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S. Sakarya

Publications and source records attributed to S. Sakarya.

9 recordsLinked to original sources
arXiv2008

Critical Scaling of the Magnetization and Magnetostriction in the Weak Itinerant Ferromagnet UIr

The weak itinerant ferromagnet UIr is studied by magnetization and magnetostriction measurements. Critical behavior, which surprisingly extends up to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is analyzed using Arrott and Maxwell relations. Critical exponents are found that do not match with any of the well-known universality classes. The low-temperature magnetization $M_s\simeq0.5$ $μ_B \cong const.$ below 3 T rises towards higher fields and converges asymptotically around 50 T with the magnetization at $T_C$. From the magnetostriction and magnetization data, we extract the uniaxial pressure dependences of $T_C$, using a new method presented here, and of $M_s$. These results should serve as a basis for understanding spin fluctuations in anisotropic itinerant ferromagnets.

cond-mat.str-el↗
arXiv2007

Ferromagnetic quantum critical point in URhGe doped with Ru

We have investigated the thermal, transport and magnetic properties of URh$_{1-x}$Ru$_x$Ge alloys near the critical concentration $x_{cr} = 0.38$ for the suppression of ferromagnetic order. The Curie temperature vanishes linearly with $x$ and the ordered moment $m_0$ is suppressed in a continuous way. At $x_{cr}$ the specific heat varies as $c \sim TlnT$, the $γ$-value $c/T|_{0.5K}$ is maximum and the temperature exponent of the resistivity $ρ\sim T^n$ attains a minimum value $n=1.2$. These observations provide evidence for a ferromagnetic quantum phase transition. Interestingly, the coefficient of thermal expansion and the Grüneisen parameter $Γ$ remain finite at $x_{cr}$ (down to $T = 1$ K), which is at odds with recent scaling results for a metallic quantum critical point.

cond-mat.str-el↗
arXiv2007

Evolution of ferromagnetic order in URhGe alloyed with Ru, Co and Si

We have investigated the evolution of ferromagnetic order in the correlated metal URhGe (Curie temperature $T_{\rm C} = $9.5 K) by chemical substitution of Ru, Co and Si. Polycrystalline samples URh$_{1-x}$Ru$_x$Ge ($x \leq $0.6), URh$_{1-x}$Co$_x$Ge ($x \leq $0.9) and URhGe$_{1-x}$Si$_x$ ($x \leq $0.2) have been prepared and the magnetic properties have been investigated by magnetization and transport experiments. In the case of Ru doping, $T_{\rm C}$ initially increases, but then decreases linearly as a function of $x$ and is completely suppressed for $x_{\rm cr} \approx 0.38$. The Curie temperature in the URh$_{1-x}$Co$_x$Ge series has a broad maximum $T_{\rm C} = 20$ K near $x=0.6$ and then drops to 8 K for $x=0.9$. In the case of Si doping $T_{\rm C}$ stays roughly constant. We conclude that the alloy systems URh$_{1-x}$Ru$_x$Ge and URh$_{1-x}$Co$_x$Ge are interesting candidates to study the ferromagnetic instability.

cond-mat.str-el↗
arXiv2005

Studies of R2Ti2O7 (R=Gd and Yb); new results

Specific heat and muon spin rotation and relaxation data are presented for two geometrically frustrated systems: Gd2Ti2O7 which antiferromagnetically orders and Yb2Ti2O7 which presents dynamical short range correlations at low temperature. The muon data help to characterize the spin dynamics of these two compounds.

cond-mat.str-el↗
arXiv2005

Suppression of ferromagnetism in URhGe doped with Ru

In the correlated metal URhGe ferromagnetic order (T_C = 9.5 K) and superconductivity (T_s= 0.25 K) coexist at ambient pressure. Here we report on alloying URhGe by Ru, which enables one to tune the Curie temperature to 0 K. URuGe has a paramagnetic ground state and is isostructural to URhGe. We have prepared a series of polycrystalline URh_{1-x}Ru_{x}Ge samples over a wide range of x values. Magnetization and electrical resistivity data (T > 2 K) show, after an initial increase, a linear suppression of T_C with increasing x. The critical Ru concentration for the suppression of ferromagnetic order is x_cr ~ 0.38.

cond-mat.str-el↗
arXiv2005

Magnetic density of states at low energy in geometrically frustrated systems

Using muon-spin-relaxation measurements we show that the pyrochlore compound Gd2Ti2O7, in its magnetically orderered phase below ~ 1 K, displays persistent spin dynamics down to temperatures as low as 20 mK. The characteristics of the induced muon relaxation can be accounted for by a scattering process involving two magnetic excitations, with a density of states characterized by an upturn at low energy and a small gap depending linearly on the temperature. We propose that such a density of states is a generic feature of geometrically frustrated magnetic materials.

cond-mat.str-el↗
arXiv2002

Dilatometry study of the ferromagnetic order in single-crystalline URhGe

Thermal expansion measurements have been carried out on single-crystalline URhGe in the temperature range from 2 to 200 K. At the ferromagnetic transition (Curie temperature T_C = 9.7 K), the coefficients of linear thermal expansion along the three principal orthorhombic axes all exhibit pronounced positive peaks. This implies that the uniaxial pressure dependencies of the Curie temperature, determined by the Ehrenfest relation, are all positive. Consequently, the calculated hydrostatic pressure dependence dT_C/dp is positive and amounts to 0.12 K/kbar. In addition, the effective Gruneisen parameter was determined. The low-temperature electronic Gruneisen parameter Γ_{sf} = 14 indicates an enhanced volume dependence of the ferromagnetic spin fluctuations at low temperatures. Moreover, the volume dependencies of the energy scales for ferromagnetic order and ferromagnetic spin fluctuations were found to be identical.

cond-mat.str-el↗