Critical Behavior of Linear and Nonlinear Susceptibilities near Curie Temperature in Au<sub>82</sub>Fe<sub>18</sub>Alloy

Two different ferromagnetic-paramagnetic transitions are detected in (Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition at a higher temperature results from (Ga,Mn)As cluster phases with [110] uniaxial anisotropy and that at a lower temperature is associated with a ferromagnetic (Ga,Mn)As matrix with 100 cubic anisotropy. A change in the magnetic easy axis from [100] to [110] with increasing temperature can be explained by the reduced contribution of 100 cubic anisotropy to the magnetic properties above the transition temperature of the (Ga,Mn)As matrix.Ferromagnetism in Mn-doped p−type semiconductors can theoretically be understood by the p − d exchange interaction between hole carriers and doped Mn spins [1,2,3,4], which can be manipulated by electric-field [5] or optical-hole generation [6]. Recent studies of magnetic anisotropy in (Ga,Mn)As/GaAs(001) epilayers, on the other hand, have shown a significant change in the magnetic anisotropy with increasing temperature [7,8,9,10]; uniaxial anisotropy along [110] ([110] uniaxial anisotropy) [7,8,9,10,11,12] becomes predominant with increasing temperature [7,8,9, 10] as well as increasing hole concentration [13]. In spite of these intensive studies, the origin of [110] uniaxial anisotropy is still unclear within the current theoretical framework and an understanding of the change in the magnetic anisotropy with temperature is therefore of fundamental importance in revealing the physics of magnetic semiconductors.The aim of this study is to give a comprehensive description of the magnetic anisotropy in (Ga,Mn)As epilayers.In this Letter, two different peaks in temperature-dependent ac susceptibility that are associated with ferromagnetic-paramagnetic transitions are clearly shown. The peak profile at a higher transition temperature has a considerable dependence on frequency, indicating a blocking process in magnetic clusters, while that at a lower transition temperature shows no frequency dependence. The results provide evidence that the magnetic transitions at the lower and higher temperatures are associated with magnetic phases with cubic anisotropy and [110] uniaxial anisotropies, respectively, and the crossover of the magnetic easy axis from 100 to [110] can be interpreted by the ferromagneticparamagnetic transition of the magnetic phase with 100 cubic magnetocrystalline anisotropy accordingly. 100 nm-thick (Ga,Mn)As epilayers were grown on top of a 400-nm-thick GaAs buffer layer grown at 590• C on a semi-insulating GaAs (001) substrate using lowtemperature molecular beam epitaxy (MBE) at 190 − 235• C under an As-rich growth condition. To increase the hole carrier concentration, some epilayers were subject to post-growth annealing in an N 2 atmosphere for 60 − 240 min at 250• C [14]; hole concentration was controlled by changing the Mn content and/or lowtemperature annealing [13]. Hole carrier concentrations p (= ionized Mn acceptor concentration) were measured with electrochemical capacitance-voltage (ECV) method at room temper...

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“…We measured the temperature dependent ac susceptibility in an ac magnetic field h. In general, magnetization m can be written as [17] …”

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confidence: 99%

Mixed Magnetic Phases in(Ga,Mn)AsEpilayers

et al. 2005

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“…χ 3 has also been used to distinguish a spin glass from a superparamagnet [3,4,5]. Among long range order systems, though χ 3 deduced from dc magnetisation measurements has been used for studying the effect of quadrupolar interactions in rare earth compounds [6], it is interesting to note that nonlinear susceptibility measurements on ferromagnetic [7,8] and antiferromagnetic [9] materials are not common, and very few reports exist in literature. Moreover , most of the previous experimental works on nonlinear susceptibility in long range order systems are predominantly qualitative and not quantitative in nature.…”

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confidence: 99%

Probing a ferromagnetic critical regime using nonlinear susceptibility

Nair

Banerjee

2003

Phys. Rev. B

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The second order para−ferromagnetic phase transition in a series of amorphous alloys (F e5Co50N i17−xCrxB16Si12) is investigated using nonlinear susceptibility. A simple molecular field treatment for the critical region shows that the third order suceptibility (χ3) diverges on both sides of the transition temperature, and changes sign at T C . This critical behaviour is observed experimentally in this series of amorphous ferromagnets, and the related assymptotic critical exponents are calculated. It is shown that using the proper scaling equations, all the exponents necessary for a complete characterization of the phase transition can be determined using linear and nonlinear susceptiblity measurements alone. Using meticulous nonlinear susceptibility measurements, it is shown that at times χ3 can be more sensitive than the linear susceptibility (χ1) in unravelling the magnetism of ferromagnetic spin systems. A new technique for accurately determining T C is discussed, which makes use of the functional form of χ3 in the critical region.

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“…Apart from this, the theoretical understanding about the non-linear susceptibilities is far from being satisfactory as far as these magnetic systems are concerned, though treatments of the critical regimes based on the simple mean field models [30] as well as more complicated Sherrington-Kirkpatric [31], Bethe approximation models [32] exist. However, there are a few experimental studies of the third ordered susceptibility (χ 3 ) on ferromagnetic systems [30,33,34] which though predominantly qualitative in nature have included attempts on characterizing these transitions by the determination of the critical exponents. Recently, a study has been made to understand the hysteresis effect in ferromagnet through the measurement of non-linear susceptibilities [35].…”

Section: Probing Long Range Orderingmentioning

confidence: 99%

Probing Magnetic Phases in Different Systems using Linear and Non Linear Susceptibility

Banerjee¹,

Bajpai

Nair

Frontiers in Magnetic Materials

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Critical Behavior of Linear and Nonlinear Susceptibilities near Curie Temperature in Au₈₂Fe₁₈Alloy

Cited by 32 publications

References 31 publications

Mixed Magnetic Phases in(Ga,Mn)AsEpilayers

Mixed Magnetic Phases in(Ga,Mn)AsEpilayers

Probing a ferromagnetic critical regime using nonlinear susceptibility

Probing Magnetic Phases in Different Systems using Linear and Non Linear Susceptibility

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Critical Behavior of Linear and Nonlinear Susceptibilities near Curie Temperature in Au82Fe18Alloy

Cited by 32 publications

References 31 publications

Mixed Magnetic Phases in(Ga,Mn)AsEpilayers

Mixed Magnetic Phases in(Ga,Mn)AsEpilayers

Probing a ferromagnetic critical regime using nonlinear susceptibility

Probing Magnetic Phases in Different Systems using Linear and Non Linear Susceptibility

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Product

Resources

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Critical Behavior of Linear and Nonlinear Susceptibilities near Curie Temperature in Au₈₂Fe₁₈Alloy