Temperature Dependence Of Saturation Magnetization Research Articles

Magnetic properties of Pd/Co multilayers

Measurements of the magnetic anisotropy of a series of Pd/Co multilayers grown by magnetically enhanced dc triode sputter deposition revealed an interface contribution of 0.53 erg/cm2 and a net volume anisotropy of −13.2×108 erg/cm3. A characteristic reduction of perpendicular anisotropy for ultrathin Co layers (<4 Å) is explained by using a pair interaction model to evaluate a thickness dependence of the interface anisotropy. For Pd-Co interfaces with perfectly sharp composition modulation an interface anisotropy of 0.79 erg/cm2 is predicted. By modeling the magnetization behavior a domain-wall energy density of 2±0.5 erg/cm2 is obtained for Pd/Co (2 Å) multilayers with Pd thicknesses in the range of 4–20 Å. For perpendicular Pd75Co25 alloy thin films the same model gives domain-wall energy densities in the range of 1–2 erg/cm2. For ultrathin Co layers the interlayer Co–Co coupling range is ∼20 Å. Temperature dependence of saturation magnetization of a Pd(11 Å)/Co(7.8 Å) multilayer demonstrates complete mixing of Pd and Co by 380 °C.

Magnetic properties of amorphous (Fe−1xNix)75Si10B15 alloys

Abstract Amorphous (Fe1−xNix)75Si10B15 (0.1 ⩽ x ⩽ 1, the step of x is 0.1) alloys were preparedby the rapid quenching technique and their magnetization measurements have been performed by utilizing a vibrating sample magnetometer from 77 K up to 800 K. The Curie temperature, Bloch coefficient, and range of exchange interaction were calculated from the temperature-dependent saturation magnetization curves. The low temperature dependence of magnetization is in good agreement with Bloch's relation, M s (T) = M s (0) (1 - BT 3 2 - CT 5 2 ) . The range of exchange interaction becomes shorter with the addition of nickel concentration. The observed mean square ranges of exchange interaction shows that this alloy system loses the ferromagnetic ordering when x is larger than 0.9.

Magnetic analysis of rare earth-rich RE 100- xFe x (RE = Pr, Nd; 2.5 ≤ x ≤ 40) as-cast binary alloys

Binary alloys RE 100- x Fe x (RE = Nd, Pr) with nominal compositions 2.5 ≤ x ≤ 40 were analyzed by means of thermomagnetic analysis and magnetization measurements from 2 K to the ordering temperature of the magnetic phases present. Special attention was paid to the compositions around the eutectic point. A hard anisotropic phase exists in the as-cast alloys, with a room-temperature anisotropy field value of 19.5 and 18.3 kOe for Nd- and Pr-systems, respectively. In alloys in which this new hard magnetic phase is the only magnetic phase detected, the temperature dependence of saturation magnetization, intrinsic coercivity and anisotropy field is reported.

Electrochemical studies on CoCr films as a function of substrate temperature and post-deposition heat treatment

The corrosion resistance of dc magnetron sputtered Co79Cr21 thin films is studied by electrochemical means as a function of substrate temperature Ts ranging from −196 to 375 °C. The corrosion activity increases with Ts and peaks at ∼300 °C. This behavior correlates with the substrate temperature dependence of saturation magnetization of the films. The source of corrosion is suggested to be primarily associated with the segregated Co-rich material. Heat treatment in vacuum at 500 °C significantly improves the corrosion resistance. Evidence is provided suggesting dilution of Co concentration in segregated Co-rich regions is responsible for this improvement.

Magnetic and Magneto-Optical Properties of Co-(Pr, Nd) Artificial Superlattice

Artificial superlattices of Co-(Pr, Nd) were fabricated on glass substrates using electron beam evaporation. Magnetic properties such as (i) the temperature dependence of saturation magnetization M s ; (ii) the temperature dependence of the perpendicular magnetic anisotropy constant K? and (iii) the wavelength dependence of the polar Kerr rotation angle ? K were systematically investigated. For Co/Pr and Co/Nd artificial superlattices, rare earth atoms within 25 A of the interface were found to be coupled ferromagnetically with Co atoms at 77 K. The K? increases with decreasing artificial period D, for both the Co/Pr and Co/Nd artificial superlattices. The maximum values of K? at 77 K are 10×106 erg/cm3 and 4×106 erg/cm3 for Co/Pr and Co/Nd respectively. The wavelength at which the minimum ? K is observed shifts from 0.45 ?m to 0.65 ?m with decreasing artificial period.

Structure and magnetic properties of Nd/sub 2/(Fe/sub 1-x/Co/sub x/)/sub 14/B/sub 1-y/C/sub y/ alloys

The reorientation temperature and magnetocrystalline anisotropy field (H/sub a/) of Nd/sub 2/(Fe/sub 1-x/Co/sub x/)/sub 14/B/sub 1-y/C/sub y/ in the temperature range 200-450 K were determined by AC initial susceptibility measurements and the singular point detection technique, respectively. The temperature dependence of saturation magnetization was measured on finely powdered polycrystalline samples in an extraction magnetometer in fields up to 80 kOe. It was found that the Nd/sub 2/(Fe/sub 1-x/Co/sub x/)/sub 14/C (X<or=0.4) series consisted of a mixture of two phases, Nd/sub 2/(Fe,Co)/sub 17/C/sub x/ and alpha -(Fe,Co), irrespective of heat treatment schedules. Partial substitution of C for boron led to a slight increase of H/sub a/, whereas substitution of Co for Fe (at low Co concentration) causes an increase of H/sub a/ at low temperature. Although the concentration dependence of M/sub s/ is reminiscent of the Slater-Pauling curve, no maximum was found at either 1.5 K or 300 K, as one would expect in Fe-Co and Nd/sub 2/(Fe,Co)/sub 14/B alloys.<<ETX>>

Grain structure and magnetism of nanocrystalline ferromagnets

Amorphous ribbons of composition Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ have been annealed above their crystallization temperature, which produces a homogeneous, ultrafine grain structure of alpha FeSi with typical grain diameters of 10-20 nm. The temperature dependence of saturation magnetization reveals two different magnetic phases which correspond to the alpha -FeSi grains and the grain boundary phase, respectively. The nanocrystalline material exhibits excellent soft magnetic properties which are discussed within the framework of the random anisotropy model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phase separation as a possible interpretation of large Barkhausen jumps in amorphous ferromagnets

Static hysteresis loops at low magnetic field and temperature dependence of saturation magnetization for the amorphous Co 72.8Fe 5.2Si 11B 11 alloy were investigated and compared with that ones for the amorphous Co 72Fe 6Si 11B 11 alloy. Anomalous hysteresis loop behaviour for Co 72.8Fe 5.2Si 11B 11 was attributed to the existence of two magnetic phases separated during rapid quenching. Hysteresis loop model in case of presence of two magnetic phases (one of them is soft and the second relatively hard) was proposed.

Effect of negative substrate bias on the film structure and magnetic properties in sputter-deposited Co–Cr films

Film structure and magnetic properties are investigated in Co–Cr films sputter deposited with an applied substrate bias voltage. Large grains with c-axis orientation are found at negative bias between 40 and 75 V. Coercivity decreases remarkably in these films. These changes in film structure and magnetic properties by applying low bias originate from the moderate bombardment by Ar ions under low oxygen contamination as well as little Ar incorporation. With further increase of negative bias, saturation magnetization decreases to the bulk value and perpendicular magnetic anisotropy decreases to zero, because violent ion bombardment yields complete solid solution of Co and Cr. Temperature dependence of saturation magnetization in zero bias Co–Cr films with perpendicular magnetization reveals a compositional inhomogeneity in which concentration of Cr distributes between 10 and 30 at. %. The compositional inhomogeneity is eliminated by the substrate bias.

FeCr sputter-deposited films with perpendicular anisotropy

The origin of the perpendicular anisotropy in sputter-deposited Fe 1-x Cr x (X=0.3-0.4) films was investigated by measuring the temperature dependences of saturation magnetization (M s ) and perpendicular anisotropy (K u ) and by SEM observation of the chemically etched surface of these films. M s and K u of the films did not show meaningful temperature dependences between -150 and 100°C. SEM photographs as well as X-ray diffraction patterns showed the existences of Cr-rich and Fe-rich phases. Cr-rich bcc phase which is nonmagnetic grows up perpendicularly and segregates the ferromagnetic phases. Shape anisotropy seems to play an important part of the perpendicular anisotropy in FeCr films, which is consistent with the temperature dependences of M s and K u .

Exchange anisotropy and thermal expansion of iron alloys with Ni and Cr

Temperature dependences of saturation magnetization and thermal expansion coefficient have been investigated on Fe 70 Ni 30-x Cr x alloys in the temperature range from 4,2 to 300 K. The data show that small additions of chromium, cause a stabilization of f.c.c, phase in Fe 70 Ni 30 alloy and appearance of invar anomalies on thermal expansion coefficient α(T) and saturation magnetization I s (T). Subsequent increasing of Cr content lead to long-range antiferromagnetism.

Perpendicular anisotropy in Co-Cr films

The temperature dependence of saturation magnetization and perpendicular magnetic anisotropy for 16 and 18% Cr-Co sputtered films was studied. The following were found: (i) the Curie temperatures of films are higher than those of bulk alloys; (ii) the perpendicular anisotropy constant increases after being heated to 400°C; and (iii) it changes from positive to negative at about 640°C.

Behaviour of Curie temperature of NiCu-H systems during phase transitions under high pressure gaseous hydrogen

Miniature devices let follow the influence of H 2 up to 10 kbar on temperature dependence of saturation magnetization ( M s- T) and electrical resistance ( R- T) of ferromagnetic NiCu in regions up to 300°C in which normally corresponding hydrides do not exist. Pressure dependent changes of M s- T-, R- T-shapes and Curie temperatures suggest, e.g, precipitation-like phase transitions.

Temperature Dependence of Saturation Magnetization in Amorphous Co–B Alloys

Temperature Dependence of Saturation Magnetization in Amorphous Co–B Alloys

Magnetization and magnetic anisotropy in evaporated GdCo amorphous films

Saturation magnetizations and magnetic anisotropy constants were determined for a series of amorphous GdCo films prepared by thermal evaporation. The films covered the composition range from Gd0.05Co0.95 to Gd0.40Co0.60 and were studied by means of ferromagnetic resonance and a force balance magnetometer. The films, in contrast to those prepared by sputtering, had a hard perpendicular direction of magnetization when Co was less than 91 at.%, and easy and moderate directions within the plane of the film. The anisotropy constant can be expressed in terms of sublattice magnetizations by Ku=0.660MCo2 +2.218MCoMGd+0.097MGd2. The results are explained based on a pair-ordering mechanism. The composition and temperature dependence of saturation magnetization is essentially the same in evaporated and sputtered films.

Magnetic properties of amorphous Gd-Fe films prepared by evaporation

Amorphous GdxFe1−x films with 0.18&amp;lt;x&amp;lt;0.33 were prepared by electron-beam coevaporation of the elements. The composition dependence of anisotropy and the composition and temperature dependence of saturation magnetization of the films were studied. In contrast to evaporated Gd-Co films, where anisotropy is in-plane, the Gd-Fe films were found to have strong perpendicular anisotropy with the uniaxial anisotropy constant (Ku) decreasing monotonically from 3.8×105 erg/cm3 at x=0.18 to 2.0×105 erg/cm3 at x=0.33. The perpendicular anisotropy field (HK) reached a maximum at the compensation composition (x=0.26) and fell off rapidly on both sides. The findings suggest that anisotropy in evaporated films is due to a longer-range structural ordering than the pair ordering which is assumed to exist in sputtered films. Saturation magnetization measurements showed that magnetization of the amorphous alloys could be closely approximated from the moments of pure crystalline Gd and Fe. The 0 °K moment of Fe was found to be 2.20μB (0.23&amp;lt;x&amp;lt;0.31) suggesting less charge transfer than in crystalline GdFe3. Q values (HK/4πMs) of the alloys exceeded unity in the range 0.19&amp;lt;x&amp;lt;0.31.

Optimizing the combination treatment of Ticonal magnets

1. Optimization of the combination isothermal thermomagnetic treatment of Ticonal permanent magnets depends on the time the magnets are subjected to the isothermal treatment. 2. The criterion for selecting the optimal loading time is the level of saturation magnetization after cooling. This value is determined from the inflection on the ascending branch of the temperature dependence of saturation magnetization and corresponds to 0.65–0.75 I0 (saturation magnetization of the material at room temperature). 3. The variation of the magnetic properties does not exceed 3% for the coercive force, 2% for remanence, and 6% for magnetic energy, which substantially exceed the requirements of GOST 17809-72.

Temperature and field dependence of magnetization of Si-doped YIG crystals

Temperature dependence of saturation magnetization and of magnetization at low fields of Si-doped yttrium iron garnet single cystals are reported. For samples of the composition Y3Fe4.63+(Fe2+Si4+)0.2O12, the lattice parameter, saturation magnetization at room temperature, and Curie point are 12.364 Å, 22.6 G cm3 g−1, and 264±2°C, respectively. Values of these parameters are compared with those for unsubstituted YIG. It is discussed why at low fields dσ/dT is positive, whereas it is negative for the saturated samples.

Late Mesozoic palaeomagnetism from Spitsbergen; implications for continental drift in the Arctic

Thermal and alternating-current demagnetization combined with ore microscopy and measurements of the temperature dependence of saturation magnetization have been carried out on some Mesozoic, probably Cretaceous, basaltic lavas from two areas (Seidfjell and Sørlifjell) at Spitsbergen. The experimental studies suggest that the Seidfjell locality has undergone extensive oxidations, which resulted in remagnetization. The estimated palaeomagnetic pole for this area is 77°N 107°E, which suggests a remagnetization, probably some time in the Late Tertiary. On the other hand the experimental data from the Sørlifjell locality suggest that the magnetization is primarily of deuteric origin. The mean palaeomagnetic pole position for this latter formation is at 75°N 235°E, which is significantly different from previously published European Mesozoic data. However, closing the Neo-Arctic basin by rotating Spitsbergen towards the Lomonosov Ridge, makes the suggested Cretaceous pole coincide with poles of similar age from North-America. This suggests that the estimated pole from Sørlifjell is a good approximation for a Late Mesozoic palaeomagnetic pole for Europe and it also confirms that the process of continental separation in the Arctic has taken place in Tertiary time.

Palaeomagnetic properties of the Middle-Upper Devonian Volcanics of the Orkney Islands

Thermal demagnetization and ore microscopy combined with the magnetic colloid technique and measurements of the temperature dependence of saturation magnetization have been carried out on the Middle-Upper Devonian Volcanics of the Orkney Islands. The investigations show that the original remanence has been replaced by subsequent chemical magnetizations. These low temperature processes probably encompassed a long time interval, ranging upwards to about 50 my. Switching of the Earth's field polarity during this time yielded composite magnetizations resulting in intermediate or deviating natural remanence directions. Reliable estimates of separate components may pose severe experimental problems. However, some few acceptable data have been extracted tentatively suggesting an ancient relative pole position at 149.5°E, 23.7°N. This result is in good agreement with polar estimates based on the Norwegian Old Red Sandstone rocks. Furthermore, there is evidence that the Orkney volcanics originated in a reversed polarity epoch. This latter suggestion fits into a Devonian polarity/time sequence as previously suggested.