Magnetic Critical Behavior Research Articles

Magnetic, Magnetocaloric, and Critical Properties of Fe84-xCr2+xB2Co2Zr10 Melt-Spun Ribbons

Magnetic properties, magnetocaloric effect, and critical behavior of Fe84-xCr2+xB2Co2Zr10 (x = 1, 2, 3, 4, 5, and 6) rapidly quenched alloy ribbons prepared by melt-spinning method have been investigated. X-ray diffraction analysis shows that the ribbons are almost amorphous. All the ribbons exhibit soft magnetic behavior with a low coercivity, Hc 0.8 J.kg−1.K−1 (under a magnetic field change of 12 kOe), and the wide working temperature range, δT > 90 K, around room temperature, have been achieved on these alloy ribbons. The obtained results reveal that Fe84-xCr2+xB2Co2Zr10 alloys are potential candidates for the magnetic refrigerants at room temperature region. Using the Arrott-Noakes method, critical analyses around the ferromagnetic-paramagnetic phase transition elucidated the magnetic orders in the alloys. The critical parameters determined for Fe84-xCr2+xB2Co2Zr10 ribbons are close to those of the mean-field theory applied for the long-range ferromagnetic orders.

Magnetocaloric properties and critical behavior in double perovskite RE2CrMnO6 (RE = La, Pr, and Nd) compounds

Magnetocaloric effect (MCE) is a thermodynamic response of the coupling effect between the magnetic sub-lattice(s) with applied magnetic fields, which is strongly correlated with the corresponding magnetic transition. In this work, the magnetic properties, magnetic phase transition, MCE and critical behavior of the paramagnetic (PM) to ferromagnetic (FM) transition in double perovskite RE2CrMnO6 (RE = La, Pr, and Nd) compounds are investigated. The double perovskite compounds reveal a second-ordered magnetic phase transition around TC of 112, 93, and 80 K for RE of La, Pr, and Nd, respectively. The corresponding values of peak magnetic entropy change (-ΔSMmax) around TC are 1.31, 1.86, and 2.23 J kg−1K−1 under the ΔH of 0–7 T. Moreover, the critical exponent study was conducted to probe the nature of critical behavior around the PM to FM transition by the modified Arrott plot (MAP), Kouvel-Fisher (K–F), ΔH dependence of -ΔSMmax, and universal scaling hypothesis methods. The evaluated reliable critical exponents (β, γ, and δ) data for RE2CrMnO6 (RE = La, Pr, and Nd) follows the mean-field theory model, proving the existence of long-range FM orders in these double-perovskite oxide compounds.

Multiple magnetic-phase transitions and critical behavior of charge-density wave compound TbTe3

We report multiple magnetic phase transitions and critical behavior of the 2D charge-density wave compound TbTe3 studied by μSR measurements and dc magnetization measurements. Zero-field μSR has shown three magnetic transitions below 7 K. The longitudinal field measurements under 50 G has confirmed the first transition at TN = 6.3 K. Scaling analysis from above TN gives the critical exponent w = 0.63(5), suggesting the Ising 3D antiferromagnetic nature of the ordering, which is likely mediated by the 2D correlations. However, the obtained w = 0.81(5) below TN indicates the ferromagnetic phase, which arises over the multiphase transitions at lower temperatures. Temperature-dependent transverse frequency shift gives a relatively smaller exponent γ = 1.0(1) than the Ising 3D model. The different transitions were also observed by dc magnetization measurements, suggesting two magnetic transitions at 7.4 K and 3.1 K, which correspond to the antiferromagnetic and ferromagnetic phases respectively.

The analysis of magnetocaloric effect and magnetic critical behavior in Mn5Ge3−xAgx compounds

Structure, critical behavior and magnetic properties of Mn5Ge3−xAgx compounds with x = 0 and 0.1 have been investigated. With the substitution of Ge by Ag, the Curie temperature decreases from 299.8 to 295.1 K. Investigations for isothermal magnetization curves by Arrott curves, the Landau theory and phenomenological universal curves reveal that this system undergoes a second-order phase transition. To investigate the nature of magnetic transition, a detailed critical parameter study obtained by modified Arrott plots, Kouvel-Fisher method, and critical isothermal analysis has been performed. In comparison with the values given by standard models, these obtained critical parameters suggest a 3D long-range magnetic coupling with the exchange distance decaying as J(r) ≈ r−4.57 and J(r) ≈ r−4.67 for Mn5Ge3 and Mn5Ge2.9Ag0.1.

3D-Ising critical behavior in antiperovskite-type ferromagneticlike Mn3GaN

In this work, a systematic investigation on magnetic critical behavior is performed for the first time on an antiperovskite-type Mn3GaN, which is prepared by intentionally modifying stoichiometry. According to the XRD results, the antiperovskite structure is well preserved, even though all lattice parameters shrink upon reducing Ga and N content down to 60%. The sample exhibits a ferromagneticlike feature with a Curie temperature (TC) of 394 K rather than frustrated behavior in stoichiometric Mn3GaN. Most importantly, the modified Arrott plots, Kouvel–Fisher plots, as well as critical isotherm method self-consistently co-confirm the critical exponents of β = 0.33, γ = 1.23, and δ = 4.7, unambiguously indicating that the critical behavior follows the 3D-Ising model around TC.

Observation of critical magnetic behavior in 2D carbon based composites.

Two dimensional (2D) carbonaceous materials such as graphene and its derivatives, e.g., graphdiyne, have enormous potential possibilities in major fields of scientific research. Theoretically, it has been proposed that the perfect atomic lattice arrangement of these materials is responsible for their outstanding physical and chemical properties, and also for their poor magnetic properties. Experimentally, it is difficult to obtain a perfect atomic lattice of carbon atoms due to the appearance of structural disorder. This structural disorder is generated during the growth or synthesis of carbon-related materials. Investigations of structural disorder reveal that it can offer both advantages and disadvantages depending on the application. For instance, disorder reduces the thermal and mechanical stability, and deteriorates the performance of 2D carbon-based electronic devices. The most interesting effect of structural disorder can be seen in the field of magnetism. Disorder not only creates magnetic ordering within 2D carbon materials but also influences the local electronic structure, which opens the door for future spintronic devices. Although various studies on the disorder induced magnetism of 2D carbon materials are available in the literature, some parts of the above field have still not been fully exploited. This review presents existing work for the future development of 2D carbon-based devices.

Metal to semimetal transition and magnetic critical behavior at room temperature in the full Heusler alloy Fe2MnSi

The crystal structure, magnetic and electrical transport properties of Fe2MnSi Heusler alloy have been investigated in the present study. It is found that the sample has been crystallized to the Fmm space group in the L21 structure. Ferromagnetic to paramagnetic phase transition (Curie temperature) has been observed at around 325 K, which is further confirmed by employing the Arrott plot technique. Critical exponent values () have been obtained by employing the Kouvel–Fisher method and Widom-scaling relation; confirming the second order phase transition observance in the magnetic transition region. These values suggest that the magnetic transition follows the mean field theory. Furthermore, the electrical resistivity and spontaneous magnetization data analysis in the low-temperature region ensures the presence of magnon in the system. Detailed analysis of the resistivity data for 50 K to 400 K reveals a metal to semimetal transition at around 325 K, which is close to the Curie temperature. A correlation between electrical transport and magnetic ordering has been observed in the Fe2MnSi alloy.

Large magnetocaloric effect and critical behavior in Cu-doped nanocrystalline La0.7Te0.3Mn1-yCuyO3 (0.1 ≤ y ≤ 0.5)

The impact of copper doping on the magnetic properties and critical behavior of the nanocrystalline La0.7Te0.3Mn1-yCuyO3 (0.1 ≤ y ≤ 0.5) system has been explored. The powder X-ray diffraction (XRD) patterns affirmed the single crystal phase for all samples without any detectable secondary phase. We have observed rhombohedral (R3‾c space group) crystal symmetry for y ≤ 0.3. With the increase in copper doping composition (y = 0.4 and 0.5) structure changes to orthorhombic (Pbnm space group). The temperature-dependent magnetization data suggests a paramagnetic (PM) to ferromagnetic (FM) phase transition upon cooling for all compositions. The Curie temperature TC is almost constant (about 226 K) for the compositions y ≤ 0.3 and after that TC decreases from 154 K (y = 0.4) to 91 K (y = 0.5). The maximal values of magnetic entropy change |ΔSMmax| were obtained from a series of magnetic isotherms and were observed to be 4.59 J/(kg-K), 4.84 J/(kg-K), 3.92 J/(kg-K), 2.49 J/(kg-K) and 1.56 J/(kg-K) for y = 0.1, 0.2, 0.3, 0.4 and 0.5 respectively up to a field change of 5 T. The critical behavior at PM-FM transition for all the samples was studied and reliability of the obtained critical exponents was checked using scaling hypothesis. The critical exponents deduced in this study were observed to follow the mean field, 3D Ising and 3D Heisenberg model.

Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures T_C ~ 85 and 23 K, respectively. UTeS and USeS crystallize in the same orthorhombic TiNiSi-type crystal structure as those of uranium ferromagnetic superconductors URhGe and UCoGe. We determine the critical exponents, beta for the spontaneous magnetization M_s, gamma for the magnetic susceptibility chi, and delta for the magnetization isotherm at T_C with several methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising model with short-range magnetic exchange interactions. Similar sets of the critical exponents have been reported for the uranium ferromagnetic superconductors UGe_2 and URhGe, and uranium intermetallic ferromagnets URhSi, UIr and U(Co_0.98Os_0.02)Al. The universality class of the ferromagnetic transitions in UTeS and USeS may belong to the same one for the uranium compounds. The novel critical phenomenon associated with the ferromagnetic transition is observed not only in the uranium intermetallic ferromagnets with the itinerant 5f electrons but also in the low carrier concentration systems UTeS and USeS with the localized 5f electrons. The large negative magnetoresistance in UTeS and USeS, and the superconductivity in UGe_2 and URhGe share the similarity of their closeness to the ferromagnetism characterized by the novel critical exponents.

Magnetic properties and critical behavior of electron doped polycrystalline Ca0.85Sm0.15MnO3 manganite

We have reported the magnetic properties and critical behavior of electron doped Ca0.85Sm0.15MnO3 (CSMO) sample prepared by solid state reaction technique. With increasing temperature the CSMO sample undergoes ferromagnetic to paramagnetic phase transition at 115 K. The positive value of the Landau coefficient b(T) estimated from the fitting of magnetization data with equation of state suggests that the CSMO sample undergoes 2nd order magnetic phase transition. The positive slopes of Arrott plots corroborate the same. Further study of the critical behavior of the CSMO sample was done by analysis of Kouvel–Fisher plot and critical isotherm. The calculated values of the critical exponents and differ significantly from the values which correspond to three dimensional mean field, tri-critical mean field, 3D Ising and 3D Heisenberg models. This indicates the nonconventional nature of ferromagnetism induced in the CSMO sample by Sm doping at the Ca site.

Effect of structural stacking on magnetocaloric and magnetodielectric properties of Ba1-xSrxCo0.9Mn0.1O3-δ (0 ≤ x ≤ 0.5)

The effect of structural stacking sequence on magnetocaloric, critical behavior and dielectric properties in the nanocrystalline Ba1-xSrxCo0.9Mn0.1O3-δ (0 ≤ x ≤ 0.5) system has been investigated. The parent BaCo0.9Mn0.1O3-δ compound exhibit 12H-hexagonal phase. With increase in Sr-doping, structure changes to 2H-phase (x = 0.5) through mixed 12H+2H-phase (x = 0.1 and 0.3) for the samples annealed at 1100 °C. The magnetocaloric properties shows promising results in the presence of 12H-phase, whereas, inclusion of 2H-phase suppresses magnetocaloric properties. The maximum entropy change for a field change of 5 T is found to be 2.50, 1.73, 0.50 and 0.12 Jkg-1K−1 for x = 0.0, 0.1, 0.3 and 0.5 respectively. The field dependence of maximum entropy change under different composition ratio is studied using phenomenological scaling behavior of magnetic entropy change model. The nature of magnetic phase transition and critical behavior of the nanocrystalline system are studied using Landau theory and Arrot plots. The obtained critical exponents show deviation from mean-field model with increase in Sr-doping. In addition, influence of structural changes on temperature and field dependent dielectric properties is studied. The temperature variation of dielectric constant (ε′) shows subtle change in the vicinity of magnetic transition and the numerical value of ε’ suppresses with 2H-phase. The value of magnetocapacitance (MC %) is also get suppressed while going mixed 12H+2H- to 2H-phase. The origin of magneto-dielectric properties in the present nanocrystalline system demonstrates the strong correlation among structural, magnetic, electrical and dielectric properties.

Critical magnetic and magnetocaloric behavior of amorphous melt-extracted Gd50(Co69.25Fe4.25Si13B13.5)50 microwires

We report on the structural, magnetic, and magnetocaloric properties and critical behavior of high-quality amorphous melt-extracted Gd50(Co69.25Fe4.25Si13B13.5)50 alloy microwires with an average diameter of 42 μm. The microwires undergo a second-order paramagnetic to ferromagnetic (PM-FM) transition around the Curie temperature, TC ∼ 174 K. Around the PM-FM phase transition temperature, the magnetic entropy change ΔSM reaches a maximum value ΔSMmax of about 5.9 J/kg K for a magnetic field change of 5 T. An iterative Kouvel-Fisher method was used to analyze the critical behavior of the second-order phase transition. The critical exponent values are β = 0.493 ± 0.005, γ = 1.321 ± 0.011, and δ = 3.678 ± 0.073, which are close to those expected for the mean-field model with long-range interactions below TC and for the 3D-Heisenberg model with short-range interactions above TC. The magnetic and magnetocaloric behaviors of the Gd alloy microwires near the PM-FM phase transition are discussed.

Magnetic Properties, Magnetocaloric Effect, and Critical Behavior of Gd – Co – Ge Amorphous Ribbons

The effect of structural disordering on the magnetic properties and magnetocaloric effect of amorphous (Gd4Co3)1–xGex (x = 0, 0.05, 0.10, 0.15) alloys is studied. The structure of the ribbons after melt-spinning is determined using an x-ray diffractometer. The thermal analysis is performed with the help of a differential scanning calorimeter. The temperature of the start of crystallization is determined. The magnetic properties are measured in a PPMS-9 system. The Curie temperature and the temperature dependence of the magnetization are determined. Different models are used for describing the critical exponents of the magnetic phase transitions.

Novel critical behavior of magnetization in URhSi: Similarities to the uranium ferromagnetic superconductors UGe2 and URhGe

We study the critical behavior of dc magnetization in the uranium ferromagnet URhSi around the paramagnetic to ferromagnetic phase transition at ${T}_{\mathrm{C}}\ensuremath{\sim}10$ K with a modified Arrott plot, a Kouvel-Fisher plot, the critical isotherm analysis, and the scaling analysis. URhSi is isostructural to uranium ferromagnetic superconductors URhGe and UCoGe. The critical exponent $\ensuremath{\beta}$ for the temperature dependence of the spontaneous magnetization below ${T}_{\mathrm{C}}$, $\ensuremath{\gamma}$ for the magnetic susceptibility, and $\ensuremath{\delta}$ for the magnetic isotherm at ${T}_{\mathrm{C}}$ in URhSi have been determined as $\ensuremath{\beta}=0.300\ifmmode\pm\else\textpm\fi{}0.002$, $\ensuremath{\gamma}=1.00\ifmmode\pm\else\textpm\fi{}0.02$, and $\ensuremath{\delta}=4.38\ifmmode\pm\else\textpm\fi{}0.04$ by the scaling analysis and the critical isotherm analysis. These critical exponents fulfill the Widom scaling law $\ensuremath{\delta}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}1+\phantom{\rule{0.16em}{0ex}}\ensuremath{\gamma}/\ensuremath{\beta}$. Magnetization has strong uniaxial magnetic anisotropy in the ferromagnetic state of URhSi. However, the universality class of the ferromagnetic transition does not belong to the three-dimensional Ising system with short-range exchange interactions between magnetic moments ($\ensuremath{\beta}=0.325$, $\ensuremath{\gamma}=1.241$, and $\ensuremath{\delta}=4.82$). The obtained exponents in URhSi are similar to those in the uranium ferromagnetic superconductors ${\mathrm{UGe}}_{2}$ and URhGe, and uranium ferromagnets UIr and $\mathrm{U}({\mathrm{Co}}_{0.98}{\mathrm{Os}}_{0.02}$)Al. We have previously reported the unconventional critical behavior of magnetization in the uranium ferromagnetic superconductors [N. Tateiwa et al., Phys. Rev. B 89, 064420 (2014)]. The universality class of the ferromagnetic transition in URhSi may belong to the same one in the uranium ferromagnetic superconductors and the uranium ferromagnets. The unconventional critical behavior of the magnetization in the uranium compounds cannot be understood with previous theoretical interpretations of critical phenomena. The absence of the superconductivity in URhSi is discussed from several viewpoints. The improvement of the sample quality in URhSi could provide a good opportunity to gain a deeper understanding of the ferromagnetic superconductivity in the uranium ferromagnets.

Magnetism and critical behavior of double perovskite RE2CoMnO6 (RE = La and Eu) compounds

Abstract The magnetic properties and critical behavior near the Curie temperature TC in the double perovskite RE2CoMnO6 (RE = La and Eu) were systematically investigated via the modified Arrott plots (MAP), the Kouvel-Fisher plot (K-F), and the critical isotherm analysis (CI). The reliable value of critical parameters (β, δ, and γ) obtained from K-F plot are to be 0.4704, 0.9978, and 3.12 with TC of 210.8 K for La2CoMnO6, and to be 0.6065, 0.9237, and 2.52 with TC of 130.3 K for Eu2CoMnO6, respectively. Moreover, the reliability of critical parameters of two samples was further verified by different methods including the Widom scaling relation and the magnetic equation. The obtained values of critical parameters are all close to the value of the mean-field theoretical model which manifested the presence of the long-range FM order for RE2CoMnO6 (RE = La and Eu) compounds.

Negative Magnetic Entropy Change and Critical Behavior of Manganite La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2)

La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2) polycrystalline samples were prepared by solid-state reaction, and their structural, Griffiths phase, magnetic entropy change, critical behavior, and electrical transport properties were systematically investigated. The results show that all polycrystalline samples are rhombohedral symmetry structures; the Griffiths phase exists above the low-temperature magnetic transition temperature (TC2) of the two samples; the magnetic field is applied to the La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2) samples. The maximum magnetic entropy change ΔSmax for 7 T is − 2.28 and − 2.36 J/(kg K), respectively. The doping of Co makes ΔSmax increase, and an obvious negative entropy change occurs at low temperature and low field; the critical behavior of La0.8Sr0.2MnO3 (LSMO) fits best with the mean field model, and the critical behavior of the sample after doping with the 3D Heisenberg model fits best; LSMO is a semiconductor material, and the metal insulator transition appears near the low-temperature magnetic transition temperature (TC2) when the Co element doping amount reaches 0.2. The conductivity of the two samples in the high-temperature region satisfies the small polaron model.

Impression of magnetic clusters, critical behavior and magnetocaloric effect in Fe3Al alloys.

Herein, we report unusual magnetic behavior in arc melted bulk stoichiometric Fe3Al alloy with a D03 structure. The temperature variation in the magnetization measurements revealed two transitions, i.e. one at ∼763 K and another at ∼830 K. Below 763 K, it exhibits ferromagnetic ordering and the nature of the transition is second order. However, the second transition is more complex and detailed analysis of the magnetic data suggested the coexistence of ferromagnetic and paramagnetic phases (two-phase: α + D03/α + B2) and structural transitions triggered by temperature. We observed dual peaks in the magnetic entropy change curve, in accordance with the magnetization results, which corroborate the occurrence of a two-phase system. We believe that the concurrent magnetic ordering and the complex two-phase are associated with the evolution of short-range ordered magnetic clusters having a magnetic moment of ∼103μB in the host matrix. A cluster hypothesis is proposed to explain the observed intricate magnetic behavior of this alloy at high temperature. The estimated critical exponents using a modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis lie in between the 3D-Heisenberg and 3D-Ising model, indicating a short-range interaction and magnetic inhomogeneity, which again are consistent with the magnetization results. The obtained critical exponents follow the universal scaling behavior, which indicates the renormalization of interactions around the magnetic ordering transition (TC). Despite the obvious larger thermal entropy at very high temperature, our synthesized Fe3Al alloy showed enhanced magnetic entropy changes. The obtained magnetic entropy change for binary Fe3Al alloy shows twice the value of that of other binary/ternary Fe-based alloys.

Critical behavior of the single-crystalline van der Waals bonded ferromagnet Cr2Ge2Te6

Layered ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ is a promising two-dimensional (2D) material for van der Waals bonded ferromagnetic devices since its ferromagnetism can be maintained upon exfoliating the bulk down to a few layers. However, the magnetic interaction properties and phase-transition type of this system remain controversial. In this work, we systematically study the magnetic properties and critical behavior of ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ single crystal. The angle dependence of magnetization indicates that ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ has a weak magnetic anisotropy along the $c$ axis but no magnetic anisotropy in the $ab$ plane. Based on the field-dependent magnetic entropy change $[\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)]$, the critical exponents of $\ensuremath{\beta}=0.177(9)$, $\ensuremath{\gamma}=1.746(8)$, and $\ensuremath{\delta}=10.869(5)$ are obtained around ${T}_{C}=66.4(3)$ K. With these critical exponents, the $M(T,H)$ and $\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$ curves follow the universality scaling laws, implying their high reliability and self consistency. The determined critical exponents are close to the 2D-Ising model with spatial dimensionality $d=2$ and spin dimensionality $n=1$. These results suggest that for 2D-Ising-like ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$, the weak magnetic anisotropy is crucial for the stabilization of the long-range ferromagnetic ordering, which is also consistent with the prediction of renormalized spin wave theory.

Magnetocaloric effect and critical behavior in Fe-La-Zr rapidly quenched ribbons

Abstract Fe90-xLaxZr10 (x = 1 and 2) rapidly quenched ribbons with thickness of about 15 μm were prepared by the melt-spinning method. X-ray diffraction analysis shows that the structure of the ribbons is mostly amorphous. The Curie temperature, TC, of the alloy considerably increased, from ∼262 K for x = 1 to ∼302 K for x = 2, with increasing La-concentration. The maximum magnetic entropy change, |ΔSm|max, of the alloy is about 1.1 J∙kg−1K−1 for a magnetic field change ΔH = 12 kOe. A quite large refrigerant capacity (RC ∼ 74 J∙kg−1 for ΔH = 12 kOe) near the room temperature region is obtained for the alloy. A thorough analysis on critical exponents around the ferromagnetic-paramagnetic phase transition, using the Arrott–Noakes plots and Kouvel–Fisher method, sheds light on the critical magnetic behavior and its association with the magnetocaloric effect in the Fe-La based alloys.

Magnetic and Structural Quantum Phase Transitions in CeCu_{6-x}Au_{x} are Independent.

The heavy-fermion compound CeCu_{6-x}Au_{x} has become a model system for unconventional magnetic quantum criticality. For small Au concentrations 0≤x<0.16, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature T_{s} with T_{s}→0 for x≈0.15. Antiferromagnetic order sets in close to x≈0.1. To shed light on the interplay between quantum-critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with 0≤x≤0.3. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between x≈0.1 and 0.15. The application of hydrostatic and chemical pressure allows us to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum-critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.