vs. Ag/AgCl increased up to approximately -580 A/m2 and -891 A/m2, respectively, due to the extremely large surface area of the electrodeposited Ni nanowire arrays.

Annealing temperature dependence of magnetic properties in FeCo ordered alloy thin films fabricated using the nitrogen surfactant effect

L10-FeCo has attracted attention as a new, rare-metal-free magnetic material due to its large uniaxial magnetic anisotropy. However, the low stability of the L10 phase hampers its practical application. We here intend to prepare FeCo alloy thin films by utilizing the nitrogen surfactant effect. The enhancement of the out-of-plane magnetization of this thin film was observed by stacking cobalt single atomic layer on bilayer iron nitride and subsequent annealing at 470 K. This study provides an insight into the relationship between structural changes and magnetic properties of the FeCo interface on the atomic scale, and paves the way for the development of rare metal-free magnetic materials.

Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K3C60

Magnetic impurities in superconductors are of increasing interest due to emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for fault-tolerant quantum computation. However, a direct relationship between the YSR multiple states and magnetic anisotropy splitting of quantum impurity spins remains poorly characterized. By using scanning tunneling microscopy, we systematically resolve individual transition-metal (Fe, Cr, and Ni) impurities induced YSR multiplets as well as their Zeeman effects in the K3C60 superconductor. The YSR multiplets show identical d orbital-like wave functions that are symmetry-mismatched to the threefold K3C60(1 1 1) host surface, breaking point-group symmetries of the spatial distribution of YSR bound states in real space. Remarkably, we identify an unprecedented fermion-parity-preserving quantum phase transition between ground states with opposite signs of the uniaxial magnetic anisotropy that can be manipulated by an external magnetic field. These findings can be readily understood in terms of anisotropy splitting of quantum impurity spins, and thus elucidate the intricate interplay between the magnetic anisotropy and YSR multiplets.

Continuous strain-mediated perpendicular magnetic anisotropy in epitaxial (111) CoFe2O4 thin films grown on LiTaO3 substrates

Perpendicular magnetic anisotropy (PMA) in magnetic thin films has attracted much attention due to its potential applications in spintronics devices. Here, we report the continuous strain-mediated PMA in epitaxial (111) CoFe2O4 (CFO) thin films grown on (0001) LiTaO3 substrates. A large variation in lattice strain (∼0.9%) in a continuous way is realized in the CFO thin films by changing substrate temperature during deposition due to the difference in the thermal expansion coefficient between CFO and LiTaO3. As a result, the PMA of the (111) CFO thin films can be continuously mediated by the strain with uniaxial magnetic anisotropy energy in the range of 0.12-14.69×106 erg/cm3. Furthermore, the strain as well as the consequent PMA in the (111) CFO thin films can be maintained within the thickness of 25–205 nm, which is consistent with the scenario of the magnetoelastic effect. Our results reveal that the CFO/LiTaO3 system can be regarded as an ideal platform to realize robust PMA and its continuous strain tuning in the (111) CFO thin films by virtue of strain-induced magnetic anisotropy.