M. Tessier

Structure and magnetic properties of yttrium–iron–garnet thin films prepared by laser deposition

We report on a study of thin (500–4000 A) and ultrathin (100–500 A) yttrium–iron–garnet (YIG) films deposited onto amorphous quartz substrates by the pulsed laser deposition technique. The growth conditions of well-formed polycrystalline films have been determined. The crystalline structure and the magnetic behavior of the films are strongly influenced by the processes occurring on the film–substrate interface. Primarily, a strain due to the difference in thermal expansion coefficients of the film and substrate induces a uniaxial anisotropy. Another source of strain are lattice distortions due to oxygen vacancies. The results obtained from x-ray diffraction analysis, magneto-optical, superconducting quantum interference device, vibrating sample magnetometer, and ferromagnetic resonance (FMR) measurements indicate that films thicker than 200 A can be approximated by a two-layer model. One of the layers with a highly distorted structure and low magnetization is located near the surface. The other one, the u...

Magnetic and magneto-optic properties of orthoferrite thin films grown by pulsed-laser deposition

Thin magnetic layers have been prepared by pulsed-laser deposition from targets of the orthoferrites: DyFeO3, GdFeO3, SmFeO3, and YFeO3. All layers were deposited onto quartz substrates at a temperature of 450 °C under high-vacuum conditions, i.e., in the absence of additional oxygen. The as-grown films show evidence of the following phases: RFeO3, R3Fe5O12, Fe3O4, and R2O3, where R=Dy, Gd, Sm, and Y. The magnetic properties of these films have been investigated using superconducting quantum interference device magnetometry and magneto-optic (Faraday rotation) measurements taken before and after annealing. These studies reveal that the orthoferrite phase is almost completely (>90%) recovered after an annealing treatment at 860 °C for 1 h. We also report on the temperature dependence of the Faraday rotation for these orthoferrites in the temperature range 25–250 °C.

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.

Preparation and properties of coevaporated amorphous Co‐Zr thin films

Co1–xZrx thin films (5<x<35) were prepared by coevaporation in a two E‐beam source system on glass substrates held at 30 °C. The crystallinity of all films were monitored by x‐ray diffraction techniques; the films in the composition range x⩾7.4 were found to be amorphous. Magnetization, hysteresis loop, and FMR measurements were carried out with these Co‐Zr films. The saturation magnetization as a function of composition shows similar trends as in the Co‐Ti thin films. The FMR spectra were rather complex with four to six modes for perpendicular resonance; the most intense mode gives a value for 4πMs close to the static data. The other modes at higher resonance fields may be caused by preferential oxidation of Zr or a large negative anisotropy induced by oxidation. Auger and ion probe profile analysis of the Co‐Zr films indicated the presence of oxygen throughout the bulk of these films. SEM examination of some of these Co‐Zr films showed the existence of a columnar structure, and it is possible that oxyge...

Magnetic properties of compositionally modulated Co/Mn thin films

Magnetic properties of multilayered Co/Mn films with layer thickness ranging from 7–70 A have been studied. The films were prepared by alternately depositing Co and Mn layers in an ultrahigh vacuum (UHV) evaporator. X‐ray θ‐2θ scans with Cu‐Kα radiation showed a main diffraction peak around 2θ=44° for all films and satellite peaks for some of them. The data imply the existence of α‐Co (002)/α‐Mn (330) stacking texture. Ferromagnetic resonance (FMR) study and vibrating‐sample magnetometer (VSM) measurement show that the magnetization of Co layers decreases with decreasing Co thickness as if 1.5 atomic layers lost their magnetic moments at the interface. FMR spectra of the films show a peculiar temperature dependence in that the perpendicular resonance field starts to decrease below a certain temperature. The results are discussed.

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.

Superexchange and iron valence control by off-stoichiometry in yttrium iron garnet thin films grown by pulsed laser deposition

Controlled off-stoichiometric single phase polycrystalline yttrium iron garnet (YIG) thin films have been grown by pulsed laser deposition, adjusting the oxygen partial pressure PO2 between 5 and 400 mTorr. Atomic stoichiometry by RBS shows an oxygen deficiency for PO2 Pstoich. Pstoich=30mTorr refers to films showing magnetic and structural properties of the bulk stoichiometric YIG. Curie temperature Tc and saturation magnetization 4πMs decreased for PO2 Pstoich: Increase of Tc (up to +10%) and of 4πMs (up to +20%) and lattice parameter compression. Microscopic interpretation is given in terms of superexchange interaction and creation and site selectivity of iron vacancies.

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.

Preparation and magnetic properties of strontium ferrite thin films

Strontium ferrite films were deposited by RF sputtering of a commercial strontium ferrite target onto fused quartz substrates maintained at temperatures up to 900 degrees C. Films deposited at T 800 degrees C had crystalline M-type strontium ferrite structures. The thin composition corresponded to that of the target. Films deposited at 800 degrees C were partially oriented in the [110] direction with the c-axis in the plane. Postannealing led to an increase in the magnetization, indicating incomplete formation of ferrite in the as-deposited state. Both in-plane and perpendicular hysteresis loops are rectangular with remanence ratios of 0.8 and 0.6, respectively, showing partial orientation with the c-axis. The torque curve is consistent with the above, although there are some additional anomalous peaks. >

Tuning structure and roughness in exchange biased NiO/permalloy bilayers

Polycrystalline NiO thin films have been grown by pulsed laser deposition on quartz substrates. These films exhibit a strong texture, which can be tuned by changing deposition parameters such as substrate temperature or oxygen partial pressure. By varying the deposition temperature from room temperature up to 900 °C, (220), (111), and (200) textured films are prepared. In the temperature zones separating these orientations, competition between different growth directions leads to smaller crystallites, characterized by broader diffraction lines. Surface roughness measured by atomic force microscopy is strongly correlated with these structural features. Roughness is minimum for highly textured samples (about 7A for 500 A thick films), and it exhibits two peaks in the intermediate zones, with maximum values of about 40 A. In order to correlate exchange bias with these structural features, 100 A thick FeNi layers were deposited by rf sputtering on top of the 500 A thick NiO films. Hysteresis loops were measur...