M. Porte

Magnetic properties of Ni/Pt multilayers

We have grown Ni/Pt multilayers (ML) with and without Pt buffer layer, by evaporation under UHV conditions on glass and Si substrates maintained at 30 and 200 °C. The magnetization decreases with t(Ni) and no induced moment is found on Pt from polarization effects even at 5 K. The perpendicular magnetization loops for samples with t(Ni)≤17 A are rectangular and coercivities as high as 4.7 kOe is obtained for t(Ni)=9 A at 5 K. For the samples deposited at 20 °C, due to dispersion in the results, KS could not be calculated with accuracy though it is positive. But for the samples deposited on a Pt buffer layer at 200 °C, KS is found to be +0.17 erg cm−2 at 5 K and the volume anisotropy is also higher with respect to those deposited at 30 °C.

Anisotrophy and magneto-optical studies in evaporated Co/Pt multilayers

Co/Pt multilayer films have been prepared by evaporation under UHV (ultrahigh-vacuum) conditions, and their magnetic and magnetooptical properties were studied. For samples with Co-layer thickness below about 1 nm, rectangular loops are observed with H/sub c/ on the order of 1 kOe. For these samples, the uniaxial anisotropy is as high as 1*10/sup 7/ erg cm/sup -3/, and it depends on the relative thicknesses of both Pt and Co. While the polar Kerr rotation decreases with decreasing Co-layer thickness, the Faraday rotation, on the contrary, is seen to increase strongly. This increase has been attributed to the presence of a Co-Pt alloy layer formed by mixing at the interfaces; its thickness has been estimated to be about 0.3 nm. Faraday rotation study is hence a useful tool in characterizing the multilayers. It is suggested that this layer plays an important role in the origin of K/sub u/. It has been found that M and K/sub u/ are practically independent of temperature for 5 >

Ferrimagnetic thin films prepared by pulsed laser deposition

Abstract Thin films, with thickness ranging from 25 nm up to 1.5 μm, of well-known ferrimagnetic materials such as NiFe2O4, CoFe2O4, Ni0.5Zn0.5Fe2O4, and BaFe12O19 have been prepared by PLD. Films made at low substrate temperature (T

Magnetisation and anisotropy studies in sputtered TM/V (TM Fe, Co, Ni) multilayers

Abstract We have prepared Fe/V, Co/V and Ni/V multilayers by rf sputtering and studied their magnetisation and anisotropy at 295 and 5 K. In Fe/V the dead layer thickness corresponds to one atomic layer, whereas in Co/V and Ni/V it is about 2 atomic layers. In all of these samples the surface anisotropy is practically negligible. In these sputtered samples the coupling between the magnetic layers is not modified by the V layer thickness.

Microstructure and magnetic properties of spinel and hexagonal ferrimagnetic films prepared by pulsed laser deposition

Abstract Thin films of NiFe 2 O 4 , CoFe 2 O 4 , Ni 0.5 Zn 0.5 Fe 2 O 4 , and BaFe 12 O 19 , deposited at temperatures higher than 500°C are isotropic and polycrystalline, the thickness (25 nm up to 1.5 μm), the grain size (50 nm to 1 μm) and surface roughness (1 to 100 nm) depending upon deposition parameters. Saturation magnetizations are close to the bulk values, but coercivities are rather high: up to 500 Oe for Ni-ferrites and more than 3 kOe for the hexaferrite.

Study of the interdiffusion at the interfaces of NiOαFe2O3 multilayers prepared by pulsed laser deposition

Abstract We prepared NiO α Fe 2 O 3 multilayer films by pulsed laser ablation. Interdiffusion leads to the formation of the nickel ferrite NiFe2O4 at the interfaces. Its ferrimagnetism provides a local probe on the admixture of the antiferromagnetic oxides NiO and αFe2O3 which is macroscopically measurable. We performed magnetization, torque and magnetooptical measurements on the multilayer samples. Several phenomena were observed. As a function of the substrate temperature a kinetically (due to the incoming particle energies) and a thermally activated regime of NiFe2O4 formation were observed. In the thermally activated regime, the duration of the deposition per layer and therefore the temperature dependent diffusion at the interfaces plays a crucial role to the formation of the ferrite as can be seen from the magnetic moment m which tends to saturate for long in-situ annealing times. Surprisingly, an oscillation of m as a function of the number of interfaces was observed for the NiO α Fe 2 O 3 multilayer films. This indicates a magnetically and perhaps structurally non equivalence of the NiO α Fe 2 O 3 and the α Fe 2 O 3 NiO interfaces. This oscillation is observed in the magnetization, the Faraday and the coercive fields.

METHODS OF DETERMINING MAGNETIZATION AND UNIAXIAL ANISOTROPY OF MULTILAYERS BY MEANS OF TORQUE MAGNETOMETRY

Torque data for Pd‐Ni and Pt‐Co multilayers are analyzed within simple models in order to obtain, analytically or by numerical analysis, the anisotropy constant(s) and the magnetization. The analysis of such data can be performed in two ways: first, by considering second‐order anisotropy or, second, two uncoupled magnetic regions. Finally, a generalization of the well‐known treatment of (L/H)2 vs L plots is proposed in order to determine the first‐ and second‐order uniaxial anisotropy constant together with the magnetization.

Bulk and surface anisotropy in ultrahigh vacuum deposited Co / Ag and Fe / Ag multilayers

Abstract We have studied the bulk and surface anisotropy energies in the range 295-5 K, in polycrystalline Co / Ag and Fe / Ag multilayers prepared by sequential evaporation in ultrahigh vacuum. The K s at 5 K are found to be +0.16 and +0.3 erg cm −2 for Co and Fe systems respectively and are practically independent of temperature. Our values are comparable to those published in the literature. We also show that the intrinsic anisotropy obtained from curve fitting agrees with that experimentally obtained on samples with relatively thicker layers.

Magnetic studies of Co/Ag multilayers

Abstract Co/Ag multilayers have been prepared by evaporation in UHV. For a Co layer thickness below about 2 nm some increase in the magnetization above that of the bulk and a strong uniaxial anisotropy are observed. The latter is considered to be of surface origin.

Single crystal growth and magnetic properties of YIG:Pr4+

Single crystals of Y3−x−zCaxPr4+xPr3+z−xFe5 O12 have been successfully grown. Their magnetic moments have been measured and interpreted on the basis of Neel’s model. Cubic magnetocrystalline anisotropy and growth induced uniaxial anisotropy have been obtained on spherical samples using torque measurements.