Non-Fermi-liquid nature of the normal state of itinerant-electron ferromagnets

Abstract

A century of research on magnetic phenomena had led to the view that the normal state of itinerant-electron ferromagnets such as Fe, Ni and Co could be described in terms of the standard model of the metallic state or its extension known as the nearly ferromagnetic Fermi liquid theory. In recent years, however, a large body of observations has accumulated from various complex intermetallic systems that raises the possibility that this assumption might be wrong. Here we examine this issue by means of high-precision measurements of the electrical transport and magnetic properties of pure ferromagnets-in particular, MnSi-in which the Curie temperature is tuned towards absolute zero by the application of hydrostatic pressure. With this method, it is possible for us to study the normal state over an extraordinarily large range of temperature of up to five orders of magnitude above the Curie temperature. Our results using MnSi reveal a particularly striking combination of properties-most notably a T3/2 power law for the resistivity-showing clearly that the normal state of this itinerant-electron ferromagnet cannot be described in terms of the standard model of metals.

Quantum criticality in NbFe2induced by zero carrier velocity

“…[13][14][15][16][17] The shortcomings of current theories for itinerant quantum criticality have been re-emphasized recently. 18 A necessary assumption is an underlying well behaved systems of non-interacting fermions. Imada et al 19 have suggested itinerant quantum criticality arises either from proximity to a first-order transition (quantum tricriticality), a metal-insulator transition (not the case here), or a Lifshitz transition, which accompanies a change in topology of the Fermi surface.…”

Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3

“…In the same way as pressure can initially decrease the freezing point of water, physicist have been able to use pressure to decrease the Curie temperature to absolute zero temperature, leading to a quantum phase transition. Surprisingly, a variety of unconventional properties have been unveiled near the ferromagnetic quantum phase transition [1], including superconductivity [2][3][4][5], non-Fermi liquid behavior [6], tri-criticality [5,[7][8][9][10], and complex magnetic structures [11][12][13][14][15][16].…”

1.5 GPa compact double-wall clamp cell for SANS and NSE studies at low temperatures and high magnetic fields

“…The press used at the ILL is equipped with an electronic load cell that accurately measures the load force of the press and the displacement sensor of the piston, which makes it possible to determine the friction and the pressure at room temperature by increasing and decreasing the load. Figure 4 shows the relation between the applied force or the expected pressure in the cell at room temperature, and the effective pressure applied to the sample below 50 K. The pressure at low temperature is estimated from the critical temperature of MnSi as reported in ref [17], where the long range helimagnetic order sets-in at zero field. The figure shows that the pressure losses due to friction and the freezing of Fluorinert amount to about approximately 20%.…”

“…Relation between the applied force or the expected pressure in the cell at room temperature, and the effective pressure applied to the sample below 50 K as deduced from the critical temperature of MnSi. The pressure at low temperatures is estimated from the critical temperature of the helimagnetic order at zero field as reported in [17]. …”

“…The cell has been successfully tested at the Institute Laue-Langevin (ILL) and the ISIS neutron source. It has been used to investigate the magnetic properties of the archetype helimagnet MnSi beyond the critical pressure of ∼1.4 GPa where a non-Fermi Liquid behaviour sets-in [17]. We show that this pressure cell produces a low-enough and flat neutron background in the Q-range covered by typical SANS instruments and that it can also be used for NSE.…”