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Register a new userElectronic transport and magnetism in the alternating stack of metallic and highly frustrated magnetic layers in Co$_{1/3}$NbS$_2$
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Added by
Petar Pop\\v{c}evi\\'c
Publication date
2020
fields
Physics
and research's language is
English
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Co$_{1/3}$NbS$_2$ is the only magnetically intercalated layered transition metal dichalcogenide (TMD) suggested to experience the complete suppression of magnetic order under pressure. From elastic neutron scattering we report the direct evidence for the reduction of the antiferromagnetic ordering temperature under pressure, up to complete suppression of magnetic order around 1.7 GPa. The static and ac magnetic susceptibility measurements reveal strong frustration in the magnetic subsystem, and spin canting responsible for the appearance of ferromagnetic (FM) component in dominantly antiferromagnetic (AF) ordered state. The electric transport in directions perpendicular and parallel to layers is explored for the first time in magnetically intercalated TMDs, in the wide temperature and pressure ranges. We show that electric transport reacts differently to magnetic ordering in directions along and perpendicular to layers, with the in-plane conductivity increasing, and the out-of-plane conductivity decreasing in the ordered state. At pressures above 3 GPa, we identify the appearance of the Kondo scattering regime. We use ab-initio calculations to explore the electronic structure in magnetically ordered state, the nature of magnetic interactions, and the mechanism responsible for the changes observed under pressure. The mechanisms of suppression of magnetic order under pressure are scrutinized in the light of these experimental and theoretical findings. We conclude that magnetic couplings beyond nearest-neighbors determine the nature of magnetic ordering. The suppression of ordering under pressure is ascribed to the pressure-induced shift in balance between super-exchange and Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic couplings, leading to amplified magnetic frustration.
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First-principles calculations and a model consideration of magnetically frustrated layered material PdCrO$_2$ are performed. The results on the exchange parameters are in agreement with the experimental data on the Curie-Weiss temperature ($theta$). We show that experimentally observed strong suppression of the Neel temperature ($T_N$) in comparison with the Curie-Weiss temperature is due to three main factors. First, as expected, this is connected with the layered structure and relatively small exchange interaction along the $c$ axis. Second, deformation of the ideal in-plane 120$^{circ}$ magnetic structure is crucial to provide finite $T_N$ value. However, these two factors are still insufficient to explain low $T_N$ and the large frustration factor $|theta|/T_N$. Thus, we suggest a scenario of an exotic non-Fermi-liquid state in PdCrO$_2$ above $T_N$ within the frameworks of the Anderson lattice model, which seems to explain qualitatively all its main peculiarities.
In this letter we describe the ground-state magnetic structure of the highly anisotropic helimagnet Cr$_{1/3}$NbS$_2$ in a magnetic field. A Heisenberg spin model with Dyzaloshinkii-Moriya interactions and magne- tocrystalline anisotropy allows the ground state spin structure to be calculated for magnetic fields of arbitrary strength and direction. Comparison with magnetization measurements shows excellent agreement with the predicted spin structure.
The crystal structure of a disordered form of Cr$_{1/3}$NbS$_2$ has been characterized using diffraction and inelastic scattering of synchrotron radiation. In contrast to the previously reported symmetry (P6$_3$22), the crystal can be described by a regular twinning of an average P6$_3$ structure with three disordered positions of the Cr ions. Short-range correlations of the occupational disorder result in a quite intense and structured diffuse scattering; a static nature of the disorder was unambiguously attributed by the inelastic x-ray scattering. The diffuse scattering has been modeled using a reverse Monte-Carlo algorithm assuming a disorder of the Cr sub-lattice only. The observed correlated disorder of the Cr sub-lattice reduces the temperature of the magnetic ordering from 130 K to 88 K and drastically modifies the field dependence of the magnetization as it is evidenced by the SQUID magnetometery. We conclude, that in contrast to the helicoidal spin structure assumed for P6$_3$22 form, the compound under study is ferromagnetically ordered with a pronounced in-plane anisotropy.
Layered transition metal dichalcogenides (TMDCs) host a plethora of interesting physical phenomena ranging from charge order to superconductivity. By introducing magnetic ions into 2H-NbS$_2$, the material forms a family of magnetic intercalated TMDCs T$_x$NbS$_2$ (T = 3d transition metal). Recently, Fe$_{1/3+delta}$NbS$_2$ has been found to possess intriguing resistance switching and magnetic memory effects coupled to the N{e}el temperature of T$_N sim 45$ K [1,2]. We present comprehensive single crystal neutron diffraction measurements on under-intercalated ($delta sim -0.01$), stoichiometric, and over-intercalated ($delta sim 0.01$) samples. Magnetic defects are usually considered to suppress magnetic correlations and, concomitantly, transition temperatures. Instead, we observe highly tunable magnetic long-ranged states as the Fe concentration is varied from under-intercalated to over-intercalated, that is from Fe vacancies to Fe interstitials. The under- and over- intercalated samples reveal distinct antiferromagnetic stripe and zig-zag orders, associated with wave vectors $k_1$ = (0.5, 0, 0) and $k_2$ = (0.25, 0.5, 0), respectively. The stoichiometric sample shows two successive magnetic phase transitions for these two wave vectors with an unusual rise-and-fall feature in the intensities connected to $k_1$. We ascribe this sensitive tunability to the competing next nearest neighbor exchange interactions and the oscillatory nature of the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. We discuss experimental observations that relate to the observed intriguing switching resistance behaviors. Our discovery of a magnetic defect tuning of the magnetic structure in bulk crystals Fe$_{1/3+delta}$NbS$_2$ provides a possible new avenue to implement controllable antiferromagnetic spintronic devices.
The topologically-protected, chiral soliton lattice is a unique state of matter offering intriguing functionality and it may serve as a robust platform for storing and transporting information in future spintronics devices. While the monoaxial chiral magnet Cr$_{1/3}$NbS$_2$ is known to host this exotic state in an applied magnetic field, its detailed microscopic origin has remained a matter of debate. Here we work towards addressing this open question by measuring the spin wave spectrum of Cr$_{1/3}$NbS$_2$ over the entire Brillouin zone with inelastic neutron scattering. The well-defined spin wave modes allow us to determine the values of several microscopic interactions for this system. The experimental data is well-explained by a Heisenberg Hamiltonian with exchange constants up to third nearest neighbor and an easy plane magnetocrystalline anisotropy term. Our work shows that both the second and third nearest neighbor exchange interactions contribute to the formation of the helimagnetic and chiral soliton lattice states in this robust three-dimensional magnet.
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