Tuning magnetic spirals beyond room temperature with chemical disorder

Abstract

In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature.

Multiferroic Magnetic Spirals Induced by Random Magnetic Exchanges

“…This mechanism results in a T spi of the order of a typical exchange coupling. Our Monte Carlo simulations for YBaCuFeO 5 yield T spi as high as 250 K depending on the concentration of the impurity bonds and their strength, in a manner that is consistent with the experimentally observed dependence of T spi and q spi on the amount of Fe 3+ /Cu 2+ occupational disorder [16].…”

“…The value of Q increases smoothly from Q(T spi ) = 0 as temperature is decreased. Impor-tantly, the reported values of T spi range from 180 K to 310 K [11][12][13][14][15][16] depending on the preparation conditions, and it was recently shown [16] that T spi and Q increase systematically with Fe 3+ /Cu 2+ occupational disorder. These observations suggest that chemical disorder plays an essential role in stabilizing the magnetic spiral motivating our search for a microscopic mechanism by which disorder facilitates, or even drives, magnetic spiral order.…”

Design of magnetic spirals in layered perovskites: Extending the stability range far beyond room temperature

“…We showed recently that T spiral can be shifted from 154 to 310 K by adjusting the average Cu/Fe occupations n Cu and n Fe of the square-pyramidal sites in the crystal unit cell ( Fig. 1A ) ( 21 ). We also established the existence of a positive correlation between the spiral ordering temperature and the degree of Cu/Fe intermixing (maximal for n Cu = n Fe = 50%).…”

“…The aim of the present study is to explore the design space opened by this novel, disorder-based spiral control mechanism. After having shown its potential and limitations for the particular case of YBaCuFeO 5 ( 21 ), we combine it here with a targeted lattice tuning of some magnetic exchanges. The idea behind this is to add up the effect of both mechanisms to stabilize spin spirals at temperatures higher than those obtained using these two strategies separately.…”

Room-temperature structural phase transition in the quasi-2D spin- 12 Heisenberg antiferromagnet Cu(pz)2(ClO4

“…In harmonic crystals, U i j -s can be interpreted in terms of time-averaged mean-square displacements resulting from the normal modes of vibration. In disordered materials, however, they can also capture displacements due to positional disorder [24][25][26] [27]. The β i j values, defined as β i j = 8π 2 U i j x i x j /4, with x i and x j the reciprocal-cell parameters, were obtained from Rietveld fits with the FullProf suite package [12].…”