Magnetic Compensation Temperature Research Articles

Temperature and field dependencies of the magnetization of ferrimagnetic Gd-Co films: Chemical inhomogeneity or spin-flop transition

Magnetic properties of amorphous Gd-Co ferrimagnetic films prepared by magnetron sputtering have been studied for various thicknesses. In a certain temperature range close to the magnetic compensation temperature, triple hysteresis loops and the characteristic features of the tempera-ture dependencies of magnetization were observed for all samples under consideration. Two-layer film model with an inhomogeneous chemical composition and a spin-flop transition scenario in two sub-lattice ferrimagnet was employed for understanding the origins of these phenomena. Within the framework of the spin-flop transition, the inter sub-lattice exchange coupling constant was estimated using various methods.

Tuning magnetization compensation temperature of Gd3Fe5O12 epitaxially grown on Gd3Sc2Ga3O12

The compensated ferrimagnetic insulator Gd3Fe5O12 (GdIG) with a magnetization compensation point (TM ∼ 286 K) near room temperature has recently gained significant attention because of its long spin transmission length and absence of Ohmic loss. However, previously reported GdIG films with perpendicular magnetic anisotropy have a TM far below room temperature, which is unfavorable for practical applications. Here, we show the tuning of TM from 268 to 303.7 K in perpendicularly magnetized 15 nm GdIG films epitaxially grown on (111) Gd3Sc2Ga3O12 by manipulating the epitaxial strain through controlling the rapid cooling temperature during the annealing process. By varying the film thickness between 5 and 40 nm, the TM of the film can be further extended to a range of 246–380 K. We have also demonstrated highly efficient switching of the GdIG spin-sublattices driven by current at room temperature in the GdIG/Pt heterostructures with various TM values, especially with TM slightly higher than 300 K. Our findings reveal potential opportunities for insulating compensated ferrimagnetic films of GdIG in the development of high-density, high-speed, and energy-efficient spintronic devices.

Magnetic properties and compensation temperatures of a graphene bilayer by Monte Carlo simulation

We used Monte Carlo simulation to study the magnetic properties and compensation behavior of a ferrimagnetic mixed-spin (3/2; 1/2) Ising system in a graphene bilayer. The effects of exchange interactions, crystal field, external magnetic field and temperature on the total magnetization, partial magnetizations, magnetic susceptibility, phase diagram and hysteresis behavior of the system were examined. Interesting results were obtained in this work, such as the compensation behavior and the multi-loop hysteresis phenomenon for specific values of the system’s physical parameters. Our results conform to those of other theoretical studies.

The magnetic and electronic properties of Ho6Fe23−xCox (x = 0, 1, 2, 3)

Magnetic and electronic properties of Ho6Fe23−xCox (x = 0, 1, 2, 3) compounds were investigated for the first time by experimental measurements on their polycrystalline samples combining with first-principles calculation. The samples of Ho6Fe23−xCox were successful prepared by a vacuum arc furnace. The XRD analysis and Rietveld refinement results show that Ho6Fe23−xCox crystallize in a face-centered cubic Th6Mn23-type structure with space group Fm3¯m (No.225), and their lattice parameters decrease with the increasing Co content. The M−T curves indicates that AFM-FM transition occurred at Neél temperature TN, the FM-PM transition occurred at Currie temperature TC for Ho6Fe23−xCox and the FM-PM transition belongs to a second-order transition. The Currie temperature and magnetic compensation temperature for all the samples increases with the increase of the content of Co. The maximum magnetic entropy change (-ΔSM) for the Ho6Fe23−xCox compounds under an applied magnetic field of 15 k Oe are 0.594, 1.023, 0.726 and 0.48 J kg−1 K−1 around their Currie temperature (TC = 542, 580, 622 and 654 K), respectively. This relatively large -ΔSM of Ho6Fe23−xCox occurred in a relatively high temperature region and under low applied magnetic field, pointing to the potential application as magnetic refrigeration materials using at higher temperature. The experimental results show that Co doping can regulate the magneto-thermal properties of the materials, so as to improve the magnetic entropy change of the existing magnetic refrigeration materials. The electronic properties of Ho6Fe23−xCox was studied by using the first-principle calculation. The band structures and density of states indicate that Ho6Fe23−xCox are good conductor.

Thermally generated magnonic spin currents in a polycrystalline gadolinium iron garnet thin film with perpendicular magnetic anisotropy

Rare-earth iron garnets (REIGs) are the benchmark systems for magnonics, including the longitudinal spin Seebeck effect (LSSE). While most research has focused on single-crystalline REIGs on complimentary garnet substrates, moving to more, cost-effective complementary metal-oxide semiconductor (CMOS)-compatible substrates is important to integrate REIG thin films with existing technology. In this regard, we grow a 130 nm-thick polycrystalline gadolinium iron garnet (GdIG) film on the Si/SiO2 substrate and investigate the temperature-dependent LSSE. Interestingly, the polycrystalline GdIG film exhibits perpendicular magnetic anisotropy (PMA) at room temperature which is induced by tensile in-plane (IP)-strain originating from the thermal-expansion mismatch between the GdIG film and the substrate during rapid thermal annealing. Further, a spin-reorientation transition from the out-of-plane IP direction below TS = 180 K is observed. Additionally, the film reveals a magnetic compensation temperature, TComp, of ≈240 K. The LSSE voltage not only demonstrates a sign-inversion around TComp, but also shows noticeable changes around TS. As compared to a single-crystalline GdIG film, the lower LSSE voltage for the polycrystalline GdIG is attributed to the higher effective magnetic anisotropy and enhanced magnon scattering at the grain boundaries. Our study not only paves the way for the cost-effective growth of CMOS-compatible REIG-based systems with PMA for magnonic memory and information processing applications, but also highlights the fact that the spincaloritronic and spin-insulatronic properties of the polycrystalline REIGs follow those of their single-crystalline counterparts with reduced spin-to-charge conversion efficiency through LSSE which can be tuned further by controlling the average gran size and interface engineering.

Tailoring compensated ferrimagnetic state and anomalous Hall effect in quaternary Mn-Ru-V-Ga Heusler compounds

Abstract Cubic Mn2Ru x Ga Heusler compound is a typical example of compensated ferrimagnet with attractive potential for high-density, ultrafast, and low-power spintronic applications. In the form of epitaxial thin films, Mn2Ru x Ga was shown to exhibit high spin polarization and high tunability of compensation temperature by freely varying the Ru content x over a broad range (0.3 < x < 1.0). Here, we systematically studied Mn-Ru-Ga-based polycrystalline bulk buttons prepared by arc melting and found that, in equilibrium bulk form, the cubic structure is unstable when x < 0.75. To overcome this limitation, we alloyed Mn-Ru-Ga with a fourth element V. By adjusting the content of V in the Mn2Ru0.75V y Ga and Mn2.25-y Ru0.75V y Ga quaternary systems, the magnetic compensation temperature was regulated. Compensation was achieved near 300 K which was confirmed by both the magnetic and anomalous Hall effect measurements. Analyses of the anomalous Hall effect scaling in quaternary Mn-Ru-V-Ga alloys revealed the dominant role of skew scattering, notably that contributed by the thermally excited phonons, in contrast to many other 3d ferromagnets and Heusler compounds. We further showed that the Ga antisites and V content can simultaneously control the residual resistivity ratio (RRR) as well as the relative phonon and defect contribution to the anomalous Hall effect a’’/a’ in Mn-Ru-V-Ga, leading to a scaling relation a’’/a’ ∝ RRR1.8.

Reconfigurable spin current transmission and magnon–magnon coupling in hybrid ferrimagnetic insulators

Coherent spin waves possess immense potential in wave-based information computation, storage, and transmission with high fidelity and ultra-low energy consumption. However, despite their seminal importance for magnonic devices, there is a paucity of both structural prototypes and theoretical frameworks that regulate the spin current transmission and magnon hybridization mediated by coherent spin waves. Here, we demonstrate reconfigurable coherent spin current transmission, as well as magnon–magnon coupling, in a hybrid ferrimagnetic heterostructure comprising epitaxial Gd3Fe5O12 and Y3Fe5O12 insulators. By adjusting the compensated moment in Gd3Fe5O12, magnon–magnon coupling was achieved and engineered with pronounced anticrossings between two Kittel modes, accompanied by divergent dissipative coupling approaching the magnetic compensation temperature of Gd3Fe5O12 (TM,GdIG), which were modeled by coherent spin pumping. Remarkably, we further identified, both experimentally and theoretically, a drastic variation in the coherent spin wave-mediated spin current across TM,GdIG, which manifested as a strong dependence on the relative alignment of magnetic moments. Our findings provide significant fundamental insight into the reconfiguration of coherent spin waves and offer a new route towards constructing artificial magnonic architectures.

Determination method for magnetic momentum compensation temperature of ferrimagnets by extrapolating from narrow temperature range

We propose here an experimental method to determine the magnetization compensation temperature of ferrimagnets. Our method utilizes the first-order derivative of the spontaneous net magnetization with respect to the temperature and then analyzes the results within the context of the Bloch's law of ferrimagnetic materials. This method enables us to extrapolate the compensation temperatures, even when they exceed the measurement limit. Consequently, a wide range of compensation temperatures can be determined using a single experimental setup. The present method provides a versatile tool for analyzing huge compensation temperature in the emerging field of ferrimagnetic and antiferromagnetic spintronics.

Bipolar magnetic switching and large exchange-bias in Fe-substituted SmCrO3

Rare-earth orthochromite is an interesting system in the view of its complex magnetic ordering due to competing interaction between different magnetic ions. Here, Fe-substituted SmCrO3 samples were prepared by solid-state route to investigate their intriguing magnetic properties towards exploring its application potential. The magnetic studies revealed antiferromagnetic (AFM) ordering at Nèel temperature (T N) ∼ 181 K, magnetic compensation temperatures (T COMP) at ∼137 K and 50 K, and spin-reorientation temperature (T SR) at 64 K in SmCr0.8Fe0.2O3 sample. Additionally, the system exhibited negative magnetization under field-cooled conditions which allowed the field as well as temperature controllable magnetization switching behavior. Notably, the Fe-substituted SmCrO3 sample displayed a remarkable exchange bias (H EB) value of ∼1.39 T at 10 K due to the coexistence of ferromagnetic and AFM ordering at different cationic sites. The M–H loops recorded under positive and negative field-cooled conditions ruled out the minor-loop effect. Theoretical models applied on the training effect studies confirmed the observed exchange-bias effect.

Comment on "Magnetization Compensation Temperature and Frustration-Induced Topological Defects in Ferrimagnetic Antiperovskite Mn_{4}N".

Comment on "Magnetization Compensation Temperature and Frustration-Induced Topological Defects in Ferrimagnetic Antiperovskite Mn_{4}N".

Sublattice spin reversal and field induced Fe3+ spin-canting across the magnetic compensation temperature in Y1.5Gd1.5Fe5O12 rare-earth iron garnet

In the present work Fe3+ sublattice spin reversal and Fe3+ spin-canting across the magnetic compensation temperature (T) are demonstrated in polycrystalline Y1.5Gd1.5Fe5O12 (YGdIG) by means of in-field Mössbauer spectroscopy measurements. Corroborating in-field Mössbauer measurements, both Fe3+ & Gd3+ sublattice spin reversal has also been manifested in hard x-ray magnetic circular dichroism (XMCD) measurements. From in-field 57 Fe Mössbauer measurements, estimation and analysis of effective internal hyperfine field (H), relative intensity of absorption lines in a sextet elucidated unambiguously the signatures of Fe3+ spin reversal and field induced spin-canting of Fe3+ sublattices across T. Gd L3-edge XMCD signal is observed to consist of an additional spectral feature, identified as Fe3+ magnetic contribution to XMCD spectra of Gd L3-edge, enabling us the extraction of both the sublattices (Fe3+ & Gd3+) information from a single absorption edge analysis. The evolution of the XMCD amplitudes, which is proportional to magnetic moments, as a function of temperature for both magnetic sublattices extracted at the Gd L3-edge reasonably match with values that are extracted from bulk magnetization data of YGdIG and YIG (Y3Fe5O12) and corresponding Fe K-edge XMCD amplitudes for Fe contribution. These measurements pave new avenues to investigate how the magnetic behavior of such complex system acts across the compensation point.

Aging and passivation of magnetic properties in Co/Gd bilayers

Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging the gap between volatile information in the photonic domain and nonvolatile information in the magnetic domain, without the need for any intermediary electronic conversion. Specifically, these systems exhibit strong spin–orbit torque effects, fast domain wall motion, and single-pulse all-optical switching of the magnetization. An important open challenge to bring these materials to the brink of applications is to achieve long-term stability of their magnetic properties. In this work, we address the time-evolution of the magnetic moment and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with various capping layers. Over the course of three months, the net magnetic moment and compensation temperature change significantly, which we attribute to quenching of the Gd magnetization. We identify that intermixing of the capping layer and Gd is primarily responsible for this effect, which can be alleviated by choosing nitrides for capping as long as reduction of nitride to oxide is properly addressed. In short, this work provides an overview of the relevant aging effects that should be taken into account when designing synthetic ferrimagnets based on Co and Gd for spintronic applications.

Anomalies in the magnetic properties of bismuth-substituted diluted yttrium iron garnet

The magnetic properties and Mössbauer spectra of the Y1.8Bi1.2Fe3.5Ga1.5O12 compound were investigated. A linear temperature dependence of the saturation magnetization, hysteresis, and stability of the coercive field in the magnetically ordered state were found. Using the Mössbauer measurements, the distribution of iron ions over octahedral and tetrahedral sites and the concentration of paramagnetic iron ions were determined. Two critical temperatures – the sublattice magnetization compensation temperature and the ferrimagnet–paramagnet transition temperature – were established. The disappear of the phonon mode in the vicinity of the magnetic transition was observed. The experimental data have been interpreted in terms of the spin–lattice interaction model.

Control of Compensation Temperature in CoGd Films through Hydrogen and Oxygen Migration under Gate Voltage.

Electrical control of magnetic properties is crucial for low-energy memory and logic spintronic devices. We find that the magnetic properties of ferrimagnetic CoGd can be altered through ionic liquid gating. Gate voltages manipulate the opposite magnetic moments in Co and Gd sublattices and induce a giant magnetic compensation temperature change of more than 200 K in Pt/CoGd/Pt heterostructures. The electrically controlled dominant magnetic sublattice allows voltage-induced magnetization switching. Both experiments and theoretical calculations demonstrate that the significant modulations of compensation temperature are relevant to the reduced Gd moments due to the presence of hydrogen ions at positive voltages as well as the enhanced Co moments and reduced Gd moments due to the injection of oxygen ions at negative voltages. These findings expand the possibilities for all-electric and reversible magnetization control in the field of spintronics.

Magneto-ionic Control of Ferrimagnetic Order by Oxygen Gating.

Ferrimagnets are considered an excellent spintronic material candidate which combines ultrafast magnetic dynamics and straightforward electrical detectability. However, efficient routes toward magneto-ionic control of ferrimagnetic order remain elusive. In this study, a solid-state oxygen gating device was designed to control the magnetic properties of the ferrimagnetic CoTb alloy. Experimental results show that applying a small voltage can irreversibly tune a Tb-dominant device to a stable Co-dominant state and decrease the magnetization compensation temperature by 130 K. In addition, a reversible voltage control of the magnetization axis between out-of-plane and in-plane states is observed, which indicates that the migrated oxygen ions can bond to both Tb and Co sublattices. First-principles calculations indicate that voltage can dynamically control the flow-in and flow-out of oxygen ions that bond to the Co sublattice. Our work provides an effective means to manipulate ferrimagnetic order and contributes to the development of ultra-low-power spintronic devices.

Piezostrain-controlled magnetization compensation temperature in ferrimagnetic GdFeCo alloy films

The electrical control of magnetization compensation temperature (${T}_{\mathrm{com}}$) is investigated in ferrimagnetic GdFeCo alloy deposited on ferroelectric $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}30%\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-PT). It is found that the applied electric field can cause a 19 K shift in ${T}_{\mathrm{com}}$. ${T}_{\mathrm{com}}$ under different applied electric fields across the PMN-PT substrate suggests that such electrical control is induced by piezostrain at the ferroelectric-ferrimagnetic interface. Spin-polarized first-principles calculations show that the change of exchange coupling strength in GdFeCo are caused by the lattice strains. Nonvolatile switching of resistance and direct bipolar control of exchange bias are achieved when an electric field is applied to appropriately designed multilayers. Our findings pave the way for electric field control of ${T}_{\mathrm{com}}$ in ferrimagnetic GdFeCo alloy and have implications for the development of energy efficient and nonvolatile ferrimagnetic magnetic random access memory.

Magnetization switching of a nearly compensated ferrimagnet by enhanced spin-orbit torque

Spin–orbit torques (SOTs) provide an efficient way to electrically manipulate the magnetic order in spintronic devices. Compared with conventional ferromagnetic materials, ferrimagnetic materials have the advantages of antiferromagnetically coupled sublattices and induced ultrafast spin dynamics. In this paper, we study the current-induced magnetization switching in the ferrimagnetic Ta/GdFeCo/MgO system. Robust SOT-induced magnetization switching can be achieved at the magnetic compensation temperature point of around 70 K, where the magnetization is nearly zero and the coercivity can reach almost 3 T. The temperature dependence of the SOT efficiency is quantified by the second harmonic method, and the enhanced SOT efficiency near the magnetic compensation temperature is attributed to the negative exchange coupling between the two sublattices of CoFe and Gd. This work demonstrates the SOT switching of the nearly compensated ferrimagnet, with great potential for future magnetic interaction-free and ultrafast ferrimagnetic applications.

Anomalous hysteresis loops of ferrimagnetic Gd-Co films of different thickness near the magnetic compensation temperature

Triple hysteresis loops were observed for amorphous ferrimagnetic Gd-Co films near the magnetic compensation temperature, which can be a consequence of both the spin-flop transition and the chemical composition gradient. In the work, an assessment of the possible chemical inhomogeneity of the films based on magnetic measurements was carried out and its relationship with the thickness of the samples was observed. Keywords: amorphous magnetic films, perpendicular magnetic anisotropy, ferrimagnetism, magnetic domain structure, magnetic hysteresis.

Аномальные петли гистерезиса ферримагнитных пленок Gd-Co различной толщины вблизи температуры магнитной компенсации

Triple hysteresis loops were observed for amorphous ferrimagnetic Gd-Co films near the magnetic compensation temperature, which can be a consequence of both the spin-flop transition and the chemical composition gradient. In the work, an assessment of the possible chemical inhomogeneity of the films based on magnetic measurements was carried out and its relationship with the thickness of the samples was observed.

Unconventional magnetoresistive behavior near magnetic compensation temperature in ferrimagnetic Mn2.21Ru0.86Ga films

Ferrimagnets with magnetic compensation temperature (Tcomp) around room temperature are desirable due to their potential applications in low-energy consuming and high-frequency spintronic devices. In this study, the Tcomp of ferrimagnetic Mn2.21Ru0.86Ga (MRG) is tuned to near room temperature by strain. Moreover, we observed unconventional magnetoresistance behaviors for MRG-based Hall bar devices near Tcomp. First-principles calculations suggest two kinds of Mn moments, which lead to two anomalous Hall channels with opposite signs and consequently correspond to the peak structure and triple loops of the anomalous Hall effect loops. The unconventional temperature dependence of longitudinal resistivity is caused by the combined effects of two types of Mn moments and the anisotropic magnetoresistance of the MRG film. Interestingly, the spontaneous Hall angle of the MRG film is calculated to be ∼2.2%, which is one order of magnitude larger than those of other 3d ferromagnets. Therefore, our study demonstrates MRG to be a ferrimagnet with the Tcomp near room temperature, which enables its potential applications in spintronic devices.