Spin Glassiness and Ferromagnetism in Disordered Ni-Mn Alloys

1982 ◽  
Vol 19 ◽  
Author(s):  
James S. Kouvel
Keyword(s):  
Spin Glass ◽  
Critical Field ◽  
Curie Point ◽  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Uniaxial Anisotropy ◽  
Hysteresis Loops ◽  
Initial Susceptibility ◽  
Unidirectional Anisotropy ◽  
Glass Properties

ABSTRACTFrom magnetic measurements, the alloy Ni78Mn22 is found to undergo a field-induced transition from spin glassiness to ferromagnetism at a critical field that decreases from ∼140 Oe to zero as the temperature is raised from 4.2 K to 40 K, the ferromagnetic Curie point being ∼270 K. The alloy Ni74Mn26 is found to transform at 80 K from a spin glass to a state of infinite initial susceptibility but no spontaneous magnetization and to remain so up to 155 K, where it becomes paramagnetic. The spin-glass properties of Ni78Mn22 below 40 K and of Ni74Mn26 below 80 K include displaced hysteresis loops produced by cooling in a field. The changes in the hysteresis loops upon subsequent warming correspond to a gradual conversion of a unidirectional anisotropy to a uniaxial anisotropy.

Spin Glass Magnetic Behavior of Iron/Silica Gel Nanocomposites

1990 ◽  
Vol 195 ◽  
Author(s):  
Robert D. Shull ◽  
Joseph J. Ritter
Keyword(s):  
Spin Glass ◽  
Silica Gel ◽  
Spin Glasses ◽  
Hysteresis Loops ◽  
Magnetic Behavior ◽  
Hydrogen Gas ◽  
Ferric Nitrate ◽  
Susceptibility Data ◽  
History Effects ◽  
Unidirectional Anisotropy

ABSTRACTHomogeneous gelled composites of iron and silica containing 5-40 wt.%Fe prepared by low temperature polymerization of aqueous solutions of ferric nitrate, tetraethoxysilane, and ethanol (with an HF catalyst) were heated to 380°C in the presence of hydrogen gas. X-ray diffraction and M6ssbauer effect measurements, and transmission electron microscope (TEM) observations show these materials are comprised of nanometer-sized regions of iron compounds embedded in a silica gel matrix. Magnetic susceptibility data indicate the materials became either superparamagnetic or ferromagnetic at room temperature. On cooling, the magnetization data furthermore show that the hydrogenated materials containing ll-30% Fe become magnetic spin glasses at temperatures less than 30 K. Magnetic history effects are observed in addition to displaced hysteresis loops below their spin freezing temperatures (Tf). For field-cooled materials at 10 K, the displacement of the hysteresis loops along the field axis indicates the presence of a unidirectional anisotropy which decreases with the cooling field. Both superparamagnetic-to-spin glass and ferromagnetic-to-spin glass transitions are observed in these nanocomposites. Tf varies with the Fe content from ∼30 K for the 11%Fe nanocomposite to ∼10 K for a content near 33%Fe.

The spontaneous magnetization of alloys I. Copper nickel alloys

1953 ◽  
Vol 219 (1136) ◽  
pp. 1-17 ◽  
Keyword(s):  
Magnetocaloric Effect ◽  
Temperature Rise ◽  
Curie Point ◽  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Additional Advantage ◽  
Temperature Range ◽  
Copper Nickel ◽  
New Feature ◽  
Important Position

The spontaneous magnetization is of fundamental importance in the theory of ferromagnetism but only meagre experimental data are at present available. The paper describes the initial stage of a project to determine the temperature variation of spontaneous magnetization for a number of ferromagnetics. It is impossible to deduce the spontaneous magnetization unequivocally over the complete temperature range from purely magnetic measurements so that a determination of the magnetocaloric effect must also be made. An alloy from the system copper-nickel (23.9 atomic % copper, rest nickel) was chosen for the first investigation because the system occupies an important position in the electron theory of ferromagnetism, whilst it also has the additional advantage of freedom from metallurgical complications. The experimental work is in two parts. An apparatus was constructed which enables the temperature rise in the magnetocaloric effect (Δ T ) to be measured accurately over a wider temperature range than hitherto. This incorporates a galvanometer amplifier and the overall sensitivity is 1000 mm/°C. The specific intensity of magnetization (σ) was obtained by using the balance devised by Sucksmith (1939). Both the sets of measurements were made at closely spaced intervals up to the Curie point and, in the case of the magnetocaloric effect, considerably above this. In addition, the susceptibility above the Curie point was measured from 170 to 775° C and was found to obey the Curie-Weiss law x = C /( T — θ) over most of this range with C = 3.90 x 10 -3 and θ = 111° C. The three methods of deducing the spontaneous magnetization from observations are critically discussed in general, and then in relation to the particular results obtained, which are similar to those obtained for other materials except that the dependence of the temperature rise on σ 2 above the Curie point is not linear. This is a new feature which it is considered may have important theoretical consequences. The values of the spontaneous magnetization deduced from purely magnetic measurements are in agreement, but these differ from the values obtained by using the magnetocaloric effect. The spontaneous magnetization-temperature curve deduced from the magnetocaloric effect lies below that obtained from magnetic measurements in the immediate neighbourhood of the Curie point, and is notable for the absence of any ‘ tail '. The departure of the reduced σ against T curve from the law of corresponding states is firmly established by the present work in which the purely magnetic measurements are in fair agreement with earlier investigations.

scholarly journals Exchange-bias and magnetic anisotropy fields in core–shell ferrite nanoparticles

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
F. G. Silva ◽  
J. Depeyrot ◽  
Yu. L. Raikher ◽  
V. I. Stepanov ◽  
I. S. Poperechny ◽  
...  
Keyword(s):  
Spin Glass ◽  
Magnetic Moment ◽  
Exchange Bias ◽  
Uniaxial Anisotropy ◽  
Thermal Fluctuations ◽  
High Amplitude ◽  
Spin Coupling ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
Core Shell Nanoparticles

AbstractExchange bias properties of MnFe$$_2$$ 2 O$$_4$$ 4 @$$\gamma$$ γ –Fe$$_2$$ 2 O$$_3$$ 3 core–shell nanoparticles are investigated. The measured field and temperature dependencies of the magnetization point out a well-ordered ferrimagnetic core surrounded by a layer with spin glass-like arrangement. Quasi-static SQUID magnetization measurements are presented along with high-amplitude pulse ones and are cross-analyzed by comparison against ferromagnetic resonance experiments at 9 GHz. These measurements allow one to discern three types of magnetic anisotropies affecting the dynamics of the magnetic moment of the well-ordered ferrimagnetic NP’s core viz. the easy-axis (uniaxial) anisotropy, the unidirectional exchange-bias anisotropy and the rotatable anisotropy. The uniaxial anisotropy originates from the structural core–shell interface. The unidirectional exchange-bias anisotropy is associated with the spin-coupling at the ferrimagnetic/spin glass-like interface; it is observable only at low temperatures after a field-cooling process. The rotatable anisotropy is caused by partially-pinned spins at the core/shell interface; it manifests itself as an intrinsic field always parallel to the external applied magnetic field. The whole set of experimental results is interpreted in the framework of superparamagnetic theory, i.e., essentially taking into account the effect of thermal fluctuations on the magnetic moment of the particle core. In particular, it is found that the rotatable anisotropy of our system is of a uniaxial type.

Spin-Glass with Local Uniaxial Anisotropy

1982 ◽  
Vol 49 (16) ◽  
pp. 1190-1193 ◽  
Author(s):  
Dinah M. Cragg ◽  
David Sherrington
Keyword(s):  
Spin Glass ◽  
Uniaxial Anisotropy

Overlapping energy bands and the theory of collective electron ferromagnetism

1953 ◽  
Vol 49 (1) ◽  
pp. 115-129 ◽  
Author(s):  
A. B. Lidiard
Keyword(s):  
Curie Point ◽  
Energy Band ◽  
Spontaneous Magnetization ◽  
Copper Alloys ◽  
Implicit Assumption ◽  
Energy Bands ◽  
Unknown Parameters ◽  
Nickel Copper ◽  
Predicted Values ◽  
A Minor

ABSTRACTThe theory of collective electron ferromagnetism given by Stoner applies to a system of electrons in a single energy band; for iron, cobalt and nickel this is identified with the band of states derived from atomic 3d functions. To bring in the generally assumed overlapping of the 3d band by the wide 4s band in these metals, the theory has been extended to take account of the transfer of electrons from 3d to 4s states with change of temperature. A previous calculation of this transfer effect must be regarded as inadequate, for the part played by the exchange energy in determining the distribution of electrons between the two sets of states was omitted. The general equations are derived in § 2 and used as a basis for discussion of the properties of nickel-copper alloys at absolute zero in § 3. In §§4 and 5 numerical results are presented which show the effect of the overlapping 4s band on the magnetic properties of a system such as nickel both above and below its Curie point. Comparison with the measured paramagnetic susceptibility of pure nickel above the Curie point strongly suggests that for this metal the overlapping 4s band has only a minor influence, although in principle the effect could be very large (cf. Fig. 4). This result is not unambiguous, however, because values thus inferred for the two unknown parameters lead to inaccurate predictions below the Curie point. First, the predicted values for the spontaneous magnetization are too small. Secondly, the theory demands that the nickel-copper alloys should only be ferromagnetic below a copper content of about 20 %, whereas experimentally the limit is known to be about 60 %. In conclusion, it is suggested that the implicit assumption of Stoner's theory that the exchange integrals between all pairs of 3d states are equal to one another is a more serious restriction on the theory than the consideration of only a single energy band.

Colossal magnetoresistance and spin-glass properties of La1-xTexMnO3 (x = 0.04, 0.1)

2003 ◽  
Vol 48 (13) ◽  
pp. 1321-1324 ◽  
Author(s):  
Guotai Tan ◽  
Peng Duan ◽  
Shouyu Dai ◽  
Zhenghao Chen ◽  
Huibin Lu ◽  
...  
Keyword(s):  
Spin Glass ◽  
Colossal Magnetoresistance ◽  
Glass Properties

X-Ray and Magnetic Measurements of TmFeTi2O7

2014 ◽  
Vol 215 ◽  
pp. 470-473 ◽  
Author(s):  
Tamara V. Drokina ◽  
German A. Petrakovskii ◽  
Dmitrii A. Velikanov ◽  
Maksim S. Molokeev
Keyword(s):  
Spin Glass ◽  
Solid Phase ◽  
Magnetic Measurements ◽  
Diffraction Method ◽  
Freezing Temperature ◽  
Solid Phase Reaction ◽  
Phase Reaction ◽  
X Ray Diffraction ◽  
X Ray ◽  
History Of

In this paper we are reported about a peculiarity of the crystal structure and the magnetic state of TmFeTi2O7. The compound TmFeTi2O7 has been synthesizedusing the solid-phase reaction method. Using X-ray diffraction method the disorder in the distribution of the iron ions over five nonequivalent crystal sites was observed, also the populations of the iron atoms positions were determined. We show that below Tf = 6 K the magnetization of TmFeTi2O7 depends on the magnetic history of the sample. There are indications for spin glass state. This results allow us to assume the state of spin glass is realized below freezing temperature Tf = 6 K in TmFeTi2O7.

Rotational spin‐glass properties of amorphous (Fe1−xMnx)75P16B6Al3

1991 ◽  
Vol 70 (10) ◽  
pp. 6089-6091 ◽  
Author(s):  
H. P. Goeckner ◽  
J. S. Kouvel
Keyword(s):  
Spin Glass ◽  
Glass Properties

EFFECTIVE MAGNETIC ANISOTROPY AND COERCIVITY IN Fe NANOPARTICLES PREPARED BY INERT GAS CONDENSATION

2006 ◽  
Vol 20 (01) ◽  
pp. 37-47
Author(s):  
LUBNA RAFIQ SHAH ◽  
BAKHTYAR ALI ◽  
S. K. HASANAIN ◽  
A. MUMTAZ ◽  
C. BAKER ◽  
...  
Keyword(s):  
Room Temperature ◽  
Size Range ◽  
Magnetic Measurements ◽  
Uniaxial Anisotropy ◽  
Inert Gas ◽  
Condensation Process ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Fe Nanoparticles ◽  
Characterization Studies

We present magnetic measurements on iron ( Fe ) nanoparticles in the size range 10–30 nm produced by the Inert Gas Condensation process (IGC). Structural characterization studies show the presence of a core/shell structure, where the core is bcc Fe while the surface layer is Fe -oxide. Analysis of the magnetic measurements shows that the nanoparticles display very large uniaxial anisotropy, K eff ≈3 - 4 × 106 erg/cc. The observed room temperature coercivities lie in the range ≈600 – 973 Oe , much larger than those expected from the Stoner–Wohlfarth model using the bulk iron anisotropy. It can be inferred from the coercivity variation with the particle size that there is a general trend of the coercivity increasing with size, culminating finally in a decrease for high sizes (30 nm) possibly due to the onset of non-coherent magnetization reversal processes.

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