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Hard magnetic MnBi films were obtained by appropriate heat treatments of pulsed laser deposited (PLD) (Bi/Mn) films. X-ray diffraction patterns indicated a slight texture of MnBi crystallites and magnetometry measurements showed a slight preferential growth of the crystallites with their c-axis perpendicular to the film plane. Magnetic force microscopy (MFM) measurements displayed the presence of magnetic domains, whose size was in the micrometer range, and which were correlated to the MnBi grains observed in the sample. The addition of extra Mn layers did not modify significantly the previous structural and magnetic results. Nevertheless, the size of the magnetic domains increased to a few microns. However, on adding extra Bi layers, upon annealing, the MnBi grains grew with their c-axes perpendicular to the film plane. A perpendicular to the film magnetic anisotropy was deduced from the hysteresis loops, where an increase in the remanence of the magnetization was measured when the magnetic field was applied perpendicular to the film plane. In these samples, by measuring the magnetic domain configuration of the samples by MFM, we observed that the size of the magnetic domains exceeded the dimensions of the grains. This change in the magnetic structure of the films was assumed to be due to the coupling of the magnetization in the neighboring grains, and it was responsible for the decrease of the coercivity in the Bi rich samples. The authors acknowledge the partial finantial support from Universidad Publica de Navarra and from Gobierno de Espana. Open access funding by Universidad Publica de Navarra.

Hard magnetic MnBi films were fabricated using pulsed laser deposition (PLD). The films consisted of Mn/Bi bilayers and the thickness of each sample constant was 185 nm. The number of bilayers (5 to 80 bilayers) and consequently, the thickness of the Mn and Bi layers changed among the different samples, although the proportion of Mn and Bi remained constant in each bilayer. The structural and morphological changes in the Mn/Bi multilayered films were produced by thermal treatments and were monitored by measuring the change in their resistance as a function of the temperature. These measurements, along with the magnetic measurements, allowed us to determine the optimum heat treatments that induced the formation of the low temperature (LT) α-MnBi phase. A maximum value of both the magnetisation (460 emu/cm3) and the maximum BH product (46 kJ/m3) was observed in the sample with 40 bilayers, showing, in addition, a magnetic anisotropy, wherein the easy magnetisation direction was predominantly perpendicular to the plane of the sample. A detailed explanation of these changes and of the atomic diffusion processes present for such optimisation has been achieved.

Amorphous-nanocrystalline Co/Fe/Co soft magnetic multilayers were deposited by a pulsed laser. The thickness of the Co layers was constant at 18.7 nm for each layer and the Fe layer was varied between 0 and 110 nm. The spontaneous magnetization of the films was proportional to the Co and Fe layer thicknesses. Their isotropic saturation magnetostriction coefficients (λs) were determined. The λs changed from negative to positive values depending on the thickness of the Fe layer. The magnetostriction of the multilayers was greater than what would be expected from the proportional superposition of λs(Co) and λs(Fe) in the interval 0 ≤ x ≤ 50 at.% Fe. The maximum magnetostriction deviation was seen at an iron content of ≈26%. The larger experimental magnetostriction values are explained by an interface contribution, in which Fe and Co atoms diffuse into the adjacent layers. Assuming this interface contribution is due to the formation of two layers of Fe50Co50 in the trilayer structure, we were able to calculate the thickness and the magnetostriction coefficient of each interdiffusion layer, t(FeCo) = (1.4 ± 0.3) nm and λs(FeCo) = +(240 ± 10) × 10−6.

Non-crystalline Co films have been deposited on the cylindrical surface of copper wires by pulsed laser ablation deposition. These films are magnetoelastic. In particular, they exhibit the inverse Wiedemann effect (IWE): when they are twisted and an electrical current flows through the wires, a longitudinal component of the magnetization is observed. The value of the spontaneous magnetization, M s , of these films is achieved by the measurement of this effect. The dependence of the IWE on the torsion as well as on the circular magnetic field has been measured. The magnetostriction constant, λ s , has been found to be negative and λ s ≈−(9.5±0.8)×10 −6 .

The magnetic susceptibility of Fe–Al off-normal pulsed laser deposited thin films was measured at ultra high frequencies, UHF. Different Fe 1− x –Al x films from pure Fe to x = 0.2 Al were prepared. The films were ≈40 nm thick and non-crystalline peaks were detected by the X-ray diffractometry studies. The magnetization of the films remained between 2.0 and 1.8 T for composition less than or equal to 20% Al. A magnetic anisotropy, from H k ≈ 18 Oe for pure Fe to H k ≈ 130 Oe for 20% Al was measured. These samples exhibited a well-defined ferromagnetic resonance at frequencies between ≈2.0 GHz and 3.8 GHz depending on composition. The broad resonance peaks had a width, at half maximum, w h , in the interval from 2.5 GHz to 4.0 GHz depending on Al content. After fitting the magnetic hysteresis loops using a simple distribution of anisotropy values, we used the Landau–Lifshitz–Gilbert equation to fit the UHF magnetic susceptibility. From this last fit we obtained a high damping coefficient value (≈4 times higher than that corresponding to Co or CoFe films), explaining this broad ferromagnetic resonance of these Fe 1− x –Al x films.

We prepared pulsed laser deposited planar and cylindrical amorphous–nanocrystalline Co–Fe thin films using the corresponding target with composition Co 1− x Fe x , x = 0, 0.02, …, 1.0. Their room temperature spontaneous magnetization, M s (film), was always a fraction of the M s of the corresponding crystalline alloy, M s (film) = γ M s (crystal): γ ≈ 0.8 for pure Co, γ ≈ 0.88 for the Co 35 Fe 65 film and γ ≈ 0.94 for pure Fe. Their isotropic magnetostriction coefficient, λ s , was also determined. From pure Co to 30 at.% Fe λ s values were similar to those corresponding to the crystalline alloys: from pure Co to 4 at.% Fe was negative and of the order of 10 −6 ; λ s increased to 10 −5 up to 25 at.% Fe and achieved 10 −4 from 30 at.% Fe to 90 at.% Fe; λ s decreased to 10 −5 for pure Fe. A chemical short-range order between the Co atoms surrounded by the Fe ones, increasing the magnetic moment of Fe atoms, was used to explain the observed behavior.

Amorphous Co pulsed laser off-normal deposited films have shown uniaxial magnetic anisotropy. They have exhibited values of the anisotropy field between H u =12 and 770 Oe depending on the deposition angle and on the film thickness. We show for the first time the different like nano-string structures—8 to 20 nm width by 120 nm large—of these films. Also the magnetic domain pictures—sharpness zigzag charged walls for high magnetic anisotropic films and big zigzag Bloch walls for films with low anisotropy—are presented.

Amorphous Co films, ≈270 nm thick, were prepared by pulsed laser ablation-deposition. Substrates of glass, monocrystalline Si(1 1 1), copper and tungsten were used. The surface morphology of the films, studied by means of scanning tunneling microscopy, STM, as well as the coercive field, H c , and room temperature spontaneous magnetization, M s , was determined. The M s values were approximately the same for all films independent of the substrate; on the contrary, significant variation of H c was found for the films grown on different substrates. The lowest coercive field, H c ≈1.2 Oe, corresponds to the samples grown on glass and H c ≈1.6 Oe to the films deposited over Si(1 1 1) substrates, whereas H c ≈2.2 and 5 Oe were measured for the samples deposited over tungsten and copper substrates, respectively. The STM studies allowed us to correlate the different magnetic softness of the films—from both magneto-optical transverse Kerr effect and vibrating sample magnetometry—with their surface morphology.

CoP multilayers grown over Cu wires exhibit magnetoimpedance phenomenon. The change in the real part of the measured voltage is V R = [ V ( H = 0 Oe)- V ( H max )]/ V ( H max ) ≈ 3300%( I rms = 500 mA, 90 kHz); the maximum d V R /d H , is 1280%/Oe at H DC = 1.2 Oe. These quantities are enhanced if the wire is subjected to an angular deformation by means of a torque applied to the wire; V R ≈ 7000% and d V R /d H ≈ 2400%/Oe, are found at 9 and 1.2 Oe, respectively, for a 90° twisted sample, produced by the change in the magnetic anisotropy direction, from the longitudinal to the helical one.

In this work, we report the magnetic properties of a set of magnetic multilayers whose particular nanostructure allows control of their in-plane, uniaxial magnetic anisotropy value and consequently the magnetic susceptibility measured at ultra high frequencies. Particularly, two sets of samples with the compositions ((Co15 nm-54°) (Cox nm-0°) (Ta6 nm-54°)) n and ((Fe10 nm-54°) (Fex nm-0°) (Ta6 nm-54°)) n where n is the number of trilayers. In every sample, the obliquely and normally deposited ferromagnetic layers were strongly exchange-coupled. Consequently, the value of the uniaxial in-plane magnetic anisotropy could be controlled by changing the thickness of the normally deposited layer (x). Subsequently, the magnetic susceptibility of the samples could be tailored. Thus, the ferromagnetic resonance frequency value may be controlled and increased to up to 6.3 GHz for the samples with larger magnetic anisotropy values.

Over a 60 μm film with perpendicular anisotropy, a composition modulated multilayer, of the same material, has been grown. Investigations using Bitter domain configuration observations and surface hystetic loop measurements using magneto-optic Kerr rotation show that the multilayer magnetization process is coupled with the underlayer anisotropy for multilayer thickness of the order of the bulk stripes domain width.

CoP electrolytic monolayers and multilayers were grown over copper wires using a constant or pulsed electrical current density, exhibiting radial or planar anisotropy, respectively. Over the surface of a monolayer, multilayers of different thicknesses were deposited. The surface radial anisotropy evolves to a planar one as the overlayer thicknesses increase. The surface magnetization is coupled with the bulk anisotropy for overlayer thickness up to ≈ 2 μm.