Itinerant Electron Metamagnetism Research Articles

Reduction of Hysteresis Loss in Itinerant-Electron Metamagnetic Transition of La<SUB>1−<I>z</I></SUB>Ce<I><SUB>z</SUB></I>(Fe<I><SUB>x</SUB></I>Mn<I><SUB>y</SUB></I>Si<SUB>1−<I>x</I>−<I>y</I></SUB>)<SUB>13</SUB> Magnetic Refrigerants at Low Temperatures

Since La 0.75 Ce 0.25 (Fe 0.85 Mn 0.03 Si 0.12 ) 13 itinerant-electron metamagnet exhibits large magnetocaloric effects at low temperatures because of the itinerant-electron metamagnetic (IEM) transition, the reduction of hysteresis loss E h estimated from the enclosed area between the ascendant and descendant magnetization has been investigated. We have found that E h associated with the IEM transition of La 0.75 Ce 0.25 (Fe 0.85 Mn 0.03 Si 0.12 ) 13 is remarkably reduced from 78 to 3 J/kg by a slight adjustment of compositions, that is, the increase of the Ce concentration up to z = 0.35 and the decrease of the Fe concentration down to x = 0.84. What is important is that such improvement is achieved without a striking decrease of the isothermal magnetic entropy change ΔS m at low temperatures.

Magnetic properties and magnetic entropy changes of La 1- x Pr x Fe 11.5 Si 1.5 compounds with 0 ≤ x ≤ 0.5

Magnetic properties and magnetic entropy changes in LaFe11.5Si1.5 have been investigated by partially substituting Pr by La. It is found that La1-xPrxFe11.5Si1.5 compounds remain cubic NaZn13-type structures even when the Pr content is increased to 0.5, i.e. x = 0.5. Substitution of Pr for La leads to a reduction in both the crystal constant and the Curie temperature. A stepwise magnetic behaviour in the isothermal magnetization curves is observed, indicating that the characteristic of the itinerant electron metamagnetic (IEM) transition above TC becomes more prominent with the Pr content increasing. As a result, the magnetic entropy change is remarkably enhanced from 23.0 to 29.4 J/kgK as the field changes from 0 to 5 T, with the value of x increasing from 0 to 0.5. It is more attractive that the magnetic entropy changes for all samples are shaped into high plateaus in a wide range of temperature, which is highly favourable for Ericsson-type magnetic refrigeration.

Enhancement of Magnetocaloric Effects in Single Phase La<sub>1-z</sub>Nd<sub>z</sub>(Fe<sub>0.88</sub>S <sub>0.12</sub>)<sub>13</sub>

The single phase of a cubic NaZn13-type La1-zNdz(Fe0.88Si0.12)13 is obtained in the region z ≤ 0.2. The field-induced first-order transition from the paramagnetic to ferromagnetic state, that is, the itinerant-electron metamagnetic (IEM) transition is kept after the substitution of Nd. In addition, a discontinuous change of magnetization at the Cure temperature becomes larger with increasing z. As a result, the isothermal magnetic entropy change and the relative cooling power in the magnetic field change from 0 to 5 T increase to –27 J/kg K and 518 J/kg, respectively, by the partial substitution of z = 0.2.

Local Tunneling Spectroscopy across a Metamagnetic Critical Point in the Bilayer RuthenateSr3Ru2O7

The local spectroscopic signatures of metamagnetic criticality in Sr(3)Ru(2)O(7) were explored using scanning tunneling microscopy (STM). Singular features in the tunneling spectrum were found close to the Fermi level, as would be expected in a Stoner picture of itinerant electron metamagnetism. These features showed a pronounced magnetic field dependence across the metamagnetic critical point, which cannot be understood in terms of a naive Stoner theory. In addition, a pseudogap structure was observed over several tens of meV, accompanied by a c(2 x 2) superstructure in STM images. This result represents a new electronic ordering at the surface in the absence of any measurable surface reconstruction.

X-ray magnetic circular dichroism study of the decoupling of the magnetic ordering of the Er and Co sublattices inEr1−xYxCo2systems

We present an x-ray magnetic circular dichroism (XMCD) study performed at the Co $K$ edge and at the Er ${L}_{2,3}$ edges in the ${\mathrm{Er}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Co}}_{2}$ series. Our results indicate that both Er and Co magnetic sublattices order at the same temperature for all the investigated compounds. In the case of the ${\mathrm{Er}}_{0.6}{\mathrm{Y}}_{0.4}{\mathrm{Co}}_{2}$ compounds, XMCD data do not show the decoupling of the magnetic ordering for both Er and Co sublattices. Moreover, no experimental evidence of the occurrence of an inverse itinerant electron metamagnetism has been found for applied magnetic fields of up to ${\ensuremath{\mu}}_{0}H=10\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. In addition, a nonzero magnetic moment is found at the Co sites in the case of the ${\mathrm{Er}}_{0.5}{\mathrm{Y}}_{0.5}{\mathrm{Co}}_{2}$ compound.

Landau Coefficients Determined from Pressure-Induced Susceptibility Maximum in Itinerant-Electron Metamagnet La(Fe0.89Si0.11)13

The itinerant-electron metamagnetic (IEM) La(Fe 0.89 Si 0.11 ) 13 exhibits a susceptibility maximum phenomenon by applying the critical pressure p c = 1.3 GPa for the disappearance of the ferromagnetic state. Based on the relation between the maximum susceptibility and the critical field of the IEM transition, the 2nd, 4th and 6th-order terms of the Landau coefficients for the free energy have been obtained. A large negative value of the 4th-order coefficient is a marked feature in the present compound, resulting in a large entropy change at the transition.

Magnetic entropy change of itinerant electron metamagnetic systemCo(S1−xSex)2

The magnetic entropy change, $\mathrm{\ensuremath{\Delta}}{S}_{M}$, of $\mathrm{Co}({\mathrm{S}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x}{)}_{2}$ has been studied for $0\ensuremath{\le}x\ensuremath{\le}0.11$. Compounds with $0.03\ensuremath{\le}x\ensuremath{\le}0.11$ undergo a first-order magnetic transition and exhibit itinerant electron metamagnetism (IEM) just above the Curie temperature. We observed that the peak value of $\mathrm{\ensuremath{\Delta}}{S}_{M}$ shows a maximum at around $x=0.07$. The results are compared with the theoretically calculated results based on the spin fluctuation theory of IEM reported by Yamada and Goto. It is found that the experimental results are well described by the theoretical calculations. The origin of the peak of $\mathrm{\ensuremath{\Delta}}{S}_{M}$ is discussed from the thermodynamical point of view.

Reduction of hysteresis loss in itinerant-electron metamagnetic transition by partial substitution of Pr for La in La(Fe xSi 1−x) 13

The magnetocaloric effects (MCEs) and hysteresis loss in the itinerant-electron metamagnetic (IEM) transition process of La(Fe 0.86Si 0.14) 13 have been investigated by the partial substitution of Pr for La. The La 0.3Pr 0.7(Fe 0.86Si 0.14) 13 exhibits large MCEs in the magnetic field change from 0 to 5 T, which are almost the same as those of the higher Fe concentration of La(Fe 0.88Si 0.12) 13. Additionally, hysteresis loss in the IEM transition process of the former is smaller than that of the latter. Consequently, the La 1− z Pr z (Fe x Si 1− x ) 13 compounds are useful to realize large MCEs with smaller hysteresis loss as compared with that of La(Fe x Si 1− x ) 13.

Relative cooling power of La(Fe xSi 1−x) 13 after controlling the Curie temperature by hydrogenation and partial substitution of Ce

The relative cooling power (RCP) was evaluated in the itinerant-electron metamagnetic (IEM) La(Fe x Si 1− x ) 13 after controlling T C by hydrogenation and partial substitution of Ce for La. It is found that RCP is related to the temperature dependence of the IEM transition field B C and the change in the magnetization Δ M at the first-order Curie temperature T C. Since d B C/d T is irrelevant to T C, Δ M dominates the magnitude of RCP. The change of Δ M after controlling T C is caused by stability of the ferromagnetic state because of the increase of the Fe–Fe distance due to hydrogenation and by the hybridization of electron bands between Ce and Fe in the partially substituted system.

Pressure effect on thermopower of [formula omitted] alloy system

Thermopower of Y 1 - x Gd x Co 2 pseudobinary compounds has been measured at temperatures from 1.5 to 300 K under hydrostatic pressure up to 2 GPa and in magnetic field 0–15 T. In the inhomogeneous and paramagnetic regions of the phase diagram the main contribution to the electronic transport is related to the strong static magnetic fluctuations, which arise due to interplay of structural disorder within Gd-sublattice and Co-3d itinerant electron metamagnetism. This complex magnetic disorder brings about novel transport phenomena, such as anomalous positive magnetoresistance found in ferrimagnetic state of the alloys. The low-temperature thermopower is almost independent of alloy composition in the ferrimagnetic range of the phase diagram ( x > 0.3 ) indicating that the alloying does not change electronic structure of the compounds in a close vicinity of Fermi energy. However, the thermopower shows substantial variation with the composition in the inhomogeneous and in the paramagnetic regions of the phase diagram reflecting evolution of the magnetic structure with the composition.

Relation Between High-Field Magnetization and Microstructure in Bulk SmCo$_2.5$Cu$_2.5$

By varying the preparation, the microstructure of the rare-earth transition metal compound is modified. The samples were prepared by induction melting and, alternatively, by arc melting and at different annealing route afterwards. The occurring microstructure exhibits a phase separation within the hexagonal CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> -type structure. In a certain sample, a high-field transition was found. The temperature dependence of the transition field excludes the possibility of an itinerant electron metamagnetism. It could be shown that the microstructure is important for the field induced high-field transition

Magnetic instability within the seriesTCu3N(T=Pd, Rh, and Ru): A first-principles study

The binary nitride ${\mathrm{Cu}}_{3}\mathrm{N}$ is a semiconductor with a rather open, cubic crystal structure built up from rigid, perpendicular Cu-N-Cu covalent bonds. It has been reported experimentally that the voids in this structure can be filled with Pd atoms and that one ends up with $\mathrm{Pd}{\mathrm{Cu}}_{3}\mathrm{N}$, a rather unexplored member of the antiperovskite structure with semimetallic behavior. In an attempt to find new, weak itinerant magnetic materials composed of usually nonmagnetic elements, we have investigated the effect of adding Rh and Ru instead of Pd into the host ${\mathrm{Cu}}_{3}\mathrm{N}$ by employing density functional theory. We found out that $\mathrm{Rh}{\mathrm{Cu}}_{3}\mathrm{N}$ is very close to a magnetic critical point and thus is a good candidate for exhibiting either quantum critical behavior or itinerant electron metamagnetism. Contrarily, $\mathrm{Ru}{\mathrm{Cu}}_{3}\mathrm{N}$ already has a stable magnetic moment, but only the former compound $\mathrm{Rh}{\mathrm{Cu}}_{3}\mathrm{N}$ seems to be stable.

Itinerant-electron metamagnetic transition and giant magnetocaloric effect in La0.8Ce0.2Fe11.4Si1.6 compound

The itinerant-electron metamagnetic (IEM) transition and magnetocaloric effects (MCE’s) in the La0.8Ce0.2Fe13−xSix (x=1.6,1.4,1.2,1.0) compounds have been investigated by x-ray powder diffraction and magnetic measurements. The La0.8Ce0.2Fe11.4Si1.6 compound exhibits giant values of the isothermal magnetic entropy change ΔSM around the Curie temperature TC∼186K in low magnetic fields. The maximum value ∣ΔSM∣max∼78.29J∕kgK is under a field of 3T. Such large MCE’s are attributed to the sharp change of the magnetization, the field-induced IEM transition and a strong temperature dependence of the critical field BC. The substitution of Ce for part of La in La0.8Ce0.2Fe11.4Si1.6 increases the value of a(T)c(T)∕b(T)2 and enhances the property of IEM.

Large Magnetocaloric Effects and Thermal Transport Properties of La(FeSi)13 and Their Hydrides.

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Application of Large Magnetocaloric Effects in Itinerant-Electron Metamagnets to Cooling Systems

The La(FexSi1-x)13 compounds exhibit large magnetocaloric effects (MCEs) due to the itinerant-electron metamagnetic (IEM) transition. By hydrogen absorption, the Curie temperature TC increases up to room temperature with retaining the IEM transition. The La(Fe0.90Si0.10)13H1.1 compound indicates a large isothermal magnetic entropy change of ∆Sm = - 28 J/kg K at 287 K in the magnetic field change from 0 to 2 T (∆B = 2 T). In addition, the MCEs are enhanced by partial substitution of Ce for La. The value of TC for La(FexSi1-x)13 is decreased by partial substitution of Mn for Fe, keeping excellent MCEs. Consequently, the La(FexSi1-x)13 and their modified compounds are promising as magnetic refrigerants working at a wide range of temperature covering room temperature.

Pressure dependence of the Curie temperature and the spontaneous magnetization in ferromagnetic [formula omitted

Pressure effects on the Curie temperature and spontaneous magnetization in ferromagnetic Hf ( Fe 1 - x Co x ) 2 with the cubic Laves phase structure have been investigated under high pressures up to 1.2 GPa. An anomalously strong pressure dependence of the Curie temperature is observed around x = 0.725 . A collapse of ferromagnetic moment under pressure is also observed at x=0.6 and 0.65. These results are discussed on the basis of the spin fluctuation model of itinerant-electron metamagnetism.

Formula omitted] quasiparticles and avoided quantum criticality in U(Ru,Rh) 2Si 2

We discuss recent specific heat data in high magnetic fields on URu 2Si 2 and 4% Rh-doped URu 2Si 2 as well as previously published de Haas-van Alphen data at lower magnetic fields in pure URu 2Si 2; both of which are consistent with quasiparticle bands formed from a hybridization between 5f-electron Γ 5 doublets and regular conduction electrons. The system exhibits itinerant electron metamagnetism that gives rise to a putative quantum critical point at ∼34 −37 T (depending on the % of Rh) that is subsequently unstable to field-induced phases.

Low-temperature magnetostriction of Sr 3Ru 2O 7

Itinerant-electron metamagnetism in the bilayer ruthenate Sr 3Ru 2O 7 is studied by c-axis magnetostriction measurements on a high-quality single crystal in magnetic fields up to 18 T and at temperatures down to 20 mK. The positive linear magnetostriction coefficient suggests an initial decrease of the magnetization under c-axis uniaxial pressure. A highly enhanced magnetic Grüneisen parameter Γ H = 106 indicates a strong magnetoelastic coupling. The system is particularly sensitive to c-axis strain.

Temperature-induced itinerant electron metamagnetism

In multisublattice compounds consisting of a stable and magnetically unstable (metamagnetic) sublattices, the molecular field acting on the latter one, B mol ( met ) , decreases monotonously with increasing temperature. Hence temperature can be considered as an additional external parameter that can drive the magnetic state of the unstable sublattice. If the metamagnetic sublattice is in a high magnetic state at low temperatures, with increasing temperature at a certain critical value T m the internal field B mol ( met ) ( T m ) becomes equal to the critical field of the metamagnetic transition B m( T m). Then, above T m the metamagnetic sublattice will turn into a low magnetic state. This effect is named a temperature-induced itinerant-electron metamagnetism (TIMT). Recently TIMT has been found in the RCo 3 series. In most of these intermetallics, due to a strong intersublattice R-Co molecular field, the Co sublattice is in a high magnetic state at low temperatures and can be changed with increasing temperature into a lower magnetic one at a critical temperature for which B mol ( RCo ) ( T m ) = B m ( T m ) . The experimental results for some RCo 3 compounds are presented and discussed.

The 3d magnetization at first-order transitions of the rare earth Laves phasesR1−xYxCo2 studied by measurements of magnetic hyperfine fields

The magnetic phase transitions of pseudo-binary rare earth (R) Laves phasesR1−xYxCo2 have been investigated by perturbed angular correlation (PAC)measurements of the magnetic hyperfine fields at the probe nucleus111Cd forR = Tb, Sm and Ho at variousY concentrations x and for R = Gd, Dy, Er, Nd and Pr at the concentrationx = 0.3. First-order transitionswere observed in Tb1−xYxCo2 and Sm1−xYxCo2 for x≥0.3,in Ho1−xYxCo2 forx≤0.4 andin R0.7Y0.3Co2 forR = Dy, Ho, Er, Ndand Pr. For Gd0.7Y0.3Co2, the temperature dependence of the average magnetic hyperfine fieldis compatible with a second-order transition. The discontinuity of themagnetic hyperfine interaction at the first-order transitions of heavyR1−xYxCo2, which mainly reflects the jump of 3d magnetization of the Co subsystem atTC, was found to increase monotonically with decreasing order temperature. TheTC dependence of the normalized magnetic frequency with T0 = 203(5) K for the boundary temperature between first- and second-order transitionscan be explained by the temperature dependence of the coefficient of theM4 term of the free energy in the Wohlfarth–Rhodes–Shimizu theory of itinerant electronmetamagnetism.