TbCo Alloy Research Articles

Coexistence of large anomalous Nernst effect and large coercive force in amorphous ferrimagnetic TbCo alloy films

The anomalous Nernst effect (ANE) has garnered significant interest for practical applications, particularly in energy harvesting and heat flux sensing. For these applications, it is crucial for the module to operate without an external magnetic field, necessitating a combination of a large ANE and a substantial coercive force. However, most materials exhibiting a large ANE typically have a relatively small coercive force. In our research, we have explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the coercive force peaks at the magnetization compensation point (MCP). We observed that transverse Seebeck coefficients are amplified with Tb doping, reaching more than 1.0 μV/K over a wide composition range near the MCP, which is three times greater than that of pure Co. Our findings indicate that this enhancement is primarily due to direct conversion, a product of the transverse thermoelectric component and electrical resistivity. TbCo films present several significant advantages for practical use: a large ANE, the capability to exhibit both positive and negative ANE, the flexibility to be deposited on any substrate due to their amorphous nature, a low thermal conductivity, and a large coercive force. These attributes make TbCo films a promising material for advancing ANE-based technologies.

Observation of spin-glass-like characteristics in ferrimagnetic TbCo through energy-level-selective approach

Rare earth (RE)–transition metal (TM) ferrimagnetic alloys are gaining increasing attention because of their potential use in the field of antiferromagnetic spintronics. The moment from RE sub-lattice primarily originates from the 4f-electrons located far below the Fermi level (EF), and the moment from TM sub-lattice arises from the 3d-electrons across the EF. Therefore, the individual magnetic moment configurations at different energy levels must be explored to clarify the microscopic mechanism of antiferromagnetic spin dynamics. Considering these issues, here we investigate the energy-level-selective magnetic moment configuration in ferrimagnetic TbCo alloy. We reveal that magnetic moments at deeper energy levels are more easily altered by the external magnetic field than those near the EF. More importantly, we find that the magnetic moments at deeper energy levels exhibit a spin-glass-like characteristics such as slow dynamics and magnetic moment freezing whereas those at EF do not. These unique energy-level-dependent characteristics of RE-TM ferrimagnet may provide a better understanding of ferrimagnet, which could be useful in spintronic applications as well as in spin-glass studies.

Direction‐Sensitive Magnetophotonic Surface Crystals

Magnetophotonic Crystals In article number 2100119 by Richard M. Rowan-Robinson, Alexandre Dmitriev, Vassilios Kapaklis, and co-workers, microscale magnetophotonic surface crystals are revealed by building arrays of magnetoplasmonic nanoantennas with nanosized rare-earth transition metal ferrimagnetic TbCo alloys, displaying perpendicular magnetic anisotropy. Magneto-optics is dramatically enhanced in such crystals via nanoantennas plasmons and their coupling into collective surface lattice modes. The result is a highly light-direction-sensitive optical surface with nanomagnetic functionality for the plasmon-assisted all-optical magnetization switching.

The deterministic field-free magnetization switching of perpendicular ferrimagnetic Tb-Co alloy film induced by interfacial spin current

Current-induced magnetization switching in compensated ferrimagnetic materials by the spin–orbit torque (SOT) effect is promising for the next generation information storage devices. In this work, we report the current-induced deterministic field-free magnetization switching of the perpendicular Tb-Co ferrimagnet layer in a Co/Ti/Tb-Co trilayers. We found that the switching proportion and polarity of the Tb-Co ferrimagnet depend on the magnetization direction of the in-plane Co layer. The switching process revealed by magneto-optical Kerr microscope imaging further confirmed the current-induced field-free switching of the Tb-Co layer. We also demonstrated the large SOT effective field and the perpendicular effective field acting on the Tb-Co layer, by utilizing the second harmonic voltage measurement and the current-induced loop shift method. The large interfacial SOT efficiency and deterministic field-free magnetization switching in the trilayers structure may accelerate the application of ferrimagnet in SOT memory devices.

Magnetization-dependent inverse spin Hall effect in compensated ferrimagnet TbCo alloys

In this paper, we demonstrate the magnetization-dependent inverse spin Hall effect (MD-ISHE) in ${\mathrm{Tb}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}/\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ devices using the spin Seebeck effect. It was found that a thermally injected spin current is precessed around the magnetization of the ${\mathrm{Tb}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}$ alloy before it is converted into a charge current. Furthermore, the sign of the MD-ISHE voltage was found to depend on the Co magnetic moment direction, whereas the sign and magnitude of the conventional ISHE voltage are independent of the ${\mathrm{Tb}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}$ magnetization direction. Meanwhile, the spin rotation angle was estimated to be \ensuremath{\sim}12% in ${\mathrm{Tb}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}/\mathrm{Pt}$. Our findings demonstrate that perpendicularly magnetized ${\mathrm{Tb}}_{x}{\mathrm{Co}}_{100\ensuremath{-}x}$ supplies additional symmetry to the ISHE and provides advantages in terms of tailoring the sign of the spin-current polarization through adjusting the alloy composition.

Temperature dependence of spin-orbit torques across the magnetic compensation point in a ferrimagnetic TbCo alloy film

The temperature dependence of spin-orbit torques (SOTs) and spin-dependent transport parameters is measured in bilayer Ta/TbCo ferrimagnetic alloy films with bulk perpendicular magnetic anisotropy. We find that the dampinglike (DL)-SOT effective field diverges as temperature is swept through the magnetic compensation temperature (${T}_{\mathrm{M}}$), where the net magnetization vanishes due to the opposing contributions from the Tb and Co sublattices. We show that DL-SOT scales with the inverse of the saturation magnetization (${M}_{\mathrm{s}}$), whereas the spin-torque efficiency is independent of the temperature-dependent ${M}_{\mathrm{s}}$. Our findings provide insight into spin transport mechanisms in ferrimagnets and highlight low-${M}_{\mathrm{s}}$ rare-earth/transition-metal alloys as promising candidates for SOT device applications.

Conditions for thermally induced all-optical switching in ferrimagnetic alloys: Modeling of TbCo

We present atomistic spin dynamics modeling of thermally induced magnetization switching (TIMS) of disordered ferrimagnetic TbCo alloys varying the Tb concentration, laser pulse fluence, and its duration. Our results indicate that deterministic TIMS occurs in a wide range of Tb concentrations and at large laser fluences with a pulse duration of 50 fs. We furthermore demonstrate that the occurrence of the transient ferromagneticlike state is necessary, but after first reversal, the system may switch back. The presence of a magnetization compensation point or going through it is shown not to be required. With the increase of the laser pulse duration TIMS becomes stochastic so that for a 1 ps laser pulse width and beyond the deterministic heat-assisted AOS does not exist.

Thermal reduction of the threshold current density for current-induced domain wall motion in Tb-Co magnetic alloy wire

We investigated the current-induced domain wall motion (CIDWM) in Pt (3 nm)/Tb0.34Co0.66 (6 nm) alloy wire at various temperatures (T). The threshold current density (Jth) for the CIDWM in the Tb-Co alloy wire was 0.85 × 1011 A/m2 at room temperature, and drastically decreased as T was increased. Particularly, at T = 343 K, Jth (= 0.13 × 1011 A/m2) was almost 7 times lower than that at room temperature. The reduction in Jth can be attributed to thermally activated creep motion and a reduction in the depinning current density. These results indicate that devices using CIDWM can be thermally assisted.

Novel magnetic wire fabrication process by way of nanoimprint lithography for current induced magnetization switching

Nanoimprint lithography (NIL) is an effective method to fabricate nanowire because it does not need expensive systems and this process is easier than conventional processes. In this letter, we report the Current Induced Magnetization Switching (CIMS) in perpendicularly magnetized Tb-Co alloy nanowire fabricated by NIL. The CIMS in Tb-Co alloy wire was observed by using current pulse under in-plane external magnetic field (HL). We successfully observed the CIMS in Tb-Co wire fabricated by NIL. Additionally, we found that the critical current density (Jc) for the CIMS in the Tb-Co wire fabricated by NIL is 4 times smaller than that fabricated by conventional lift-off process under HL = 200Oe. These results indicate that the NIL is effective method for the CIMS.

Enhancement of spin orbit torques in a Tb-Co alloy magnetic wire by controlling its Tb composition

We investigated the current-induced domain wall motion (CIDWM) in Pt(3 nm)/TbxCo1-x(6 nm) alloy wires with various Tb composition (x). We found that the threshold current density (Jth) for the CIDWM in the TbxCo1-x alloy wires decreases with increasing x. In particular, the Jth with x = 0.37 is almost 3 times smaller than that with x = 0.23. We estimated Dzyaloshinskii-Moriya interaction (DMI) effective field (HDMI) by measuring CIDWM in a longitudinal magnetic field. We found that DMI constant (D) estimated by the HDMI also strongly depends on x. The size of the DMI may be modified by changing electronegativity or local atomic arrangement in Tb-Co alloy. These results suggest that Tb can induce strong HDMI and effectively affect CIDWM in TbxCo1-x alloy wires.

Investigation and Effective Control of Perpendicular Magnetic Anisotropy for TbCo Films with Different Underlayers

We performed a detailed study on the perpendicular magnetic anisotropy (PMA) of TbCo film by using two kinds of nonmagnetic underlayers, Ta and Ta/Cu with different thicknesses. We found that for both the Tb-rich and Co-rich TbCo alloy films, the PMA strength decreases considerably with the increase of Ta underlayer thickness, while their net saturation magnetization [Formula: see text] exhibit opposite varying trends. The [Formula: see text] value continues to increase for the Co-rich TbCo samples while decrease for the Tb-rich films. Interestingly, an additional Cu layer inserted between the Ta and TbCo layers can efficiently recover the PMA and [Formula: see text]. We attribute such observed variation behaviors of magnetic properties to the increased disordering of Tb magnetic moments at the Ta/TbCo interface, which has been verified by both experimental measurements and micromagnetic simulations.

Domain size criterion for the observation of all-optical helicity-dependent switching in magnetic thin films

To understand the necessary condition for the observation of all-optical helicity-dependent switching (AO-HDS) of magnetization in thin films, we investigated ferromagnetic Co/Pt and Co/Ni multilayers as well as ferrimagnetic TbCo alloys as a function of magnetic layer compositions and thicknesses. We show that both ferro-and ferrimagnets with high saturation magnetization show AO-HDS if their magnetic thickness is strongly reduced below a material-dependent threshold thickness. By taking into account the demagnetizing energy and the domain wall energy, we are able to define a criterion to predict whether AO-HDS or thermal demagnetization (TD) will be observed. This criterion for the observation of AO-HDS is that the equilibrium size of magnetic domains forming during the cooling process should be larger than the laser spot size. From these results we anticipate that more magnetic materials are expected to show AO-HDS. However, the effect of the optical pulses' helicity is hidden by the formation of small magnetic domains during the cooling process.

Generation and manipulation of domain walls using a thermal gradient in a ferrimagnetic TbCo wire

We demonstrate the ability to create, control the propagation, and annihilate domain walls in 25-nm thick Tb22Co78 ferrimagnetic alloy wires using a temperature gradient under a constant applied field. The temperature gradient is generated by passing a current through the wire, and the domain wall properties are imaged using Kerr microscopy. The manipulation of the domain wall is made possible by creating a temperature gradient such that the temperature at one end of the wire is above the compensation temperature for the TbCo alloy, while the other end remains below the compensation temperature. By tuning the intensity of the applied magnetic field and the current flowing inside the wire, it is possible to carefully control the domain wall position that can then be stabilized under zero applied field and current.

Extraordinary Hall effect based magnetic logic applications

Extraordinary Hall Effect (EHE) based original concepts of a reconfigurable logic gate and a multi-bit logic comparator are presented. They exploit the EHE voltage that develops on cross cells connected in series that has no size limitation down to the nanometer scale. Experimental demonstrations are performed on both micro- and nanometer lateral size crosses made of ferrimagnetic TbCo alloy. The simplicity of the device architecture and its robustness make it advantageous when compared with existing systems.

Subpicosecond magnetization dynamics in TbCo alloys

Since the discovery of all-optical magnetization switching in rare-earth transition-metal alloys the underlying magnetization dynamics of multisublattice magnets has become a hot topic of modern magnetism. We studied the ultrafast magnetization dynamics in TbCo alloys as a function of the alloy composition and the laser fluence using either 800 nm or 400 nm probe pulses. Direct comparison between TbCo samples with different compositions for equal excitation conditions demonstrates that the magnetization dynamics of the Co sublattice strongly depends on the Tb concentration. For ${\mathrm{Tb}}_{32}{\mathrm{Co}}_{68}$ the magnetization of the sublattices can even transiently be reversed on a subpicosecond time scale.

Energy-resolved magnetic domain imaging in TbCo alloys by valence band photoemission magnetic circular dichroism

We report magnetic domain imaging of a terbium cobalt (TbCo) alloy thin film with a high perpendicular magnetic anisotropy in one- and two-photon photoemission electron microscopy (PEEM). Both photoemission processes deliver a clear magnetic circular dichroism (MCD) whose strength is strongly energy dependent. Comparing the energy dependence of the MCD signal in one- and two-photon photoemission, we conclude that the magnetic contrast is mainly an initial state effect. Our results ultimately show that MCD contrast can be obtained in PEEM in valence band photoemission from a material supporting all-optical magnetization switching. This opens the way for the investigation of the all-optical switching process with simultaneous ultrahigh temporal and spatial resolution.

Light-induced magnetization reversal of high-anisotropy TbCo alloy films

Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.

Magnetoresistive effects in perpendicularly magnetized Tb-Co alloy based thin films and spin valves

Tb-Co ferrimagnetic alloy thin films and spin valves have been grown to study their magnetoresistance response in various geometries. The studied Tb-Co alloys show strong perpendicular anisotropy and tunable magnetization by several orders of magnitude. Magnetoresistance signals such as giant magnetoresistance (GMR), anisotropic magnetoresistance (AMR), extraordinary Hall effect (EHE), and magnon magnetoresistance (MMR) have been studied. The angular dependence of those magnetoresistive effects is also investigated. Finally we demonstrate that by adjusting the Tb-Co layer composition in a spin valve structure, the sign and the amplitude of the GMR and EHE signal can be tuned.

Structure and magnetic properties of sputtered Tb/Co multilayers

Multilayers of Tb/Co with equal thicknesses of the single layers ( d Tb = d Co) were prepared on water-cooled quartz and glass substrates by means of a two-source rf-sputtering method. Small-angle X-ray diffraction analysis and transmission electron microscopy on cross-sections of the films revealed a layered structure in all samples with d Tb , d Co ≥ 15 A ̊ . The films with d Tb , d Co ≤ 10 A ̊ behaved as homogeneous TbCo alloys. The existence of compensation points in the temperature dependence of the magnetization of the multilayers indicates a magnetic order in the Tb layers with an antiferromagnetic coupling between the Tb and Co atoms in spite of the fact that pure Tb is paramagnetic at room temperature ( T C = 219.5 K). The extension of the magnetically coupled regions in the Tb layers was calculated from the dependence of the saturation magnetization M S and the compensation temperature T comp on the layer thickness d L of the Tb/Co multilayers. It is about 15 Å at each boundary of the Tb layers and therefore much larger than one would expect from the direct exchange interaction in the ferromagnetic transition metals. The magnetic anisotropy constant K u eff of the films was determined by a torque magnetometer. The linear dependence of K u eff on the inverse layer thickness 1/ d L of the multilayers indicates the existence of a surface anisotropy at the Tb/Co interfaces. The surface anisotropy constant is about K s = 0.46 erg/cm 2.

Magnetic properties and anisotropy of amorphous Tb-Co alloys

Magnetization in amorphous alloys Tb/sub x/ Co/sub 100-x/ (10<x<40) obtained by ion sputtering in the fields of up to 70 kOe in the 1.5-300-K temperature region has been studied. Induced uniaxial anisotropy with the axis in the film plane was observed. It has been found that easy axis is reoriented under the applied magnetic field. Complex reorientation spin transitions in magnetic field applied along the hard magnetization axis have been found in Tb/sub 21/Co/sub 79/ alloy with compensated magnetic moments of Tb and Co magnetic sublattices. The obtained results are discussed on the theory of fluctuations of the amorphous alloy's magnetic moments.<<ETX>>