Spin-flop Transition Research Articles

Antiferromagnetism and the emergence of frustration in the sawtooth lattice chalcogenide olivines Mn2SiS4−xSex ( x=0–4 )

The magnetism in the sawtooth lattice of Mn in the olivine chalcogenides, ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4\ensuremath{-}x}{\mathrm{Se}}_{x}$ ($x=1--4$), is studied in detail by analyzing their magnetization, specific heat, and thermal conductivity properties and complemented with density functional theory calculations. The air-stable chalcogenides are antiferromagnets and show a linear trend in the transition temperature ${T}_{N}$ as a function of Se content ($x$), which shows a decrease from ${T}_{N}\ensuremath{\approx}86\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4}$ to 66 K for ${\mathrm{Mn}}_{2}{\mathrm{SiSe}}_{4}$. Additional magnetic anomalies are revealed at low temperatures for all the compositions. Magnetization irreversibilities are observed as a function of $x$. The specific heat and the magnetic entropy indicate the presence of short-range spin fluctuations in ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4\ensuremath{-}x}{\mathrm{Se}}_{x}$. A spin-flop antiferromagnetic phase transition in the presence of applied magnetic field is present in ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4\ensuremath{-}x}{\mathrm{Se}}_{x}$, where the critical field for the spin flop increases from $x=0$ towards 4 in a nonlinear fashion. Density functional theory calculations show that an overall antiferromagnetic structure with ferromagnetic coupling of the spins in the $ab$ plane minimizes the total energy. The band structures calculated for ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4}$ and ${\mathrm{Mn}}_{2}{\mathrm{SiSe}}_{4}$ reveal features near the band edges similar to those reported for Fe-based olivines suggested as thermoelectrics; however the experimentally determined thermal transport data do not support superior thermoelectric features. The transition from long-range magnetic order in ${\mathrm{Mn}}_{2}{\mathrm{SiS}}_{4}$ to short-range order and spin fluctuations in ${\mathrm{Mn}}_{2}{\mathrm{SiSe}}_{4}$ is explained using the variation of the Mn-Mn distances in the triangle units that constitutes the sawtooth lattice upon progressive replacement of sulfur with selenium. Overall, the results presented here point towards the role played by magnetic anisotropy and geometric frustration in the antiferromagnetic state of the sawtooth olivines.

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.

Magnetism study on a triangular lattice antiferromagnet Cu2(OH)3Br

Magnetism of Cu2(OH)3Br single crystals based on a triangular lattice is studied by means of magnetic susceptibility, pulsed-field magnetization, and specific heat measurements. There are two inequivalent Cu2+ sites in an asymmetric unit. Both Cu2+ sublattices undergo a long-range antiferromagnetic (AFM) order at K. Upon cooling, an anisotropy crossover from Heisenberg to XY behavior is observed below 7.5 K from the anisotropic magnetic susceptibility. The magnetic field applied within the XY plane induces a spin-flop transition of Cu2+ ions between 4.9 T and 5.3 T. With further increasing fields, the magnetic moment is gradually increased but is only about half of the saturation of a Cu2+ ion even in 30 T. The individual reorientation of the inequivalent Cu2+ spins under field is proposed to account for the magnetization behavior. The observed spin-flop transition is likely related to one Cu site, and the AFM coupling among the rest Cu spins is so strong that the 30 T field cannot overcome the anisotropy. The temperature dependence of the magnetic specific heat, which is well described by a sum of two gapped AFM contributions, is a further support for the proposed scenario.

Thermodynamic properties of a multiferroic antiferromagnetic spin system: The influence of Dzyaloshinskii Moriya interaction

In this paper, we address the influence of Dzyaloshinskii Moriya (DM) interaction on the thermodynamic properties of a multiferroic antiferromagnetic spin system using the spin wave theory (SWT) as a diagonalization method which, associated to the statistical physics, helps to evaluate the statistical sum. The basic factors in thermodynamics, such as the Boltzmann entropy and the specific heat capacity at thermal equilibrium, are obtained. Analyzing the numerical results, it follows that the DM interaction is the best candidate that can help to maintain in long time the system in its coherent state. Furthermore, we find that the influence of the DM interaction is more accentuated at low-temperature and that it enables the system to release heat energy. On the other hand, the fact that the specific heat capacity tends to the constant clearly shows that the system obeys the Dulong–Petit law. In addition, our results also show that for high magnetic field (greater than B[Formula: see text]=[Formula: see text]30 Tesla), the magnetic field dependence of both entropy and specific heat shows a peak-like behavior and that the DM interaction raises the corresponding critical magnetic field but lowers the peak amplitude. It follows that the spin-flop transition occurs in the system and that the strong magnetic field withdraw the antiferromagnetic phase. Overall, we find that the DM interaction is a promising candidate for the control of our system.

Magnetic structure and spin-flop transition in the A -site columnar-ordered quadruple perovskite TmMn3O6

We present the magnetic structure of $\mathrm{TmMn_3O_6}$, solved via neutron powder diffraction - the first such study of any $R\mathrm{Mn_3O_6}$ A-site columnar-ordered quadruple perovskite to be reported. We demonstrate that long range magnetic order develops below 74 K, and at 28 K a spin-flop transition occurs driven by $f$-$d$ exchange and rare earth single ion anisotropy. In both magnetic phases the magnetic structure may be described as a collinear ferrimagnet, contrary to conventional theories of magnetic order in the manganite perovskites. Instead, we show that these magnetic structures can be understood to arise due to ferro-orbital order, the A, A$'$ and A$''$ site point symmetry, $mm2$, and the dominance of A-B exchange over both A-A and B-B exchange, which together are unique to the $R\mathrm{Mn_3O_6}$ perovskites.

Magnetocaloric effect in antiferromagnetic TmNiSn compound

Abstract The low-temperature magnetic, thermal, electrical transport and magnetocaloric properties of the TmNiSn compound were investigated. A polycrystalline sample was prepared by arc-melting. Powder X-ray diffraction confirmed the formation of TmNiSn with orthorhombic TiNiSi-type crystal structure (space group Pnma, no. 62). It was found that TmNiSn undergoes paramagnetic to antiferromagnetic state transition at the Neel temperature TN = 2.4 K. A week inflection of isothermal magnetization curve taken at 1.8 K, can indicate a spin-flop transition. Magnetocaloric properties obtained from isothermal magnetization curves demonstrate positive and negative magnetocaloric effect. In the magnetic field change of 3 T the maximum magnetic entropy change of −10.5 J/(kg K) was obtained at 3.5 K along with the corresponding relative cooling power (RCP) value of 81 J/K. The electrical resistivity result shows metallic behavior from 2 K up to 400 K with clear anomaly at TN.

Transition in a Magnetic Non-Collinear Spin-Flop State in a Fe/Pd/Gd/Pd Superlattice

The influence of a Pd spacer on the magnetic properties of Gd/Fe heterostructures has been studied. We have prepared using ultrahigh vacuum sputtering multilayered [Fe(3.5 nm)/Pd(1.2 nm)/Gd(5.0 nm)/Pd(1.2 nm)]12 structure. By using Polarized Neutron Reflectometry at temperature of 10 K we have observed strong increase in the intensity of neutron spin-flip scattering above magnetic field of 1.5 kOe. Combined analysis of magnetometry and polarized neutron reflectometry data allowed us to find out that the observed increase in spin-flip scattering is related to the spin-flop transition. Although the spin-flop transition were already seen in Fe/Gd systems, the use of Pd in our case allowed the suppression of the magnetic field of the transition making thus possible the use of Fe/Pd/Gd systems for diverse spintronic applications.

Superparamagnetic clusters at room temperature, anomalous magnetic coercivity and spin-flop transition in novel dilute antiferromagnetic nanoparticles of La2Fe0.875Cr0.125GaO6

Abstract Magnetism at the nanoscale is intriguing, but that on the magnetic properties of a dilute antiferromagnetic (AFM) system is rarely studied. Presence of uncompensated spins at the lattice as well as on the nanoparticle surfaces could lead to interesting magnetic behaviour. We present the combined effect of reduction in particle size and dilution of exchange interactions on the magnetic properties of an AFM perovskite oxide. A dilute AFM compound, La2Fe0.875Cr0.125GaO6 nanoparticles (average particle size ∼ 44.5 (7) nm), has been synthesized where non-magnetic Ga-ions are introduced to interrupt the superexchange pathways. The compound crystallizes in orthorhombic structure with Pbnm space group, where Fe, Cr and Ga ions are distributed randomly in the B-site. DC magnetic studies show superparamagnetic behaviour at room temperature, spin-flop transition and a prominent hysteresis loop with sufficiently high coercivity around 6.69 kOe at ∼138 K. The analysis of thermoremanent and isothermoremanent magnetization curves reveal SPM behaviour at 300 K and 2-dimensional dilute antiferromagnetic in field like nature at 5 K. AC magnetic susceptibility analysis confirms the presence of non-interacting clusters having SPM behaviour with blocking temperature ∼280 K. Furthermore, temperature variation of coercivity shows a Gaussian nature, mainly associated with competing Dzyaloshinskii-Moriya interactions between disordered B-site ions along with strong uncompensated surface spin effects.

Element selective magnetism in Ho0.5Nd0.5Fe3(BO3)4 single crystal probed with hard X-ray magnetic circular dichroism

Abstract We present a study of a Ho 0.5 Nd 0.5 Fe 3 ( BO 3 ) 4 single crystal aiming at understanding the roles of each magnetic sublattices in magnetic transitions at low temperatures. The crystal structure is determined to have the R32 symmetry in whole studied temperature range but the crystal appears to be racemic. Element selective magnetic properties studied with X-ray magnetic circular dichroism at the L 2 , 3 -edges of Ho and Nd, and at the Fe K-edge at T = 3 K under magnetic fields of ±17 T are compared with the results of macroscopic magnetization measurements in pure and substituted crystals. All three magnetic sublattices are shown to be strongly coupled and to undergo a spin-reorientation transition when magnetic field is applied along the trigonal c-axis. On the contrary, when magnetic field is applied in the ab-plane only the holmium atoms exhibit a sizeable magnetization jump. This result allows us to conclude that the spin-flop transitions observed in macroscopic magnetization curves and associated anomalies of electric polarization are due to the Ho3+ magnetic moment reorientation.

Finite-size scaling for a first-order transition where a continuous symmetry is broken: The spin-flop transition in the three-dimensional XXZ Heisenberg antiferromagnet.

Finite-size scaling for a first-order phase transition where a continuous symmetry is broken is developed using an approximation of Gaussian probability distributions with a phenomenological "degeneracy" factor included. Predictions are compared with data from Monte Carlo simulations of the three-dimensional, XXZ Heisenberg antiferromagnet in a field in order to study the finite-size behavior on a L×L×L simple cubic lattice for the first-order "spin-flop" transition between the Ising-like antiferromagnetic state and the canted, XY-like state. Our theory predicts that for large linear dimension L the field dependence of all moments of the order parameters as well as the fourth-order cumulants exhibit universal intersections. Corrections to leading order should scale as the inverse volume. The values of these intersections at the spin-flop transition point can be expressed in terms of a factor q that characterizes the relative degeneracy of the ordered phases. Our theory yields q=π, and we present numerical evidence that is compatible with this prediction. The agreement between the theory and simulation implies a heretofore unknown universality can be invoked for first-order phase transitions.

Magnetic and thermodynamic properties and spin-flop-driven magnetodielectric response of the antiferromagnetic Pb2Fe2Ge2O9 single crystals

Abstract Orthorhombic Pb2Fe2Ge2O9 antiferromagnetic single crystals have been synthesized by a modified pseudo-flux technique and their magnetic, thermodynamic, and magnetodielectric properties have been investigated. It has been found that, below the Neel temperature (45.2 K), iron moments are arranged in a canted antiferromagnetic structure with a weak ferromagnetic moment parallel to the a axis. According to the specific heat measurement data, the TN value remains invariable in applied magnetic fields of up to 50 kOe within the experimental accuracy. The magnetic entropy in the investigated crystals attains 2Rln(2S + 1) right above TN, which is indicative of a purely magnetic nature of the transition. It has been shown that the weak ferromagnetic moment is induced by the interplay between the single-ion anisotropy and antisymmetric Dzyaloshinskii–Moriya exchange interaction, with the latter contribution being dominant. It has been established from the angular dependences of the magnetization in three orthorhombic planes that the symmetries of the magnetic and crystal structure are identical. The magnetodielectric properties of the Pb2Fe2Ge2O9 single crystals have been studied at different mutual orientations of the electric and magnetic fields. The most prominent anomalies have been observed in the vicinity of the spin-flop transition in a magnetic field applied along the c axis.

Magnetic properties of double perovskite Ln2CoIrO6 (Ln=Eu, Tb, Ho) : Hetero-tri-spin 3d−5d−4f systems

The field of double perovskites is now advancing to three magnetic elements on the A, B and B$'$ sites. A series of iridium-based double perovskite compounds, $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho) with three magnetic elements were synthesized as polycrystalline samples. The compounds crystalize in monoclinic structures with the space group $P2_1/n$. Magnetic properties of these hetero-tri-spin $3d$-$5d$-$4f$ systems were studied by magnetic susceptibility and field dependent magnetization in both DC and pulsed magnetic fields. All these compounds show ferrimagnetic transitions at temperatures $T_C$ above 100 K, which are attributable to antiferromagnetic coupling between Co$^{2+}$ and Ir$^{4+}$ spins. For Eu$_2$CoIrO$_6$, the magnetic properties are similar to those of La$_2$CoIrO$_6$. The Eu$^{3+}$ spins show Van Vleck paramagnetism that don't significantly interact with transition-metal cations. By contrast, Tb$_2$CoIrO$_6$ and Ho$_2$CoIrO$_6$ reveal a second transition to antiferromagnetic order below a lower temperature $T_N$. The temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might be explained by a spin-reorientation transition. Moreover, a magnetic-field-induced spin-flop transition with a small hysteresis was observed below $T_N$ in these two compounds. The magnetic moment of all three compounds do not saturate up to 60 T at low temperatures. Moderate magnetocaloric effect was also observed in all three compounds. Our results should motivate further investigation of the spin configuration on single crystals of these iridium-based double perovskites.

Single-crystal investigation of the proposed type-II Weyl semimetal CeAlGe

We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in noncentrosymmetric I4$_1$md space group, in line with predictions of non-trivial topology. Magnetization, specific heat and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of $\Delta$ = 9.11 K from heat capacity and hole-like carrier density of 1.44 $\times$ 10$^{20}$ cm$^{-3}$ from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal $\it{ab}$-plane below 7 K. A spin-flop transition to less than 1 $\mu_B$/Ce is observed to occur below 30 kOe at 1.8 K in the $M(H)$ ($\bf{H}\|\bf{a}$) data. Small magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order when applied along the $\it{a}$- and $\it{c}$-axes, respectively, resulting in a complex $\it{T-H}$ phase diagram for $\bf{H}\|\bf{a}$ and a simpler one for $\bf{H}\|\bf{c}$.

Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully compensated half-metallic Mn2RuxGa thin films

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 $\Omega^{-1}.m^{-1}$ 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$^3$ and predict the magnetic resonances frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems.

Magnetic phase diagram and magnetoresistance of Gd–Tb–Dy–Ho–Lu hexagonal high-entropy alloy

We present a study of the magnetic phase diagram and the magnetoresistance of a Gd–Tb–Dy–Ho–Lu "ideal" hexagonal high-entropy alloy (HEA), composed of the elements from the heavy half of the rare earth series only. The phase diagram contains an antiferromagnetic (AFM) state, a field-induced ferromagnetic (FM) state above the AFM-to-FM spin-flop transition and a low-temperature spin-glass state. The complex (H,T) phase diagram is a result of competition between the periodic potential arising from the electronic band structure that favors periodic magnetic ordering, the substitutional-disorder-induced random local potential that favors spin-glass-type spin freezing in random directions, the Zeeman interaction with the external magnetic field that favors spin alignment along the field direction and the thermal agitation that opposes any spin ordering. The magnetoresistance reflects complexity of the (H,T) phase diagram. Its temperature dependence can be explained by a continuous weakening and final disappearance of the periodic potential upon cooling that leads to the destruction of long-range ordered periodic magnetic structures. The magnetoresistance is large only at temperatures, where the AFM and field-induced FM structures are present and exhibits a maximum at the critical field of the AFM-to-FM transition. Within the AFM phase, the magnetoresistance is positive with a quadratic field dependence, whereas it is negative with a logarithmic-like field dependence within the field-induced FM phase. At lower temperatures, the long-range periodic spin order "melts" and the magnetoresistance diminishes until it totally vanishes within the low-temperature spin glass phase. The magnetoresistance is asymmetric with respect to the field sweep direction, reflecting nonergodicity and frustration of the spin system.

Spin dynamics in the staircase kagome lattice compound PbCu3TeO7

Spin dynamics of the staircase kagome lattice ${\mathrm{PbCu}}_{3}{\mathrm{TeO}}_{7}$ was investigated by static magnetic susceptibility $\ensuremath{\chi}(T)$, high-field magnetization $M(H)$, and muon spin rotation/relaxation $(\ensuremath{\mu}\mathrm{SR})$ measurements. $\ensuremath{\chi}(T)$ displays a sub-Curie power-law behavior $\ensuremath{\chi}(T)\ensuremath{\sim}{T}^{\ensuremath{-}\ensuremath{\alpha}}$ with changing exponent from $\ensuremath{\alpha}=0.5$ to 0.3 crossing ${T}^{*}=150$ K. We identify a spin-flop transition at ${\ensuremath{\mu}}_{0}H=8.5$ T and another field-induced anomaly at ${\ensuremath{\mu}}_{0}{H}^{*}=30$ T in $M(H)$. Our $\ensuremath{\mu}\mathrm{SR}$ results unveil that the magnetically inequivalent Cu(1) and Cu(2) spins develop site-specific magnetic structures through the successive magnetic transitions at ${T}_{\mathrm{N}1}=36$ K, ${T}_{\mathrm{N}2}=25$ K, and ${T}_{\mathrm{N}3}=17$ K. The magnetic anomalies of ${\mathrm{PbCu}}_{3}{\mathrm{TeO}}_{7}$ suggest that the Cu(1) and Cu(2) subsystems feature a largely distinct magnetism due to the presence of a dozen competing exchange interactions having largely different energy scales and thus the magnetism of ${\mathrm{PbCu}}_{3}{\mathrm{TeO}}_{7}$ is far more complex than the staircase kagome lattice.

Magnetic and magnetotransport properties of single-crystalline R2PdGe6 (R = Pr, Gd and Tb)

Single crystals of R2PdGe6 (R = Pr, Gd and Tb) compounds were grown by the Bi-flux method. Pr2PdGe6 is an antiferromagnetic compound with Néel temperature TN = 15 K, in which a field-induced magnetic transition (spin flip) occurs when a magnetic field is applied along either a or b axis; a small magnetization and hysteresis loop were observed when a field is applied along c axis. Gd2PdGe6 is a collinear antiferromagnetic compound with TN = 37 K along b axis. Tb2PdGe6 is an antiferromagnetic compound with TN = 48 K and its hard magnetization direction is along b axis. The temperature dependences of the resistance of the entire three compounds present inflection points at the respective TN. A large resistance (as well as magnetoresistance) change can be found at the spin flip transition of Pr2PdGe6, but the change is not obvious at the spin flop transition of Gd2PdGe6.

Spin-flop transition and magnetic phase diagram in CsCo2Se2 revealed by torque and resistivity measurements

Abstract The magnetic properties of CsCo2Se2, possessing a ThCr2Si2-structure, are systematically studied by using specific heat, resistivity, and torque measurements. Our results reveal that CsCo2Se2 undergoes a paramagnetic state to antiferromagnetic order at T N ≈ 80 K at zero magnetic field. The T N is nearly independent of the external magnetic field for H ‖ c-axis, and can be suppressed for H ‖ ab-plane below 4 T, above which spin-flop phase transition sets in. At 2 K, the magnetoresistance has a small value of 2.3% for H ‖ c-axis while goes up to 60% for H ‖ ab-plane at 9 T. A hump-like behavior in resistivity was discovered, which was ascribed to a field-induced spin-flop phase transition. The magnetoresistance results suggest that a crossover of spin-flop phase transition occurs at low temperatures in the field range of 2–4 T for H ‖ ab-plane. Furthermore, the magnetic torque results reveal a novel ordered Co spin structure at low temperatures under 6 T for H ‖ ab-plane. Finally, we summarize the magnetic phase diagram of CsCo2Se2 based on resistivity and torque results.

Neutron diffraction study on magnetic structures and transitions in Sr2Cr3As2O2

Sr2Cr3As2O2 is composed of alternating square-lattice CrO2 and Cr2As2 stacking layers, where CrO2 is isostructural to the CuO2 building-block of cuprate high-Tc superconductors and Cr2As2 to Fe2As2 of Fe-based superconductors. Current interest in this material is raised by theoretic prediction of possible superconductivity. In this neutron powder diffraction study, we discovered that magnetic moments of Cr(II) ions in the Cr2As2 sublattice develop a C-type antiferromagnetic structure below 590 K, and the moments of Cr(I) in the CrO2 sublattice form the La2CuO4 -like antiferromagnetic order below 291 K. The staggered magnetic moment 2.19(4){\mu} B /Cr(II) in the more itinerant Cr2As2 layer is smaller than 3.10(6){\mu}_B/Cr(I) in the more localized CrO2 layer. Different from previous expectation, a spin-flop transition of the Cr(II) magnetic order observed at 291 K indicates a strong coupling between the CrO2 and Cr2As2 magnetic subsystems.

Tuning the magnetic anisotropy via Mn substitution in single crystal Co4Nb2O9

By using the optical floating-zone technique to grow a series of high-quality Co4-xMnxNb2O9 single crystals, the effect of Mn doping on the magnetic anisotropy and spin-flop is investigated. The antiferromagnetic phase transition and spin-flop transition for these samples (x ≤ 3.9) are similar to those in the parent phase of Co4Nb2O9, revealing that Co2+ ions in Co4-xMnxNb2O9 possess a strong single-ion anisotropy. The critical doping content, above which the magnetic anisotropy changes from easy-plane to easy-axis, has been identified as x = 3.95 with an additional kink observed in the magnetization curve below the N é el temperature. A spin-flop transition is reported for the first time in Mn4Nb2O9 at a field of 10.9 T at 2 K.