Effect of interface magnetization depinning on the frequency shift of ferromagnetic and spin wave resonance in YIG/GGG films

Nowadays the yttrium iron garnet(Y3Fe5O12, YIG) films are widely used in the microwave and spin wave devices due to their low damping constant and long propagation distance for spin waves. However, the performances, especially the frequency stability, are seriously affected by the relaxation of the interface magnetic moments. In this study, the effect of out-of-plane magnetization depinning on the resonance frequency shift(△ fr) was investigated for 3-μm YIG films grown on Gd3Ga5O12(GGG)(111) substrates by liquid-phase epitaxy. It is revealed that the ferromagnetic resonance(FMR) and spin wave propagation exhibit a very slow relaxation with relaxation time τ even longer than one hour under an out-of-plane external magnetic bias field. The △ fr span of 15.15–24.70 MHz is observed in out-of-plane FMR and forward volume spin waves. Moreover, the △ fr and τ depend on the magnetic field. The △ fr can be attributed to that the magnetic moments break away from the pinning layer at the YIG/GGG interface. The thickness of the pinning layer is estimated to be about9.48 nm to 15.46 nm according to the frequency shifting. These results indicate that △ fr caused by the pinning layer should be addressed in the design of microwave and spin wave devices, especially in the transverse magnetic components.

Unusual magnetic relaxation in a single-molecule magnet with toroidal magnetic moments

We report the synthesis and characterization of a single-molecule magnet composed of triangular clusters of dysprosium ions.The structural study shows that the symmetry changes from one polar point group(mm2)at room temperature to another polar point group(m)at low temperature.Magnetic studies and theory calculations illustrate that the vortex distribution of magnetic dipoles in the triangular dysprosium clusters forms a toroidal magnetic moment.Interestingly,the analysis of AC magnetic susceptibility reveals the coexistence of three distinct magnetic relaxation processes,corresponding to the Raman,Orbach,and QTM relaxation pathways,respectively.The sum of three modified Debye functions is successfully used to describe the multiple relaxation behavior.

AN IMPROVED MODEL FOR COMPUTING SOLUTION DYNAMICS OF NATURAL PRODUCTS WITH ^(13)C NUCLEAR MAGNETIC RELAXATION

The fully anisotropic molecular overall tumbling model with methyl conformation jumps internal rotation among three equivalent sites is proposed,the overall tumbling rotation rates and the methyl internal rotation rates of ponicidin are computed with this model from ~C relaxation parameters.

Measurement of Magnetization Curve and Magnetic Relaxation for 2H-NbSe_2 Crystals

The characteristics of electronic transport properties: behaviors of magnetization curve and magnetic relaxation of a typical normal superconductor 2H?NbSe2 are investigated. The results show thatT c and ΔT c of the samples are 7. 2, 0. 18 K, indicating that superconducting energy gap at zero temperature is 1. 1. meV. No fish tail shape is found in the magnetization curves at several temperatures. The relationship between remnant magnetic moment and time reveals that the magnetic flux creep of the sample agrees with the Kim-Anderson thermal activation model with the relaxation rateS=0.00036 atT=6 K. Key words magnetization curve - magnetic relaxation - flux pinning CLC number O 511+. 4 Foundation item: Supported by the National Natural Science Foundation of China (10174056)Biography: Zhang Ning (1978-), male, Master candidate, reseach direction: high temperature superconductor.

A Simulation Study on the Specific Loss Power in Magnetic Hyperthermia in the Presence of a Static Magnetic Field

Our purpose in this study was to present a method for estimating the specific loss power (SLP) in magnetic hyperthermia in the presence of an external static magnetic field (SMF) and to investigate the SLP values estimated by this method under various diameters (D) of magnetic nanoparticles (MNPs) and amplitudes (H0) and frequencies (f) of an alternating magnetic field (AMF). In our method, the SLP was calculated by solving the magnetization relaxation equation of Shliomis numerically, in which the magnetic field strength at time t (H(t)) was assumed to be given by , with Hs being the strength of the SMF. We also investigated the SLP values in the case when the SMF with a field-free point (FFP) generated by two solenoid coils was used. The SLP value in the quasi steady state (SLPqss) decreased with increasing Hs. The plot of the SLPqss values against the position from the FFP became narrow as the gradient strength of the SMF (Gs) increased. Conversely, it became broad as Gs decreased. These results suggest that the temperature rise and the area of local heating in magnetic hyperthermia can be controlled by varying the Hs and Gs values, respectively. In conclusion, our method will be useful for estimating the SLP in the presence of both the AMF and SMF and for designing an effective local heating system for magnetic hyperthermia in order to reduce the risk of overheating surrounding healthy tissues.

Methods for Estimating Specific Loss Power in Magnetic Hyperthermia Revisited

Our purpose in this study was to present three methods for estimating specific loss power (SLP) in magnetic hyperthermia with use of an alternating magnetic field (AMF) and magnetic nanoparticles (MNPs) and to compare the SLP values estimated by the three methods using simulation studies under various diameters of MNPs (D), amplitudes (H0) and frequencies of AMF (f). In the first method, the SLP was calculated by solving the magnetization relaxation equation of Shliomis numerically (SLP1). In the second method, the SLP was obtained by solving Shliomis’ relaxation equation using the complex susceptibility (SLP2). The third method was based on Rosensweig’s model (SLP3). The SLP3 value changed largely depending on the magnetic field strength (H) in the Langevin parameter (§) and it became maximum (SLP3max) and minimum (SLP3min) when H was 0 and ±H0, respectively. The relative difference between SLP1 and SLP2 was the largest and increased with increasing D and H0, whereas that between SLP1 and was the smallest and was almost constant regardless of D and H0, suggesting that H in ξ should be taken as H0 in estimating the SLP using Rosensweig’s model. In conclusion, this study will be useful for optimizing the parameters of AMF in magnetic hyperthermia and for the optimal design of MNPs for magnetic hyperthermia.

Interfacial DMI in Fe/Pt thin films grown on different buffer layers

We study the interfacial Dzyaloshinskii-Moriya interactions(i-DMI)of Fe/Pt bilayers grown on Si substrates with MgO,SiO_(2),or Ta each as a buffer layer on the basis of wave-vector-resolved Brillouin light scattering(BLS)measurement.The obtained i-DMI energy values for Fe/Pt on MgO,Ta,and SiO_(2) buffer layers are 0.359,0.321,and 0.274 mJ/m~2,respectively.The large i-DMI value observed in Fe/Pt system on the MgO buffer layer can be attributed to the good interfacial quality and the Rshaba effect at the MgO/Fe interface.Moreover,the MgO/Fe/Pt system,benefiting from better sample quality,exhibits a lower damping factor.Furthermore,layer-resolved first-principles calculations are carried out to gain a more in-depth understanding of the origin of the i-DMI in the Fe/Pt system.The results indicate that in the Fe(110)/Pt(111)system,the substantial DMI energy between Fe spins at the interface is related to a significant change in spin-orbit coupling(SOC)energy in the neighboring Pt layer.In contrast,for the MgO(002)/Fe(002)system,both the DMI and its related SOC energy are concentrated at the interfacial Fe layer.Our investigation will provide a valuable insight into the spintronic community in exploring novel devices with chirality dependence.

Spontaneous magnetization and resistivity jumps in bilayered manganite (La_(0.8)Eu_(0.2))_(4/3)Sr_(5/3)Mn_2O_7 single crystals

Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal （La0.8Eu0.2）a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For （Lao.sEuo.2）a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.

Influence of nanosized magnesia on the hydration of borehole-sealing cements prepared using different methods

Gas drainage is an efective technology for gas control in coal mines.A high borehole-sealing quality is the fundamental precondition for efcient gas drainage.The expansibilities of cement pastes used in borehole-sealing processes are critical for the borehole-sealing efect.Nanosized magnesia expansive agents are used to improve the expansibilities of cement pastes and improve the borehole-sealing efect.Nuclear magnetic resonance spectrometry and scanning electron microscopy were adopted to study the efects of nanosized magnesia on the hydration of borehole-sealing cements used with diferent preparation methods.The results showed that an increase in the mass fraction of the nanosized magnesia promoted cement hydration,and the mass fraction was positively correlated with the promotion efect.The use of diferent preparation methods did not change the water-phase distribution in the cement.When using the wet-mixing preparation method,nanosized magnesia promoted the induction,acceleration,and deceleration periods of hydration;when using the dry-mixing preparation method,the nanosized magnesia promoted the induction period of cement hydration,and the promotion efect was less obvious than that seen when using the wet-mixing method.When using the wet-mixing preparation method,the nanosized magnesia was uniformly dispersed,thus enlarging the surface area of the reaction,which provided more nucleation sites for the hydration products of the cement and therefore accelerated the hydration reaction.When using the dry-mixing preparation method,the nanosized magnesia powders were dispersed nonuniformly and aggregated.Under these conditions,only a few nanosized magnesia particles on the surfaces of the aggregated clusters took part in hydration,so only a small number of nucleation sites were provided for the hydration products of cement.This led to inconsistent hydration of cement pastes prepared using the dry-mixing method.The surface porosity of the cement prepared with the wet-mixing preparation method frst decreased and then increased with increases in the mass fraction of the nanosized magnesia.The cement surface exhibited compact hydration products and few pores,and the surface was relatively smooth.In comparison,the surface porosity of the cement prepared using the dry-mixing method fuctuated with increasing mass fraction of the nanosized magnesia,resulting in a rough cement surface and microfractures on some surfaces.The two preparation methods both reduced the surface porosity of the cement.The wet-mixing preparation was more efective and consistent in improving the compactness of the cement than the dry-mixing preparation.These results provide important guidance on the addition of nanosized magnesia in borehole-sealing engineering and the selection of cement preparation methods,and they also lay a solid foundation for realizing safe and efcient gas drainage.

A Dinuclear Dysprosium-2-quinolinecarboxylate-1,10-Phenanthroline Compound:Crystal Structure and Magnetism

A dinuclear dysprosium（III） compound,[Dy2（μ2-OH）2（QLC）4（1,10-phen）2]·4H2O（1）（QLC-= 2-quinolinecarboxylate and 1,10-phen = 1,10-phenanthroline）,was synthesized and structurally and magnetically characterized.Compound 1 crystallizes in triclinic system,space group P1 with a = 10.9439（3）,b = 11.2823（3）,c = 12.2323（4） ？,α = 107.446（3）,β = 91.700（3）,γ = 91.511（2）°,V = 1439.25（8） A3,Z = 1,C（64）H（50）N8O（14）Dy2,Mr = 1480.12,Dc = 1.708 g/cm3,μ = 2.653 mm-1 and F（000） = 734.The final R = 0.0366 and w R = 0.0736 for 5816 observed reflections with I 〉 2σ（I）.Compound 1 contains the mononuclear [Dy（QLC）2（1,10-phen）] subunit formed from one 1,10-phen and two QLC-ligands chelating Dy（III） ion.Two mononuclear [Dy（QLC）2（1,10-phen）] subunits are bridged by a pair of μ2-OH groups to give a centrosymmetric dinuclear [Dy2（μ2-OH）2（QLC）4（1,10-phen）2] with each Dy（III） ion being eight-coordinated.Detailed susceptibility measurements revealed that compound 1 does not show slow magnetic relaxation under zero direct-current field but exhibits field-induced slow magnetic relaxation under 2 kOe applied field.

Resonant tunnelling of the magnetization in molecular crystal of [（Mn1-xCrx）12O12 （CH3COO）16（H2O）4]·2CH3COOH·4H2O（x=0,0.03,0.04,0.05）

The quantum tunnelling of magnetization （QTM） in single crystals of the single molecule magnet （Mn1-xCrx）12- Ac （x=0, 0.03, 0.04, 0.05） has been investigated. In comparison with its parent Mnl2-Ac, a greater rate of magnetization relaxation and a lower effective potential-energy barrier have been observed in Cr-doping samples. This modulation of QTM due to the Cr-doping could be attributed to the small change of Sz due to the smaller spin of Cr itself and additional intrinsic but distributed transverse and longitudinal anisotropy raised by a subtle change of the local environment in the magnetic Mn12 core.

COMPATIBILITY IN POLYMER BLENDS OF POLY (VINYL ACETATE) AND POLY (METHYL METHACRYLATE)STUDIED BY NMR

Compatibility of poly (vinyl acetate) (PVAc) with poly (methyl methacrylate) (PMMA) mixtures has been studied by using nuclear magnetic relaxation, differential scanning calorimeter and small-angle X-ray scattering techniques. The nuclear magnetic relaxation time T_1's were measured as a function of composition in blends of PMMA and PVAc prepared from chloroform solution. The results show that the system is miscible for casting from chloroform solution.

Water Efflux in Red Blood Cells of Sickle Cell Patients under Spontaneous Deoxygenation

The water transport through Red Blood Cells (RBC) membrane has been previously studied in Sickle Cell Disease (SCD) using oxygenated RBC or under complete deoxygenation. In this work, the water efflux in RBC of sickle cell patients was studied under spontaneous deoxygenation conditions. With that purpose, a magnetic resonance method was used to evaluate the water exchange time (τe) and the permeability through the erythrocyte membrane (P) measuring the spin-spin relaxation time (T2) in doped and non-doped RBC. Carr-Purcell-Meiboon-Gill (CPMG) pulse sequence was used to measure T2 in a magnetic resonance console coupled to one homogeneous magnet system (0.095 T). An increase of the water transport in RBC from sickle cell patients was observed and characterized with a τe value of 15.2 ± 0.8 ms. The abnormal activation of the Psickle, Gardos, and potassium chloride cotransporter channels starting from deoxygenation, as well as, the possible appearance of new pores due to the increase of the hemoglobin-membrane interaction, are suggested to explain this abnormal transport phenotype. The change of the water volume to surface ratio (V/S) in the sickle cells is also suggested to be considered in P calculation under deoxygenation. The results obtained in this work increase the fundamental knowledge about molecular mechanism involved in SCD and could be useful in the development of new methods for diagnostic and treatment evaluation.

Pinning Characteristics in a Single Crystal Nd-123 Superconductors at Low, Intermediate and High Temperatures Using Flux Creep-Flow Model

The pinning characteristics of a single crystal NdBaaCu3Oy superconductor at low （40 K）, intermediate （77.3 K） and high （88 K） temperatures were investigated. The experimental results of the critical current density dc and the apparent pinning potential u o which estimated from magnetic relaxation measurements are compared with the theoretical analysis based on the flux creep-flow model, taking the distribution of the flux pinning strength into account. The number of flux lines in the flux bundle （g2）, the most probable value of pinning strength （Am）, distribution width of pinning strength （σ-2） and other pinning parameters such as m, γ,δ are determined so that a good fit is obtained between the experimental and theoretical results. The behavior of these parameters is discussed in correspondence to the pinning characteristics of low, intermediate and high temperatures. The observed results are approximately consistent with the theoretical predictions of Brandt et al. model of the order-disorder transition.

Syntheses of new di-nuclear and tetra-nuclear lanthanide 9-anthracenecarboxylates:Magnetocaloric effect,slow magnetic relaxation and luminescent properties

Lanthanide complex-based materials with magnetic and luminescent properties have received a great deal of attention,owing to their importantly potential applications in diverse fields.In this work,the 9-anthracenecarboxylic acid(9-Haca)as bridging ligand was applied in combination with optically activeπ-conjugated 2,4,6-tri(2-pyridyl)-1,3,5-triazine(tptz)to construct a series of new di-nuclear and tetranuclear lanthanide 9-anthracenecarboxylates[La_(2)(9-aca)_(6)(tptz)_(2)(μ-H_(2)O)]·0.25H_(2)O(1),[Ln_(2)(9-aca)_(6)(tptz)_(2)(H_(2)O)_(2)]·0.5AQ·CH_(3)COOH_(2)H_(2)O[Ln=Sm(2a),Eu(2b),Gd(2c),Tb(2d),Dy(2e),Tm(2f);AQ=9,10-anthracenedione]and[Ln_(4)(9-aca)_(10)(tptz)_(2)(CH3COO)2]·H_(2)O[Ln=Eu(3a),Gd(3b),Dy(3c)].1 displays a di-nuclear centrosymmetric moiety[La_(2)(9-aca)_(6)(tptz)_(2)(μ-H_(2)O)]built up from two complex[La(9-aca)_(2)(tptz)]groups bridged by one H_(2)O molecule and two syn-syn-μ2-η1:η1-9-aca-bridging ligands,while 2a-2f are isostructural and co mprise another di-nuclear centrosymmetric moieties[Ln_(2)(9-aca)_(6)(tptz)_(2)(H_(2)O)_(2)]based on two complex[Ln(9-aca)_(2)(tptz)(H_(2)O)]groups connected by two syn-syn-μ2-η1:η1-9-aca-bridging ligands,3a-3c are isostructural and show tetra-nuclear centro symmetric moieties[Ln4(9-aca)10(tptz)2(CH3COO)2]containing three types of coordination modes of 9-aca-ligands.The present compounds offer the only examples of lanthanide 9-anthracenecarboxylates decorated by optically active tptz.Magnetic investigations of 2a,2c-2f,and 3b-3c indicate that 3c is typical of slow relaxation of the magnetization,while 2c and 3b show significant magnetocaloric effect(MCE)with the value of-ΔSm of 5.26 J/(kg·K)at 4 K and 15.65 J/(kg·K)at 2 K(ΔH=7 T),respectively.The luminescent properties were also studied and reveal that the characteristic luminescent properties of the 7r-conjugated aromatic ligands are introduced into magnetic lanthanide 9-anthracenecarboxylates,simultaneously exhibiting slow magnetic relaxation(or MCE)and luminescent properties.

Magnetocaloric effect and slow magnetic relaxation behavior in binuclear rare earth based RE_(2)(L)_(2)(DMF)4(RE=Gd,Tb,and Dy) complexes

Three binuclear rare earth based complexes combining RE ions with semirigid tricarboxylic ligand(H_(3)L).namely,[RE_(2)(L)_(2)(DMF)_(4)][RE=Gd,Tb,and Dy;H_(3)L=5-((4-Carboxybenzyl)oxy)isophthalic acid;DMF=N,N-dimethylformamide]complexes,were fabricated success fully.The RE_(2)(L)_(2)(DMF)_(4) co mplexe s consist of two central RE ions with the same coordination environment which were connected by two tridentate bridging carboxylic groups and two syn-syn bidentate bridging carboxylic groups originating from the L^(3-)ligands to form the{RE_(2)}dimeric unit,and thus provides the basis for further constructing a dense three-dimensional(3 D)network structure.Moreover,the present RE_(2)(L)_(2)(DMF)_(4) complexes can be described by a topology diagram with the topology point symbol of{4^(2)·6}_(2){4^(4)·6^(2)·8^(7)·10^(2)}.Weak antiferromagnetic(AFM)coupling between the adjacent RE ions for all the present complexes was found according to the magnetic calculations.The observed significant cryogenic magnetocaloric effect(MCE)with the maximum magnetic entropy change-ΔS_(M)^(max) to be 26.3 J/(kg·K)withΔH=7 T in Gd_(2)(L)_(2)(DMF)_(4) complex makes it competitive for the cryogenic magnetic refrigerant.Moreover,the slow magnetic relaxation behavior at 0.2 T dc field with an obvious large U_(eff)/k=45(4)K and τ_(0)=6.5(2)×10^(-10)s was confirmed in Dy_(2)(L)_(2)(DMF)_(4)complex.This work not only provides an effective strategy for obtaining molecular materials with high MCE,but also confirms that tricarboxylate ligands are the ideal choice for constructing stable high dimensional geometric structures.

Synthesis of two lanthanide clusters Ln^(Ⅲ)_(4)(Gd_(4) and Dy_(4)) with [2×2] square grid shape:Magnetocaloric effect and slow magnetic relaxation behaviors

Two isostructural tetranuclear lanthanide clusters named [Ln_(4)(L)_(4)(CH_(3) O)_(4)]·CH_(3) OH(Ln=Gd(Ⅲ) for 1,Dy(Ⅲ) for 2,H_(2) L=N’-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl) picolinohydrazide) were successfully isolated by using a polydentate Schiff based ligand and Ln(Ⅲ) nitrate salts.The structures of 1 and 2 were characterized by X-ray structural analyses,they are held by four double deprotonated ligands L2-.In them all the lanthanide ions are eight-coordinated and distributed over four vertices of a parallelogram,presenting a Ln4 cluster with a strict [2 × 2] square grid pattern.The details of magnetic analysis show that 1 displays weak anti-ferromagnetic exchange between neighboring Gd(Ⅲ) ions through carboxylate oxygen and methanol oxygen ligand atoms.Furthermore,1 exhibits significant magnetocaloric effect with the maximum entropy change-ΔSm value of 28.5 J/(kg K) for ΔH=7.0 T at 2.0 K.For compound 2,remarkable slow magnetic relaxation behaviors are observed in the presence of zero magnetic field with τ0=1.02 × 10^(-6) s and energy barrier ΔE/kB=43.24 K.

Two lanthanide(Ⅲ)-copper(Ⅱ) chains based on[Cu_2Ln_2]clusters exhibiting high stability,magnetocaloric effect and slow magnetic relaxation

Two 3d-4f heterometallic one-dimensional chains with neutral 4,4＇-bipyridine ligands as linkers and[Cu2Ln2] clusters （Ln = Gd for 1, Dy for 2） as nodes have been hydrothermally synthesized and structurally characterized. Magnetic studies indicate that complex 1 exhibits a relatively large magnetocaloric effect, with an entropy change -△Smax m= 24.8 J kg 1 K^-1, whilst, complex 2 features slow magnetic relaxation at low temperature.

Magnetic relaxation behavior of a spatially closed dysprosium(Ⅲ) phthalocyaninato double-decker complex

The SMM properties of the spatially closed Dy（Ⅲ） double-decker Pc complex Dy（obPc）2 （1）, which is equivalent to a pseudo dinuclear complex, are reported. Complex 1 crystallized with ethanol in the crystal lattice in the monoclinic space group P22/n and was isomorphous with Tb（obPc）2 （3）, which is arranged in a dimer structure along the b axis. The intermetallic Dy-Dy distance was determined to be 0.756 nm. ZMT versus T plots for 1 decreased with a decrease in T, which suggests the existence of an antiferromagnetic （AF） interaction between the Dy3＋ ions. The M-H curve for 1 at 1.8 K showed magnetic hysteresis. In ac susceptibility measurements on a powder sample of 1, which were dependent on the applied ac field, indicating that 1 is an single molecule magnet （SMM）, a maximum appeared at 22 K at an ac frequency 09 of 1488 Hz. The shape of the peaks dras- tically changed, and the peaks did not shift when an Hd~ large enough to suppress the quantum tunneling of the magnetization （QTM） was applied. The energy barrier （A/hc） was estimated to be 44 cm-1 with a pre-exponential factor （r0） of 1.6 × 10-5 s from an Arrhenius plot. Our results suggest that the SMM/magnetic properties of 1 significantly change in a dc magnetic field. These relaxation mechanisms are related to the energy gap of the ground state and to QTM.

Slow magnetic relaxation in a 3D dysprosium(Ⅲ)-fluoro-oxalate framework containing zig-zag [Dy-F]n chains

Dysprosium complexes based on [F-Dy] or near-linear [F-Dy-F] unit are of great concern in the field of single-molecule magnets due to their large magnetic anisotropy.Here,the crystal structure and the magnetic relaxation dynamics were reported for a three-dimensional(3 D) metal-organic framework(MOF):[DyF(C_(2)O_(4))(H_(2)O)2]n·2nH_(2)O(1),which is the unique MOF containing zig-zag [Dy-F]_(n) chains.Magnetic susceptibility characterization reveals that 1 is one of the few 3 D MOFs which show slow magnetic relaxation under zero dc field.And the effective energy barrier of 72 K for 1 is also higher than most Dy-based 3 D MOFs.The diamagnetic ion dilution study shows that the ferromagnetic exchange couplings mainly transmitted by F^(-) bridges in 1 contribute little to the energy barrier,but effectively suppress the quantum tunneling process and result in a smooth hysteresis loop with no waist-restricted step.