Canted Magnetic Structures Research Articles

Geometrical Spin Frustration and Monoclinic-Distortion-Induced Spin Canting in the Double Perovskites Ln2LiFeO6 (Ln = La, Nd, Sm, and Eu) with Unusually High Valence Fe5.

We discovered new B-site-ordered double perovskites Ln2LiFeO6 (Ln = La, Nd, Sm, and Eu) with most likely unusually high valence Fe5+, which was stabilized by strong oxidizing high-pressure synthesis. Despite large antiferromagnetic interactions between Fe5+ spins in these compounds, the magnetic ordering is strongly suppressed due to the geometrical frustration of Fe5+ located in a face-centered cubic lattice. In addition, canted magnetic structures are stabilized only in those with Ln = Sm and Eu, which is most likely due to significant Dzyaloshinskii Moriya interaction caused by large monoclinic structural distortion. These results provide a deep understanding of the structure-property relationships in geometrically frustrated B-site-ordered double perovskites.

Metamagnetic transition, magnetocaloric effect and electronic structure of the rare-earth anti-perovskite SnOEu3

Rare-earth anti-perovskites with oxygen are an interesting magnetic materials family at the boundary between intermetallics and oxides, they however remain largely unexplored. Here, magnetic and heat capacity investigations, as well as density functional theory (DFT) calculations, were carried out on SnOEu3. At low magnetic field (B ≤ 0.5 T), a Néel temperature separates antiferromagnetic and paramagnetic phases at 31 K. When applying higher magnetic field below the Néel temperature, successive transformations toward a ferromagnetic state via a number of intermediate canted magnetic structures are observed and are associated with only modest latent heat and transition entropy. High-pressure magnetic measurements confirm the stable divalent state of Eu up to 1.05 GPa. A direct magnetocaloric effect progressively increases with applied magnetic field above the Néel temperature, reaching −16 J kg–1 K−1 for ΔB = 7 T. On the other hand, the inverse magnetocaloric effect of the field-induced transition below TN saturates at ~+5 J kg−1 K−1. DFT calculations support magnetic instabilities observed experimentally in SnOEu3 and reveal an unusual exchange mechanism and band topology near the Fermi level.

Long-range chiral exchange interaction in synthetic antiferromagnets.

The exchange interaction governs static and dynamic magnetism. This fundamental interaction comes in two flavours-symmetric and antisymmetric. The symmetric interaction leads to ferro- and antiferromagnetism, and the antisymmetric interaction has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise fast, energy-efficient devices. So far, the antisymmetric exchange interaction has been found to be rather short ranged and limited to a single magnetic layer. Here we report a long-range antisymmetric interlayer exchange interaction in perpendicularly magnetized synthetic antiferromagnets with parallel and antiparallel magnetization alignments. Asymmetric hysteresis loops under an in-plane field reveal a unidirectional and chiral nature of this interaction, which results in canted magnetic structures. We explain our results by considering spin-orbit coupling combined with reduced symmetry in multilayers. Our discovery of a long-range chiral interaction provides an additional handle to engineer magnetic structures and could enable three-dimensional topological structures.

Symmetry analysis of the magnetic structure of Mn3Sb

To estimate the reliability of the previously published results concerning the magnetic structure of Mn3Sb, a symmetry analysis of possible magnetic structures characterized by a wave vector k 12 = 0 has been performed. In this work, we quite briefly describe and apply the previously developed technique for the calculations of the basis functions of the irreducible representations of the space group O h 1 (Pm \(\bar 3\) m) entering into the composition of the magnetic representation with the above wave vector. Results of the calculations of these basis functions for the Mn atoms located in 3c positions are given and discussed in detail. A conclusion is made that the magnetic moments of Mn atoms in this intermetallic compound can be oriented along any crystallographic direction with the formation of collinear or canted magnetic structures. The total magnetic moments of separate Mn atoms in the unit cell of the crystal structure can coincide or differ in magnitude.

Temperature dependence of the magnetization of canted spin structures

Numerous studies of the low-temperature saturation magnetization of ferrimagnetic nanoparticles and diamagnetically substituted ferrites have shown an anomalous temperature dependence. It has been suggested that this is related to freezing of canted magnetic structures. We present models for the temperature dependence of the magnetization of a simple canted spin structure in which relaxation can take place at finite temperatures between spin configurations with different canting angles. We show that the saturation magnetization may either decrease or increase with decreasing temperature, depending on the ratio of the exchange coupling constants. This is in agreement with experimental observations.

Canted magnetic structure arising from rare-earth mixing in the Laves-phase compound(Nd0.5Tb0.5)Co2

The crystal and magnetic structures of Laves-phase compound $({\mathrm{Nd}}_{0.5}{\mathrm{Tb}}_{0.5}){\mathrm{Co}}_{2}$ have been investigated by high resolution neutron powder diffraction at different temperatures. Magnetization measurement and neutron diffraction reveal two magnetic transitions at ${T}_{\mathrm{C}}\ensuremath{\approx}173\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{M}}\ensuremath{\approx}47\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively. At room temperature, the compound crystallizes in the $\mathrm{Mg}{\mathrm{Cu}}_{2}$-type (C15) structure. Below ${T}_{\mathrm{C}}$, rhombohedral distortion and large anisotropic magnetostriction take place and persist down to $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In contrast to the binary rare earth $(R)\text{\ensuremath{-}}\mathrm{Co}$ Laves-phases $R{\mathrm{Co}}_{2}$, a noncollinear magnetic structure (canted) is deduced for $({\mathrm{Nd}}_{0.5}{\mathrm{Tb}}_{0.5}){\mathrm{Co}}_{2}$, based on the Rietveld refinement of the neutron diffraction data at $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In addition, the correlation between lattice distortion and easy magnetization direction (EMD) commonly observed for binary $R{\mathrm{Co}}_{2}$ is violated in $({\mathrm{Nd}}_{0.5}{\mathrm{Tb}}_{0.5}){\mathrm{Co}}_{2}$. Though the crystal structure remains rhombohedral, the EMD of the $R$ sublattice is close to the [110] direction at $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ of the pseudocubic lattice and along the [111] direction at $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively. The difference of the canting angle between the magnetic structures at $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is small, indicating stable canted configurations. The lattice parameters exhibit a discontinuity around ${T}_{\mathrm{M}}$, suggesting a first-order transition between the two canted magnetic structures. The dilution of magnetic anisotropy of the $R$ sublattice and the contribution of the magnetic anisotropy of the Co sublattice are responsible for the observations.

Magnetostructural phase transitions of DyFe 4Ge 2: Part II Neutron diffraction

We present the temperature magnetic phase diagram of the compound DyFe 4Ge 2 determined from neutron diffraction data for the entire magnetically ordered regime. DyFe 4Ge 2 undergoes at T N , T c = 55 K a simultaneous structural and magnetic transition of second order (or weakly first order) followed by two subsequent isostructural first-order magnetic transitions at T ic 2 = 45 K and T ic 1 = 28 K : P 4 2 / mnm , T N , T c = 55 K → Cmmm , q 1 = ( 0 1 2 0 ) T ic 2 = 45 K → q 2 = ( 0 q y 0 ) T ic 1 = 28 K → q 1 . The re-entrant lock-in magnetic phase q 1 = ( 0 1 2 0 ) is stable in the high-temperature range T ic2– T N and in the low-temperature range 1.5 K– T ic1 while the incommensurately modulated q 2 = ( 0 q y 0 ) magnetic phase is sandwiched in the intermediate range T ic1– T ic2 between the two commensurate phases. The wave vector q 2 has a temperature-dependent length with a minimum in the middle of the incommensurate range and corresponds to a multiaxial amplitude modulated phase. Symmetry analysis leads for both propagation vectors in Cmmm to a twofold and fourfold splitting of the tetragonal Dy 2 b site and the Fe 8 i sites, respectively. The low temperature q 1 = ( 0 1 2 0 ) and the q 2 = ( 0 q y 0 ) phases correspond to 3D canted magnetic structures described by the irreducible representations (Irreps) Γ 2 + Γ 3 while the high-temperature q 1 phase to 2D canted magnetic structures described by a single Irrep Γ 2. The T ic2 transition is connected with reorientations of both Fe and Dy moments.

Field-induced phase transitions in Sc-substituted ytterbium–iron–garnet under high dc fields

High magnetic field measurements were performed on Yb3Fe5−xScxO12 (YbIG:Sc), x=0.5, single crystals platelets oriented along the [111] and [100] crystallographic axes, in the 4.2 K–250 K temperature range in a magnetic field up to 230 kOe. When T=4.2 K, a first-order transition is observed at 63 kOe for H applied parallel to [111]. For 4.2 K<T<25 K, an anisotropy of magnetization is observed below 70 kOe, the differential magnetic susceptibility presenting a maximum independent of temperature at H=125 kOe. In this temperature range, [111] is the “easy” magnetic axis in the spontaneous state. For T>25 K, isotherms are linear as usually observed in ferrites. However, isofield curves reveal the presence of a singular point at 60 K that indicates that the field-induced canted magnetic structures remain until this temperature. The magnetic phase diagram is then established. The spontaneous magnetization data are analyzed within the frame of the Dionne-refined Néel model.

Angular dependence of the metamagnetic process in the frustrated tetragonal compound ErRu 2Ge 2

Angular dependences of the magnetization components parallel and perpendicular to the applied field were measured at 1.65 K on a single crystal during the metamagnetic process of the frustrated tetragonal compound ErRu 2Ge 2. An additional transition appears when the field is applied out of a symmetry direction of the basal plane. Starting from the complex zero field canted planar magnetic structures, the different phases induced by the field have then been clarified and the metamagnetic process has been quantitatively analyzed using a phenomenological model in which the demagnetizing field has been considered. The angular dependences of the transition fields were quite satisfactorily accounted for. Finally, the huge second-order anisotropy constant K 1 and the large anisotropy constant K 3 in the basal plane have been quantitatively determined.

Magnetic properties of (Ho,Y) 6Fe 23 intermetallic compounds

Intermetallic ingots of Ho 6− x Y x Fe 23 alloys were synthesized with compositions x=0, 0.47, 0.92, 1.86, 4.85 and 6. Magnetization M( H, T) measurements were performed on the samples from 4 K to above Curie temperature T C(∼500 K) in a magnetic field up to 17 kOe. Magnetic properties near T C are weakly influenced by yttrium substitution, in agreement with preponderant Fe–Fe magnetic interactions. In contrast, when x increases the magnetic compensation temperature T comp is shifted to low temperature and vanishes when x∼1.5. At 4.2 K, the magnetization of the compounds increases at a rate of ∼9.3 μ B per at. Ho substituted, close to the free Ho 3+ value. The magnetic properties M( H, T, x) are discussed within the frame of the molecular field theory model of Herbst and Croat which takes into account canted magnetic structures present in R–T compounds. The mean canting angle θ between Ho and Fe moments is found greater than its value in pure Ho 6Fe 23 but remains less than 10° for the most canted structures corresponding to x=0.92 and 1.86. The calculated temperature dependences of the magnetization of the compounds, assuming a linear variation of the parameters of the Fe sublattice from Ho 6Fe 23 to Y 6Fe 23, are in fairly good agreement with experimental data.

Competing magnetic interactions in La0.8Y0.2Mn2Si2 - coexistence of canted ferromagnetism and antiferromagnetism

The magnetic structures of tetragonal La0.8Y0.2Mn2Si2 have been investigated by neutron diffraction measurements over the temperature range ~2 - 513 K. This compound corresponds to the critical concentration xc ~ 0.2 in the La1 - xYxMn2Si2 series for the transition from the antiferromagnetism of YMn2Si2 to the predominant ferromagnetism of LaMn2Si2. The high temperature antiferromagnetic region of La0.8Y0.2Mn2Si2, ~ 300 K < T < TN1 ~ 410 K, exhibits the planar antiferromagnetism common to the La-rich compounds in the La1 - xYxMn2Si2 series, with c-axis canted antiferromagnetic and ferromagnetic structures coexisting in the region ~ 150 K < T < TN2,C ~ 300 K. Below ~ 150 K, La0.8Y0.2Mn2Si2 exhibits only the single phase canted antiferromagnetic structure. Rietveld refinements of the data demonstrate that the canted magnetic structures maintain the same angle of tilt with respect to the c-axis and the same total sublattice moment in the two phase region ~ 150 - 300 K, and that the two tetragonal phases (both with the ThCr2Si2 structure) can be distinguished crystallographically with differences in their a lattice parameters and c lattice parameters of around a ~ 0.012 Å and c ~ 0.007 Å respectively. This simple description of these magnetic structures leads to a monotonic variation of the total Mn magnetic moment below TN1 ~ 410 K with the onset of the c-axis component occurring below TN2,C ~ 300 K. The canted antiferromagnetic ground state of La0.8Y0.2Mn2Si2 can be described by the Mn moment values: µMn(2 K) = 2.25(4) µB , with the z-component of the moment µz(2 K) = 1.87(4) µB , corresponding to a tilt angle (2 K) = 33.7(9)°.

Magnetic structure of the ferro–antiferromagnet interface. II. Compensated interface

A compensated ferro–antiferromagnet interface is studied in the framework of a discrete classical spin model. The phase diagram is presented for the possible collinear and canted magnetic structures of the interface. The change in magnetization upon a transition from a collinear structure to canted form is studied.

Magnetic phase diagrams of dysprosium iron garnet (DyIG) in high dc fields

Magnetisation measurements have been performed on spherical single crystals of dysprosium iron garnet (Dy3Fe5O12) in high dc magnetic fields up to 16 T applied along the three principal crystallographic directions 〈111〉, 〈110〉 and 〈100〉. The magnetic phase transitions near the inversion (or compensation) temperature TI between the collinear and the field induced canted magnetic structures are observed and the different associated magnetic phase diagrams precisely determined in the (H,T) plane. The mean exchange field acting on the Dy ions and the effective anisotropy field are deduced to be (12.9±0.2) T and (1.2±0.1) T respectively. Above 228.2±0.5 K, only the collinear magnetic phase exists for all the directions. These results are compared to previous high pulsed magnetic fields data.

Magnetic Dipole−Dipole Interactions and Single-Ion Anisotropy: Revisiting a Classical Approach to Magnets

The weak classical through-space magnetic dipolar interactions have, in general, not been an important component in stabilizing bulk magnets, as the strong quantum-mechanical through-bond exchange couplings dominate. We show that for materials composed of strongly exchange-coupled magnetic chains with very weak interchain exchange, the interchain dipolar interactions may dominate, leading to sizable ordering temperatures. The single-ion anisotropy together with the anisotropy of the dipole interaction determine the magnetic ordering directions. The family of [Mn(porphyrin)]+[cyanocarbon]- magnets is shown to order due to classical interchain dipolar interaction in combination with the single-ion anisotropy, resulting in canted magnetic structures.

On the low temperature canted ferrimagnetic structures of Er 2Fe 14B and Tm 2Fe 14B

A simple treatment of exchange and crystal field effects is presented which reproduces well the observed canted magnetic structures of Er 2Fe 14B and Tm 2Fe 14B. Spin-flop transitions in large applied magnetic fields are predicted to occur. Consideration of previously published magnetic data on the Er 2(Fe,Mn) 14B series of compounds by Fuerst et al. allows the strength of the Er-Er exchange interaction to be estimated.

Field induced transition from collinear to canted magnetic structures in TbCo 5

The magnetization processes of a TbCo 5 single crystal have been measured. In-plane field induced transitions of the collinear ferrimagnetic to canted magnetic structures have come out. They allow an accurate determination of the Tb-Co exchange energy in the basal plane perpendicular to the six-fold axis of the hexagonal structure.

Rotational bands in nuclei as induced group representations: L. Weaver. Department of Physics, Kansas State University, Manhattan, Kansas 66502 and L. C. Biedenharn and R. Y. Cusson. Department of Physics, Duke University, Durham, North Carolina 27706

We present the temperature magnetic phase diagram of the compound DyFe4Ge2 determined from neutron diffraction data for the entire magnetically ordered regime. DyFe4Ge2 undergoes at TN,Tc=55K a simultaneous structural and magnetic transition of second order (or weakly first order) followed by two subsequent isostructural first-order magnetic transitions at Tic2=45K and Tic1=28K: The re-entrant lock-in magnetic phase q1=(0120) is stable in the high-temperature range Tic2–TN and in the low-temperature range 1.5 K–Tic1 while the incommensurately modulated q2=(0qy0) magnetic phase is sandwiched in the intermediate range Tic1–Tic2 between the two commensurate phases. The wave vector q2 has a temperature-dependent length with a minimum in the middle of the incommensurate range and corresponds to a multiaxial amplitude modulated phase. Symmetry analysis leads for both propagation vectors in Cmmm to a twofold and fourfold splitting of the tetragonal Dy 2b site and the Fe 8i sites, respectively. The low temperature q1=(0120) and the q2=(0qy0) phases correspond to 3D canted magnetic structures described by the irreducible representations (Irreps) Γ2+Γ3 while the high-temperature q1 phase to 2D canted magnetic structures described by a single Irrep Γ2. The Tic2 transition is connected with reorientations of both Fe and Dy moments.