Field-induced Spin-flop Transition Research Articles

Deconvolution of X-ray natural and magnetic circular dichroism in chiral Dy-ferroborate.

Structural chirality and magnetism, when intertwined, can have profound implications on materials properties. Using X-ray imaging and spectroscopic measurements that leverage the natural and magnetic circular dichroic effects present in magnetized chiral crystal structures, we probe the interplay between chirality and magnetism across the field-induced spin-flop transition of Dy ferroborate, ( ) . Deconvolution of natural and magnetic circular dichroic signals at the Fe K and Dy L absorption edges of the non-centrosymmetric structure was enabled by use of tunable temperature and magnetic field, providing access to element-specific magnetic information across the spin-flop transition. The magnetic response of Fe and Dy sublattices was found to be independent of domain chirality. The chiral domains were robust against both the (chirality preserving) R32 to P3 21/P3 21 structural phase transition at 280 K, and application of magnetic field up to 4 Tesla. A third flavor of X-ray dichroism, magneto-chiral dichroism, was not detected within the accuracy of our measurements. The absence of significant Fe magnetization along the screw, c-axis for the magnetic field strength used in this study, together with non-linear coupling of magnetic field to electric polarization across the spin-flop transition, may hinder observation of magneto-chiral dichroic effects in this system.

Crystal growth of CeMn0.85Sb2: Absence of magnetic order of Ce-sublattice

Single crystals of CeMn0.85Sb2 have been successfully synthesized by using the Bi as flux. Analysis of single crystal x-ray diffraction data confirms that CeMn0.85Sb2 crystallizes in the HfCuSi2-type structure with the space group P4/nmm (No. 129). In the case of H||c, CeMn0.85Sb2 displays a robust antiferromagnetic transition at ∼160 K for Mn-sublattice, and there is no sign of magnetic order regarding Ce-sublattice. In the case of H ⊥ c, the Mn-sublattice shows signs of magnetic order at 160 K and 116 K, indicating a possible spin reorientation. There is no sign of magnetic order for the Ce-sublattice either, but, alternating current magnetic susceptibility measurements reveal a spin glass state below 18 K in the case of H ⊥ c. Isothermal magnetization curves measured below magnetic order with H ⊥ c show saturation and even large hysteresis at 2 K, indicating the presence of a ferromagnetic component. In addition, a field-induced spin-flop transition is observed in the case of H ⊥ c, indicating a field-induced spin reorientation of Mn spins. Electrical resistivity measurements indicate a metallic nature for CeMn0.85Sb2 and large anisotropy which is consistent with its quasi-two-dimensional layered structure.

Two Magnetic Orderings and a Spin-Flop Transition in Mixed Valence Compound Mn3O(SeO3)3.

A mixed-valence manganese selenite, Mn3O(SeO3)3, was successfully synthesized using a conventional hydrothermal method. The three-dimensional framework of this compound is composed of an MnO6 octahedra and an SeO3 trigonal pyramid. The magnetic topological arrangement of manganese ions shows a three-dimensional framework formed by the intersection of octa-kagomé spin sublattices and staircase-kagomé spin sublattices. Susceptibility, magnetization and heat capacity measurements confirm that Mn3O(SeO3)3 exhibits two successive long-range antiferromagnetic orderings with TN1~4.5 K and TN2~45 K and a field-induced spin–flop transition at a critical field of 4.5 T at low temperature.

Robust antiferromagnetism inY2Co3

We report on a solution-growth based method to synthesise single crystals of Y$_2$Co$_3$ and on its structural and magnetic properties. We find that Y$_2$Co$_3$ crystallizes in the La2Ni3-type orthorhombic structure with space group Cmce (No. 64), with Co forming distorted kagome lattices. Y$_2$Co$_3$ orders antiferromagnetically below $T_N$ = 252 K. Magnetization measurements reveal that the moments are primarily aligned along the b axis with evidence for some canting. Band-structure calculations indicate that ferromagnetic and antiferromagnetic orders are nearly degenerate, at odds with experimental results. Magnetization measurements under pressure up to 1 GPa reveal that the N/'eel temperature decreases with the slope of -1.69 K/GPa. We observe a field-induced spin-flop transition in the magnetization measurements at 1.5 K and 21 T with magnetic field along the b direction. The magnetization is not saturated up to 35 T, indicating that the antiferromagnetic ordering in Y$_2$Co$_3$ is quite robust, which is surprising for such a Co-rich intermetallic.

Large magnetic anisotropy and field-induced spin-flop transition in Fe2(TeO3)2(SO4)·3H2O single crystals

Single crystals of Fe2(TeO3)2(SO4)·3H2O with an alternating spin-chain structure are successfully grown by a hydrothermal method. Magnetic and heat capacity measurements show that this compound possesses a short-range antiferromagetic order at ~55 K and a long-range antiferromagetic order at 32.5 K. A large magnetic anisotropy with magnetization easy c-axis is observed, in which a weak ferromagnetic component is observed along the a- and b-axes, while a spin flop transition is observed at applied field along the c-axis. Also, the magnetic anisotropy energy at 2 K is estimated to be 4.78(3) × 108 ergs/cm3. Such magnetic anisotropy may be due to a strong nonsymmetric distortion in the FeO6 octahedra.

High-Pressure Synthesis of Double Perovskite Ba2NiIrO6: In Search of a Ferromagnetic Insulator.

Double perovskite oxides with d8-d3 electronic configurations are expected to be ferromagnetic from the Goodenough-Kanamori rules, such as ferromagnetic La2NiMnO6. In search of new ferromagnetic insulators, double perovskite Ba2NiIrO6 was successfully synthesized by high-pressure and high-temperature methods (8 GPa and 1573 K). Ba2NiIrO6 crystallizes in a cubic double perovskite structure (space group: Fm3̅m), with an ordered arrangement of NiO6 and IrO6 octahedra. X-ray absorption near-edge spectroscopy confirms the nominal Ni(II) and Ir(VI) valence states. Ba2NiIrO6 displays an antiferromagnetic order at 51 K. The positive Weiss temperature, however, indicates that ferromagnetic interactions are dominant. Isothermal magnetization curves at low temperatures support a field-induced spin-flop transition.

Efficient Spin Torques in Antiferromagnetic CoO/Pt Quantified by Comparing Field- and Current-Induced Switching.

We achieve current-induced switching in collinear insulating antiferromagnetic CoO/Pt, with fourfold in-plane magnetic anisotropy. This is measured electrically by spin Hall magnetoresistance and confirmed by the magnetic field-induced spin-flop transition of the CoO layer. By applying current pulses and magnetic fields, we quantify the efficiency of the acting current-induced torques and estimate a current-field equivalence ratio of 4×10^{-11} T A^{-1} m^{2}. The Néel vector final state (n⊥j) is in line with a thermomagnetoelastic switching mechanism for a negative magnetoelastic constant of the CoO.

Spin Seebeck effect near the antiferromagnetic spin-flop transition

We develop a low-temperature, long-wavelength theory for the interfacial spin Seebeck effect (SSE) in easy-axis antiferromagnets. The field-induced spin-flop (SF) transition of N\'eel order is associated with a qualitative change in SSE behavior: Below SF, there are two spin carriers with opposite magnetic moments, with the carriers polarized along the field forming a majority magnon band. Above SF, the low-energy, ferromagnetic-like mode has magnetic moment opposite the field. This results in a sign change of the SSE across SF, which agrees with recent measurements on Cr$_2$O$_3$/Pt and Cr$_2$O$_3$/Ta devices [Li $\textit{et al.,}$ $\textit{Nature}$ $\textbf{578,}$ 70 (2020)]. In our theory, SSE is due to a N\'eel spin current below SF and a magnetic spin current above SF. Using the ratio of the associated N\'eel to magnetic spin-mixing conductances as a single constant fitting parameter, we reproduce the field dependence of the experimental data and partially the temperature dependence of the relative SSE jump across SF.

Intrinsic role of ↑↑↓↓-type magnetic structure on magnetoelectric coupling in Y2NiMnO6

Structure-property correlations are a major challenge in the investigation of magnetoelectric multiferroic materials. We have systematically investigated the intrinsic role of ↑↑↓↓-type order in magnetoelectric coupling in Y2NiMnO6. The calculated results reveal that the ferromagnetic (FM) order is the magnetic structure of the ground state and the total energy of ↑↑↓↓-type order is close to that of the FM order. The electric polarization is calculated to be 0.78 μC/cm2 along the crystallographic b-axis for UNi = UMn = 3 eV. In addition to the exchange-striction mechanism, a more noticeable contribution from redistribution of polarized charge is found in our study. Magnetic hysteresis loops show the ferromagnetism in Y2NiMnO6, which can be explained by magnetic field-induced spin flop transition from the E-type to FM order. Our DFT + U theoretical investigations also proposed a switching adiabatic path of magnetoelectric coupling, in which the 180° reverse of electric polarization is driven by rotation of spins.

Gd2Te3: an antiferromagnetic semimetal

We report high-precision magnetization (), magnetic susceptibility (), specific heat (Cp (T, H)) and ‘zero-field’ electrical resistivity, , data taken on Gd2Te3 single crystal over wide ranges of temperature and magnetic field (H), with either -axis or -plane. and unambiguously establish that the b-axis is the easy direction of magnetization whereas any direction in the ac-plane is a hard direction. The -type anomaly in ‘zero-field’ specific heat, Cp (T, H = 0), and an abrupt drop in (characteristic of the paramagnetic (PM) — antiferromagnetic (AFM) phase transition) are observed at the Néel temperature, K. and Cp (T,H) clearly demonstrate that shifts to lower temperatures with increasing H irrespective of whether H points in the easy or hard direction. When , the isotherms at temperatures in the range 2.5 K K reveal the existence of a field-induced spin-flop (SF) transition at fields 4.0 T 4.5 T. The first principles electronic band structure and density of states calculations, based on the density functional theory, correctly predict an AFM ground state (stabilized primarily by the 4f Gd3+ – 5p Te2−– 4f Gd3+ superexchange interactions) and the observed semi-metallic behavior for the Gd2Te3 compound. Moreover, these calculations yield the values for the ordered magnetic moment per Gd atom at T = 0, mJ mol−1 K−2 for the Sommerfeld coefficient for the electronic specific heat contribution and K for the Curie–Weiss temperature, respectively. These theoretical estimates conform well with the corresponding experimental values , mJ mol−1 K−2 and K.

Antiferromagnetic Kondo lattice compound CePt3P

A new ternary platinum phosphide CePt3P was synthesized and characterized by means of magnetic, thermodynamic and transport measurements. The compound crystallizes in an antiperovskite tetragonal structure similar to that in the canonical family of platinum-based superconductors APt3P (A = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion superconductor CePt3Si. In contrast to all the superconducting counterparts, however, no superconductivity is observed in CePt3P down to 0.5 K. Instead, CePt3P displays a coexistence of antiferromagnetic ordering, Kondo effect and crystalline electric field effect. A field-induced spin-flop transition is observed below the magnetic ordering temperature TN1 of 3.0 K while the Kondo temperature is of similar magnitude as TN1. The obtained Sommerfeld coefficient of electronic specific heat is γCe = 86 mJ/mol·K2 indicating that CePt3P is a moderately correlated antiferromagnetic Kondo lattice compound.

Co-ligand tuned pyrimidine-2-carboxylate Mn(ii) complexes from a 2D 63 layer to an interpenetrated srs-net.

A 63 2D layer complex [Mn3Cl3(L3)]n·H2O (1) (L = pyrimidine-2-carboxylate) was obtained by assembling 2-cyanopyrimidine and manganese chloride, in which the L ligands were generated in situ. In 1 six-membered Mn rings were constructed from MnII ions and L ligands, which were connected to each other by double chloride anions affording a 2D layer. When the chloride anions in 1 were substituted partly by formate, [Mn4Cl3L4(HCO2)]n (2) was obtained. In 2, the L ligands bridge MnII to give a 1D chain, which was further connected by the double chloride anions and Cl/formate bridges to form a two-fold interpenetrated srs-net. Interestingly, 2 exhibits an obvious SHG response of approximately 0.8 times that of KDP. Furthermore, 2 is an antiferromagnet with a field induced spin flop transition.

Magnetic diversity in three-dimensional two-fold-interpenetrated structures: a story of two compounds.

A magnetostructural correlation has been carried out for two newly synthesized two-fold-interpenetrated three-dimensional structures. Compound 1, denoted as [Ni(L1)(L2)]·2DMF (where L1 is 1,4-benzene-dicarboxylic acid (BDC), L2 is 4,4-oxybis-(N-(pyridine-4-yl)benzamide), and DMF is N,N'-dimethylformamide), was observed to have a three-dimensional structure with two-fold interpenetration. Compound 2, denoted as [Co(L3)(L2)]·2DMF (where L3 is 2,5-thiopehene-dicarboxylic acid (TDC)), was also observed to display a three-dimensional structure with an architecture identical to that of compound 1. Both compounds were well characterised using several techniques including single-crystal X-ray diffraction, powder X-ray diffraction, TGA, and IR. Magnetism and specific heat measurements of compound 1 revealed a canted-antiferromagnetic transition at TN ≈ 4 K and a field-induced spin-flop transition at a relatively low field strength. These exotic features were attributed to the low-symmetry space group P(1[combining macron]) and single-ion anisotropy of the Ni2+ sub-lattice. In contrast, compound 2 was found to be weakly antiferromagnetic in nature with a negligible interaction between the magnetic Co2+ ions.

Breaking of 1D magnetism in a spin-1 chain antiferromagnet Ni2V2O7: ESR and first-principles studies

We report the breaking of one-dimensional (1D) magnetism in a spin-1 chain antiferromagnet Ni2V2O7. First, basic structure and magnetization data are presented, showing that the compound is ordered at $ T_{N}=7$ K and a field-induced spin-flop transition occurs at $ H_{sf}=2.8$ T. Second, high-field electronic spin resonance (ESR) data demonstrate antiferromagnetic (AFM) resonance modes below T N, which can be well understood by conventional AFM resonance theory with uniaxial anisotropy. Third, the first-principles calculations based on density function theory reveal a much larger interchain AFM interaction than the intrachain couplings. Combining with all these results, we can see that Ni2V2O7 is not a 1D antiferromagnet, although it is a skew chain from the viewpoint of crystallographic structure.

Spin-flop transition and magnetic phase diagram inCaCo2As2revealed by torque measurements

The magnetic properties of CaCo$_{2}$As$_{2}$ single crystal was systematically studied by using dc magnetization and magnetic torque measurements. A paramagnetic to antiferromagnetic transition occurs at $T_N$ = 74 K with Co spins being aligned parallel to the c axis. For $H \parallel c$, a field-induced spin-flop transition was observed below $T_N$ and a magnetic transition from antiferromagnetic to paramagnetic was inferred from the detailed analysis of magnetization and magnetic torque. Finally, we summarize the magnetic phase diagram of CaCo$_{2}$As$_{2}$ based on our results in the \emph{H-T} plane.

Antiferromagnetic ordering in spin-chain multiferroic Gd2BaNiO5 studied by electronic spin resonance

High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < TN = 55 K) of spin-chain multiferroic Gd2BaNiO5. The spin reorientation at TSR = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.

Two-step antiferromagnetic transition and moderate triangular frustration inLi2Co(WO4)2

We present a detailed investigation of the magnetic properties of the spin-$\frac{3}{2}$ system ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ by means of magnetic susceptibility and specific heat. Our experimental results show that in ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ short-range antiferromagnetic (AFM) correlations appear near ${\ensuremath{\chi}}_{\mathrm{max}}\ensuremath{\sim}11\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and two successive long-range AFM phase transitions are observed at ${T}_{N1}\ensuremath{\sim}9$ and ${T}_{N2}\ensuremath{\sim}7\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The frustration factor $|\ensuremath{\Theta}|/{T}_{N1}\ensuremath{\sim}3$ indicates that the system is moderately frustrated, which is identifiable by the broken triangular symmetry within both $ab$ and $bc$ planes for the triclinic crystal structure. The magnetic isotherm at temperatures below ${T}_{N2}$ shows a field-induced spin-flop transition, and a complete $H\text{\ensuremath{-}}T$ phase diagram for the two-step AFM system is mapped. Ab initio band-structure calculations suggest that the strongest exchange coupling does not correspond to the shortest Co-Co distance along the $a$ axis but rather along the diagonal direction through a Co-O-W-O-Co supersuperexchange path within the $bc$ plane.

Field-induced spin-flop transition in a one-dimensional chain of MnV2O6

The magnetic behaviors of one-dimensional chain-structured MnV2O6 single crystals are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements. Heat capacity data show a λ-like anomaly at the Neel temperature T N = 18.3 K due to the onset of an antiferromagnetic long-range order. The magnetic entropy calculated at temperature above T N gives an indication of possible short-range magnetic ordering in our low-dimensional chain compound. The magnetic susceptibility follows the conventional antiferromagnetic feature with a positive Curie-Weiss temperature. At temperature below T N , the crystallographic b-axis, which is also parallel to the chain direction, becomes a magnetic easy axis, giving MnV2O6 a strong anisotropy in the susceptibility. Moreover, we observe that the external magnetic field can control the spin direction through the field-induced spin-flop transition as a result of competition between the magnetic energy and the crystalline anisotropy.

Transition metal phosphite complexes: from one-dimensional chain, two-dimensional sheet, to three-dimensional architecture with unusual magnetic properties

Four new compounds, [Ni(HPO3)(4,4′-bpy)(H2O)3]·4H2O (1), [Co2(HPO3)2(4,4′-bpy)2(H2O)6]·9H2O (2), [Zn(HPO3)(4,4′-bpy)0.5]·H2O (3), and [Co3(PO3)2(4,4′-bpy)3(H2O)6]·3H2O (4), have been synthesized. Compounds 1 and 2 are linear chains and isostructural except for the distinction of the metal ion and the number of lattice water molecules. Compound 3 consists of a 2D sheet structure. Compound 4 is a 3D magnetic porous material with 1D channels along the c axis. Magnetic measurements indicate that compound 1 shows paramagnetic behavior, while compound 2 displays antiferromagnetic behavior. Compound 4 exhibits antiferromagnetism with a pronounced field-induced spin–flop transition. A critical field of 3 T at 2.0 K is determined from the derivative dM/dH curve. Meanwhile, compound 4 shows a strong spin frustration arising from the geometric frustration in the kagome lattice. The dehydrated phase 4a displays a characteristic of N2 adsorption with type II isotherm. We performed detailed magnetic measurements for 4a, which exhibits quite different magnetic properties from 4. Compound 4a displays a ferrimagnetic behavior with a lower transition field of 0.2 T, and a weaker spin frustration.

Y3MnAu5: Three Distinctive d-Metal Functions in an Intergrown Cluster Phase

The new Y(3)MnAu(5) intermetallic phase is obtained from the arc-melted elements in virtually quantitative yields after annealing at 1000 °C for ~3 d. Its remarkable structure [rhombohedral, R3, Z = 6; a = 8.489(1) Å, c = 18.144(2) Å] consists of a 2:1 cubic-close-packed intergrowth between edge-shared Mn-centered Au rhombohedra (Mn@Au(8)) with gold-centered antiprismatic (Au@Y(6)) clusters via a common gold network. Magnetic susceptibility (χ) data for Y(3)MnAu(5) were fitted by a Curie-Weiss law. The Curie constant indicates a large effective moment corresponding to nearly localized Mn spins S = 5/2, and the Weiss temperature demonstrates the dominance of ferromagnetic (FM) interactions. An antiferromagnetic (AFM) transition at T(N) = 75 K and a possible spin reorientation transition at 65 K were observed. Analysis of the χ data for T < T(N) suggests a planar noncollinear helical AFM structure that arises from competing AFM interactions between FM-aligned layers of spins in the ab-plane with a turn angle of 69° between the spins along the helix c-axis. A magnetic field-induced spin flop transition is observed below T(N). Spin-polarized LMTO-LSDA calculations indicate an ~2 eV splitting of the Mn 3d states and a metallic ground state, and their COHP analyses demonstrate that ~81% of the total Hamilton populations originate from heteroatomic polar Y-Au and Mn-Au bonding. The Mn 3d, Y 4d, and Au 5d characteristics are remarkably diverse: localized and magnetically polarized for Mn; reducing and cationic for Y; and relativistically strongly bonded and oxidizing for Au, bonding of the latter two being broadly delocalized.