We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pulses are studied to reveal the roles played by the spin and intersublattice exchange. We find a two-step demagnetization process, similar to the well-established case of Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization rates. The behaviour is analysed using a four-temperature model, assigning different temperatures to the two manganese spin baths. Even in this strongly exchange-coupled system, the two spin reservoirs have considerably different behaviour. The half-metallic nature and strong exchange coupling of Mn$_2$Ru$_x$Ga lead to spin angular momentum conservation at much shorter time scales than found for Gd(FeCo)$_3$ which suggests that low-power, sub-picosecond switching of the net moment of Mn$_2$Ru$_x$Ga is possible.
Here we study both static and time-resolved dynamic magnetic properties of the compensated ferrimagnet from room temperature down to 10K, thus crossing the magnetic compensation temperature $T_{M}$. The behaviour is analysed with a model of a simple collinear ferrimagnet with uniaxial anisotropy and site-specific gyromagnetic ratios. We find a maximum zero-applied-field resonance frequency of $\sim$160GHz and a low intrinsic Gilbert damping $α$$\sim$0.02, making it a very attractive candidate for various spintronic applications.
High TC fully compensated ferrimagnets are potential candidates for spin transfer torque based spintronic devices. We report the structural and magnetic properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and ribbon form respectively. For Mn2V0.5Co0.5Al this turned o…
Max-Planck-Institut for Sustainable Materials（马克斯·普朗克可持续材料研究所）；Christian Doppler Laboratory for magnet design through physics informed machine learning, Department for Integrated Sensor Systems, University for Continuing Education Krems（克雷姆斯继续教育大学综合传感器系统系克里斯蒂安·多普勒物理信息机器学习磁设计实验室）；Ruhr-Universität Bochum（波鸿鲁尔大学）；Carl-von-Ossietzky University of Oldenburg（奥尔登堡卡尔·冯·奥西茨基大学）；Mercedes-Benz Turk A.S.（梅赛德斯-奔驰土耳其股份公司）；BAM Federal Institute for Materials Research and Testing（联邦材料与测试研究所）；Universitat de Barcelona（巴塞罗那大学）
Laser-induced magnetization precessional dynamics was investigated in epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, the precession frequency for which exceeded 0.5 THz and originated from the large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. The effective damping constant was approximately 0.03. The corresponding effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable to those of the similar Mn-Ga materials. The physical mechanisms for the …
Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al, Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic ferrimagnets. Such materials are of large interest for spintronics because they combine small magnetic moment with high spin polarization over a wide temperature range. We assess their thermodynamic stability by their formation enthalpies obtained from density functional theory calculations. All compounds under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect to the elemental constituents, but decompose into binary phases. …
Due to the difficulty in detecting and manipulating magnetic states of antiferromagnetic materials, studying their switching dynamics using electrical methods remains a challenging task. In this work, by employing heavy metal/rare earth-transition metal alloy bilayers, we experimentally studied current-induced domain wall dynamics in an antiferromagnetically coupled system. We show that the current-induced domain wall mobility reaches a maximum close to the angular momentum compensation. With experiment and modelling, we further reveal the internal structures of domain walls and the underlying…
We present an ab-initio study of the temperature-dependent longitudinal and anomalous Hall resistivities in the compensated collinear ferrimagnet Mn$_{1.5}$V$_{0.5}$FeAl. Its transport properties are calculated using the general fully relativistic Kubo--Bastin formalism and their temperature dependency is accounted for magnetic and structural disorder. Both scattering sources, together with the residual chemical disorder, were treated equally provided by the CPA (Coherent Potential Approximation) SPR-KKR (Spin-Polarized Relativistic Korringa-Kohn-Rostoker) method. All calculated properties sho…
Half-metallic fully compensated ferrimagnets (HM-FCFMs), a special class of half-metals exhibiting zero magnetization at absolute zero, are promising candidates for next-generation spintronics applications. For over 25 years, theoretical studies have been conducted to realize HM-FCFM materials for practical applications. Herein, we experimentally demonstrate a NiAs-type hexagonal-structured (CrFe)S compound that could serve as an HM-FCFM material. It has a half-metallic nature, with 100% spin-polarized Fermi surfaces and zero magnetization. Further, the magnetization shows a linear behavior as…
Recent experimental work on Mn2RuxGa demonstrates its potential as a compensated ferrimagnetic half-metal (CFHM).Here we present a set of high-throughput ab initio density functional theory calculations and detailed experimental characterisation, that enable us to correctly describe the nominal Mn2RuxGa thin films, in particular with regard to site-disorder and defects. We then construct models that accurately capture all the key features of the Mn-Ru-Ga system, including magnetic compensation and the spin gap at the Fermi level. We find that electronic doping is neccessary, which is achieved …
Electronic structure calculations from first-principles are employed to design some new half-metallic fully-compensated ferrimagnets (or as they are widely known half-metallic antiferromagnets) susceptible of finding applications in spintronics. Cr$_2$MnZ (Z= P, As, Sb, Bi) compounds have 24 valence electrons per unit cell and calculations show that their total spin moment is approximately zero for a wide range of lattice constants in agreement with the Slater-Pauling behavior for ideal half-metals. Simultaneously, the spin magnetic moments of Cr and Mn atoms are antiparallel and the compounds…
We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a non-monotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by us…
We report the structural, magnetic and transport properties of polycrystalline CrVTiAl alloy along with first principles calculations. It crystallizes in the LiMgPdSn type structure with lattice parameter 6.14 Å at room temperature. Absence of (111) peak along with the presence of a weak (200) peak indicates the antisite disorder of Al with Cr and V atoms. The magnetization measurements reveal a ferrimagnetic transition near 710 K and a coercive field of 100 Oe at 3 K. Very low moment and coercive field indicate fully compensated ferrimagnetism in the alloy. Temperature coefficient of resistiv…
We theoretically investigate the spin Seebeck effect (SSE) in antiferromagnets and ferrimagnets, and show that the SSE vanishes in antiferromagnets but survives in ferrimagnets even at the magnetization compensation point despite the absence of its saturation magnetization. The non-vanishing SSE in ferrimagnets stems from two non-degenerate magnons. We demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across the magnetization compensation point.
A thin Hafnium film is shown to act both as an effective diffusion barrier for manganese at a thickness of 0.7 nm, and as an effective exchange coupling layer in a sandwich structure with perpendicular magnetic anisotropy. The magnetic layers are Co$_{20}$Fe$_{60}$B$_{20}$ and the low moment ferrimagnet Mn$_2$Ru$_x$Ga (MRG). The coupling changes sign at the compensation temperature of MRG and the exchange energy reaches 0.11 mJm$^{-2}$ for the thinnest Hf interlayers. Ruthenium, the usual metal of choice for coupling ferromagnetic layers in thin film heterostructures, cannot be used with the z…
Despite the potential advantages of information storage in antiferromagnetically coupled materials, it remains unclear whether one can control the magnetic moment orientation efficiently because of the cancelled magnetic moment. Here, we report spin-orbit torque induced magnetization switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic anisotropy. Current induced switching is demonstrated in all of the studied film compositions, including those near the magnetization compensation point. The spin-orbit torque induced effective field is further quantified in the domain wall moti…
Spintronics provides an efficient platform for realizing non-volatile memory and logic devices. In these systems, data is stored in the magnetization of magnetic materials, and magnetization is switched in the writing process. In conventional spintronic devices, ferromagnetic materials are used which have a magnetization dynamics timescale of around the nanoseconds, setting a limit for the switching speed. Increasing the magnetization switching speed has been one of the challenges in spintronic research. In this work we take advantage of the ultrafast magnetization dynamics in ferrimagnetic ma…
Geometry-Driven Magnetoelectric Coupling in Two-Dimensional Compensated Ferrimagnets
School of Emerging Technology and Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China（中国科学技术大学新兴技术学院与微观物质科学国家研究中心）；State Key Laboratory of Precision and Intelligent Chemistry, School of Chemistry and Materials Science, and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), University of Science and Technology of China（中国科学技术大学精密与智能化学国家重点实验室、化学与材料科学学院及能源材料化学协同创新中心）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
Coexistence of Altermagnetic and Compensated Ferrimagnetic Motifs in a Noncollinear Multiferroic
Institute of Materials Science, Technical University of Darmstadt（达姆施塔特工业大学材料科学研究所）；Physics Department and CSMB, Humboldt-Universität zu Berlin（柏林洪堡大学物理系和CSMB）；Department of Physics, Stockholm University（斯德哥尔摩大学物理系）；Leibniz Institute for Solid State and Materials Research Dresden（德累斯顿莱布尼茨固体与材料研究所）；Department of Physics, Birla Institute of Technology Mesra（米斯拉比尔拉理工学院物理系）；Suzhou Laboratory（苏州实验室）；Würzburg-Dresden Cluster of Excellence ctd.qmat（维尔茨堡-德累斯顿卓越集群ctd.qmat）；Institute of Theoretical Physics, Technische Universität Dresden（德累斯顿工业大学理论物理研究所）；Department of Chemistry and Physics of Materials, University of Salzburg（萨尔茨堡大学材料与化学物理系）
Degeneracy and trajectory control of spin eigenmodes excited by fs-optical pulses in a nearly compensated ferrimagnet
Lomonosov Moscow State University（莫斯科国立大学）；Russian Quantum Center（俄罗斯量子中心）；Prokhorov General Physics Institute of the Russian Academy of Sciences（俄罗斯科学院普罗霍洛夫普通物理研究所）；Physics and Technology Institute, Vernadsky Crimean Federal University（维尔纳茨基克里米亚联邦大学物理与技术研究所）
One fundamental obstacle to efficient ferromagnetic spintronics is magnetic precession, which intrinsically limits the dynamics of magnetic textures, We demonstrate that the domain wall precession fully vanishes with a record mobility when the net angular momentum is compensated (TAC) in DWs driven by spin-orbit torque in a ferrimagnetic GdFeCo/Pt track. We use transverse in-plane fields to reveal the internal structure of DWs and provide a robust and parameter-free measurement of TAC. Our results highlight the mechanism of faster and more efficient dynamics in materials with multiple spin lat…
The ultrastrong coupling of (quasi-)particles has gained considerable attention due to its application potential and richness of the underlying physics. Coupling phenomena arising due to electromagnetic interactions are well explored. In magnetically ordered systems, the quantum-mechanical exchange-interaction should furthermore enable a fundamentally different coupling mechanism. Here, we report the observation of ultrastrong intralayer exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We experimentally study the spin dynamics in a gadolinium iron garnet single crystal us…
We predict a magnetic Weyl semimetal in the inverse Heusler Ti2MnAl, a compensated ferrimagnet with a vanishing net magnetic moment and a Curie temperature of over 650 K. Despite the vanishing net magnetic moment, we calculate a large intrinsic anomalous Hall effect (AHE) of about 300 S/cm. It derives from the Berry curvature distribution of the Weyl points, which are only 14 meV away from the Fermi level and isolated from trivial bands. Different from antiferromagnets Mn3X (X= Ge, Sn, Ga, Ir, Rh, and Pt), where the AHE originates from the non-collinear magnetic structure, the AHE in Ti2MnAl s…
Indian Institute of Technology Palakkad（印度理工学院帕拉卡德分校）；Indian Institute of Technology Bombay（印度理工学院孟买分校）；Indian Institute of Technology Kharagpur（印度理工学院卡拉格普尔分校）；Central University of Haryana（哈里亚纳邦中央大学）；Indian Institute of Science Education and Research, Thiruvananthapuram（印度科学教育与研究机构，特鲁万得琅校区）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）；Bhabha Atomic Research Centre（巴哈原子研究中心）；Homi Bhabha National Institute（霍米·巴巴国立研究所）
Ferromagnetic materials dominate as the magnetically active element in spintronic devices, but come with drawbacks such as large stray fields, and low operational frequencies. Compensated ferrimagnets provide an alternative as they combine the ultrafast magnetization dynamics of antiferromagnets with a ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets in spintronic devices their advantageous properties must be retained also in ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x thin films in the thickness range t = 2-20 nm were grown on h…
Beijing Institute of Technology（北京理工大学）；Beijing Key Laboratory of Quantum Matter State Control and Ultra-Precision Measurement Technology（北京量子物质态控制与超精密测量技术重点实验室）
While current-induced spin-orbit torques (SOTs) have been extensively studied in ferromagnets and antiferromagnets, ferrimagnets have been less studied. Here we report the presence of enhanced spin-orbit torques resulting from negative exchange interaction in ferrimagnets. The effective field and switching efficiency increase substantially as CoGd approaches its compensation point, giving rise to 9 times larger spin-orbit torques compared to that of non-compensated one. The macrospin modelling results also support efficient spin-orbit torques in a ferrimagnet. Our results suggest that ferrimag…
We report on a systematic investigation of the longitudinal spin Seebeck effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an in-plane magnetic easy axis with a compensation temperature (T_Comp) that decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31 nm, respectively. For all the films, the LSSE signal flips its sign below T_Comp. We demonstrate a universal scaling behavior of the temperature dependence of LSSE signal for our GdIG films around their respective T_Comp. Additionally, we demonstrate LSSE in a 31 nm GdIG film grown on a lattice…
XX'YZ equiatomic quaternary Heusler alloys (EQHA's) containing Cr, Al, and select Group IVB elements ($\textit{M}$ = Ti, Zr, Hf) and Group VB elements ($\textit{N}$ = V, Nb, Ta) were studied using state-of-the-art density functional theory to determine their effectiveness in spintronic applications. Each alloy is classified based on their spin-dependent electronic structure as a half-metal, a spin gapless semiconductor, or a spin filter material. We predict several new fully-compensated ferrimagnetic spin filter materials with small electronic gaps and large exchange splitting allowing for rob…
Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature 155 K, where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673 $Ω^{-1}.m^{-1}$ and the coercivity exceeds 9 T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216 kJ/m$^3…
The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to the magnetisation of a magnetically ordered metallic sample; in metallic ferrimagnets with chemically distinct sublattices, such as rare-earth transition-metal alloys, it depends on the difference between the sublattice contributions. Here we show that in a highly spin polarized, fully compensated ferrimagnet, where the sublattices are chemically similar, MOKE is observed even when the net moment is strictly zero. We analyse the spectral ellipsometry and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a …
Fully compensated ferrimagnetic triferroics and multistate transport in hidden-phase wurtzite MnSe monolayer
Zhoukou Normal University（周口师范学院）；Huazhong University of Science and Technology（华中科技大学）；Chongqing University of Posts and Telecommunications（重庆邮电大学）；Columbia University（哥伦比亚大学）；University of West Bohemia（西波希米亚大学）
THz magnetization dynamics is excited in ferrimagnetic thulium iron garnet with a picosecond, single-cycle magnetic field pulse and seen as a high-frequency modulation of the magneto-optical Faraday effect. Data analysis combined with numerical modelling and evaluation of the effective Lagrangian allow us to conclude that the dynamics corresponds to the exchange mode excited by Zeeman interaction of the THz field with the antiferromagnetically coupled spins. We argue that THz-pump IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to co…
Antiferromagnets and compensated ferrimagnets offer opportunities to investigate spin dynamics in the 'terahertz gap' because their resonance modes lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when compared to ferromagnets, these materials have not been extensively studied due to difficulties in exciting and detecting the high-frequency spin dynamics, especially in thin films. Here we show that spin-obit torque in a single layer of the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably efficient at generating spin-orbit fields μ_0H_eff, which approach 0…
Ferrimagnets containing several partially compensated magnetic sublattices are considered the most promising materials for all-optical data storage and for ultrafast communications based on spin waves. There are two magnetic phases of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics in ferrimagnets has been studied mostly in the collinear state without paying much attention to the kind of the magnetic phase. Here we investigate laser induced ultrafast spin dynamics in a rare-earth iron garnet film in the noncollinear phase as well. We identify a crucial influence of …
Compensated ferrimagnets, like antiferromagnets, show no net magnetization but their transport and magneto-optic properties resemble those of ferromagnets, thereby creating opportunities for applications in high-frequency spintronics and low-energy loss communications. Here we study the modification the noncollinear ferrimagnetic spin structure of Mn4N by a variety of metallic substitutions Z (Z = Cu - Ge and Ag - Sn) to achieve compensation at room temperature. The noncollinear frustrated 2.35 Bohr magneton moments of Mn on 3c sites of the (111) kagome planes tilt about 20 degree out-of-plane…
