Showing papers on "Metamagnetism published in 2005"

Electric polarization rotation in a hexaferrite with long-wavelength magnetic structures.

Abstract: We report on the control of electric polarization (P) by using magnetic fields (B) in a hexaferrite having magnetic order above room temperature (RT). The material investigated is hexagonal Ba0.5Sr1.5Zn2Fe12O22, which is a nonferroelectric helimagnetic insulator in the zero-field ground state. By applying B, the system undergoes successive metamagnetic transitions, and shows concomitant ferroelectric order in some of the B-induced phases with long-wavelength magnetic structures. The magnetoelectrically induced P can be rotated 360 degrees by external B. This opens up the potential for not only RT magnetoelectric devices but also devices based on the magnetically controlled electro-optical response.

Spin Canting and Metamagnetism in a 3D Homometallic Molecular Material Constructed by Interpenetration of Two Kinds of Cobalt(II)‐Coordination‐Polymer Sheets

Abstract: O(1),a3Dnetworkconsistingoftwodifferent,interpenetrating2D neutral polymers. With strong anisotropyfrom single ions arranged in the chains, sheets, and finally the3D structure, 1 exhibits spin canting and typical metamag-netism.Crystal-structure determination by X-ray crystallographyshowed that each of the four Co

Coexistence of Spin-Canting, Metamagnetism, and Spin-Flop in a (4,4) Layered Manganese Azide Polymer

Abstract: A novel molecule-based magnetic polymer Mn(N3)2(btr)2 1 (btr = 4,4‘-bi-1,2,4-triazole) was synthesized and characterized crystallographically and magnetically. 1 crystallizes in the monoclinic system, space group P21/c, formula C8H8N18Mn, with a = 12.2831(4) A, b = 6.3680(1) A, c = 10.2245(3) A, β = 105.064(1)°, and Z = 2. Bridged by end-to-end azides, the Mn2+ ions form a two-dimensional layer with (4,4) topology; the layers are further connected to the three-dimensional network by the weak hydrogen bonds between ligands of btr. Magnetic studies on a polycrystalline sample show the existence of strong antiferromagnetic couplings between the adjacent Mn2+ ions, and the Neel temperature is TN = 23.7 K. In the ordered state below TN, detailed investigations on an oriented single-crystal sample of 1 reveal that the hidden spin-canting, metamagnetic transition, and spin-flop transition can appear in different circumstances. The ground state is of an antiferromagnet with hidden spin-canting. An external field ...

Magnetic-field induced transition to the 1/2 magnetization plateau state in the geometrically frustrated magnet CdCr2O4.

Abstract: The magnetization of the geometrically frustrated spinel $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_{2}{\mathrm{O}}_{4}$ was measured in pulsed fields of up to 47 T. We found a metamagnetic transition to a very wide magnetization plateau state with one half of the full moment of $S=3/2$ ${\mathrm{C}\mathrm{r}}^{3+}$ at 28 T, independent of the field direction. This is the first observation of magnetization plateau state realized in Heisenberg pyrochlore magnet. The plateau state can be ascribed to a collinear spin configuration with three-up and one-down spins out of four spins of each Cr tetrahedron. A large magnetostriction is observed at the transition in spite of the negligible spin-orbit couplings. We argue that spin frustration plays a vital role in this large spin-lattice coupling.

Magnetic, transport and magnetotransport properties of Mn3+xSn1-xC and Mn3ZnySn1-yC compounds

Abstract: The magnetic, transport, and magnetotransport properties of Mn3+xSn1-xC (0 <= x <= 0.4) and Mn3ZnySn1-yC (0 <= y <= 0.9) compounds are investigated systematically. For Mn3+xSn1-xC, a sharp rise in temperature dependence of resistivity is observed for x <= 0.1, accompanied by a magnetic phase transition from a paramagnetic state to a complicated spin arrangement composed of antiferromagnetic and ferromagnetic sublattices. A different behavior appears in the resistivity of Mn3.2Sn0.8C, which decreases monotonically with decreasing temperature. A partial Zn substitution for Sn in Mn3SnC leads to dramatic changes of magnetic and transport properties. As the temperature decreases, a magnetic transition from the ferromagnetic (or ferrimagnetic) to antiferromagnetic state occurs at about 170 and 142 K for Mn3Zn0.4Sn0.6C and Mn3Zn0.5Sn0.5C compounds, respectively, which strongly affects their transport properties. A significant magnetoresistance as large as 34% is observed for Mn3Zn0.5Sn0.5C at 95 K, in accordance with a field-induced metamagnetic transition. The origin of the magnetoresistance effect is discussed in terms of the reconstruction of the Fermi surface.

Magnetocaloric effect in itinerant electron metamagnetic systems La(Fe1-xCOx)11.9Si1.1

Abstract: The NaZn13-type compounds La(Fe1−xCox)11.9Si1.1 (x=0.04, 0.06, 0.08) were successfully synthesized, in which the Si content is the limit that can be reached by arc-melting technique. TC is tunable from 243 to 301 K with Co doping from x=0.04 to 0.08. Great magnetic entropy change ΔS in a wide temperature range from ∼230 to ∼320K has been observed. The adiabatic temperature change ΔTad upon changing magnetic field was also directly measured. ΔTad of sample x=0.06 reaches ∼2.4K upon a field change from 0 to 1.1 T. The temperature hysteresis upon phase transition is small, ∼1K, for all samples. The influence of Co doping on itinerant electron metamagnetic transition and magnetic entropy change is discussed.

Metamagnetic phase transition of the antiferromagnetic Heisenberg icosahedron.

Abstract: The observation of hysteresis effects in single molecule magnets like Mn12-acetate has initiated ideas of future applications in storage technology. The appearance of a hysteresis loop in such compounds is an outcome of their magnetic anisotropy. In this Letter we report that magnetic hysteresis occurs in a spin system without any anisotropy, specifically where spins mounted on the vertices of an icosahedron are coupled by antiferromagnetic isotropic nearest-neighbor Heisenberg interaction giving rise to geometric frustration. At T = 0 this system undergoes a first-order metamagnetic phase transition at a critical field Bc between two distinct families of ground state configurations. The metastable phase of the system is characterized by a temperature and field dependent survival probability distribution.

Itinerant metamagnetism induced by electronic nematic order

Abstract: It is shown that metamagnetic transition in metals can occur via the formation of electronic nematic order. We consider a simple model where the spin-dependent Fermi surface instability gives rise to the formation of an electronic nematic phase upon increasing the applied Zeeman magnetic field. This leads to two consecutive metamagnetic transitions that separate the nematic phase from the low-field and high-field ``isotropic'' metallic phases. Possible connection to the physics of the bilayer ruthenate, ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$, is also discussed.

Unique Magnetic Phases in an Antiferromagnet CeCoGe3

Abstract: We report on the magnetic properties of CeCoGe 3 by measuring the electrical resistivity, magnetic susceptibility, magnetization and specific heat, together with the magnetic properties of a reference compound LaCoGe 3 . The measurements were performed on a single crystal grown from a high-temperature solution using a third element, bismuth as flux. From the magnetic susceptibility and magnetization measurements, CeCoGe 3 is an antiferromagnet with a Neel temperature T N1 =21 K and undergoes two successive transitions T N2 =12 K and T N3 =8 K. The magnetization for H ∥[001] indicated a metamagnetic transition with three steps. We constructed a magnetic phase diagram from the magnetization measurements, which is very complex and is roughly similar to the previous result performed on a polycrystalline grain-aligned sample.

Field-Induced Suppression of the Heavy-Fermion State in YbRh2Si2

Abstract: We report dc-magnetization measurements on YbRh2Si2 at temperatures down to 0.04 K, magnetic fields B< or =11.5 T, and under hydrostatic pressure P< or =1.3 GPa. At ambient pressure a kink at B* =9.9 T indicates a new type of field-induced transition from an itinerant to a localized 4f state. This transition is different from the metamagnetic transition observed in other heavy-fermion compounds, as here ferromagnetic rather than antiferromagnetic correlations dominate below B*. Hydrostatic pressure experiments reveal a clear correspondence of B* to the characteristic spin fluctuation temperature determined from specific heat.

Possible metamagnetic origin of ferromagnetism in transition-metal-doped SnO2

Abstract: Room-temperature ferromagnetism has been observed recently in Co and Fe doped SnO2 powders. In Sn0.99Co0.01O2 powders prepared at 600 °C, ferromagnetism emerged following a sharp transition in the M vs H data at a critical field ∼25kOe. Broad susceptibility maxima were observed in ferromagnetic Sn1−xCoxO2 and Sn1−xFexO2 powders centered near 290 and 260 K, respectively, indicating spin fluctuation effects. High temperature magnetic measurements of Sn0.99Co0.01O2 and Sn0.99Fe0.01O2 obtained TC’s of 440 and 850 K respectively. However, unlike conventional ferromagnets, the magnetic transitions at the TC were associated with sharp changes in M. It is argued that these observed unusual magnetic features indicate a metamagnetic origin of the room-temperature ferromagnetism in Co and Fe doped SnO2.

Magnetic and magnetocaloric properties of the intermetallic compound TbNiAl

Abstract: The magnetic and magnetocaloric properties of TbNiAl are studied by investigating the magnetization (M) and entropy change (/spl Delta/S) as a function of temperature (T) and magnetic field (H). From the M-T plots, thermogravimetric irreversibility and a few kinks at temperatures lower than T/sub C/, which may be due to the frustrated moments in the compound, is observed. The magnetic ordering temperature (T/sub N/) is found to be 48 K. A sharp metamagnetic transition with a critical field of /spl sim/52 kOe, saturation magnetization of 8.5 /spl mu//sub B//f.u. and remanence ratio at 2 K are obtained from the M-H curve. The magnetocaloric effect, in terms of /spl Delta/S, is calculated from the magnetization isotherm near T/sub N/. The maximum value of /spl Delta/S is found to be 13.8 J Kg/sub -1/K/sub -1/ at 50 kOe, and is observed to decrease to 7.1 J Kg/sub -1/K/sub -1/ at 20 kOe.

Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds

Abstract: Magnetocaloric effect and magnetoresistance have been studied in Dy(Co1−x,Six)2 (x=0, 0.075, and 0.15) compounds. Magnetocaloric effect has been calculated in terms of adiabatic temperature change (ΔTad) as well as isothermal magnetic entropy change (ΔSM) using the heat-capacity data. The maximum values of ΔSM and ΔTad for DyCo2 are found to be 11.4JKg−1K−1 and 5.4 K, respectively. Both ΔSM and ΔTad decrease with Si concentration, reaching values of 5.4JKg−1K−1 and 3 K, respectively for x=0.15. The maximum magnetoresistance is found to be about 32% in DyCo2, which decreases with increase in Si. These variations are explained on the basis of itinerant electron metamagnetism occurring in these compounds.

Magnetism on the Surface of the Bulk Paramagnetic Intermetallic Compound YCo 2

Abstract: Using full-potential electronic structure calculations, we predict that the (111) surface of the cubic Laves phase Pauli paramagnet $\mathrm{YC}{\mathrm{o}}_{2}$ is ferromagnetic. The magnetism of the (111) surface is independent of the termination of the surface, does not extend beyond two Co layers, and is related to the field-induced metamagnetism of the bulk. $\mathrm{YC}{\mathrm{o}}_{2}$ appears to be a prominent candidate to demonstrate the phenomenon of surface-induced itinerant magnetism localized in two dimensions.

Charge instabilities at the metamagnetic transition of itinerant electron systems

Abstract: We investigate instabilities in the charge channel in the vicinity of (meta)magnetic transitions of itinerant electron systems. Based on a weak-coupling analysis we argue that in a one-band $t\text{\ensuremath{-}}{t}^{\ensuremath{'}}$ Hubbard model near the van Hove filling and dominant ferromagnetic fluctuations it is difficult to account for a microscopic mechanism for a $d$-wave Pomeranchuk deformation of the Fermi surface. A similar deformation has been considered for the metamagnetic transition in ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$. As an alternative we discuss the possibility of charge inhomogeneity on the nanoscale. This extends the analogy of the metamagnetic transition to a liquid-gas transition.

Giant isotope effect on the itinerant-electron metamagnetism in YFe{sub 2}(H{sub y}D{sub 1-y}){sub 4.2}

Abstract: The YFe{sub 2}(H{sub y}D{sub 1-y}){sub 4.2} compounds (y=0,0.64,1) crystallize in the same monoclinic structure with a linear increase of the cell volume reaching 0.80% between the hydride and the deuteride. These compounds undergo a first-order magnetovolumic transition from a ferromagnetic to an antiferromagnetic structure, which is related to an itinerant electron metamagnetism (IEM) transition of one of the Fe sites that is surrounded by about 5 (H, D) atoms. A large H/D isotope effect is observed on the magnetic properties: the hydride presents a larger spontaneous magnetization and a 50% higher transition temperature T{sub M0} than the deuteride. This large isotope effect is attributed to the large cell volume difference between the hydride and the deuteride, which plays a dominant role due to the strong interplay between magnetic and elastic energy in IEM compounds.

Strain Induced Changes in the Magnetic Phase Diagram of Metamagnetic Heteroepitaxial EuSe / PbSe 1 − x Te x Multilayers

Abstract: Multilayers of strained metamagnetic EuSe intercalated with nonmagnetic ${\mathrm{PbSe}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ were grown by molecular beam epitaxy under conditions optimized by electron diffraction. From detailed structural and magnetic characterization using anomalous synchrotron x-ray diffraction and magnetization measurements, the phase transition temperatures and the magnetic phase diagrams of strained EuSe as a function of the in-plane lattice constant are determined. In this way, it is demonstrated that the magnetic properties of the samples can be significantly changed by applying biaxial strain on EuSe in superlattice structures.

Effects of cation disorder and size on metamagnetism in A-site substituted Pr0.5Ca0.5MnO3 system

Abstract: The effects of A-site cation disorder and size on metamagnetism of ABO3 type charge and orbital ordered Pr0.5Ca0.5MnO3 system have been studied by substituting Ba+2 for Ca+2 or La+3 for Pr+3. Substitution of 5% Ba+2 or 5% La+3 drastically reduces the critical magnetic field (Hc) for metamagnetism and induces successive steplike metamagnetic transitions at low temperatures. Interestingly, with further increase in substitution, Hc rises. We find that there is a sharp decrease in electrical resistivity corresponding to the metamagnetic transitions, which is indicative of strongly correlated magnetic and electronic transitions in these manganites.

Development of an Antiferromagnetic Organic Superconductor κ-(BETS)2FeBr4

Abstract: The first antiferromagnetic organic superconductor, κ-(BETS) 2 FeBr 4 [BETS = bis(ethylenedithio)tetraselenaful-valene], was developed in the search for novel magnetic molecular conductors. This salt shows successive antiferromagnetic and superconducting transitions at T N = 2.5 K and T c = 1.1 K, respectively, at ambient pressure. Specific heat measurements and anisotropic behavior of intraplanar conducting properties under applied magnetic fields prove the coexistence of the antiferromagnetic ordering and superconductivity below T c . The combination of metamagnetism of the magnetic layer and superconductivity of the conduction layer, which makes this salt a dual-functional system, yields two characteristic magnetic field-induced superconducting states around 1.6 and 12.5 T in terms of the Jaccarino-Peter compensation effect. Systematic studies on both the chemical pressure effect by a halogen exchange in the alloy system K-(BETS) 2 FeBr x Cl 4 - x and the physical pressure effect by an application of real pressures in κ-(BETS) 2 FeBr 4 were performed to discuss the π-d interaction in the κ-(BETS) 2 FeBr 4 system.

Severe fermi surface reconstruction at a metamagnetic transition in Ca2-xSrxRuO4 (for 0.2≤x≤0.5)

Abstract: We report an electrical transport study in Ca2-xSrxRuO4 single crystals at high magnetic fields (B). For x=0.2, the Hall constant Rxy decreases sharply at an anisotropic metamagnetic transition, reaching its value for Sr2RuO4 at high fields. A sharp decrease in the coefficient of the resistivity T2 term and a change in the structure of the angular magnetoresistance oscillations for B rotating in the planes confirms the reconstruction of the Fermi surface. Our observations and local-density-approximation calculations indicate a strong dependence of the Fermi surface on Ca concentration and suggest the coexistence of itinerant and localized electronic states in single layered ruthenates.

Large magnetocaloric effects and Landau coefficients of itinerant electron metamagnetic La(Fe/sub x/Si/sub 1-x/)/sub 13/ compounds

Abstract: The paramagnetic-ferromagnetic (P-F) transition, also known as itinerant electron metamagnetic transition, is accompanied by large magnetocaloric effects (MCEs) such as the isothermal entropy change and the adiabatic temperature. In this work, the relation between MCEs and Landau coefficients of itinerant electron metamagnetic La(Fe/sub x/Si/sub 1-x/)/sub 13/ (x = 0.87, 0.88) compounds is experimentally examined. Expressions describing the Helmholtz magnetic free energy, magnetic entropy and the equation of state H(M,T) are derived. The coefficients A(T), B(T) and C(T) are then experimentally determined from the magnetization curves by curve fitting of H(M,T), and are found to exhibit temperature dependence reflecting the thermal variation on the amplitude of spin fluctuations. The first-order P-F transition at Curie temperature appears in the region A(T) > 0, C(T) > 0, B(T) < 0 and 5/28 < A(T)C(T)B(T) < 3/16. From these Landau coefficients, the energy barrier between the F and P states and its influence in the demagnetisation process is calculated.

Antiferromagnetic ordering in the heavy-fermion system Ce 2 Au 2 Cd

Abstract: La2Au2Cd and Ce2Au2Cd were prepared from the elements by reactions in sealed tantalum tubes in a water-cooled sample chamber of an induction furnace. These intermetallics crystallize with the tetragonal Mo2FeB2 type, space group P4/mbm. While La2Au2Cd is Pauli paramagnetic, Ce2Au2Cd shows Curie-Weiss behaviour above 100 K with an experimental magnetic moment of 2.41(2) muB/Ce atom, indicating trivalent cerium. Antiferromagnetic ordering is detected for Ce2Au2Cd at 5.01(2) K and magnetization measurements reveal a metamagnetic transition at 3 K at a critical field of around 20 kOe with a saturation moment of 1.50(2)muB/Ce atom at 80 kOe. The low-temperature heat capacity properties characterize Ce2Au2Cd as a heavy fermion material with an electronic specific heat coefficient (gamma) = 807(5) mJ/mol K2 as compared to La2Au2Cd with gamma = 6(5) mJ/mol K2.