Weak arrest-like and field-driven first order magnetic phase transitions of itinerant Fe3Ga4 revealed by magnetization and magnetoresistance isotherms

The detailed magnetic study of complex 3d-electron based Fe3Ga4 is reported. It undergoes paramagnetic to antiferromagnetic (T-N) and antiferromagnetic to ferromagnetic (T-c) transitions respectively around 380 and 70 K. The thermal hysteresis of field-cooled cooling (FCC) and field-cooled warming (FCW) hints at first order phase transition below Curie temperature. A weak phase coexistence of ferro and anti ferromagnetic phases is suggested by exploring the arrest-like first-order phenomenon. In the intermediate temperature range, field-driven metamagnetic transition from antiferro to ferromagnetic phase is confirmed. Further bringing the system very near to TN, field-induced transitions disappear and above TN predominant paramagnetic contribution is evident. The magnetic H-T phase diagram distinguishing different magnetic phases of Fe3Ga4 is obtained. (C) 2016 Elsevier B.V. All rights reserved

Critical exponents and universal magnetic behavior of noncentrosymmetric Fe0.6Co0.4Si

The critical magnetic properties of a non-centrosymmetric B20 cubic helimagnet Fe0.6Co0.4Si are investigated using magnetization isotherms. It belongs to the 3D-Heisenberg universality class with short range magnetic coupling as inferred from the self-consistent critical exponents beta = 0.411 +/- 0.003, gamma = 1.325 +/- 0.062, delta = 4.223 +/- 0.004 and alpha = -0.115 +/- 0.007 in combination with exchange interaction J(r) approximate to r-(4.88). Itinerant magnetic nature of the compound is realized by the Rhodes-Wholfarth analysis. Field-induced weak first (para?helical) to second (para?field-polarized) order transition is reported to occur at low critical field due to the weak spin-orbit coupling arising from the weak Dzyaloshinksii-Moriya interactions. Our study suggests the distinct phenomenological magnetic structures for Fe-based cubic magnets (Fe1-xCoxSi and FeGe) and MnSi which cause contrasting physical properties

Critical behavior, universal magnetocaloric, and magnetoresistance scaling of MnSi

We report the critical behavior of a B20 cubic compound MnSi, known by its helical, conical and skyrmion phases in low fields, in its magnetic field-induced ferromagnetic (high-field) phase by means of magnetic-entropy (magnetoresistance) methods. The evaluated critical exponents are beta = 0.25 +/- 0.02(0.19 +/- 0.04), gamma = 1.29 +/- 0.27 (1.32 +/- 0.16), and delta = 6.18 +/- 0.28 (7.79 +/- 0.52). The self-consistency of the newly adopted methods is established by comparing the thus obtained exponents with those estimated using the modified Arrott's plot method and neutron diffraction. The field controlling parameter is n similar to 0.5 and its deviation from the mean-field model exponent confirm the weak first-order and field-induced ferromagnetic behavior. A direct proportional relation between magnetic entropy and magnetoresistance infers itinerant magnetic nature. The collapse of high-field data onto the more generalized magnetic-entropy master curve confirms the field-induced first-to second-order phase transition and thereby tricritical phenomenon in MnSi

Quantum phase transition and non-Fermi liquid behavior in Fe1-xCoxSi (x >= 0.7)

We report on the nature of electron correlations in Fe1-xCoxSi (0.7 <= x < 1) using combined results of magnetization, specific heat and transport properties. Doping driven quantum critical point is observed to occur at x similar to 0.75. The magnetically unstable regime is identified to be centered around x is an element of [0.75, 0.95]. The emergence of non-Fermi liquid behaviors in x = 0.8 (near to ferromagnetic quantum critical point) and x = 0.9 (disorder-induced) compositions are discussed on the basis of the power-law dependence of susceptibility chi similar to T-g (g similar to 1.07 for x = 0.8 and 0.55 for x = 0.9), specific heat C/T similar to T-1+lambda (lambda similar to 1.52 for x = 0.8 and 0.9) and resistivity Delta rho similar to T-d (d similar to 1.56 for x = 0.8 and 1.38 for x = 0.9). Further, a comprehensive classification of doping dependent physical properties of Fe1-xCoxSi is presented in the revisited temperature-composition (T-x) phase diagram

Spin-flop quasi-first order phase transition and putative tricritical point in Gd3Co

Magnetic nature of Gd3Co is investigated using detailed measurements of temperature and field dependent magnetization. The antiferromagnetic phase is field-instable due to prevailing ferromagnetic exchange correlations above Neel temperature T-N similar to 130 K. Below T-N, with gradually increasing magnetic fields, the compound undergoes a quasi-first order phase transition from AFM to spin-flop over region and eventually acquires ferromagnetic phase in higher fields. Further the point at which the quasi-first order transition ends and second order transition sets in is the tricritical point, T-TCP similar to 125: 6 K, H-TCP similar to 4: 4 kOe. (C) 2017 Elsevier B.V. All rights reserved

Competing magnetic and spin-gapless semiconducting behavior in fully compensated ferrimagnetic CrVTiAl: Theory and experiment

We report the structural, magnetic, and transport properties of the polycrystalline CrVTiAl alloy along with first-principles calculations. The alloy crystallizes in a LiMgPdSn-type structure with a lattice parameter of 6.14 angstrom at room temperature. The absence of the (111) peak along with the presence of a weak (200) peak indicates the antisite disorder of Al with Cr and V atoms, which is different from the pure DO3 type. Magnetization measurements reveal amagnetic transition near 710 K, a coercive field of similar to 100 Oe at 3 K, and a moment of similar to 10(-3) mu(B)/f.u. These observations are indicative of fully compensated ferrimagnetism in the alloy, which is confirmed by theoretical modeling. The temperature coefficient of resistivity is found to be negative, signaling the semiconducting nature. However, the absence of exponential dependence indicates the semiconducting nature with gapless/spin-gapless behavior. Electronic and magnetic properties of CrVTiAl for all three possible crystallographic configurations are studied theoretically. All the configurations are found to be different forms of semiconductors. The ground-state configuration is a fully compensated ferrimagnet with band gaps of 0.58 and 0.30 eV for the spin-up and -down bands, respectively. The next-higher-energy configuration is also fully compensated ferrimagnetic but has a spin-gapless semiconducting nature. The highest-energy configuration corresponds to a nonmagnetic, gapless semiconductor. The energy differences among these configurations are quite small (< 1 mRy/atom), which hints that, at finite temperatures, the alloy exists in a disordered phase, which is a mixture of the three configurations. By taking into account the theoretical and experimental findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with a predominantly spin-gapless semiconducting nature

Spin fluctuations in Cr doped MnSi

Transport and calorimetric properties of Mn1-xCrxSi (x = 0.025) down to 2 K and magnetic fields up to 13 T are reported. Electrical resistivity in zero field as well as in magnetic fields, below a magnetic transition temperature, T-c = 23.6 K could be described using a T-2 term with large coefficient, invoking the role of spin fluctuations. Sommerfeld coefficient 'gamma' of specific heat is an enhanced one as compared to the pure MnSi. Negative magnetoresistance (35% at 13 T) with maximum at T-c and a decrease in coefficient of T-2 term in resistivity suggests the suppression of spin fluctuations in high magnetic fields. This is further supported by negative magneto-specific heat in the vicinity of T-c coupled with a decrement in the Sommerfeld coefficient 'gamma' of specific heat under a field of 10 T. Kadowaki-Woods ratio places the system close to other systems showing strong spin fluctuations. (C) 2017 Elsevier B.V. All rights reserved