Gd Magnetization Research Articles

Magnetization of Gd

Theoretical studies of the temperature (T) dependence of magnetization of Gd13 clusters have been carried out within a classical Heisenberg model using Monte-Carlo simulations. It is shown that for a broad range of values of , defined as the ratio between competing ferro and anti-ferro magnetic couplings, the cluster magnetization increases with T in the low T region, as seen in experiment. The clusters are also shown to exhibit a wide distribution of moments at a given T, which broadens significantly with increasing T. It is suggested that this may affect the observed magnetic behavior of magnetic clusters in Stern-Gerlach experiments.

Magnetic, Optical and Microwave Properties of Rare-Earth-Substituted Fibrous Yttrium Iron Garnet Single Crystals Grown by Floating Zone Method

We studied the crystallographic, magnetic, optical and microwave propagation properties of fibrous rare-earth-substituted Y2.7R0.3Fe5O12 (R:YIG) single crystals, grown by a simple floating zone (FZ) method with yttrium aluminium garnet (YAG) laser heating assisted by infrared irradiation, for all rare-earth elements. The first purpose of our studies was to seek outstanding properties of R:YIG crystals and the second aim was to obtain data in order to develop crystals with complex properties, such as large Faraday rotation and low saturation magnetization, by substituting two or more rare-earth elements for Y into the YIG crystal. The lattice constant, saturation magnetization, Faraday rotation, optical absorption coefficient, full-width at half aximum (ΔH) of ferromagnetic resonance and microwave propagation in magnetostatic wave (MSW) modes were measured for R:YIG single crystals. Low saturation magnetization in Gd:YIG and Tb:YIG, large Faraday rotation in Ce:YIG and low loss propagation of MSW in Lu:YIG were found. Our comprehensive results will also contribute to identifying new materials applicable in for optical and microwave devices utilizing R:YIG crystals.

Oxygen induced suppression of the surface magnetization of Gd(0001).

The effects of oxygen adsorption on the surface magnetization of Gd(0001) have been determined by measuring the polarization of the Gd 4f core levels and the oxygen induced states with spin-resolved photoemission. Calculations of the partial density of states of O/Gd(0001) using the LMTO-ASA method support the photoemission measurements, which indicate that oxidation occurs at low coverages. The loss of surface magnetic order with oxygen exposure is explained in terms of decreasing indirect coupling.

Temperature Dependence of the Mcxd at the GD Lm Edge

AbstractAn energy dispersive spectrometer is used to measure the temperature dependence of the Magnetic Circular X-ray Dichroism (MCXD) effect at the gadolinium (Gd metal) LIII absorption edge from 94 K to 335 K. In ferromagnetic Gd, the MCXD spectrum consists of the main positive peak with pre- and post-edge features. Only the main positive peak exhibits a temperature dependence similar to that of Gd magnetization. All other features decrease as the temperature increases and vanish slightly above the transition temperature (293 K). Well above the ordering temperature (paramagnetic Gd), the MCXD consists only of the positive peak, with a post-edge background that slowly decays away from it over a range of 90 eV.

The spin turning in ferromagnetic Gd studied by positive muons

We have studied the muon precession frequency in a ferromagnetic single crystal of Gd metal. The overall features of our findings are compatible with earlier results on polycrystalline material. In the temperature region between 245 and 220 K where the Gd magnetization starts to turn away from the c-axis, we observe an increase in the muon depolarization rate, and a complex precession signal which can be separated into two frequency components meaning that spin turning does not occur simultaneously in different parts of the sample (domains). From these more detailed data follows that previously obtained values forBfc andBdip can not both be correct. Two explanations for our new result are possible: EitherBfc undergoes a change around 230 K which is directly coupled to the spin turning angle, or the value of the dipolar field contribution used in the earlier evaluation is too low. This imposes some uncertainty as to the value of the angle at the onset of spin turning derived fromμSR frequencies.

Magnetization behaviour of Gd lead borate and Fe lead borate glasses under high magnetic field (20 T)

Magnetization of Gd and Fe lead borate glasses of varying composition was measured in magnetic fields up to 20 T and temperatures up to 7 K. A convenient variable to represent the data is η = gμ B H/ k B T and the data extend up to η 4. Low concentration data fit the Brillouin function, B J(η), and the value of effective magnetic moment per ion, P eff, thus deduced agrees well with that determined from the susceptibility measurement. For higher concentrations, where the magnetic interaction between ions had been deduced from susceptibility measurements, it is discussed how the data can be used, qualitatively at the moment, to infer the existence of magnetic clusters in the case of short ranged interaction of relatively closed Gd ions. In the case of Fe ions where it is believed that the interaction is stronger and is relatively long ranged, it is shown that M vs. H data at different temperatures do not collapse to single curve in M vs. η representation.

Gd magnetism studied by μSR at high pressure

Gd magnetism studied by μSR at high pressure

Magnetic anisotropy of perpendicular media on grooved structure substrate

Magnetic anisotropies were investigated for CoCr perpendicular magnetic films on grooved structure substrates (pitch length 2.1 mu m) prepared by CF/sub 4/-reactive-ion etching. Perpendicular magnetic anisotropy decreases in the region where groove depth GD >650 A. The reduction is due to the inclination of the crystal growth axis on the groove surface. In-plane magnetic anisotropy, K/sub u///, strongly depends on GD and saturation magnetization M/sub s/. In a region of large GD and large M/sub s/, Ku/sub /// is mainly due to shape anisotropy. In a region of small GD and small M/sub s/, K/sub u/// is caused by perpendicular magnetic anisotropy, in addition to shape and magnetorestrictive anisotropy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Surface magnetization of Gd at the bulk Curie temperature.

Surface magnetization of Gd at the bulk Curie temperature.

Origin of magnetic anisotropy in R2Fe14B (R=rare earth) compounds: Crystalline electric field model calculations (abstract)

The tetragonal R2Fe14B compounds have attracted a great deal of attention because of the permanent magnet applications of the Nd-Fe-B system. Nd2Fe14B shows a spin reorientation from an axial arrangement at 300 K to a conical-type structure below 140 K. In contrast, Pr2Fe14B remains axial down to 4.2 K. We show that this behavior in the Pr and Nd compounds results from an interplay of crystalline electric field (CEF) effects and the R-Fe exchange interaction. There are two inequivalent R sites ( f and g) in these compounds which are magnetically further split into f 1, f 2 and g1,g2 sites. The CEF parameters B02 and B22 for each site are taken from the 155Gd Mössbauer measurements in Gd2Fe14B and the R-Fe exchange field is estimated from the Gd magnetization.1 These parameters are suitably scaled for the rare-earth ion under consideration. It is shown that with the known values of B02, B22, and Hex and with B04 =0.118 K for Nd (which corresponds to B04 =0.35 K for Pr), the four-site calculation, employing these three CEF terms, predicts a spin reorientation in Nd2Fe14B at about 130 K but an axial behavior in Pr2Fe14B at all temperatures.

Low-Temperature Magnetization and Spin-Wave Excitations in Gd

The magnetization of Gd has been measured in the temperature 4<T<310 K at constant magnetic field using a vibrating sample magnetometer. We present an exact analysis of spin-wave excitations for Gd in the presence of a magnetic field, H. The low temperature magnetization is found to obey the form : Δσ(T)/σ(0)=BZ(3/2,Tg/T)T3/2+CZ(5/2,Tg/T)T5/2, where B and C are constants, Z(3/2,Tg/T) and Z(5/2,Tg/T) are the characteristic functions of T and H, indicating magnetic field effects.

3d-4f magnetic interactions and crystalline electric field in the R 2Fe 14B compounds : Magnetization measurements and Mössbauer study of Gd 2Fe 14B

Magnetization measurements on Gd 2Fe 14B single crystals show that the Fe anisotropy favors the c-axis of the tetragonal structure, as in Y 2Fe 14B. The exchange interactions between Gd and Fe spins are deduced from the temperature dependence of the Gd magnetization. A Mössbauer study with 155Gd shows the main axis of the electric field gradient to have different directions at the two rare-earth sites. Scaling the values obtained in Gd 2Fe 14 B yields values of exchange interactions between Nd and Fe spins (∼ 400 K) and of 2 nd order crystal-field parameters acting on Nd ions (∼ 300 K) in isomorphous Nd 2Fe 14B.

Magnetization of Gd and Er impurities in CEPd 3 and YPd 3

The magnetization of dilute Gd in YPd 3 and CePd 3 measured at 15 mK saturates at 7 μ B but does not follow the Brillouin curve or the magnetization calculated from the zero field CEF spectra, probably due to magneto- elastic coupling. There is a strong deficiency of the saturation magnetization of Er in CePd 3, most likely due to valence fluctuations in the matrix.

Limited quenching of the holmium moment by the crystal field in the (Gd,Y)Ni2cubic Laves phase compounds

The hyperfine interaction of $^{165}\mathrm{Ho}$ in the cubic Laves phase compounds ${\mathrm{Ho}}_{0.01}{\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Ni}}_{2}$ has been investigated by spin-echo NMR in the composition range $0&lt;x&lt;0.18$. In the end compound ($x=0$) a value of ${9.5}_{\mathrm{\ensuremath{\mu}}\mathit{B}}$ is obtained for the holmium moment which indicates a 5% quenching by the crystalline electric field. Further quenching takes place with substitution of yttrium for gadolinium. The magnetization anisotropy of these compounds is weak. The substitution of 1-at.% Ho for Gd suffices to rotate the easy axis of magnetization in Gd${\mathrm{Ni}}_{2}$ from the $〈110〉$ to the $〈100〉$ direction. This direction remains the easy magnetization direction in all compounds studied. The transferred hyperfine interaction is long range and analysis of data indicates considerable participation of the $d$ electrons in the hyperfine interaction in this series.

Magnetic properties of Gd xY 1− xNi 5 alloys

Magnetic measurements have been performed on single crystals of Yni 5 and GdNi 5 and on polycrystalline samples of Gd x Y 1− x Ni 5. YNi 5 is a Pauli paramagnet, the susceptibility of which is enhanced by exchange and slightly temperature dependent ( χ = 23 × 10 −4 emu/mole at 4.2 K). In GdNi 5, where the anisotropy is very weak, a polarization of the d band opposite to the Gd magnetization is observed. At 4.2 K, this polarization is 0.16 ± 0.02 μ B / Ni. The decrease of this polarisation with decreasing magnetic interactions has been studied in Gd x Y 1− x Ni 5-type alloys. It is concluded that the polarization is more homogeneous than that of cobalt observed in Gd x Y 1− x Co 2.

Magnetization and microwave resonance in Gd:Y alloys

Measurements of magnetization and microwave resonance have been carried out on six single crystal gadolinium-yttrium alloys, having compositions 6, 28, 53, 58, 59, and 64 at% gadolinium. From measurements in the temperature range 4K to 290K, values of the exchange parameters J(Q), J(0), Jfs have been estimated. A microwave resonance in the low temperature antiferromagnetic spiral phase has been observed for the 6 at% and 28 at% Gd alloys. Anisotropy constants have been derived from the microwave measurements in the ferromagnetic phases. The order of magnitude of K2 at 0K is 3*106 erg cm-3, and the hard axis of magnetization is the (0001)-c crystal axis.

Paramagnetic Impurities and Thermal Stability in Type II Superconductors

Magnetization, critical current, and flux-jump measurements have been made on superconducting La3In containing 1 at. % Gd. The previously reported nonmonotonic dependence of upper critical field on temperature has been confirmed. A low-temperature high-field regime is observed where critical currents increase with increasing temperature. This leads to improved thermal stability, i.e., less flux jumping, at low temperatures. The Gd magnetization data are near free-ion values, indicating only slight interaction effects.

Electrical Resistivity and Magnetization of Gd–Th and Gd–Mg Alloys

Electrical resistivity and magnetization measurements have been made over the 4.2–300-K temperature range on single crystal Gd1−xThx and on polycrystalline Gd1−xMgx samples with 0&amp;lt;x&amp;lt;0.15. This work was done because quadrivalent Th increases the number of conduction electrons and hence raises EF, whereas divalent Mg decreases the number of conduction electrons and so lowers EF. Fermi surface changes might then be expected. The most interesting result was obtained with Gd0.88Mg0.12, which showed an increase in resistivity with decreasing temperature below 260 K. The magnetic measurements indicated that all samples ordered ferromagnetically.

Green's Function Theory of a Heisenberg Ferromagnet with Strong Dipole-Dipole Interactions: Magnetization of GdCl3

We have investigated the magnetization as a function of $T$ and $H$ of a spin system with both isotropic Heisenberg exchange and dipole-dipole interactions for $S\ensuremath{\ge}\frac{1}{2}$ and a hexagonal crystal structure. The Green's functions for such a system, recently derived by Becker, are decoupled in a first-order random-phase approximation. For both Heisenberg-dipole and simple-dipole crystals, we find a lowering of the magnetization below saturation at $T=0$. The Curie-Weiss temperature $\ensuremath{\theta}$ and the ordering temperature ${T}_{c}$ are calculated and compared with experimental values on Gd${\mathrm{Cl}}_{3}$. In the limit of zero exchange, we obtain a condition for the type of lattice and shape of domains which make ferromagnetic ordering possible.

Direction of Easy Magnetization in Gadolinium

The direction of easy magnetization in Gd is studied as a function of temperature and pressure. The pertinent experimental results have already been given by Robinson, Milstein, and Jayaraman. A Gd sample was used as the core of a small transformer; a constant input voltage was supplied to this transformer. The secondary voltage was monitored as a function of temperature at several constant pressures. The secondary voltage of the transformer, being proportional to the permeability of the sample, is a sensitive indicator of changes in magnetic structure in the Gd sample. Typically, the secondary voltages behave as follows as the temperature of the transformer is lowered: A sharp rise in the secondary voltage occurs at the Curie temperature, followed by another sharp rise at a temperature well below the Curie point. The magnitude of the secondary voltage at this latter transition is from two to three orders of magnitude greater than at the transition from the paramagnetic to the ferromagnetic state. This transition is interpreted as a magnetic transition in which the direction of easy magnetization in Gd deviates from the $c$ axis. The angle of deviation is discussed in terms of the (small) anisotropy constants resulting from the weak crystalline field in Gd. In terms of the output voltage, one is able to obtain the relative deviations of the direction of easy magnetization from the $c$ axis. The temperatures, as a function of pressure, at which the maximum deviations occur can also be obtained. As the temperature is lowered further, the direction of easy magnetization starts to approach the $c$ axis again. Comparisons are made with other measurements of this angle of deviation.