Mn Magnetic Order Research Articles

Bonding and Suppression of a Magnetic Phase Transition in EuMn2P2.

Electrons in solids often adopt complex patterns of chemical bonding driven by the competition between energy gains from covalency and delocalization, and energy costs of double occupation to satisfy Pauli exclusion, with multiple intermediate states in the transition between highly localized, and magnetic, and delocalized, and nonmagnetic limits. Herein, we report a chemical pressure-driven transition from a proper Mn magnetic ordering phase transition to a Mn magnetic phase crossover in EuMn2P2 the limiting end member of the EuMn2X2 (X = Sb, As, P) family of layered materials. This loss of a magnetic ordering occurs despite EuMn2P2 remaining an insulator at all temperatures, and with a phase transition to long-range Eu antiferromagnetic order at TN ≈ 17 K. The absence of a Mn magnetic phase transition contrasts with the formation of long-range Mn order at T ≈ 130 K in isoelectronic EuMn2Sb2 and EuMn2As2. Temperature-dependent specific heat and 31P NMR measurements provide evidence for the development of short-range Mn magnetic correlations from T ≈ 250-100 K, interpreted as a precursor to covalent bond formation. Density functional theory calculations demonstrate an unusual sensitivity of the band structure to the details of the imposed Mn and Eu magnetic order, with an antiferromagnetic Mn arrangement required to recapitulate an insulating state. Our results imply a picture in which long-range Mn magnetic order is suppressed by chemical pressure, but that antiferromagnetic correlations persist, narrowing bands and producing an insulating state.

Multiple magnetic ordering phenomena in multiferroic o−HoMnO3

Orthorhombic HoMnO3 is a multiferroic in which Mn antiferromagnetic order induces ferroelectricity. A second transition occurs within the multiferroic phase, in which a strong enhancement of the ferroelectric polarization occurs concomitantly to antiferromagnetic ordering of Ho 4f magnetic moments. Using the element selectivity of resonant X-ray diffraction, we study the magnetic order of the Mn 3d and Ho 4f moments. We explicitly show that the Mn magnetic order is affected by the Ho 4f magnetic ordering transition. Based on the azimuthal dependence of the (0 q 0) and (0 1-q 0) magnetic reflections, we suggest that the Ho 4f order is similar to that previously observed for Tb 4f in TbMnO3, which resembles an ac-cycloid. This is unlike the Mn order, which has already been shown to be different for the two materials. Using non-resonant diffraction, we show that the magnetically-induced ferroelectric lattice distortion is unaffected by the Ho ordering, suggesting a mechanism through which the Ho order affects polarization without affecting the lattice in the same manner as the Mn order.

Magnetic and Magnetocaloric Properties of Multiferroic Oxides Gd0.5Y0.5MnO3 and Eu0.5Dy0.5MnO3

In this article, crystal structure, magnetism, heat capacity, magnetocaloric effect (MCE), and electrical resistivity of mixed rare-earth Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> manganites have been studied. Temperature-dependent magnetization M(T) measurements suggest an antiferromagnetic order just below 6 K in Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , while no magnetic transition has been observed down to 5 K in Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . Heat capacity data reveal anomalies at 40 and 42 K in Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and these may correspond to Mn magnetic order as previously reported. The magnetization values are 2.8 and 3 μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> /f.u. in 70 kOe field at 5 K for Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , respectively. MCE has been estimated in terms of isothermal magnetic entropy change (ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) at low temperatures. The maximum values of ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> are about -11 and -6.2 J kg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively, for Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples for a field change of 70 kOe at 8 K. Electrical resistivity of Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Eu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> shows variable range polaron hopping behavior in the temperature range of 210-350 K.

Long-range antiferromagnetic order of formally nonmagneticEu3+Van Vleck ions observed in multiferroicEu1−xYxMnO3

We report on resonant magnetic x-ray scattering and absorption spectroscopy studies of exchange-coupled antiferromagnetic ordering of Eu$^{3+}$ magnetic moments in multiferroic Eu$_{1-x}$Y$_{x}$MnO$_3$ in the absence of an external magnetic field. The observed resonant spectrum is characteristic of a magnetically ordered $^7F_1$ state that mirrors the Mn magnetic ordering, due to exchange coupling between the Eu $4f$ and Mn $3d$ spins. This is the first observation of long range magnetic order generated by exchange coupling of magnetic moments of formally non-magnetic Van Vleck ions, which is a step further towards the realization of exotic phases induced by exchange coupling in systems entirely composed of non-magnetic ions.

Observation of Electronic Ferroelectric Polarization in MultiferroicYMn2O5

We report the observation of a magnetic polarization of the O 2p states in YMn(2)O(5) through the use of soft x-ray resonant scattering at the oxygen K edge. Remarkably, we find that the temperature dependence of the integrated intensity of this signal closely follows the macroscopic electric polarization, and hence is proportional to the ferroelectric order parameter. This is in contrast with the temperature dependence observed at the Mn L(3) edge, which reflects the Mn magnetic order parameter. First-principles calculations provide a microscopic understanding of these results and show that a spin-dependent hybridization of O 2p and Mn 3d states results in a purely electronic contribution to the ferroelectric polarization, which can exist in the absence of lattice distortions.

Local moments and symmetry breaking in metallic PrMnSbO

We report a combined experimental and theoretical investigation of the layered antimonide PrMnSbO which is isostructural to the parent phase of the iron pnictide superconductors. We find linear resistivity near room temperature and Fermi liquid-like T^{2} behaviour below 150 K. Neutron powder diffraction shows that unfrustrated C-type Mn magnetic order develops below \sim 230 K, followed by a spin-flop coupled to induced Pr order. At T \sim 35 K, we find a tetragonal to orthorhombic (T-O) transition. First principles calculations show that the large magnetic moments observed in this metallic compound are of local origin. Our results are thus inconsistent with either the itinerant or frustrated models proposed for symmetry breaking in the iron pnictides. We show that PrMnSbO is instead a rare example of a metal where structural distortions are driven by f-electron degrees of freedom.

Heat capacity of RFexMn12−x (R = Gd,Tb and Dy) compounds: wiping out a cooperative 4f–4f exchange interaction by breakingthe 3d–4f magnetic symmetry

Using adiabatic calorimetry the heat capacity of a series ofRFexMn12−x (R = Gd,Tb and Dy) compounds has been measured from 3 to 350 K. The substitution of Fe for Mn inRFexMn12−x influences both the magnetic interactions on the 3d sublattice andthe magnetism of R (the Néel temperature doubles on going fromx = 0 to 6 and the compounds become ferromagnetic forx = 8 with Curie temperatures of around 300 K). In pureTbMn12 the heat-capacitydata shows a λ-type anomaly associated with the independent cooperative magnetic ordering of the R sublattice(∼5 K), while the anomaly related to the Mn magnetic ordering(∼100 K) is rather smooth, as observed in other itinerant magnetic systems such asYMn12. In contrast, the substitution of Fe for Mn leads, on the one hand, to a more localizedmagnetic behaviour of the 3d sublattice, and, on the other, to magnetic polarization effectsbetween the 3d and 4f sublattices, together with the disappearance of the cooperativemagnetic ordering of the R sublattice due to the breaking of the antiferromagneticsymmetry in the 3d sublattice. This is reflected in the heat-capacity curve through asmooth Schottky-like anomaly. In the case of Gd compounds the magnitude of theexchange molecular-field parameter has been deduced by fitting the magneticcontribution to the heat capacity within a simple mean-field model. From this analysiswe found that this molecular field acting on the rare-earth site increases withthe iron concentration, reaching values as large as 48 T for the concentrationx = 6. A similar analysis of the heat capacity in the ordered phase on the Tb compoundsalso leads to an enhancement of the molecular field with increasing Fe content.These results allow checking the possible crystal-field parameters for theseRFexMn12−x compounds.

Magnetic-field-induced transitions in multiferroicTbMnO3probed by resonant and nonresonant x-ray diffraction

Multiferroic ${\text{TbMnO}}_{3}$ is investigated using x-ray diffraction in high magnetic fields. Measurements on first- and second-harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the $a$ and $b$ directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below ${T}_{N}^{\text{Tb}}$ without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments, and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order, and a phase diagram on basis of these observations for magnetic fields $H\ensuremath{\parallel}a$ and $H\ensuremath{\parallel}b$ is presented. The observations point to a complicated and delicate magnetoelastic interaction as function of temperature and field.

Mn magnetic ordering in fully oxygenated Lu1−xScxMnO3 (x=, 0.5, and 1)

The magnetic properties of fully oxygenated hexagonal Lu1−xScxMnO3 (x=0, 0.5, and 1) have been investigated by means of neutron diffraction and ac magnetization measurements. All three compounds crystallized into a hexagonal symmetry of space-group P63cm. No structural changes were observed between 10 and 300 K. Anomaly of antiferromagnetic characters was observed at ∼90, 95, and 126 K for the x=0, 0.5, and 1 compounds, respectively, in the temperature dependence of the ac magnetic susceptibility, signaling the ordering of the Mn spins. Both the ferromagnetic and antiferromagnetic components, associated with the Mn spins, were revealed in the low-temperature neutron magnetic diffraction patterns. The observed magnetic intensities are consistent with a magnetic structure that can be described by using the Kovalev Γ5 irreducible representation, where the Mn moments lie in the basal MnO2 planes and the couplings between the adjacent MnO2 planes are ferromagnetic, with a saturated moment of ⟨μz⟩=3.22(3)μB and 3.15(3)μB for the x=0 and 0.5 compounds, respectively.

Mn magnetic ordering in fully oxygenated LuMnO3

Neutron magnetic diffraction and AC magnetic susceptibility measurements reveal the existence of both the ferromagnetic and noncollinear antiferromagnetic components for the Mn moments in a fully oxygenated LuMnO3. The observed magnetic intensities are consistent with a magnetic structure that can be described by using the Kovalev Γ5 irreducible representation, where the Mn moments lie in the basal MnO2 planes and the couplings between the adjacent MnO2 planes are ferromagnetic, with a saturated moment of 〈μz〉=3.22(1) μB.

Ce valence mixing and strong 3d antiferromagnetism in CeMn2Si

Transport, specific-heat, x-ray-absorption, and magnetic measurements on ${\mathrm{CeMn}}_{2}$${\mathrm{Si}}_{2}$ are presented. These results indicate that ${\mathrm{CeMn}}_{2}$${\mathrm{Si}}_{2}$ is the first example of a system where low-energy-scale (T&lt;100 K) Ce valence-mixing effects coexist with much higher-energy-scale (400 K) 3d magnetism. The case for this novel confluence of Ce demagnetization with Mn magnetic order is presented partially through analogy with the prototypic mixed-valent system ${\mathrm{CePd}}_{3}$.