Spin Reorientation in Antiferromagnetic MnPd 5 Se with an Anti-CeCoIn 5 Structure Type
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99 GENERAL AND MISCELLANEOUS↗
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Toward tunable quantum transport and novel magnetic states in Eu 1– x Sr x Mn 1– z Sb 2 ( z < 0.05)
Magnetic semimetals are very promising for potential applications in novel spintronic devices. Nevertheless, realizing tunable topological states with magnetism in a controllable way is challenging. Here, we report novel magnetic states and the tunability of topological semimetallic states through the control of Eu spin reorientation in Eu 1–x Sr x Mn 1–z Sb 2 . Increasing the Sr concentration in this system induces a surprising reorientation of noncollinear Eu spins to the Mn moment direction and topological semimetallic behavior. The Eu spin reorientations to distinct collinear antiferromagnetic orders are also driven by the temperature/magnetic field and are coupled to the transport properties of the relativistic fermions generated by the 2D Sb layers. These results suggest that nonmagnetic element doping at the rare earth element site may be an effective strategy for generating topological electronic states and new magnetic states in layered compounds involving spatially separated rare earth and transition metal layers.
36 MATERIALS SCIENCE↗
Study on the magnetothermal properties of the D y 1 - x T b x A l 2 series of compounds
Here, in this work, we developed a theoretical model Hamiltonian, in the mean field approximation, to describe the magnetic and magnetocaloric behavior of the series of compounds Dy 1-x Tb x Al 2 (x = 0.00, 0.15, 0.25, 0.30, 0.35, 0.40 and 0.75). We adjusted the exchange parameters λ DyDy , λ TbTb , and λ DyTb to obtain the spin reorientation temperatures (T SR ) and the critical temperature (T C ) for each compound in the series. The results obtained by the Hamiltonian model agree satisfactorily with the experimental results. The heat capacity curves with and without an applied magnetic field, adiabatic temperature variation and isothermal entropy variation were modeled and compared with the experimental data. As the experimental results show, our model was also able to reproduce the change in the spin reorientation process: a first order spin reorientation transition appears for concentrations x = 0.15, 0.25, 0.30, 0.35, and no spin reorientation transitions after x = 0.40.
36 MATERIALS SCIENCE↗
Magnetic transitions and magnetocaloric effect of Gd 4 Nd 1 Si 2 Ge 2
In this work, crystal structure and magnetic properties of the quaternary Gd 4 Nd 1 Si 2 Ge 2 compound were investigated using synchrotron X-ray diffraction and magnetic measurements. The compound crystallized into an orthorhombic structure in the temperature range 200-300 K. In zero field cooling, the compound undergoes a spin reorientation following a ferromagnetic-like transition at 276 K. The spin reorientation is hinted at by nonlinear changes of lattice parameters but is suppressed in a high magnetic field of 6 T. Magnetic measurements revealed a magnetocaloric effect with a high relative cooling power. It is suggested that Nd substitution for Gd enlarges magnetic anisotropy and induces a canted spin structure.
36 MATERIALS SCIENCE↗
Introducing the monoclinic polymorph of the honeycomb magnet Na 2 Co 2 TeO 6
Recent theoretical studies have suggested that the low-energy Hamiltonian of honeycomb cobaltate systems could be dominated by anisotropic Kitaev interactions. Motivated by the theory, a honeycomb layered material Na 2 Co 2 TeO 6 with a hexagonal unit cell has been studied and found to exhibit antiferromagnetic (AFM) ordering at 27 K with two spin reorientation transitions at 15 and 5 K. Here we report a monoclinic polymorph of Na 2 Co 2 TeO 6 , also with honeycomb layered structure but with a single AFM transition at 9.6 K and without spin reorientation transitions at lower temperatures. Here, using neutron diffraction, we identify an in-plane zigzag AFM order in the ground state with the spins canted out of the honeycomb planes and ferromagnetically coupled between them. The zigzag order is suppressed by a magnetic field of 6T. The lower critical temperature and field, positive Curie-Weiss temperature, and out-of-plane canting of spins in the monoclinic Na 2 Co 2 TeO 6 suggest enhanced frustration in this polymorph compared to the hexagonal one.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Single-Crystal Growth and Room-Temperature Magnetocaloric Effect of X-Type Hexaferrite Sr 2 Co 2 Fe 28 O 46
X-type hexaferrites have been receiving considerable attention due to their promising applications in many magnetic-electronic fields. However, the growth of single-crystal X-type hexaferrite is still a challenge. Herein we reported, for the first time, the preparation of single crystal X-type hexaferrite Sr 2 Co 2 Fe 28 O 46 (Sr 2 Co 2 X) with high-quality and large size using floating-zone method with laser as the heating source. The crystals show rhombohedral symmetry with space group of R-3m (No. 166, a = 5.8935(1) Å and c = 83.7438(17) Å). Co 2+ and Fe 3+ oxidation states were confirmed by the X-ray absorption near-edge spectroscopy. The prepared Sr 2 Co 2 X exhibits a spin reorientation transition from easy-cone to easy-axis at T 2 of 343 K and a ferrimagnetism–paramagnetism transition at Curie temperature (TC) of ~743 K. The spin reorientation transition was accompanied by magnetocaloric effect (MCE). Both conventional and inverse MCEs were observed near T 2 with a magnetic field applied along the c-axis. The maximum value of the magnetic entropy change along the c-axis was evaluated to be 1.1 J/kg·K for a magnetic field change of 5 T.
36 MATERIALS SCIENCE↗
Tunable competing magnetic anisotropies and spin reconfigurations in ferrimagnetic Fe 100– x Gd x alloy films
Here, we report a comprehensive study of the temperature evolution of in-plane (IP) and out-of-plane (OOP) effective magnetic anisotropies in compensated ferrimagnetic Fe 100– x Gd x alloy films by employing direct current magnetometry and radiofrequency (RF) transverse susceptibility (TS) measurements. We suggest that our Fe 100– x Gd x system is chemically inhomogeneous and phase segregates into Fe- and Gd-enriched regions. Our IP and OOP magnetometry results indicate that the system undergoes a temperature-driven transformation from an IP-spin-configuration-dominated state to an OOP-spin-configuration-dominated state below a certain temperature (spin reorientation temperature). A two-step reversal behavior emerges in the OOP $\textit{M(H)}$ loop near compensation, which we attribute to the sequential magnetization reversals of Fe- and Gd-enriched domains. Field-induced spin-flop transitions were also observed near the compensation. Our RF TS measurements indicate that the effective magnetic anisotropy for the OOP configuration dominates over that for the IP configuration below a certain spin reorientation temperature. Both IP and OOP anisotropy fields determined from our TS measurement exhibit a minimum around the compensation temperature, which has been explained in the framework of the Stoner-Wohlfarth model.
36 MATERIALS SCIENCE↗
Giant Doping Response of Magnetic Anisotropy in MnTe
Developing simple ways to control spin states in spintronic devices is a crucial step towards increasing their functionality. MnTe is a room-temperature antiferromagnet with promising spintronic properties, including for thermospintronics and magnon-based devices. Here, we show that, in MnTe, less than 1% Li is sufficient to produce a dramatic spin reorientation as observed by neutron diffraction. The behavior of the 0001 magnetic Bragg peak reveals a significant reorientation of the Mn spins from planar in the pure material to almost completely axial with minimal Li doping. Temperature dependence of the magnetic peaks in Li-doped samples indicates that axial spins shift back to planar suddenly upon approaching the Néel temperature (T N = 307 K). Density functional theory calculations support the idea that a shift in the Fermi level caused by doping is responsible for switching the material between two competing magnetic ground states. These results pave the way for developing easy switching of magnetic states in functional materials such as spintronic devices and topological insulators.
36 MATERIALS SCIENCE↗
Zero thermal expansion in non-stoichiometric and single-phase (Hf,Nb)Fe 2.5 alloy
Zero thermal expansion (ZTE) alloys are dimensionally stable under the influence of heat, which is critical in high-precision components but remains rare among single phase materials. This work reports a single phase and nearly isotropic ZTE alloy (Hf 0.8 Nb 0.2 )Fe 2.5 over a wide temperature range of 5–460 K ($α_l ≈ 1.07 × 10^{–6} K^{–1}$) via non-stoichiometric regulation. The introduction of excess Fe breaks the dual-phase nature of parent alloy, extends the magnetic ordering temperature, and induces a spin reorientation. Further, the evolution of magnetic structure versus temperature gives rise to the ZTE behavior. The design concept of changing the internal magnetic interaction through non-stoichiometric regulation provides support for the discovery of novel ZTE materials.
36 MATERIALS SCIENCE↗
Correlation-driven eightfold magnetic anisotropy in a two-dimensional oxide monolayer
Engineering magnetic anisotropy in two-dimensional systems has enormous scientific and technological implications. The uniaxial anisotropy universally exhibited by two-dimensional magnets has only two stable spin directions, demanding 180° spin switching between states. We demonstrate a previously unobserved eightfold anisotropy in magnetic SrRuO 3 monolayers by inducing a spin reorientation in (SrRuO 3 ) 1 /(SrTiO 3 ) N superlattices, in which the magnetic easy axis of Ru spins is transformed from uniaxial $\langle 001 \rangle$ direction ( N < 3) to eightfold $\langle 111 \rangle$ directions ( N ≥ 3). This eightfold anisotropy enables 71° and 109° spin switching in SrRuO 3 monolayers, analogous to 71° and 109° polarization switching in ferroelectric BiFeO 3 . First-principle calculations reveal that increasing the SrTiO 3 layer thickness induces an emergent correlation-driven orbital ordering, tuning spin-orbit interactions and reorienting the SrRuO 3 monolayer easy axis. Our work demonstrates that correlation effects can be exploited to substantially change spin-orbit interactions, stabilizing unprecedented properties in two-dimensional magnets and opening rich opportunities for low-power, multistate device applications.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Tunable structural and magnetic properties of NiAs-type Mn x Sb (1.00≤x≤1.30) compounds
Mn-based alloys can exhibit a variety of magnetic properties related to their tunable exchange interactions. Here, structural and magnetic properties of hexagonal NiAs-type Mn x Sb (1.00≤x≤1.30) compounds are studied with a combination of X-ray diffraction, neutron diffraction, and magnetic measurements. It is found that the magnetization, Curie temperature, and magnetocrystalline anisotropy of Mn x Sb compounds can be tuned by controlling Mn concentration and doping at interstitial (2d) sites. With increasing Mn concentration, magnetic moments of Mn atoms decrease and deviate gradually from the ab-plane to the c-axis for 1.20≤x≤1.22 at room temperature, which leads to a decrease of the Curie temperature T c and the spin reorientation temperature T SR . By doping with nonmagnetic elements, a substantial room-temperature magnetocaloric effect without magnetic hysteresis was achieved for Mn 1.12 Zr 0.1 Sb compound, which is highly beneficial to the practical magnetic refrigeration application.
36 MATERIALS SCIENCE↗
Cooperative spin coupling in PrFeO3
A transition from crystal-field to spin wave excitations has been experimentally observed in PrFeO3 using inelastic neutron scattering. Theoretical modeling with density functional theory and the mean field random phase approximation successfully reproduces the experimental observations and allows extraction of the values for the various exchange interactions. The study reveals that the strong coupling between the two magnetic sublattices of Pr and Fe is the fundamental mechanism underlying the low-temperature Pr magnetism. This coupling, analogous to the Dicke cooperative interaction between atoms and photons, polarizes the Pr moments, enhances the Pr-Pr interactions, and contributes to the formation of a quasidoublet, leading to the transition from single-particle to collective excitations within the Pr sublattice. Furthermore, this coupling induces spin reorientation on the Fe sublattice. The manipulation of magnetic moments via spin waves is achievable through the coupling between different magnetic sublattices in a bulk material containing multiple magnetic ions.
Garlea, Vasile [ORNL] (ORCID:0000000253227271)↗
In-plane Néel wall chirality and orientation of interfacial Dzyaloshinskii-Moriya vector in magnetic films
The interfacial Dzyaloshinskii-Moriya interaction (DMI) is of great interest as it can stabilize chiral spin structures in thin films. Experiments verifying the orientation of the interfacial DMI vector remain rare, in part due to the difficulty of separating vector components of DMI. In this study, Fe/Ni bilayers and Co/Ni multilayers were deposited epitaxially onto Cu(001) and Pt(111) substrates, respectively. By tailoring the effective anisotropy, spin reorientation transitions (SRTs) are employed to probe the orientation of the DMI vector by measuring the spin structure of domain walls on both sides of the SRTs. In our results, the interfacial DMI is found to be sufficiently strong to stabilize chiral Néel walls in the out-of-plane magnetized regimes, while achiral Néel walls are observed in the in-plane magnetized regimes. Furthermore, these findings experimentally confirm that the out-of-plane component of the DMI vector is insignificant in these fcc(001) and fcc(111) oriented interfaces, even in the presence of atomic steps.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Anomalous Electrical Transport in the Kagome Magnet YbFe 6 Ge 6
Two-dimensional (2D) kagome metals offer a unique platform for exploring electron correlation phenomena derived from quantum many-body effects. Here, in this study, we report a combined study of electrical magnetotransport and neutron scattering on YbFe 6 Ge 6 , where the Fe moments in the 2D kagome layers exhibit an 𝐴-type collinear antiferromagnetic order below 𝑇 N ≈ 500 K. Interactions between the Fe ions in the layers and the localized Yb magnetic ions in between reorient the 𝑐-axis-aligned Fe moments to the kagome plane below 𝑇 SR ≈ 63 K. Our magnetotransport measurements show an intriguing anomalous Hall effect (AHE) that emerges in the spin-reorientated collinear state, accompanied by the closing of the spin anisotropy gap as revealed from inelastic neutron scattering. The gapless spin excitations and the Yb-Fe interaction are able to support a dynamic scalar spin chirality, which explains the observed AHE. Therefore, our Letter demonstrates that spin fluctuations may provide an additional scattering channel for the conduction electrons and give rise to AHE even in a collinear antiferromagnet.
Yao, Weiliang [Rice Univ., Houston, TX (United Sta↗
Complex magnetic properties in the mixed 4 f - 5 d double perovskite iridates X 2 ZnIrO 6 ( X = Nd , Sm , Eu , Gd )
Here in this paper, we report on the synthesis and magnetic properties of a series of double perovskites Ln 2 ZnIrO 6 with Ln = Nd, Sm, Eu, Gd. These compounds present examples of the rare case of double perovskites (general formula A 2 BB'O6) with a magnetic 4ƒ-ion on the A site in combination with the strongly spin-orbit coupled 5d transition-metal ion Ir 4+ on the B sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd 2 ZnIrO 6 and Eu 2 ZnIrO 6 show ferrimagnetic or canted antiferromagnetic order below T N = 23 and 12 K, respectively. Sm 2 ZnIrO 6 orders antiferromagnetically at T N = 13 K. Nd 2 ZnIrO 6 exhibits more complex magnetic properties with a strong field dependence ranging from a two-step spin reorientation at μ 0 H = 0.01 T to an antiferromagnetic ground state at intermediate external fields to a spin-flop phase for 0H ≥ 4 T. This unique behavior suggests an interesting interplay between Nd 3+ and Ir 4+ . To further shed light on the relevant magnetic interaction, the zero-field magnetic ground state of Nd 2 ZnIrO 6 is examined via neutron powder diffraction. In general, the magnetic properties of Ln 2 ZnIrO 6 hint towards a substantial contribution of the rare-earth ions and a significant correlation between 5d and 4ƒ magnetism.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Reversible hydrogen control of antiferromagnetic anisotropy in α-Fe 2 O 3
Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe 2 O 3 (haematite) - now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe 2 O 3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe 2 O 3 .
36 MATERIALS SCIENCE↗
Crystal growth and magnetic structure of ternary silicide Eu Pd 3 Si 2
The hexagonal CaCu 5 –type structure (P6/mmm) is the prototype for more than 100 ternary borides, gallides, and silicides, with general stoichiometry of RTM 3 X 2 (R=lanthanide/alkaline earth; TM=transition metal; X=B, Ga, Si, Ge). Here we report the synthesis, crystal structure, and bulk magnetic properties of polycrystalline and single crystal samples of EuPd 3 Si 2 and its nonmagnetic analog SrPd 3 Si 2 . Both compounds crystallize in the orthorhombic space group symmetry Imma (no. 74, Z = 2, oI12) displaying pseudohexagonal symmetry. Ferromagnetic (FM) order of Eu 2+ at T C1 =78K and a spin-reorientation transition at T C2 =5K appear as distinctive features in bulk magnetization, specific heat, and resistivity/resistance measurements. Neutron powder diffraction measurements on EuPd 3 Si 2 confirm FM order of the Eu 2+ spins below T C1 , with the spins aligned along the a axis below T C2 . Electronic band structure calculations corroborate the crystal structure and the FM state for EuPd 3 Si 2 , with a Pd d–band polarization in the same direction as the Eu 4f polarization, enhancing the observed spin moment.
36 MATERIALS SCIENCE↗
Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI 3
We show that Van der Waals magnet VI 3 demonstrates intriguing magnetic properties that render it great for use in various applications. However, its microscopic magnetic structure has not been determined yet. Here, we report neutron diffraction and susceptibility measurements in VI 3 that revealed a ferromagnetic order with the moment direction tilted from the c-axis by ~36° at 4 K. A spin reorientation accompanied by a structure distortion within the honeycomb plane is observed, before the magnetic order completely disappears at $T_C$ = 50 K. The refined magnetic moment of ~1.3$μ_B$ at 4 K is much lower than the fully ordered spin moment of 2$μ_B$/V 3+ , suggesting the presence of a considerable orbital moment antiparallel to the spin moment and strong spin–orbit coupling in VI 3 . This results in strong magnetoelastic interactions that make the magnetic properties of VI 3 easily tunable via strain and pressure.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗