Magnetic properties and magnetoresistance of HfFe 6 Ge 6 -type Dy 1- x Gd x Mn 6 Ge 6 ( x =0.1-0.6) compounds (original) (raw)
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Journal of Magnetism and Magnetic Materials, 2004
The Y2CaMn3-xAlxO9 perovskites crystallize in an orthorhombic type structure having Pnma-space group. The magnetic measurements show the presence of spin-glass type behavior. The maxima in the temperature dependences of the magnetization in ZFC sample, decrease from Tm= 30 K (x=0) to 18.9 K (x=0.6). The magnetization isotherms in field up to 90 kOe show that the saturation is not obtained. Above TSRF temperature, Curie-Weiss type behavior was evidenced. The number of Mn 4+ ions increases as Mn is substituted by Al. In the temperature range Tc < T < TSRF ferromagnetically ordered clusters are coupled by random dipolar interactions.
High coercivity and giant magnetoresistance of CoAg, CoCu granular films
Journal of Magnetism and Magnetic Materials, 2007
We report our study on the structure, magnetic and giant magnetoresistance properties of two systems: Co x Ag 1Àx (x ¼ 33, 48, 49, 52 at%) and Co y Cu 1Ày (y ¼ 11, 13, 15, 17 at%) granular films prepared by RF sputtering. The thermal transition measured by the SDT 2960 apparatus revealed exothermal peaks at 400 1C, corresponding to the crystallization of FCC-Co crystallites. The studied films were annealed in a temperature range of 300-450 1C for 1 h. The structure and particle size were determined from the X-ray diffraction data. Superparamagnetic state was shown in as-deposited films. After appropriate heat treatment, coercivity increased up to 1100 Oe in the Co 52 Ag 48 film annealed at 350 1C, and 690 Oe in the Co 13 Cu 87 film annealed at 400 1C. Maximum magnetoresistance up to 4.25% in the Co 48 Ag 52 film, and 5.4% in the Co 15 Cu 85 film annealed at 400 1C was obtained. Our values for magnetoresistance are quite high compared with recent studies. r
Journal of Magnetism and Magnetic Materials, 1981
Some electrical and magnetic properties of Gd-Co f'flms obtained by de sputtering with bias voltage V b are discussed. We observed a decrease in the compensation temperature and in the anomalous Hail resistivity with increasing bias voltage while the specific resisitivity increases. The anisotropy constant, however, increases up to V b =-200 V, where it reaches a maximum and then it decreases. Electrical conductivity of the t'flms prepared with V b greater than-100 V showed tunneling character. We conclude that not only resputtering of Gd atoms but also oxidization of Gd takes place during deposition when bias voltage is applied.
Giant magnetoresistance and magnetic properties of electrodeposited Cu–Co granular films
Journal of Alloys and Compounds, 2001
The effect of NaOH with different concentrations on CoFe/Cu multilayer films was studied between pH = 3.70 and pH = 2.70. The effect of different electrolyte pH from 3.7 to 2.7, which was obtained at various NaOH concentrations, on CoFe/Cu multilayer films was studied. The structural studies by x-ray diffraction (XRD) revealed that the multilayers have face-centered cubic structure. The preferential orientation of the multilayer is in the (220), (111), (111), and (222) direction at pH = 3.7, 3.3, 3.0 and 2.7, respectively. It was observed that at pH = 3.0, the film composition, by energy dispersive x-ray spectroscopy (EDX), contains 3.22 at. Co % and 96.78 at. Cu %, and at low pH (2.7), 10.58 at. Co %, 4.18 at. Fe % and 85.24 at. Cu %. Magnetoresistance measurements made at room temperature showed that all films exhibited giant magnetoresistance (GMR), which was affected by the electrolyte pH. The observed GMR values are 4.0 %, 4.6 %, 4.2 %, and 12 % at the pH values of 3.7, 3.3, 3.0 and 2.7, respectively. Magnetic measurements of the films were made at ±20 kOe by using ADE EV 9 model a vibrating sample magnetometer. The magnetic measurements revealed that the coercivity of the films increased from 70 Oe to 93 Oe and stayed there, and the saturation magnetization monotonically increased form T. Sahin ( ) · 7.40 emu/g to 17.05 emu/g with decreasing electrolyte pH from 3.7 to 2.7.
Correlation study between structural, magnetic and transport properties of annealed Co thin films
Vacuum, 2005
This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 1C in steps of 100 1C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 1C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H c) of 26 Oe, and it is increased to 94 Oe for 500 1C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 1C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.
Synthesis and magnetic states of cobalt in three-layer Co/Ge/Co films
Physics of the Solid State, 2014
The magnetic properties of three layer Co-Ge magnetic films have been studied experimentally as a function of technological conditions of their deposition. It has been found that the films deposited at a high deposition rate have a granular structure, and the films obtained at a low deposition rate have an X ray amorphous structure. Electron microscopy and nuclear magnetic resonance studies have demonstrated that, at the same cobalt layer thickness, the semiconductor granule sizes depend on the average semiconductor layer thickness and correlate with the formation of different cobalt phases (amorphous, cubic, and hexago nal). The thermomagnetic properties of the films have been investigated.
Peculiarities of temperature behavior of magnetization in Co/Ge/Co films
Physics Letters A, 2006
In Letter the results of experimental and theoretical investigations of magnetic properties in trilayer Co/Ge/Co films are represented. The temperature dependences of films, being two phases in respect of magnetism, are studied. Experimental results are explained in the frameworks of impurity model, when the hexagonal cobalt grains are considered as quasi-Ising particles distributed chaotically and dissolved within an isotropic matrix of cubic cobalt. The fields of magnetization rise on the T-H plane are determined.
Magnetic properties and magnetocaloric effects in (GdxDy1−x)Co2 compounds
Physics Letters A, 2002
A series of (Gd x Dy 1−x )Co 2 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.55) compounds have been prepared by arc-melting method. The X-ray diffraction (XRD) analysis reveals that all samples are in the MgCu 2 -type structure. The magnetization was measured by a vibrating sample magnetometer (VSM). No first-order phase transition in these compounds (x = 0) is observed. With the increasing Gd content, Curie temperature (T C ) increases almost linearly. The magnetic entropy changes (|∆S M |) as a function of the temperature in magnetic field (1 T) for (Gd x Dy 1−x )Co 2 have been calculated. The origin of the magnetocaloric effect and the potential application of (Gd x Dy 1−x )Co 2 as a working material for magnetic refrigerants have also been discussed. (D. Wang). 0375-9601/02/$ -see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 5 -9 6 0 1 ( 0 2 ) 0 0 1 5 9 -7