Room- and low-temperature magnetic properties of 2-D magnetite particle arrays

Abstract

S U M M A R YPalaeomagnetic observations are being used in increasingly sophisticated geological and geophysical interpretations. It is therefore important to test the theories behind palaeomagnetic recording by rocks, and this can only be achieved using samples containing precisely controlled magnetic mineralogy, grain size and interparticle spacing, the last of which controls the degree of magnetostatic interactions within the samples. Here we report the room-and low temperature magnetic behaviour of a set of samples produced by the nano-scale patterning technique electron beam lithography. The samples consist of 2-D arrays of near-identical magnetite dots of various sizes, geometries and spatial configurations, with dot sizes from ranging from near the single domain threshold of 74-333 nm. We have made a series of magnetic measurements including hysteresis, first-order-reversal curve measurements and remanence acquisition, many as a function of temperature between 20 and 300 K, to quantify the samples' behaviour to routine palaeomagnetic measurement procedures. We have also examined the behaviour of saturation isothermal remanences (SIRM) to cooling and warming cycling of the sample below room temperature. In addition, we investigated the samples' responses to alternating-field demagnetization of room temperature induced SIRM, anhysteretic remanent magnetization (ARM) and partial ARM. ARM was used as a non-heating analogue for natural thermoremanence. Given the 2-D spatial distribution of the samples, in all the experiments we conducted both in-plane and out-of-plane measurements. Generally, the samples were found to display pseudo-single-domain hysteresis characteristics, but were found to be reliable recorders of weak-field remanences like ARM. For the closely packed samples, the samples' magnetic response was highly dependent on measurement orientation.

Paleomagnetic recording fidelity of nonideal magnetic systems

“…The samples' physical, room-temperature hysteresis properties, and Verwey temperatures were reported previously in Krása et al . [ 2011 ] and are summarized in Table 1 . For consistency, we use the same sample names as used in previous papers, and due to the two-dimensional nature of the samples, both the in-plane and out-of-plane measurements are referred to.…”

“… a Some of the magnetic parameters were reported previously in Krása et al . [ 2009 , 2011 ], and given here for completeness. The TRM in the final column was induced in a field of 60 µT.…”

“…In a previous study [ Krása et al ., 2009 ], we described the nanofabrication of arrays of magnetite crystals using EBL ( Figure 1 ), and in Krása et al . [ 2011 ] reported the room-temperature and low-temperature properties of 10 EBL samples. The samples contain equidimensional grains with a range of sizes from 74 nm up to 333 nm [ Krása et al ., 2011 ], and a range of controlled interparticle spacings, which are thought to be both interacting and noninteracting [ Muxworthy et al ., 2003 ].…”

“…[ 2011 ] reported the room-temperature and low-temperature properties of 10 EBL samples. The samples contain equidimensional grains with a range of sizes from 74 nm up to 333 nm [ Krása et al ., 2011 ], and a range of controlled interparticle spacings, which are thought to be both interacting and noninteracting [ Muxworthy et al ., 2003 ]. In this paper, we report high-temperature measurements, including a synthetic paleointensity investigation, to help us understand the thermomagnetic recording fidelity of PSD particles.…”

Estimation of significance levels and confidence intervals for first‐order reversal curve distributions

“…Theoretical and experimental studies have produced type FORC distributions for systems such as superparamagnetic, single domain and multidomain ferrimagnets as well as for interacting single domain systems [e.g., Pike et al , 1999; Roberts et al , 2000; Pike et al , 2001a, 2001b; Muxworthy et al , 2004; Newell , 2005; Egli , 2006; Egli et al , 2010]. Artificial samples have been examined to understand the expression of mixed magnetic mineral assemblages and magnetostatic interactions in FORC distributions [ Muxworthy et al , 2005; Carvallo et al , 2006a; Krása et al , 2009, 2011]. Fitting parametric functions to profiles taken through FORC distributions has helped to elucidate the behavior of complex systems and quantify the relative abundance of different magnetic components within natural mixing systems [ Egli , 2006; Chen et al , 2007; Yamazaki , 2009; Egli et al , 2010].…”