L. Benito

Magnetocrystalline anisotropy in a (110)?(Tb0.27Dy0.73)Fe2 thin-film

Magnetic anisotropy measurements performed in a (110) (Tb0.27Dy0.73)Fe2 (Terfenol-D) film epitaxially grown on a sapphire substrate are presented. The magnetic torque curves have been determined by using a vectorial vibrating sample magnetometer, which allows us to measure the angular dependence of magnetization components parallel, , and perpendicular, , to the applied field up to 2 T. The fourfold symmetry associated with the cubic structure within the (110) plane is clearly observed. The analysis of the experimental torque has been carried out considering magnetocrystalline anisotropy up to sixth order and magnetoelastic energy up to second order; so, the magnetocrystalline anisotropy constants in the (110) plane of the film, K1 and K2, have been obtained. This allows us to determine the direction of the magnetization easy axis for (110) Terfenol-D thin-film: it is at RT, passes through at 140 K and then changes to at 40 K. It was completely impossible to explain the angular dependence of the experimental magnetic torque without including shear and tetragonal magnetoelastic stress parameters, b2 and b1, respectively. This confirms the paramount role of the strain in the determination of the magnetic properties in this kind of Terfenol-D thin film.

High-sensitivity vector magnetometer for measuring magnetic torque at low temperatures

We present a fully automated vector vibrating-sample magnetometer where the sample can be rotated against the applied magnetic field Hap, so that the angular dependence of the longitudinal, Mlong, and transversal, Mtrans, components of M with respect to Hap on the rotation plane are determined. The magnetic field range is ±20kOe and temperature ranges between 4.2 and 340 K. The resolution is better than 2×10−7emu and the sensitivity is 5×10−6emu. Standard hysteresis loop measurements are possible as well. As examples of its capability we display torque curves performed at low temperatures in a [Ho8Lu15]50 superlattice and in a 60-nm-thick Terfenol-D thin film.

Magnetoelastic stresses in rare-earth thin films and superlattices

A study of the magnetoelastic behavior of some rare-earth based thin films and superlattices (SLs) is reported. Magnetoelastic stress (MS) measurements are made by a cantilever capacitive technique over a wide range of temperatures (10–30 K) and magnetic fields (up to 12 T). Expressions are derived which relate the cantilever curvatures and the magnetoelastic stresses in anisotropic thin films and SLs (of cubic symmetry) deposited on crystalline substrates. The magnetoelastic energy associated with the interfaces and the epitaxial stress dependence of the volume MS are investigated by studying the basal plane MS in Hon/Lu15 and Ho10/YmSLs: interface MSs even higher than the volume ones are obtained, and the effect of the epitaxial strain on the bulk MSs is large. The MS contributions are also deduced for Dy/Y and Er/Lu SLs, but for ER/Lu incomplete saturation leads to inconclusive results. Although the latter also happens in Ho/Tm SLs, the effect of the epitaxial strain on the bulk MSs is large. The MS cl...

The magnetostriction of Tb, Dy and Ho revisited

In this paper we present re-analyses of magnetostriction measurements earlier performed in terbium, dysprosium and holmium single crystals. In the framework of the standard theory of single-ion crystal-electric-field and two-ion exchange magnetostrictions, we explain the thermal variation of the anisotropic saturation magnetostriction within the basal plane by considering high-order terms in the magnetoelastic energy. Using complementary basal-plane magnetic anisotropy measurements, we have been able to obtain the second- and fourth-order magnetoelastic coupling parameters associated with the orthorhombic distortion of the hexagonal plane for the above-mentioned three heavy rare earths.

Magnetic transitions and magnetoelasticity in double rare earth superlattices

Abstract We report on zero field cool susceptibility ( χ ZFC ), magnetization ( M ) and magnetoelastic stress (MELS) measurements, in the range 8–200 K and up to 12 T applied magnetic field, on (0001) superlattices [Ho 15 /Dy 30 ] 50 and [Ho 30 /Dy 15 ] 50 . Magnetic phase diagrams are proposed, with a wide variety of magnetic phases: paramagnetic, helical, helifan, fan and ferromagnetic. Same magnetic phases for Dy and Ho coexist. Exchange polarization of Ho layers by Dy ones is manifested. Although compressed by basal plane a -lattice parameter misfit, spontaneous ferromagnetic order in Dy layers is suppressed, as well as ferro-cone phase in stretched Ho ones. However, modest applied magnetic field along b -axis ( H ≅0.6 T, at 10 K) produces ferromagnetic order in Dy (in basal plane) and ferro-cone in Ho. The basal plane hexagonal symmetry breaking magnetoelastic stress M γ ,2 ( T =0, 12 T) is separated for Ho and Dy layers, in good agreement with single-ion magnetoelastic coupling model.

Magnetostriction of Rare-Earth Based Thin Films And Superlattices

We present a study of the magnetoelastic behaviour of some Rare-Earth based thin films and superlattices. Magnetoelastic stress mea- surements, performed by using a cantilever capacitive technique, within a wide range of temperatures (10–300 K) and magnetic fields (0–12 T) are reported. To analise the experimental results and to obtain the magne- toelastic coupling parameters, we derive expressions relating the cantilever curvatures and the magnetoelastic stresses in anisotropic thin films and su- perlattices (for cubic symmetry) deposited onto crystalline substrates. The thickness and temperature dependencies of the magnetoelastic parameters are employed to determine the possible contributions to the magnetoelastic stresses and their origin.

Magnetic phase diagram of holmium/dysprosium superlattices

Abstract We report on the magnetisation measurements with a magnetic field applied along the HCP-structure b -axis for Ho/Dy magnetic superlattices (SLs). The zero-field-cool susceptibility, χ ZFC , shows the magnetic-order coexistence of the Ho and Dy layers, below their respective ordering temperatures. The magnetic-phase diagrams (MPD) of Ho/Dy SLs have been obtained from magnetisation measurements, and we found that the magnetic phases of the Ho and Dy layers are very similar to the bulk ones. Although the analysis of the high-field magnetisation indicates that Ho and Dy do not interact magnetically, this coupling exists at low field. The increment of the Neel temperature in the Ho layers with respect to the bulk could reflect some kind of polarisation between Ho and Dy layers. In the MPD that we have proposed for Ho/Dy SLs, a huge region exists where an helifan phase remains stable for both rare-earth layers, especially for the Ho 30 /Dy 15 SL. This could represent the first time that the helifan phase of Ho layers stabilises a similar phase for Dy layers, due to the coherent propagation of conduction band electrons through Ho and Dy layers. However, at low temperatures, we do not expect to find the ferro-cone phase in Ho layers as in the bulk, because of the epitaxial strain in between the Ho and Dy layers of the superlattice.