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

Abstract

Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our recent studies on the compound LaCrGe 3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.

Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by La139 NMR

“…Recently, the itinerant ferromagnet LaCrGe 3 has been discovered to be a new class of itinerant ferromagnets exhibiting the remarkable T -p-H phase diagram where both the TCW structure and AFM phase are observed [21][22][23]. LaCrGe 3 crystallizes in the hexagonal BaNiO 3type structure [space group P 6 3 /mmc(194)] [24].…”

Magnetic properties of the itinerant ferromagnet LaCrGe3 under pressure studied by La139 NMR

“…3(b) and 4(b) was determined by the measurements with modified Bridgman pressure cells which may produce larger pressure gradients compared with piston-cylinder pressure cells. The ferromagnetic instability in LaCrGe 3 has been shown to be primarily driven by the Cr-Cr distance along the c axis [33], which would be the direction of higher pressure gradients in the previous measurements in Bridgman cells [24,32]. Therefore the results of the NMR measurements by utilizing the piston-cylinder pressure cells should be compared with the phase diagram of Fig.…”

“…The above discussions are based on the phase diagram reported in Refs. [24,25,32] [see, Fig. 1(a)], however, it is important to point out that the FM1-FM2 crossover field could vary depending on different experimental set up as well as sample quality.…”

“…Since the χ s at ambient pressure has been reported to follow the CW-type behavior even though the system is itinerant [23,26,29,32], one may estimate T C from the temperature dependence of K since K at high temperatures is proportional to χ s which is proportional to C/(T − T C ) (C: Curie constant). Figure 5(b) shows the temperature dependence of 1/|K| where the intercepts of the x axis provide an estimate of T C for each pressure.…”

Magnetic and structural properties of the intermetallic Ce(1-x)LaxCrGe3 series of compounds

“…By contrast, in RECrGe 3 the Cr atoms exhibit magnetic moments which order ferromagnetically at much higher temperatures, as indicated by the end member LaCrGe 3 of particular interest here where RE magnetic moments are absent [2]. One of the interesting aspects of this system is that the ferromagnetism can be suppressed toward a purported quantum critical point (QCP) by doping, [6] * brianna@alumni.usp.br pressure, or applied magnetic field [7,8], but the system successfully evades this scenario in an interesting way. With the introduction of magnetic rare earths the emergence of magnetic interactions between the Cr atoms and the 4f -RE moments presents an interesting situation for this strongly correlated electron system.…”