Amorphous RE Research Articles

Magnetic properties and magnetocaloric effect in RE 55Co30Al10Si5 (RE = Er and Tm) amorphous ribbons

The magnetic and magnetocaloric effects (MCE) of the amorphous RE 55Co30Al10Si5 (RE = Er and Tm) ribbons were systematically investigated in this paper. Compounds with R = Er and Tm undergo a second-order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) around Curie temperature T C ∼ 9.3 K and 3 K, respectively. For Er55Co30Al10Si5 compound, an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K, possibly due to spin-glass behavior. Under the field change of 0 T–5 T, the maximum values of magnetic entropy change () reach as high as 15.6 J/kg⋅K and 15.7 J/kg⋅K for Er55Co30Al10Si5 and Tm55Co30Al10Si5 compounds, corresponding refrigerant capacity (RC) values are estimated as 303 J/kg and 189 J/kg, respectively. The large MCE makes amorphous RE 55Co30Al10Si5 (RE = Er and Tm) alloys become very attractive magnetic refrigeration materials in the low-temperature region.

Magnetic amorphous RE–Co–B–Na colloidal nanoparticles with high critical temperature

High temperature solution synthesis is afforded to the preparation of RE–Co–B–Na colloidal nanoparticles with particle size of 20nm. It is interesting that the critical temperature (TC) of Sm–Co–B–Na nanoparticle with 20nm is high, up to over 400K, for which the possible magnetic coupling mechanism is discussed.

Amorphous RE–Fe–B–Na colloidal nanoparticles: High temperature solution synthesis and magnetic properties

RE–Fe–B–Na (RE=Nd–Er) colloidal nanoparticles are prepared by high-temperature solution synthesis. These nanoparticles are ultra-small monodisperse, air-stable and amorphous, whose particle size and magnetic property are characterized by transmission electron microscope and superconducting quantum interference device. Taking Nd–Fe–B–Na nanoparticle as an example, it is found that the particle size can be controlled in less than 7nm. Besides, the magnetic properties of RE–Fe–B–Na colloidal nanoparticles can be compared for different rare earth elements. Based on the bulk ferromagnetic coupling, other possible magnetic coupling mechanism is discussed.

Large spontaneous Hall angle in [Co, CoFe/Pt] multilayer

We have quantitatively investigated the Hall effect in [Co, CoFe/Pt] multilayer films. The [Co, CoFe/Pt] multilayers exhibit large spontaneous Hall resistivity ( ρ H) and Hall angle ( ρ H/ ρ). Even though the Hall resistivity in [Co, CoFe/Pt] multilayer films (2.7–4 × 10 −7 Ω cm) is smaller than that of amorphous RE–TM alloy films which show large spontaneous Hall resistivity (<2 × 10 −6 Ω cm), the Hall angle of multilayer (6–8%) is almost twice than that in amorphous rare earth–transition metal alloy films (∼3%). The Hall angle provides evidence of the effects of the exchange interaction of the Hall scattering. The exchange is between conduction electron spins and the localized spins of the transition metal. The large Hall angle of [Co, CoFe/Pt] multilayer can be considered due to the high spin polarization and high Curie temperature of Co and CoFe transition metal layers. Even though the role of interfaces and surfaces in the magnetic properties of multilayer films may dominate that of the bulk, the Hall effects in [Co, CoFe/Pt] multilayer may be mainly dominated by the bulk effect.

Fabrication of MgO barrier for a magnetic tunnel junction in as-deposited state using amorphous RE–TM alloy

MgO (1 0 0) textured films on Fe buffer layer with (1 0 0) preferential orientation were prepared by a reactive facing targets sputtering system at a substrate temperature of 100 °C during MgO deposition. This process can allow fabrication of MgO (1 0 0) tunneling barrier layer without high-temperature annealing process after the sputter-deposition. In addition, FeCo (1 0 0) preferred orientation films prepared on GdFeCo layers were improved with GdFeCo thickness. MgO films deposited on Fe (or FeCo) buffer layers revealed apparent (1 0 0) preferred orientation at the early stage of the film growth. 3 nm-thick MgO films deposited on GdFeCo [100 nm]/Fe [3 nm] exhibited (1 0 0) texture. Magnetic characteristic of perpendicular-magnetic tunnel junction (P-MTJ) element with the structure of GdFeCo [100 nm]/Fe [3 nm]/MgO [3 nm]/Fe [3 nm]/TbFeCo [100 nm] exhibited high squareness ratio of 0.8 and coercivity of free layer as low as 117 Oe by anomalous Hall effect, and (1 0 0) preferred orientation of 3 nm-thick MgO layer was observed by an X-ray diffractometer.

Characterization of local anisotropy and anisotropy dispersion of amorphous CoZrRE with rare earth REPr and Nd

The magnetic properties of rf sputtered amorphous (Co 93Zr 7) 100− x (RE) x thin films were investigated where REPr and Nd and for a content of 0 < x < 3.5 by Transverse Biased Initial Susceptibility measurements. Clear relationships could be established between K u and K loc. The data are discussed in terms of single-ion anisotropy of the RE.

Magnetic properties of Fe-based icosahedral cluster amorphous alloys

Structural and magnetic studies of amorphous RE(Fe 1− x Al x ) 13 alloys (RE ≡ rare earth metal) have been carried out. These alloys consisted of icosahedral clusters which exist in the crystalline state. The nearest-neighbor distance of the FeFe pairs is about 2.5 Å. Their isomer shifts are almost the same, suggesting a similar electronic state. These alloys exhibit a re-entrant spin-glass behavior and the spin freezing temperature is hardly changed by replacing RE because there is not change in the FeFe distance in the icosahedral clusters. On the contrary, the Curie temperature depends on the RE in a similar manner to that of many Fe-based amorphous alloys.

Spin-reorientation phase transitions in thin films of RETM amorphous alloys

Taking into account the stochastical nature of the magnetic microstructure of amorphous RETM alloys, we have developed a description of phase transitions induced by a magnetic field. H- T diagrams corresponding to these transitions are obtained. The presence of new stochastic phases (asperomagnetic) has been found. Special features of spin-reorientation in the compensation point region are discussed. The influence of the surface anisotropy on the magnetic structure and phase diagrams has been studied. Using the Lagrange-Euler equation we have renormalized the bulk anisotropy. The theory can be applied to the amorphous films R x T 1− x , where R = Gd, Ho, Tb, Dy and T = Fe, Co.

Bulk magnetic behaviour of amorphous RE 0.67Zr 0.33 (RE = Tb, Gd) alloys

The magnetic behaviour of amorphous RE 0.67Zr 0.33 (RE = Tb, Gd) alloys has been studied by magnetization measurements in applied field up to 4.7 T, in the temperature range from 300 to 1.7 K. Both alloys show a positive paramagnetic Curie temperature (⊝ p) and the presence of a susceptibility cusp at the characteristic temperature T f. The evolution of the magnetic behaviour of RE 0.67Zr 0.33 alloys from paramagnetic state, at high temperature, to correlated clusters, below T f, through an intermediate region - superparamagnetic state in the case of a Gd 0.67Zr 0.33 alloy - has been studied. We assign the absence of magnetic saturation at 1.7 K in a field of 4.7 T for both alloys, to variations of exchange interaction sign for Gd alloy and dominant local anisotropy for Tb alloy, respectively. We show that these alloys obey the scaling law over a large temperature range and we determine the Curie temperature of clusters in agreement with the order already observed by neutron scattering.

Spin glass order parameter in RE 40Y 23Cu 37 amorphous alloys (RE = rare earth)

The low field ( H a.c. ⋍ 0.05 Oe) and low frequency (15 Hz) a.c. susceptibility has been measured for the amorphous alloys RE 40Y 23Cu 37, with RE = Gd, Tb, Dy, Ho, and Er. The susceptibility exhibits a cusp, characteristic of a spin-glass phase transition from paramagnetic state. Gd 40Y 23Cu 37 seems to exhibit a mixed ferromagnetic-spin glass phase below 62.5 K. Using the Sherrington-Kirkpatrick mean field theory, we have determined, from the observed cusps, the temperature dependence of the Edwards-Anderson spin glass order parameter, the dependence, consistent with theory, being in the form q( T) = A( T SG − T) β , with β ⋍ 1.

Planar Hall effect in thin amorphous RE–TM films with perpendicular anisotropy

The planar Hall effect (PHE) is studied in amorphous rare earth-transition metal (RE-TM) films with effective perpendicular anisotropy. Anomalous Hall resistivity, ∂H, is measured in a magnetic field applied nearly parallel to the film plane. The dependence of the shape of the PHE-loop on the effective perpendicular anisotropy is discussed on the basis of the model of simple coherent rotation of the Msvector. The effective perpendicular anisotropy field, HKeff, is determined from the PHE-loop parameters. The theoretical results are compared with those obtained experimentally for thin amorphous HoCo films. When the anisotropy of the measured samples is changed by varying the temperature, the agreement between the theoretical and experimental results depends on the temperature difference from the compensation temperature. The wider is the temperature interval the better is the agreement. This fact suggests that the anisotropy dispersion, being due to the inhomogeneities in the alloy composition is a significant source of uncertainity for the results obtained. Es wird der planare Halleffekt (PHE) in amorphen Seltenerdenubergangsmetall (RE–TM)-Schichten mit effektiver senkrechter Anisotropie untersucht. Ein anomaler Hallwiderstand, ∂H, in einem nahezu parallel zur Schichtebene angelegten Magnetfeld wird gemessen. Die Abhangigkeit der Form der PHE-Schleife von der effektiven senkrechten Anisotropie wird auf der Grundlage eines Modells einer einfachen koharenten Drehung des MsVektors diskutiert. Das effektive senkrechte Anisotropiefeld, Hgefl, wird aus den PHE-Schleifenparametern bestimmt. Die theoretischen Ergebnisse werden mit experimentellen Werten an dunnen amorphen HoCo-Schichten verglichen. Wenn die Anisotropie der gemessenen Proben durch Variation der Temperatur geandert wird, hangt die Ubereinstimmung zwischen theoretischen und experimentellen Werten von der Temperaturdifferenz von der Kompensationstemperatur ab. Je groser das Temperaturintervall ist, um so besser ist die Ubereinstimmung. Dies zeigt, das die Anisotropiedispersion infolge der Inhomogenitaten in der Legierungszusammensetzung eine wesentliche Quelle fur die Unsicherheit der erhaltenen Ergebnisse darstellt.

Magnetic properties of amorphous RE&amp;lt;inf&amp;gt;65&amp;lt;/inf&amp;gt;Al&amp;lt;inf&amp;gt;35&amp;lt;/inf&amp;gt;alloys

Ribbons of amorphous RE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">65</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf> alloys (where RE = Ce, Pr and Dy) were prepared by melt spinning under vacuum. Magnetization measurements, carried out on a vibrating sample magnetometer with magnetic fields <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H \leq 20</tex> kOe and over a temperature range 2.8°K <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\leq T \leq 300</tex> °K, are reported here. Dy <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">65</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf> and Pr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">65</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf> demonstrated a ferromagnetic-like ordering which was characterized by the appearence of a cusp at 30 °K and 7 °K, respectively. In both cases, hysteresis and relaxation effects occurred below the ordering temperature. Amorphous Ce <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">65</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</inf> exhibited a negative paramagnetic Curie temperature of -40 °K, but did not order for temperatures down to 2.8 °K. The results are discussed in terms of the random atomic arrangement and its influence on the exchange and anisotropy interactions.

Spin glasses in amorphous and crystalline RE alloys

Recent experimental results on spin glasses in crystalline and amorphous RE systems are reviewed. Main emphasis of this paper will be on the bulk magnetic properties of metallic spin glasses containing Gd. The effects of Gd in the dilute limit (x < 1 at. %) are compared with those observed in 3d impurity systems. The case of amorphous alloys is discussed. Finally, we present a cluster description of magnetic properties in concen­ trated (1 < x < 32 at. %) amorphous 'L&ao_xG&li£M20 spin glasses.

Amorphous rare-earth alloys: random-anisotropy antiferromagnetism

The model of randomly oriented single-ion uniaxial anisotropy field is extended to the case of antiferromagnetic exchange interaction between rare-earth ions. A self-consistent two-spin cluster approximation is used to calculate the magnetization curves for a model system of spin 1. The results are in good qualitative agreement with experimental data on amorphous RE x Cu 1− x and RE x Ag 1− x alloys (RE = Tb, Dy, Ho). In particular, the observed increase of the “coercive” field with increasing x in RE x Cu 1− x alloys is accounted for.

Bulk magnetic properties of the amorphous alloys RE&amp;lt;inf&amp;gt;50&amp;lt;/inf&amp;gt;Ag&amp;lt;inf&amp;gt;50&amp;lt;/inf&amp;gt;(Re = Gd, Tb, Dy, Ho, and Er)

The initial susceptibility and magnetization as a function of applied field and temperatures have been measured for the amorphous alloys RE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> Ag <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> (RE=Gd, Tb, Dy, Ho, and Er). These have been supplemented by measurement of the time dependence of magnetization. All these alloys exhibit a spontaneous magnetization at low temperatures. An order of magnitude for the magnetic anisotropy has been determined from the experimental data. The diverse phenomena responsible for magnetic ordering and the magnetic after-effect are analysed and discussed.